Final Report Summary - ELECTRICAL (NOVEL AERONAUTICAL MULTIFUNCTIONAL COMPOSITE STRUCTURES WITH BULK ELECTRICAL CONDUCTIVITY AND SELF-SENSING CAPABILITIES)
Executive Summary:
The main objective of ELECTRICAL is the development of novel multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities for rapid non destructive quality assessment.
The project exploits properly the excellent properties of CNTs as polymeric resin doping for the development of novel multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities.
ELECTRICAL investigates and developes alternative emerging methods to manufacture nanoreinforced carbon based composites compatible with current industrial manufacturing processes of composites: incorporation of nanofillers into toughening thermoplastic fibers, non-woven veils, incorporation of nanofillers into nanostructured preforms called buckypapers, incorporation of nanofillers in injection resin and carbon fiber prepregs.
ELECTRICAL incorporates the following scientific and technical objectives:
a)Improvement of bulk electrical conductivity of aeronautical composite structures to meet requirements regarding static discharge, electrical bonding and grounding, interference shielding and current return through the structure. The technical approach will be based on the conductive properties of carbon based nanoreinforcements when integrated into the laminates.
At the same time, a global electrical conductivity test method will be defined and set-up in order to have a common understanding: Standardisation of electrical measurement and assessment procedures.
b)Monitoring and optimisation of CFRP curing process by Dielectric Mapping. Taking advantage of the electrical conductivity of CNTs, the dielectric sensor system mounted in the mould will perform non invasive measurements of the electrical properties of the material in the sensor´s vicinity for material-state monitoring (degree of cure, Tg), resin flow in moulds (arrival time, flow speed and direction) and end-of-cure detection.
c)Taking advantage of the piezoresistive behaviour of CNTs, development of innovative CFRP structures with distributed or localised self-sensing capabilities for quality assurance of final component (delaminations, inclusions, etc) by Electrical Resistance Tomography (ERT)
d)Development of state of the art fabrication technologies to convert nanofillers (CNTs and others) into engineered multifunctional preforms, prepregs, buckypapers, etc.. for further use in CFRP structures. CNTs bulk doped resins are also to be considered as the main base-line for investigation in the present project. Synergistic effects of using bulk doped resins and new developed engineered structures will also be under investigation.
e)Manufacture, characterisation and testing CFRP based materials with such multifunctional engineered nanostructures and bulk doped resins. The most broadly used liquid moulding technologies will be considered, although autoclave curing and associated prepreg development will also be considered as the base line.
f)Manufacture and testing of representative panels/prototypes for proof-of-concept of the materials and technologies developed.
g)Health, Environment and Safety issues derived from CNT handling will be specially considered in the project. Partners will be trained in the processing of nanomaterials in laboratory and industrial environment, which is a major issue in current development of these technologies.
Project Context and Objectives:
Based on the needs to provide advanced concepts and technologies for increased and optimised use of light-weight composite smart materials, the main objective of ELECTRICAL is the development of novel multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities for rapid non destructive quality assessment
The main challenges of the project can be summarized as follows:
This project for the first time allows the transition from improved nanoreinforced resins to the exploitation of their enhanced electrical and mechanical properties in full laminates manufactured by automated processes. As such, next generation aircraft structures can be estimated to be approximately 5% lighter than using Boeing B787 or Airbus A350XWB technology. Furthermore, synergy effects with other markets, such as sports goods, automotive, packaging and semiconductors could benefit significantly.
Research and technology development on nanoreinforced resins has been performed under public contracts for several years. However, cost efficient infusion technologies have to date not been able to be used with these resins primarily due to particle filtering during injection. It is the aim of this project to overcome this critical bottleneck by assessing and driving alternative nanoparticle introduction techniques as well as establishing processing windows for “traditional” nanocomposite formulations.
Therefore, it is established, as main technological challenge for ELECTRICAL, to increase electrical conductivity through-the-thickness of aeronautical CFRP laminates. Achieving this would enable an important reduction of the overall airframe weight by replacing current metallic structural network (metal mesh). In order to achieve that, several methods for introducing electrically conductive nanofillers into CFRP laminates have been assessed, establishing the use of bulk doped resin as a baseline for investigation, but developing new engineered nanomaterial based structures that would overcome problems of filtration and re-agglomeration. Differently from other current ongoing projects, where surface conductivity is the main issue for other functionalities, ELECTRICAL is focused on electrical conductivity through the laminate thickness.
In terms of mechanical properties, significant improvements in impact behavior are expected in addition to electrical conductivity, leading to a reduced burden on the environment by air travel. More importantly, allowing the consideration of CFRP bulk conductivity in aircraft design will lead to new aircraft architecture concepts with further weight savings and performance increases. In addition, potential self-sensing techniques can reduce unscheduled and scheduled inspection times and will allow a rapid quality assurance and enhanced manufacturing process control, revolutionizing CFRP manufacture.
The project exploits properly the excellent properties of CNTs as polymeric resin doping for the development of novel multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities. For that, different lines of work will be approached:
Firstly, this project investigates and developes alternative emerging methods to manufacture nanoreinforced carbon based composites compatible with current industrial manufacturing processes of composites
In particular, polymer injection processes will constitute the main project’s target, this including RTM, RTI, LRI and their variants, although autoclave curing is to be considered as the reference process. During the life of the project the following topics of research have been considered:
• Incorporation of nanofillers in dry carbon preforms.- The use of performs is typical when modern liquid composite moulding technologies are used; on one hand due to the necessity to incorporate toughening thermoplastic fibres and veils, and on the other hand due to the necessity to automate the process. This project investigates which technologies would enable the incorporation of nanofillers in these preforms before resin infiltration, mostly looking at the addition of nanofillers in between structural fabric layers in order to promote through-thickness conductivity. This way, the increased viscosity of the resin and the filtration effect when nanofillers are incorporated directly into the resin can be avoided. Several approaches have been tackled:
- Incorporation of nanofillers into toughening thermoplastic fibres. One route to provide an increase in toughness for brittle resins used in liquid injection technologies is the use of thermoplastic fibres that are introduced into the textiles used for the reinforcement. This can be achieved by co-weaving or more effectively by commingling structural fibres with tough thermoplastic fibres prior to the weaving of the fabric. The thermoplastic fibres can then, either dissolve in the thermosetting resin after infusion and during cure, or they can remain in the final composite as a solid fibre. Also the fibre can be used for a secondary stitching of standard structural reinforcements. The possibility of doping thermoplastic fibres with CNTs has been addresses in this project.
- Incorporation of nanofillers in polymeric non-woven veils. Another route to provide an increase in toughness is the use of an ultra-thin veil. During the resin infusion stage these veils are dissolved in the thermosetting resin. The incorporation of CNTs into the thermoplastic before producing the veils enables a better and more homogeneous incorporation during the infiltration.
• Preforming CNTs into thin mats with well-controlled dispersion and porous structure, so called “buckypaper”
• Incorporation of CNTs in injection resin. Alternatively to the incorporation of CNTs in dry carbon preforms, the incorporation of CNTs in the bulk liquid resin is also considered. The target of the project in this case is established on how to overcome the still pending technical challenges: optimal and stable dispersion of CNTs into the resin so that the mixture can be stable across time without any re-agglomeration effect, suitable CNTs/resin interfacial bonding and preserving integrity of CNTs during dispersion process.
• Modified or new injection strategies.-. The incorporation of CNTs into injection technologies, either into dry carbon preforms or as a buckypaper or into the bulk resin, will require at least a modification of injection processes, even in some cases the set up of new injection strategies. In the case of dry carbon performs or buckypaper the fibre permeability will be modified, while in the case of doped bulk resin the viscosity increase will modify their flow and filtering effect; at the same time than changing the curing kinetic of the polymer. Among others, the following strategies will be investigated as potential solutions:
- Tuning of process parameters for traditional technologies. This task would concentrate on the development of technical solutions to overcome the problem of viscosity increase and filtration above described: Optimization of temperature and/or pressure, modification of mould configuration (injection gates and vents), flow media, textile/performs permeability, etc.
- Two step infiltration for RTM and LRI. The possibility of using the RTM or other Liquid Resin Infiltration methods with CNT-doped resins has been investigated in the past with very poor results. The fiber preform is essentially acting as a filter, preventing the CNT particles from spreading along with the resin inside the preform, effectively keeping them in a small area around the injection nozzles. An alternative 2-step process that can eliminate these problems has been studied in laboratory conditions. The process involves pre-functionalised fiber preforms and use of a carrier liquid (aqueous or organic solvents) of very low viscosity in which the CNT's are dispersed.
• Alternatively the incorporation of CNTs into carbon fibre pre-pregs is considered. As above stated, filtration phenomena occurred during infiltration of performs with doped resins is a major problem yet to overcome. The strategy to be addresses within the project is the production of carbon fibre prepregs with doped resins. The incorporation of CNTs into prepreg for further production of laminates would enable electrical conductivity enhancement along the “z” axis of the laminate; the project analyses how the addition of CNTs can modify the prepreg processing along the different steps (resin doping, prepregging, storage, handling / lay-up and curing) to understand the processing of three phase composites with CNTs and their influence on final performance.
The prepreg technique requires a high viscosity resin that undergoes minimal flow, which reduces the mobility of CNTs during the curing process and therefore their possible re-agglomeration during this phase. However, the processing side-effects can not be completely ruled out because previously cross-linking is initiated by chemical reaction, the resin undergoes a minimum viscosity level. The influence of CNT content must be evaluated.
Secondly, the multifunctionality concept is approached, which consists of the integration of three main functionalities:
• Increase of electrical conductivity of CFRP laminates for indirect lightning strike protection, static discharge, electrical bonding and grounding, interference shielding and current return through the structure. Standardisation of electrical measurement and assessment procedures.
• Monitoring and optimisation of CFRP curing process by Dielectric Mapping. In order to monitor and optimize the process dielectric sensors will be incorporated in the mould used for CFRP curing. This technology, previously developed under the framework of different R&D projects, has been adapted to the materials and processes to be studied along the project.
• Quality assurance of final component (delaminations, inclusions, etc) by Electrical Resistance Tomography (ERT). This will be achieved by the integration of CNT fibres into the CFRP laminates. More precisely, this technology will be based on PVS/CNT fibres stitched on the standard structural reinforcements; the nano-doped fibre can act as distributed conductivity sensor for NDT using ERT
Description of work
The work breakdown structure defined to meet the main technological challenges and objectives is based on seven work packages, going forward through the main challenging tasks from definition of specifications towards manufacturing issues, testing and evaluation. Six work packages were devoted to technical matters, while the seventh will deal with coordination and managerial issues, as can be seen in the following diagram:
WP1 is devoted to the definition of targeted component types (composite structural part) and their specifications. This constitutes the base for a preliminary selection of materials (polymers and CNTs) and manufacturing processes.
The development of strategies for CNTs incorporation into laminates is approached in WP2. The structures here developed constitutes the basis for further incorporation into composite components. Two main approaches are considered during the first half of the project until month 18, the first one based on the incorporation of CNTs into thermoset resins for liquid technologies (RTM, etc) or prepregs (autoclave), and the second one based on innovative structures like CNT buckypapers, or dry performs based on CNT doped thermoplastic fibres, veils or films.
In this WP, a specific Milestone has been established in Month 18 as a Preliminary Review in order to assess technical achievements regarding electrical conductivity, mechanical performance, etc in order to select the most promising strategy for the applications considered. The second half of the WP and project focuses all the efforts in those most promising materials and technologies.
WP3 deals with nanoreinforced composite production through liquid infiltration technologies, as the main route, and autoclave curing as an alternative short-term manufacturing method (risk reduction).
In parallel to WP2 and 3, the WP4 is devoted to the characterisation of composite laminates produced, mostly for electrical conductivity, and development of the sensing and damage detection approach. Furthermore, parallel structural tests are carried out in order to evaluate how the nanofillers affect to mechanical properties.
Multifunctional composite with electrical conductivity and sensing systems developed in WP4 are validated in WP5. For that, representative scaled structural components incorporating the CNT-structures were designed, fabricated and technically evaluated in order to provide guidelines for optimal design. Moreover, safety and security aspects were considered.
The commercial evaluation of products obtained from previous develop will be carried out in WP6, in order to assess the potentialities to transfer to real applications. The diffusion and exploitation aspects will also be undertaken to address future activities and to establish a roadmap for the quick introduction in the market of the structural concept developed in the project
Project Results:
3. DESCRIPTION OF THE MAIN S&T RESULTS/FOREGROUNDS
WP1. Requirements. Specification of Materials, Processes and targeted Components
The objectives for this WP are:
• To precisely define the input data necessary to manage the whole technical issues: targeted component types (composite structural part) and their mechanical and electrical specifications, materials (polymers and nanomaterials) and manufacturing processes, (prefroming and laminate manufacturing), working program and configurations to be developed and evaluated
• To define a global electrical conductivity test method in order to have a common understanding: Standardisation of electrical measurements and assessment procedures
The technology to be developed in the project to achieve the main goal of developing novel aeronautical multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities for rapid non destructive quality assessment, is the nanoreinforcement of CFRP airframes.
Definition of Target Parts
ELECTRICAL, as FP7 level 1 project, aims at contributing to mature the nanocomposite technologies for electrical application in aeronautical field, to TRL, technology readiness level, 2-3. Therefore, in this project the demonstration is planned at the level of stiffened panels, which will be representative of the selected structures (wing, fuselage).
Wing
• Composite structure: skin, stringers, ribs, ...
Figure 1 – Wing structure
Fuselage section
• Composite structure: skin, stringers, frames, ...
• Low level electrical function ESN parts (metal): frames, cross-beams, race-ways, ...
Figure 2 – Fuselage structure
Requirements
First priority objective of ELECTRICAL project is the improvement of the aeronautical CFRP structure electrical behaviour with the final aim of weight saving. The mechanical behaviour of CFRP structure at least needs to be maintained, being the mechanical enhancement in second place. Therefore, electrical requirements to be met by the nanoreinforced laminates to be developed in this project are key.
The following electrical constraints to be sustained by the aeronautical CFRP structure were identified. A detailed description is compiled within Deliverable D1.1&D1.2
a)Lightning strike: direct and indirect effects
The requirement for the resistance per square of future CFRP fuselages will be between 1 and 6 mΩ per square
b) Edge glow (CFRP edges), sparking (CFRP bolted joints)
During some lightning strike lab tests on coupons made of last generation thermoset matrix like the M21E, some sparking have been observed on the coupon edges. This phenomenon, which is called edge glow, must be avoided in fuel tank areas
c)Electrical bonding: handling of electrical current due to a short circuit inside a system
The electrical bonding is the return of fault, defect currents in the aircraft. The path of the bonding current circulates through structural CFRP elements. Currently a specific metallic network is used for new generation aircrafts with CFRP fuselage to carry out this function. The network is named MBN (Metallic Bonding Network).
This network usually merges with the metallic structural parts like seat-tracks to perform an aircraft mesh which permits to evacuate the function and fault currents of the different systems, the full network in fuselage area is the ESN (Electrical Structural Network).
Nevertheless, it is necessary to add specific components (metallic strips) to each frame and crossbeam of the aircraft to insure the electrical continuity answering to the global specifications of all the systems. The sum of the elements constitutes a complex mesh like the virtual mock-up bellow
For the electrical bonding function, a current of 2000 A for 300 ms needs to be considered
d) Short circuits between wire and CFRP
The short circuit involves the direct contact of an electrical wire with the CFRP.
3 different short circuit issues have been identified:
• Direct on CFRP
• Bundle exploded near the CFRP
• Behavior of CFRP junctions submitted to a failure
e)Electrical grounding: systems functional current return
The electrical grounding is the systems functional electrical current return. Electrical current return refers to the establishment of a low impedance current path between the power supply reference (0 V DC, 0 V AC or AC Neutral) of an electrical component and the aircraft point of voltage reference.
For electrical grounding, the following requirements need to be considered:
- Continuous electrical currents: Low: 10 A, Medium: 20 A, High: 200 A
- This current shall not lead to a resin temperature increase above a temperature at least 28°C below the resin Tg
- Electro-thermal aging
In the following table a raking of the electrical functions to be covered and aimed at by the nanocomposite technology within the ELECTRICAL project is shown. This ranking was performed taking into account the electrical requirements and, then, the probability of success.
Ranking of electrical functions
Materials and Processes
The materials and processes selected for the project are:
Laminate Materials
Thermoplastic preform materials
One of the key research lines of the ELECTRICAL project to obtain nanoreinforced infused laminates is the introduction of CNT in the infusion textile preform thermoplastic materials (veils), with the main aim of avoiding filtering problems associated to the nanodoped bulk resin infusion.
The following requirements need to be met by the nanodoped thermoplastic materials to be introduced in the infusion textile preform:
Key requirements
• No wash-out: poor solubility in the laminate matrix at the infusion temperature (120°C) during the infusion time (120 minutes / 2 hours)
• Good adhesion to the laminate matrix after cure.
• No negative influence on thermo-mechanical properties (hot-wet)
• Binding parameters: Veil target weight: 6 g/m2 for 268 g/m2 UD CFRP layer
A complete compilation of potential thermoplastic materials to be used as nanocarriers was done (refer D1.1&D1.2). From this table the following thermoplastic material was selected: Platamide Copolyamide (Arkema). Two grades: 110ºC and 135ºC melting Temperature. It is important to remark that the selected material should perform both functions: Nanocarrier and binder. Additionally, some basic infusion trials will be done by EADS IW - G with higher melting temperature polyamides, supplied by Arkema: PA6 (210 ºC) and PA12 (176 ºC).
Nanomaterials
The CNT selected for the project are compiled in the following table.
System Selected material
CNT MASTERBATCH:
First priority • PLATAMID (copolyamide): fibers and veil application to be supplied by ARKEMA
• MVR444/EF6809: premixture to be supplied by CYTEC to ARKEMA to produce a masterbacth
• CW245: CMC (carboxymethyl cellulose) based masterbatch to be supplied by ARKEMA
MWCNT
POWDER • ARKEMA-C100: for nanodoped prepreg production by Patras University and for buckypaper production by Tecnalia
Testing
Electrical testing
The proposed electrical test methods are compiled in the table below. As for the electrical conductivity, it is important to remark that it is a goal of this project to develop an appropriate test method. However, as these measurements are needed in the project early phase in order to assess the value of the different techniques before entering the phase of the listed tests, appropriate test methods have been identified to carry out these measurements.
Lightning strike direct effects on fuselage panel
The behaviour of the investigated material under lighting strike shall be compared to the one of the current baseline, i.e. the A350-900 fuselage skin configuration.
The A350-900 baseline for the fuselage skin is the following one:
9 plies of M21E/IMA, FAW: 194 g/m2, RC: 34%, lay-up: [45/0/135/90/0/90/135/0/45]
Expanded copper foil, AW: 195 g/m2, impregnated by 170 g/m2 of surfacing film
Top layers:
The external paint system shall be representative of the A350XWB-900. The targeted external paint system thickness will be about 330 μm. With such a thickness and taking into account around 30 μm of basic primer and 90 μm of surfacing film on top of the ECF, the total thickness on top of the ECF should be around 450 μm.
Sample dimensions:
For lightning strike tests at the LCOE lab (Getafe, Spain) or at Lightning Technologies (Culham, UK), the samples shall have the dimensions presented in figure 12.
For lightning strike tests at the DGA-TA, the dimensions of the samples need to be indicated by the relevant specialists.
Mechanical testing
The proposed mechanical tests in the project are compiled in the following table. These tests should be done at room temperature, that is hot/wet tests will not be carried out, due to the relatively low TRL of the ELECTRICAL project.
Physico-chemical testing
The proposed physico-chemical tests are included in the next table.
Non-destructive ultrasonic inspection of all the manufactured panels / specimens were carried out in order to ensure their quality.
Microscopy evaluation (SEM) was performed to assess the quality of the nanomaterial dispersion in the manufactured panels / specimens. More detail information can be found within D1.1 (definition and requirements of structural parts) and D1.2 (definition of materials and processes).
WP2. Development of Strategies for Incoporation of CNTs
This work package aims at the development of strategies for the incorporation of CNTs into the composite laminates, which constitutes the basis for further incorporation into composite components. Different approaches for CNT incorporation were considered:
• Incorporation of CNT into thermoset resins for liquid technologies (RTM,etc) or prepregs
• Incorporation of CNTs as innovative structures like buckypapers, or dry preforms based on doped thermoplastic fibers, veils or films.
Due to concern related to the use of nanomaterials, health, Environment and Safety issues derived from CNT handling were specially considered in the project. Partners were trained prior to the start of the activities related to the handling and use of nanomaterials in both laboratory and industrial environment since it is considered a major issue in the current development and uptake of these technologies. A security training course for the handling of nanomaterials and in particular carbon nanotubes (CNT) materials was organised. This training course took place during the Electrical meeting organized in France by Arkema at the research center of Lacq (GRL) in october 2011. CANOE organized this training course in collaboration with Arkema. This training course was organized for a day and was composed of 5 parts:
- 1st part : General aspects of nanomaterials and nanotechnologies (by Pr Daniel Bernard) : 8H30-9H00
- 2nd part : Regulation and normalization at international level (by Pr Daniel Bernard) : 9h30-10h00
- 3d part : Health and safety at work station/Metrology and characterization problems (by Serge Bordere, ARKEMA) : 10h00-10h45
- 4th part : Visit of GRL work stations : 10h45 – 12h30
- 5th part : Discussions with partners : 12H30-13H00
The 6M Progress meeting was deliberately held at ARKEMA in order to include the security training ahead of the main scientific programme. Eventhough it was scheduled within WP5 the consortium considered to celebrate the workshop at the earliest possible date (see D5.3).
In WP2 two major technologies are approached. Each of them covers two research lines where different partners took part:
• Bulk resin doping
o 2.1A Liquid technologies (doped resin)
CYTEC, ARKEMA, TECNALIA, BOMBARDIER
o 2.1B Prepreg development
CYTEC, ARKEMA, UoP
• Novel engineered structures
o 2.2A Dry preform development
ARKEMA, CANOE, TECPAR, TECNALIA, EADS-IW-G, BOMBARDIER
o 2.2B Buckypaper development
TECNALIA, UoP, BOMBARDIER
The work carried out in WP2 during the 36 months of the project is contained in the 1st and 2nd periodic reports. The following paragraphs intend to give a general overview of objectives, activities and results obtained in this WP.
BULK RESIN DOPING
Liquid technologies
The activities of Tecnalia have been focused on the development of CNT doped resin to be used in composite laminates manufacturing by liquid technologies. Tecnalia has been working in close cooperation with Cytec for the development and supply of the MVR 444 resin in two parts and with ARkema for the development of CNT masterbatches. In summary the activities related to bulk resin doping answer to three Approaches:
-Approach 1: the MB based on part A of the MVR444 resin (extrusions)
-Approach 2: Two MB based on MVR444 (A+B) containing 25%wt of CNTs, in two formats: pellets (p) and granules (g)
-Approach 3: For this approach, the MB based on part A of the MVR444 resin (approach 1) was converted to pellets by Arkema.
The work performed in the frame of this activity (masterbatches treatment, characterization –rheology, electrical and mechanical- is carefully described in D 2.6. Main conclusions of the work carried out in the doping of epoxy resin with part A based masterbatch in pellet form, it can be summarized as follows: Electrical conductivity of E-6 S/m is obtained with 0.1 wt.% CNT. This conductivity value is similar to that obtained with CNTs in powder form, and approximately 4 orders of magnitude higher than the conductivity obtained with the previous masterbatches. Rheological results reveal that the quality of dispersion is good and carbon nanotubes have an accelerating effect in the curing of epoxy resin. However, the nanocomposites based on this nanomaterial show narrower processing window than that required by BAB.
Prepreg developement
UOP lead this task along with support from CYTEC. Objective of this WP was to develop various strategies for the incorporation of CNTs into the composite laminates, which constituted the basis for further incorporation into composite components.
The Process Development Plan agreed (11/01/2012) that takes into account CYTEC material IP limitations consists of three (3) distinct Routes:
Route 1 (Direct Doping): Direct doping of EF6809 resin system used to produce CYTEC pre-pregs. Part A of EF6809 is shipped to UOP where the CNT dispersion was performed. CNT doped part A of EF6809 is returned to CYTEC where complete EF6809 formulation is created. This CNT-doped EF6809 resin system is used by CYTEC to produce a CNT-doped EF6809 pre-preg.
Route 2 (Resin Film Treatment): CNT- treatment of conventional EF6809 resin films of CYTEC. Fully formulated resin film (EF6809) is shipped to UOP. UOP using various CNT deposition/integration techniques produces CNT treated ELE-EF6809 film.
Route 3 (Prepreg Treatment): CNT-Treatment of conventional EF6809 prepreg materials of CYTEC. Conventional EF6809 pre-preg is shipped to UOP. UOP using various CNT deposition techniques produces the CNT-treated EF6809 pre-preg. Two bacthes were manufactured with the second having improvements over the first
All the activities UoP performed for the development and manufacturing of CNT treated prepreg are compiled within D2.6
NOVEL ENGINEERED STRUCTURES
Dry preform development
Nano-doped fibres
The activities performed by CANOE followed the objectives:
- Fibers fabrication based on thermoplastic and thermoplastics co-polymers (different grades of copolyamide were prepared and doped with CNT by ARKEMA) with different weight fractions CNT,
- Optimization of the fibers processing methods by extrusion process
- Characterization of mechanical and electrical properties of these fibers and TECPAR manufactured fibers
The activities related to CANOE are compiled within D 2.6
CANOE developed and adapted the fabrication line of the fibers for CNT doped fibers. The work carried out by TECNALIA involved the stitching of CNT doped fibres into carbon fibre panels as a means of introducing CNTs into the bulk of the composite. EADS IW Germany performed trials using a tufting robot in order to insert conductive fibres (Polyamide +CNTs) in the transverse direction of the preform to improve the electrical conductivity in the z-direction. Initial basic mechanical testing (manual stretching to assess fibre response) showed that 4 fibres were unsuitable due to fragility and low cross sectional areas. These properties meant that the fibres could not be fed through the stitching rig without breaking. The stitching tests, revealed the doped fibers being developed by CANOE were not suitable for tecnalia’s type of processing. A lower elongation at break and a higher Young’s modulus would be necessary to realize the stitching trials. To obtain these mechanical properties, a higher stretch has to be applied to the fibers during the process. However, a higher stretching implies a higher orientation of CNT in the fiber. Several tests showed that an increase of stretching implies a decrease of electrical conductivities, below the value fixed by EADS IWG and TECNALIA.
In spite of several tests with higher stretching, the combination of electrical conductivity of 10 S/m with a higher young modulus was not achieved for the stitching trials. The activities related to stitching by TECNALIA and tufting by EADS IW G are compiled within D 2.6. CANOE continued the developments with new fibre based on other grades of polyamide with different melting points (i.e.Platamid HX2598). However initial trials suggest CNT % loading will not be sufficient for expected electrical properties. This line was abandoned and not considered to be implemented within the demonstrators
Dry Preform Development (based on non-woven veils)
TECPAR activities have the objective to develop and manufacture CNT doped veils. The objectives are:
- non-woven veil fabrication based on thermoplastic co-polyamide with different weight fractions of MWCNT,
- up-scaling of the veil fabrication method using melt blown technique and adjusting the veil fabrication parameters to obtain required GSM and homogeneous fibres distribution within the veil.
TECPAR started to work with the half-industrial scale machine for veils production – melt-blown process. Additionally, veils from fibers (fabricated by TECPAR as well as received from CANOE) were produced using pressing lab scale method by hot-pressing (details of the technique were reported in the P1 report). Master-batches were produced and supplied by ARKEMA, France. TECPAR succeed in manufacturing good quality veils with required areal weight (below 10g/m2 with 5.5wt.% MWCT from 7 wt.% MWCT MasterBatch. The average areal weight was 7.1 g/m2. Details of the manufacturing and characterization of veils can be found within D2.6 and P3.
The objectives of EADS IW G on dry preform development were the characterization, screening and selection of the Polyamide based materials (with and without carbon nanotubes). The objective was to investigate which new techniques are suitable for the incorporation of CNT into dry fibre preforms to obtain through thickness conductivity in composite laminates manufactured by liquid infiltration technologies. Among the most relevant methods to be investigated the following method was selected by EADS-IWG: the possibility of inserting the CNTs with non-woven veils as carrier in between the layers of structural fibres. After the results being obtained with the different grades of Polyamides, it was agreed on a single thermoplastic material to be used for non-wovens manufacturing: Platamid HX2598. This materials shows a melting domain (based on DSC) between 130-155ºC. EADS IW G set up a measurement protocol in order to measure the electrical conductivity of non-woven veils manufactured by TECPAR
A transverse conductivity of σDC = 5.10-4 S/m was found. Far below the requirements expected for this thermoplastic CNT carrier. The main problem encountered is the insufficient transverse electrical conductivity of the non-wovens materials delivered. This issue has been taken very seriously and is currently investigated by all partners involved in the development of the non-woven materials. All the activities developed by EADS on polyamide binder materials development is compiled within D2.6 and P3.
BAB addressed the theoretical analysis of materials available to achieve that objective (task mainly developed by scientific partners, where BAB has worked as support). Materials were assessed for their manufacturability and how well each can be integrated into the laminate using our standard processes. All materials were tested for their suitability/manufacturing capabilities:
1) The handling/application of the material
2) Preform capabilities (melt/tacking abilities)
3) Possible problems with infusion (incomplete wet-out resulting in washout)
4) Moisture Absorption
Then, the practical manufacturing test of materials identified to assess their suitability to the purpose in terms of range of working temperatures for preforming, infusion, cure and water absorption. These trials were made on three material versions: an extruded fibre veil, a melt-blow veil and granular masterbatch. It proved difficult to evenly spread the supplied granules, which varied in size, over the carbon fabric. In an effort to increase the dispersion, a sieve was used to remove the larger particles from the sample. Due to the nature of the materials it was necessary to vary the areal weight of the granule layers to maintain a network over each ply. Due to this variation in the homogeneity of the delivered materials, it’s difficult to draw a comparison of the preforming performances in between each. What we can say is that most of the materials can be used for preforming within the 150°C range originally specified by BAB for potential industrial use of the material itself with facilities in place at this moment. As a summary; in terms of manufacturing capabilities, all of the screened materials could be used in the manufacturing process of BAB, though; the granules are not recommended by BAB due to the method of application plus the health and safety risks posed by airborne particles and the PA12 would require the addition of a binder material to aid preforming.
Buckypaper development
CNT sheets or “buckypapers” are the last nanostructured preform addressed in the project by TECNALIA focusing the work on its development to be further manufactured in a continuous process pilot line, including design, building and setting up. The lab scale production facility was developed in previous FP7 projects (ADVITAC and LAYSA). During the first stages of ELECTRICAL the BP production at a lab scale was enhanced and adapted to the raw materials being prepared by Arkema. The step forwards to a pilot plant allowed to produce bigger BP with controlled properties (porosity, thickness) and high electrical conductivity.
BPs produced at this pilot plant did give good and promising results to achieve the main objective followed by Electrical: integration of CNT in common CFRP manufacturing processes to enhance the out of plane electrical properties. BP where selected as a technology to be further implemented in the production processes of CFRP laminates by the project partners. The BP dimensions and quality produced in the pilot plant were good enough to further analyse their potential in developing electrical functions. This fact meant that Tecnalia would have to manufacture a big amount of BP that would be introduced in CFRP manufacturing processes by Tecnalia, BAB, AESI and EADS F and combined with doped resin and CNT treated prepreg developed by UoP. Furthermore, an optimization of the dispersion and filtration processes was needed to be carried out at pilot plant scale since the properties of the different batches of the Arkema products presented several changes, causing problems in both steps: the new CNTs presented a higher agglomeration degree, to avoid the dangerous finest particles, therefore providing a reduction in the final properties of the manufactured BPs.
An important effort was also made with regard to provide a safer material to the end users, avoiding the direct handling of the BPs: An encapsulation process has been developed, in which the BP is placed between two CNT doped resin films (developed by Cytec), so the final preform can be handled in a safer way. A modified MSDS was generated for the encapsulated BP, in order to fulfil the requirements defined by BAB and to have their agreement on the delivery of this material (according to their H+S procedures)
This scenario lead to slight change in the project programme: the pilot plant was adopted as the BP manufacturing facility for the whole project. A continuous production equipment was designed but not built as described in D2.5. BP development history, from the lab scale to the plant scale is covered in D2.4
A basic scheme of the continuous pilot line has been established. The manufacturing processes involve three main phases that comprise the parameters to be analyzed:
• Initial phase: For the initial phase related to the manufacturing the BP as such, different parameters will be defined and tested, as the dispersion quality and the stability of the dispersion provided by Arkema, to avoid the powder manipulation. The most suitable filter material will also be assessed. For this purpose, different large scale commercially available filters will be analysed and different trials with different filters materials will be carried out. The quantity of dispersed CNT to be deposited must be optimized also according to the desired final BP thickness and to assure the reproducibility of the final BP. The vacuum system to be applied, the cleaning mechanism and the drying step will be studied as well.
• The second phase of the manufacturing process is related to the preparation and packing of the BP. Different optional parallel lines will be studied, according to the end users requirements and targets. Different final presentation of the BP could be made by different methods, enveloping the BP between resin films, preimpregnated in liquid resin, etc. In this case, the health and safety aspects will be fulfilled also, as the end users could receive the final product in safe conditions for further handling.
• The third phase will consist of the final BP characterization: Different properties as dimensions, thickness, density, porosity, permeability and electrical conductivity will be tested. SEM analyses will be also carried out to characterize the final product. The parameters setting up in each manufacturing stage must lead to have the BP with the final desired properties.
Once the final design is finished, the large scale pilot line will be outlined. Specific equipment will be necessary to use, including the tools that allow the quality control in each step of the product line.
Tecnalia is dedicated to the continued development of the BP manufacturing process and as such has brought together a consortium and coordinated a proposal for the H2020-NMP-PILOTS-2014 call. The proposed project will continue the development of the BP manufacturing line, with the work specifically focused on scaling the process up to a full pilot plant scale. The continuous BP manufacturing system detailed briefly here has been assessed further for the H2020 proposal. If successful, the system will be developed to process larger quantities of BPs whist at the same time offering greater in line control over the BP properties.
Composite Processing Set-up (WP3) and Development of multifunctionality (WP4)
WP3 dealt with nano-reinforced composite production through liquid infiltration technologies, as the main route, and autoclave curing as an alternative short-term manufacturing method. The strategies developed for CNT incorporation into composite laminates constitute the basis for further incorporation into composite components. Next table summarizes the different approaches considered for CNT incorporation into laminates, the level of success reached for the developments based on the ability to integrate CNTs within the carrier, the stability of the hosting matrix-CNT and the resulting properties
Technology Ability for CNT integration Stability matrix-CNT Properties Success
Bulk resin doping CNT doped resin Good Good high
CNT treated prepreg good good high
Novel engineered structures Fibers tufting good good Low
Fibers stitching good good Low
Veils good good high
Buckypapers good good high
The tuning of manufacturing processes is necessary in order to integrate successfully the CNTs. Process parameters such as temperature, pressure and resin curing kinetic will be adapted in order to obtain the required CFRP laminate quality (fibre volume content, good impregnation and CNT dispersion, lack of voids…), as well as to overcome the possible issues associated to the CNT introduction into the process.
The objectives for composite processing set up (WP3) are:
• Development of a manufacturing process to incorporate electrically conductive additives in the CFRP laminates: liquid infiltration of nanoreinforced resin as the main and baseline route, and autoclave technology as an alternative short-term manufacturing methos (risk-reduction)
• Design, fabrication, process optimization and overall characterization of small scale components using engineered multifunctional (Sensing and structural) nanomaterial-based elements
The processing routes for laminate manufactured are summarized in the following table.
Processing routes for the manufacture of functional laminates
Liquid Injection Technologies (RTM and Infusion)
Liquid doped resin and Buckypapers (Tecnalia)
Tecnalia focused its activity in optimizing the integration of CNTs in the CFRP laminates, using Liquid Injection Technologies. One of the proposed approaches in this line is related to the use of, on one hand doped resin, and on the other hand buckypapers as the first layer in the laminate. In the same way, the use of the doped resin and the buckypaper simultaneously in the same laminate was also considered. In every panel manufactured the presence of the filtering effect was carefully evaluated. Manufactured panels were based on the next formulations:
1. Undoped resin + carbon fabric (reference panel)
2. Doped resin (developed in WP2.1) + carbon fabric
3. Undoped resin + carbon fabric + buckypaper (developed in WP2.2)
4. Doped resin (developed in WP2.1) + carbon fabric + buckypaper (developed in WP2.2)
The infusion parameters for the composite manufacturing were established finding the following conclusions: In general a good dispersion can be observed. It is remarkable to see the presence of CNTs in the outlet part of the laminate, in the central area also, which can rule out the possible total filtering effect in the laminate. Regarding the doped resin + BP based laminate, also the BP has been well impregnated and well dispersed CNTs can be found in the central area of the laminate, even in the outlet part, in the central area. With respect to mechanical properties (ILSS) the doped laminate presents slightly higher values with respect to the neat resin laminate. Can be observed also that the BP, as expected, does not affect the mechanical properties, but unexpectedly the doped resin and BP based laminate show a slightly decrease with respect to the neat resin. These small differences can be due to the variability usually found in the infusion process.
In parallel to this study and taking into account that one of the aims of the project is to define and set-up a global electrical conductivity test method in order to have a common understanding, Tecnalia coordinated a cross check taking into account the high influence of the surface treatment in the final electrical conductivity values, especially in the case of X/Y direction. The cross check was performed between partners, in order to assess and compare the different methodologies in surface treatment and EC testing used by EADS-IW-F (applying pressure), AIR-F and TECNALIA (according to the AITM standard). As part of the study different surface treatments for the samples and the partner in charge to perform such treatment were identified
The results of the cross check are detailed in D3.3 and in the P2 report. As a summary: Regarding the EC results, different metallization and testing methods have been compared between different partners: For the X/Y direction, lower results are found for the doped resin based laminates. The electrodeposition type and the testing method affects to the final EC results. Regarding the Z direction results, the different metallization types give the same results except for the silver paste. In the same way as in the X/Y EC results, the CNT presence leads to have lower results than the ones get in the reference panel. The best formulation seem to be the doped resin+BP based laminate where an improvement of 30% has been found in Kz with respect to the neat resin panels, but on the contrary, a 26% decrease is observed for the X/Y direction
Two-Step Infiltration (University of Patras)
Two step infiltration techniques for LRI (TSI-LRI) involve the use of a carrier liquid (aqueous or organic solvent) of very low viscosity in which the CNT's are optimally dispersed. As first step of LRI process the CNT doped carrier liquid is injected into the mold and then drained from it. During this step, the large quantities of CNTs are attached on the fiber pre-form. The treated fiber pre-form is allowed via vacuum application to dry. The second step compromises from the conventional LRI procedure of resin injection. During this process the CNT treated fabric pre-form succeeds to retain most of its sticking CNTs allowing the production of a nano-doped composite FRP plate.
Under the framework of the ELECTRICAL project the TSI-LRI process is decided to be evaluated with CNT products from ARKEMA (CW2-45 Water soluble pellets or C-100 CNT raw powder product), MVR-444 advanced RTM resin system from CYTEC. Glass fiber reinforced composites (GFRP) were evaluated at the beginning in order to facilitate the process development while at final stage also trials with Carbon fiber reinforced composites (CFRP) were planned. All the trials carried out related to this technique are well documented within D3.2.
Final assessment is that TSI-LRI technique is most applicable for GFRP material due to its high potential on transforming electrical insulating materials to conductive. For CFRP materials due to the inherent high conductivity of carbon fibers the CNT “coating” provided with the additional step of TSI technique is not providing any further benefit.
CNT-modified preforms (non-woven Veils)
BAB carried out a series of mechanical (ILSS) and electrical tests (surface conductivity and through thickness conductivity) with the aim of identifying the most promising material(s) to be used in future primary aerospace structures manufactured via Resin infusion processes.
The qualitative and quantitative results of the so called preliminary test campaign for selection of materials are summarized in table below. To evaluate each material, we used a series of screening tests to assess its capabilities both pre and post cure. The areas looked at were;
• The handling/application of the material
• Its preforming capabilities (melt/tacking abilities)
• Possible problems with infusion (incomplete wet-out resulting in washout)
• Homogeneity/dispersion
• Electrical conductivity
• Mechanical properties (ILSS)
electrical mechanical
areal weight and CNT % conductivity ILSS
technology innovation area detailed description TRL surface - no mesh surface - with mesh volume RT H/W
BASELINE BASELINE .020 psf 97.6 gsm in use - 8 100% 100% 100% 100% 100%
thermoset doped carrier MVR444 epoxy powder binder 20 gsm, 25%CNT 2 175% N/A 333% 60% 73%
thermoplastic doped carrier Platamide PA80 115C melt 12 gsm, 7%CNT 2 95% N/A 286% 102% 42%
thermoplastic doped carrier blend of PA80 and PA12 20 gsm, 20%CNT 2 100% N/A 100% 80% 58%
thermoplastic doped carrier Platamide HX2598 12 gsm, 7%CNT 2 175% N/A 400% 90% 36%
thermoplastic doped carrier PA 12 12 gsm, 7%CNT 2 100% N/A 90% 90% 38%
Electrical & Mechanical Properties Matrix
Regarding the manufacturing impact, the materials supplied in granules were not easy to integrate into the carbon preforms with a good dispersion level. Only the panel that was manufactured with the blend of PA80 and PA12 displayed problems with infusion (dryness in the panel).
All of the doped carrier materials with the exception of the doped B-stage epoxy displayed ILSS results similar to that of the baseline when tested at room temperature, although when tested at hot wet, all materials had a negative effect relative to the baseline, with the most promising result coming from the B-stage epoxy, as can be seen in the table.
In relation to electrical conductivity, all materials performed as good as, if not better than the baseline through the thickness, though only the doped B-stage epoxy and the high temp melt Platamid performed better than the baseline on the surface.
Based on results above (compiled in D3.2 and D3.3) the following solutions were developed to be further implemented and characterized:
Material solution 1 Material ARKEMA Platamid TP HX2598 is the only selected thermoplastic carrier, and two routes are recommended to integrate it in veils:
• Between plies: the use of 5-7 gsm veils could help not to affect mechanical properties;
• As multiple layers on top of the laminate: for lightning Strike protection.
Material solution 2 to allocate CNT doped epoxy film (CYTEC-ARKEMA) on the outer layers to impact LSP.
Material solution 3 a layer of buckypaper (TECNALIA) fully encapsulated in two layers of CNT doped epoxy film to impact LSP.
EADS IW G performed preliminary trials mostly with two thermoplastic copolyamide based non-woven veils (unmodified and modified with 7,10%wt. CNT by ARKEMA) with high melting point (PA12), and low melting point (Platamid H106 PA80) manufactured and delivered by CANOE or TECPAR
EADS IW G performed trials to assess the implementation of CNTs in the preform using CNT modified polyamide veil (followed by vacuum assisted infusion) in order to improve the electrical conductivity in the z-direction
The materials were used as interlayers placed between each interlayer of preforms that were infused following vacuum assisted infusion afterwards. In order to evaluate the influence of the use of a polyamide CNT carrier, an investigation on the process-ability of the veils, the quality of the manufactured CFRP panel, water uptake and mechanical properties (ILSS) was done. The conclusion for this study (D3.2) was that an intermediate melting temperature copolyamide could behave better in process-ability and could bring the laminate to better properties. CNT-doped thermoplastic non-wovens veils were specially designed and manufactured for this purpose by Technology Partners, by melt-mixing an intermediate temperature melting (ITM: Platamid HX2598) copolyamide polymer with 5wt% CNTs. For comparison an unfilled Intermediate Temperature Melting veil (Platamid HX2598 without CNT) and a commercially available veil with 12 g/m² Low Temperature Melting Polyamide (Spunfab PA1541A) was used. Manufactured laminates were evaluated in terms of quality. Mechanical (Gic) and Electrical conductivity measurements were measured (D 3.3).
Unfortunately, no increase in conductivity could be observed due to the addition of CNTs, remaining far from the targeted conductivity. One explanation could be the insufficient conductivity provided by the doped non-wovens. Thus far, it was not yet possible to determine the electrical conductivity of the non-wovens themselves with the available equipment, though further trials are planned to determine the electrical conductivity of such non-woven material and explain these results. Moreover the Platamid HX2598 material exhibits a slightly lower conductivity compared to the Spunfab baseline material, which may be explained by varying thicknesses of the veil, causing a thicker insulation layer between the carbon layers, though this remains to be verified.
Prepreg Technology
Incorporation of Buckypapers with undoped prepregs (EADS-IW F)
To study the process-ability of buckypaper EADS IW F manufactured a specific laminate with some area with only prepreg; some area with prepreg and film resin between plies, some area with prepreg and buckypaper between plies and some area with prepreg buckypaper and film resin between plies to verify if the buckypaper could be infiltrated by the resin of the prepreg or if an additional layer of resin film with the buckypaper is needed. Details for the manufacturing and characterization are compiled within D3.2 D3.3 and P3
C-Scan observations on the manufactured panel revealed that the impregnation of the dry buckypaper by the resin of the prepreg is not possible when dry buckypaper are inserted between prepreg plies. Based on the obtained results with high level of porosity in the dry buckypaper, we stopped developing composite prepreg with addition of dry buckypaper between each prepreg layer. But when dry buckypaper is positioned on the top of the laminate as a first ply, the resin of the prepreg can impregnate correctly the dry buckypaper. The addition of a layer of dry buckypaper on the surface of composite laminate is possible at the lab scale. To asses the influence of the presence of BP in the electrical properties of the laminate only the addition of a dry buckypaper layer on the surface of the laminate was investigated for electrical characterization.
CNT doped prepregs
University of Patras developed the up-scaled prepreg treatment setup. Semi-automated hardware pre-preg modification assembly to allow the continuous treatment of higher amounts of EF6809 pre-pregs needed by EADS-IW-F for the envisioned manufacturing and testing. The final assessment for the selection of the nano-treated prepreg:
Processing Technologies CNT carrier Processing ability
Good (g)
Bad (b) Properties improvement:
Yes/no Comments &
GO/NO GO
Process Technology
Electrical
[S/m] Mechanical
PREPREG NANO-DOPED CS1-25 Medium YES ([0]14:KZ=0.01→0.51) NO NO-GO
NANO-TREATED CM2-20 Good YES ([0]16:KZ=0.78→4.55) NO GO
UOP worked on repairs and further upgrading plans for the semi-automated hardware pre-preg modification assembly.
UOP acted as CNT-treated prepreg material provider for EADS-IW-F using EF6809 prepreg material from CYTEC and CM2-20 powder from ARKEMA. EADS IW F assessed the processability of composite with CNT treated prepreg prepared by UoP from CNT doped thermoplastic powder with prepreg manufactured by Cytec.
First results on Electrical conductivity obtained did not show any no-go to continue the evaluation of this technology.
Based on the work performed on composite processing set-up and documented in deliverables D3.1 D3.2 and D3.3 the following technologies were selected to be further investigated for multifunctionality development (WP4)
The objectives for the development of multifunctionality phase were:
• Characterisation of composite laminates produced, mostly electrical behaviour characterisation and correlation with possible applications (static discharge, default current discharge, current return, interface shielding,…)
• Development of quality control technologies: Dielectric Mapping for monitoring and optimisation of CFRP curing process, and Electrical Resistance Tomography ERT for quality assurance of CFRp laminates
• To ensure multifunctional testing towards final user requirements
The manufacturing plan established for the characterization of composite laminates, mostly for electrical conductivity and the development of the sensing and damage detection approach is depicted in the next table
The testing plan:
Following the manufacturing and testing plans composite laminates were manufactured and tested during WP4 to see if they met the requirements in terms of, quality of the material, electrical conductivity, physic-chemical and mechanical properties. For that purpose a test matrix was defined. According to the test matrix BAB and TECPAR were responsible to measure the mechanical properties. BAB, EADS IW F, and AIR F were responsible to measure the electrical conductivity of developed material and performed lightning strike tests with damage expertise on material developed in the project
Liquid technologies
Mechanical properties (D4.3)
Sample Manufactured
by Solution G1C [J/m2] AITM 1.0005 Std. Dev. G2C [J/m2) AITM 1.0006 Std. Dev. DMA-Tg [C]
ASTM D 7028 Std. Dev. Charpy impact test
acu [kJ/m2] ISO 179 Std. Dev.
MVR-I-UD-8-1 TECNALIA
Infusion BASELINE 452 45 670 88 194,3 0,3 100,3 22,6
MVR-BP-A-CNT-0,1-I-UD-8-1 TECNALIA
Infusion 0,1%CNT doped resin+BP on top 373 12 620 64 193,6 0,6 116,3 12,0
13.49.02 Baseline EADS-IW-G
Infusion BASELINE
Non woven veils
Platamide HX2598 787 110 727 65 208,9 1,2 94,3 11,7
13.50.01 +CNTs EADS-IW-G
Infusion Doped non woven veils
(5%CNT) 464 61 974 207 209,4 0,7 93,8 16,6
Mode I fracture toughness (G1C) decreases for laminates with a layer of buckypaper on top of the laminates. This result appears strange as in principle the buckypaper should not affect the delamination of the laminate. For the laminates integrating non-woven veils as an interlayer between each fibre layer, Mode I shows a decrease while mode II fracture remains stable. With respect to impact the presence of the buckypaper increases the impact strength of the laminate as expected.
Looking at the results on CAI performed by BAB (see next figure) the following comments can be taken. The Encapsulated BP panel was very resin rich which is reflected in the results where it was the worst performing in terms of ultimate load. As there is only a layer of enhancement placed on the outside of the e-Buckypaper panel and the doped film panel, the performance is not expected to differ much from the baseline panel – this can be seen with the doped film panels having similar results across the three impact energies.
For the non-woven veils – there is no influence due to the presence of veils on the ultimate load nor on the delamination area
For the doped resin+ BP- BP slightly increases the ultimate load in the CAI testing while the delamination area becomes smaller as a result of the presence of the BP on top of the laminate.
Electrical properties were also measured for each of the configurations (D4.1).
Electrical conductivity measurements have been done on the manufactured composite with the methodology described in the D4.1 and in the P3. The results for EC are far from the requirements set at the beginning of the project. The best values are given by the samples based on the Technology 3 (e-BP), but in general, the nanotechnologies do not show improvement of the conductivity.
AIRF performed the LST on the infused panels manufactured by Tecnalia based on doped resin and a layer of BP (non- encapsulated) on top: The observation of the surface of the panel reveals puncture on the skin. This kind of damages is not acceptable
BAB performed the LST on the panels manufactured by infusion with the three technologies being approached and described in P3. Details of testing, figures and graphs are well presented in D4.1.
The best performing technology selected to be implemented in the demonstrative part was the Technology 3 based on e-buckypaper. The selection was based on the analysis of the different temperatures that were induced by each of the strikes on the panel as this result is indicative of how conductive the laminate is. The buckypaper fully encapsulated displayed the lowest temperature among the three technologies and close to that of the reference panel (including a Cu mesh).
Prepreg Technologies
Sample Manufactured
by Solution G1C [J/m2] AITM 1.0005 Std. Dev. G2C [J/m2) AITM 1.0006 Std. Dev. DMA-Tg [C]
ASTM D 7028 Std. Dev. Charpy impact test
acu [kJ/m2] ISO 179 Std. Dev.
JCI 1058 5557 EADS-IW-F
Prepreg BASELINE 378 32 468 37 218,3 0,4 120,1 10,3
REP 5601
Batch 1 CNTs EADS-IW-F
Prepreg CNT Doped prepreg
Batch1 392 23 2505 361 209,9 0,4 117,9 4,2
Batch 2 TECNALIA
Prepreg CNT doped prepreg
Batch 2 289 23 398 20 220,8 0,9 115,7 12,6
Batch 2 BP TECNALIA
Prepreg CNT doped prepreg batch2+ e-BP on top surface 274 21 417 27 219,9 0,2 118,3 12,0
With respect to the mechanical properties, higher ultimate load and lower delamination area for the CNT treated prepreg(batch 1) in the whole range of impact energies studied. Results are compiled in D4.3
EADS IW F performed LST on the prepreg based laminates:
The addition of a layer of dry buckypaper (during curing, the resin of the prepreg fill the gaps of the buckypaper) seems to improve the lightning strike properties of the composite if we consider the visible surface damage after lightning strike impact. The presence of the buckypaper on the composite surface reduces the delaminated area in the composite of about 25%. But the damage is still important and the buckypaper alone could not be used for lightning strike protection. The mixing of extended copper foil with buckypaper could be investigated in future program to verify if a weight reduction of the extended copper foil could be a possibility. If the buckypaper is embedded between 2 layers of resin film EF2713, the obtained results gives visually a very important damage area on the surface of the impact and also a visible delamination on the opposite face of the composite. The addition of CNT in the prepreg gives visually a more important damage on the impacted surface of the composite compare to the reference sample of composite The lightning strike impact results are very poor.
EADS IWF performed activities to set up the electrical conductivity measurements in x,y and z direction of the UD and QI composite materials manufactured integrating CNT treated prepreg and Buckypapers. The details for the tests and the results are compiled within P3 and D4.1. A summary of results can be seen in the table below:
Electrical conductivity measurement results on composite materials
WP5: Validation of technologies
The objectives of the WP are to validate the multifunctional composite with electrical conductivity and quality control systems developed in WP4 through its application on a macroscale representative aeronautic structure. Through this WP, design and manufacturing of scaled structural technological components will be carried out and the necessary testing and technical evaluations will be performed on the fabricated components. Representative scaled structural components incorporating the technologies developed and matured through the project were fabricated. Three type of demonstrators were manufactured integrating the three technologies. Two demonstrators were manufactured by infiltration and a third one was manufactured by prepreg.
Technology Technology developer demonstrator Manufacturer
Infusion/doped resin and encapsulated buckypaper on top TECNALIA representative aircraft fuselage panel AESI
Infusion/e-buckypaper TECNALIA representative aircraft fuselage panel BAB
Prepreg/CNT treated prepreg UoP representative aircraft fuselage panel EADS IW F
The purpose to assess the developed technologies by the fabrication of representative demostrators was twofold:
- To assess the manufacturability when integrating the technology and also to evaluate the scale up issues
- To evaluate the behaviour of the demonstrator against the lightning strike
All the details related to the manufacturing of the demonstrator can be found within D5.1. AESI and BAB were able to manufacture reference demonstrators as well as demonstrators integrating developed technologies for CNT integration into laminates. EADS IW F was not able to manufacture the demonstrator integrating CNT due to health and security reasons, since working with prepreg containing CNT has been forbidden by Airbus Group Innovation security department without any modification of the working conditions. The last modifications to allow working with prepreg containing CNT should be operational in October 2014. Due to that reason the manufacturing of the composite demonstrator with prepreg including CNT batch 2 from Patras University has been postponed.
The quality control techniques developed by INASCO were implemented during the manufacturing of the demonstrators at AERNNOVA facilities (D5.2)
Demonstrators manufactured by AESI and BAB were subjected to LST. The following conclusions can be drawn below:
Conclusions for AESI demonstrators:
The direct lightning effects on aircraft structures are of great importance nowadays, because of the massive use of composite materials in the new generations of aircrafts. In this project, Aernnova have tested four panels (two reference panels, plain and curved, with expanded copper foil and two panels with a buckypaper layer) under lightning strike test. The test results have shown some differences between the Copper mesh and buckypaper tested panels. The copper mesh performed a little better in resisting damage depth penetration than the buckypaper. The main conclusion is that the use of Buckypaper layer as a lightning strike protection is not suitable compared with copper mesh.
Conclusion for BAB demonstrator:
In terms of manufacturing, there is still some work to be done to reduce the defects that were identified in both of the panels, however it didn’t cause any major issues. At this stage, the encapsulated Buckypaper is not suitable for use as a lightning strike protection
Details for demonstrators testing are carefully explained within D5.2
WP6. Economical Evaluation, Exploitation and Dissemination
During the last stages of the project it was foreseen to develop the economical evaluation of the developed multifunctional systems, to include; material costs, manufacturing costs, operation costs and maintenance costs. These costs will be compared with the current costs of the traditional, ‘state-of-the-art’ systems. A detailed weight evaluation of the developed multifunctional systems will be done in order to determine the savings due to the enhanced electrical and mechanical performances. It was discussed and agreed in the presence of the project officer and co-ordinator at project meeting in Seville (13th June 2014) that devoting time and resources to this detailed evaluation and analysis would not be practical due to the technologies developed not being deemed viable for such application.
With respect to the exploitation plan D6.2 refers to an exploitation plan of the technologies and processes that have been developed within the project. The potential outputs for exploitation include;
• Innovative solution for bulk electrical conductivity with an important aircraft weight saving. This can be considered as the main outcome of the activity with potential applications in composite structures in different aeronautical products.
• An innovative solution for the control of manufacturing processes (proper resin curing status) and quality assurance of final component (delamination, inclusions etc.), with an important maintenance cost reduction.
• Innovative CNT engineered structures and CNT doped resin formulations
• Innovative solution for nano-reinforcements integration in CFRP
• Based on all partner inputs, the exploitation plan will be developed. The plan will establish the steps to bring the technology closer to an industrialized scheme.
Though there was no optimised multifunctional nanocomposite material developed within this project, there was a lot of knowledge and experience gained in areas such as doping methods, manufacturing procedures and developments in the screening of composite materials for electrical properties. The materials, with some further developments within the framework of, for example Horizon 2020, have potential application opportunities, as identified above, even beyond that of the aerospace industry
Within this framework, the consortium had the aim to disseminate and share, for financial and scientific reasons, the non-confidential, publishable information developed within the project, through media streams such as scientific and trade magazines and conferences. There was a lot of activity from all partners to write papers, organise and deliver presentations at various events throughout Europe. The work towards this deliverable started in month 24 when it was agreed with the organising committee of SETEC ’13 that there would be two sessions based around the work that was being carried out within the ELECTRICAL Project. The two sessions took place on the afternoon of Thursday 11th September and contained 6 papers consisting of inputs from all partners of the ELECTRICAL Consortia. The conference was attended by representatives from industrial and research communities.
When the 9 month extension in the project was granted, it was identified that there was an opportunity for further dissemination activity as a group and so papers were submitted during the call for ECCM16 to take place in Seville in June 2014. A session entitled ‘Electrical Properties of Continuous Fibre Reinforced Composites’ was organised and chaired by partners from Tecnalia and the University of Patras. Six out of the eight papers presented at this session came directly from the work within the ELECTRICAL project. Alongside these two group events, partners individually submitted papers, delivered presentations and submitted posters to various events to diffuse the work within the project, all of which are contained in D6.3.
Final remarks
The project for the first time allowed the transition from improved nanoreinforced resins to the exploitation of their enhanced electrical and mechanical properties in full laminates manufactured by automated process.
During the project, different strategies to incorporate carbon nanotubes in composite laminate using the common manufacturing process (infusion, RTM and/or prepreg) have been successfully investigated. The strategies supposed the study and understanding of the mechanisms that govern the behaviour of the doped resin during the infusion process, the development of dry engineered structures such as buckypapers to be implemented in infusion and prepreg, the exploitation of the thermoplastic interlayers commonly used as toughening materials as potential carbon nanotubes carriers to be implemented in infusion and prepreg and the development of specific treatments for commercial prepregs with carbon nanotubes. The three technologies further matured up to the end of the project: buckypapers, doped veils and CNT treated prepreg have been well adapted to the common composite manufacturing routes. The first goal of the project is that the technologies can be implemented in current manufacturing processes for composite laminates. The objective of the enhancement of the through the thickness electrical properties has been partly reached as the technologies allow to enhance the electrical conductivity in the z direction but none of them reach the conductivity values initially set in the project. With respect to lightning strike performance the technologies do not pass the minimum requirements as the surface impacted is damaged. However, the presence of the technologies diminishes on the lightening impacted surface and reduces lightly the total delaminated area the damage when compared to the panel with no Cu mesh on it. Therefore, the combination of the technologies with a lighter Cu mesh could be the basis for future activities. With respect to mechanical properties,
The fact that the CNT doped composite systems did not perform as well as existing solutions for the aggressive lightning strike tests, does not exclude them from use in other less aggressive electrical and thermo-electrical applications within the aircraft structure. These uses might include applications for edge glow, anti-icing and de-icing in which the inherent performance of the current solutions are more closely suited to the requirements of these systems. Further development and enhancement of doped composite structures, or the use of hybrid solutions, could enable the properties of these composite solutions to approach the requirements needed for LST protection.
WP7. Management and Coordination
The coordinator and the partners involved in project management have normally dealt with all the day to day administrative aspects:
• Management of funding
• Distribution of information from the EC to the consortium
• Organisation of consortium progress review meetings
• Preparation of periodic report
• Distribution of project reports and further deliverables to the EC
• Resolving of problems occurring between the partners during the project
More in detail, management activities are listed:
• Website of the project www.electrical-project.eu with the update information of the project. The website is divided in two different areas, one for public dissemination of the project and, the second one, only for project members.
• Organization of progress project meetings (KOM, 6 months, 12 months, 18 months and 24 months, 30months, 36 months and final meeting (45 months)
• Organization of the 36M PM in parallel to SAMPE Congress in Wuppertal (Germany) and 45M PM in parallel to ECCM16 in Sevilla (Spain).
• Organization of several technical teleconferences
• Preparation of the official reporting documents.
• Distribution of the funding between partners.
• Coordination of the diffusion actions in different forums (Aerodays 2011, SAMPE SETEC 2013, ECCM16, JEC Composites Show 2013)
• Preparation of two Amendments to the Contract (July 2011 and July 2013)
Potential Impact:
This project will increase the competitiveness of an important group of European Aeronautical companies, being the aeronautic sector one of the most innovative sectors with high R&D investments in Europe. Without this project, the parity situation with US manufacturers will not be maintained due to rapid developments at Boeing. Against Brazilian, Canadian, Russian and Chinese manufacturers Airbus leads by one generation (CFRP fuselage). With the work conducted within ELECTRICAL, this lead can be maintained. Without ELECTRICAL, these manufacturers will rapidly close the technological gap.
Targeted markets of ELECTRICAL are mainly the following:
- Primary market: composite fuselage parts for the next generation of large aircrafts. AIRBUS and EADS are the main beneficiaries of the products among the partners. AERNNOVA, as large composite structures manufacturer, either for AIRBUS and BOEING, will also benefit from the project outcomes.
For AIRBUS ELECTRICAL represents one of the major milestones of its internal Nanocomposite roadmap for the further development and implementation of Nanocomposites into commercial aircrafts. This foresees TRL2 to be reached in Q2 2010 and TRL3 in 2012. The implementation of ELECTRICAL is the key stepping stone for achieving this goal as well as the advancement to TRL4 post 2012
EADS strategy is to develop a full composite fuselage. ELECTRICAL will give potential solution to overcome the problem of poor electrical conductivity of composite materials.
- Second market: wings for business, regional and small commercial jet aircrafts. BAB as main end-user, and AERNNOVA as composite parts are the main beneficiaries of ELECTRICAL. The strategic importance to BAB is that it contributes to keep technological leadership with respect to other non-european major players. BAB is expecting a time-to-market of materials and technologies developed in a medium term to be implemented in future aircraft production
- Third market: Composite fuselage parts for helicopters. EADS group is the main end-user represented in the consortium (Eurocopter) and Aernnova a composite parts manufacturer for the main helicopter producers worldwide.
- Another important market, and fully in line with product development and market strategies of the company CYTEC, is related to advanced composite materials for aircrafts and other related markets where the new materials (prepregs, films, etc) developed in ELECTRICAL are to be applied (space, automotive,rail).
- Finally, related to nanomaterials, an important market addressed in the present project is referred to CNTs and new CNTs based resin formulations, with a big economic impact not only for the aerospace sector, but also for other sectors such as rail, automotive, sport and goods. ARKEMA, as one of the main European CNTs and CNTs based products manufacturers, is specially interested to participate in Electrical due to the expected economical benefit from the commercialization of the new products developed.
The main expected outputs for potential exploitation are summarised:
- Innovative solution for bulk electrical conductivity, with an important aircraft weight saving. This can be considered as the main outcome of the activity with potential applications in composite structures in different aeronautical products.
- Innovative solution for control of manufacturing process (proper resin curing status) and quality assurance of final component (delaminations, inclusions,.), with an important maintenance cost reduction.
- Innovative CNT engineered structures and CNTs doped resin formulations.
- Innovative solution for nanoreinforcements integration in CFRP and out-of-autoclave manufacturing methods for composites
The main objective of ELECTRICAL is the development of novel multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities for rapid non destructive quality assessment.
The project exploits properly the excellent properties of CNTs as polymeric resin doping for the development of novel multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities.
ELECTRICAL investigates and developes alternative emerging methods to manufacture nanoreinforced carbon based composites compatible with current industrial manufacturing processes of composites: incorporation of nanofillers into toughening thermoplastic fibers, non-woven veils, incorporation of nanofillers into nanostructured preforms called buckypapers, incorporation of nanofillers in injection resin and carbon fiber prepregs.
ELECTRICAL incorporates the following scientific and technical objectives:
a)Improvement of bulk electrical conductivity of aeronautical composite structures to meet requirements regarding static discharge, electrical bonding and grounding, interference shielding and current return through the structure. The technical approach will be based on the conductive properties of carbon based nanoreinforcements when integrated into the laminates.
At the same time, a global electrical conductivity test method will be defined and set-up in order to have a common understanding: Standardisation of electrical measurement and assessment procedures.
b)Monitoring and optimisation of CFRP curing process by Dielectric Mapping. Taking advantage of the electrical conductivity of CNTs, the dielectric sensor system mounted in the mould will perform non invasive measurements of the electrical properties of the material in the sensor´s vicinity for material-state monitoring (degree of cure, Tg), resin flow in moulds (arrival time, flow speed and direction) and end-of-cure detection.
c)Taking advantage of the piezoresistive behaviour of CNTs, development of innovative CFRP structures with distributed or localised self-sensing capabilities for quality assurance of final component (delaminations, inclusions, etc) by Electrical Resistance Tomography (ERT)
d)Development of state of the art fabrication technologies to convert nanofillers (CNTs and others) into engineered multifunctional preforms, prepregs, buckypapers, etc.. for further use in CFRP structures. CNTs bulk doped resins are also to be considered as the main base-line for investigation in the present project. Synergistic effects of using bulk doped resins and new developed engineered structures will also be under investigation.
e)Manufacture, characterisation and testing CFRP based materials with such multifunctional engineered nanostructures and bulk doped resins. The most broadly used liquid moulding technologies will be considered, although autoclave curing and associated prepreg development will also be considered as the base line.
f)Manufacture and testing of representative panels/prototypes for proof-of-concept of the materials and technologies developed.
g)Health, Environment and Safety issues derived from CNT handling will be specially considered in the project. Partners will be trained in the processing of nanomaterials in laboratory and industrial environment, which is a major issue in current development of these technologies.
Project Context and Objectives:
Based on the needs to provide advanced concepts and technologies for increased and optimised use of light-weight composite smart materials, the main objective of ELECTRICAL is the development of novel multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities for rapid non destructive quality assessment
The main challenges of the project can be summarized as follows:
This project for the first time allows the transition from improved nanoreinforced resins to the exploitation of their enhanced electrical and mechanical properties in full laminates manufactured by automated processes. As such, next generation aircraft structures can be estimated to be approximately 5% lighter than using Boeing B787 or Airbus A350XWB technology. Furthermore, synergy effects with other markets, such as sports goods, automotive, packaging and semiconductors could benefit significantly.
Research and technology development on nanoreinforced resins has been performed under public contracts for several years. However, cost efficient infusion technologies have to date not been able to be used with these resins primarily due to particle filtering during injection. It is the aim of this project to overcome this critical bottleneck by assessing and driving alternative nanoparticle introduction techniques as well as establishing processing windows for “traditional” nanocomposite formulations.
Therefore, it is established, as main technological challenge for ELECTRICAL, to increase electrical conductivity through-the-thickness of aeronautical CFRP laminates. Achieving this would enable an important reduction of the overall airframe weight by replacing current metallic structural network (metal mesh). In order to achieve that, several methods for introducing electrically conductive nanofillers into CFRP laminates have been assessed, establishing the use of bulk doped resin as a baseline for investigation, but developing new engineered nanomaterial based structures that would overcome problems of filtration and re-agglomeration. Differently from other current ongoing projects, where surface conductivity is the main issue for other functionalities, ELECTRICAL is focused on electrical conductivity through the laminate thickness.
In terms of mechanical properties, significant improvements in impact behavior are expected in addition to electrical conductivity, leading to a reduced burden on the environment by air travel. More importantly, allowing the consideration of CFRP bulk conductivity in aircraft design will lead to new aircraft architecture concepts with further weight savings and performance increases. In addition, potential self-sensing techniques can reduce unscheduled and scheduled inspection times and will allow a rapid quality assurance and enhanced manufacturing process control, revolutionizing CFRP manufacture.
The project exploits properly the excellent properties of CNTs as polymeric resin doping for the development of novel multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities. For that, different lines of work will be approached:
Firstly, this project investigates and developes alternative emerging methods to manufacture nanoreinforced carbon based composites compatible with current industrial manufacturing processes of composites
In particular, polymer injection processes will constitute the main project’s target, this including RTM, RTI, LRI and their variants, although autoclave curing is to be considered as the reference process. During the life of the project the following topics of research have been considered:
• Incorporation of nanofillers in dry carbon preforms.- The use of performs is typical when modern liquid composite moulding technologies are used; on one hand due to the necessity to incorporate toughening thermoplastic fibres and veils, and on the other hand due to the necessity to automate the process. This project investigates which technologies would enable the incorporation of nanofillers in these preforms before resin infiltration, mostly looking at the addition of nanofillers in between structural fabric layers in order to promote through-thickness conductivity. This way, the increased viscosity of the resin and the filtration effect when nanofillers are incorporated directly into the resin can be avoided. Several approaches have been tackled:
- Incorporation of nanofillers into toughening thermoplastic fibres. One route to provide an increase in toughness for brittle resins used in liquid injection technologies is the use of thermoplastic fibres that are introduced into the textiles used for the reinforcement. This can be achieved by co-weaving or more effectively by commingling structural fibres with tough thermoplastic fibres prior to the weaving of the fabric. The thermoplastic fibres can then, either dissolve in the thermosetting resin after infusion and during cure, or they can remain in the final composite as a solid fibre. Also the fibre can be used for a secondary stitching of standard structural reinforcements. The possibility of doping thermoplastic fibres with CNTs has been addresses in this project.
- Incorporation of nanofillers in polymeric non-woven veils. Another route to provide an increase in toughness is the use of an ultra-thin veil. During the resin infusion stage these veils are dissolved in the thermosetting resin. The incorporation of CNTs into the thermoplastic before producing the veils enables a better and more homogeneous incorporation during the infiltration.
• Preforming CNTs into thin mats with well-controlled dispersion and porous structure, so called “buckypaper”
• Incorporation of CNTs in injection resin. Alternatively to the incorporation of CNTs in dry carbon preforms, the incorporation of CNTs in the bulk liquid resin is also considered. The target of the project in this case is established on how to overcome the still pending technical challenges: optimal and stable dispersion of CNTs into the resin so that the mixture can be stable across time without any re-agglomeration effect, suitable CNTs/resin interfacial bonding and preserving integrity of CNTs during dispersion process.
• Modified or new injection strategies.-. The incorporation of CNTs into injection technologies, either into dry carbon preforms or as a buckypaper or into the bulk resin, will require at least a modification of injection processes, even in some cases the set up of new injection strategies. In the case of dry carbon performs or buckypaper the fibre permeability will be modified, while in the case of doped bulk resin the viscosity increase will modify their flow and filtering effect; at the same time than changing the curing kinetic of the polymer. Among others, the following strategies will be investigated as potential solutions:
- Tuning of process parameters for traditional technologies. This task would concentrate on the development of technical solutions to overcome the problem of viscosity increase and filtration above described: Optimization of temperature and/or pressure, modification of mould configuration (injection gates and vents), flow media, textile/performs permeability, etc.
- Two step infiltration for RTM and LRI. The possibility of using the RTM or other Liquid Resin Infiltration methods with CNT-doped resins has been investigated in the past with very poor results. The fiber preform is essentially acting as a filter, preventing the CNT particles from spreading along with the resin inside the preform, effectively keeping them in a small area around the injection nozzles. An alternative 2-step process that can eliminate these problems has been studied in laboratory conditions. The process involves pre-functionalised fiber preforms and use of a carrier liquid (aqueous or organic solvents) of very low viscosity in which the CNT's are dispersed.
• Alternatively the incorporation of CNTs into carbon fibre pre-pregs is considered. As above stated, filtration phenomena occurred during infiltration of performs with doped resins is a major problem yet to overcome. The strategy to be addresses within the project is the production of carbon fibre prepregs with doped resins. The incorporation of CNTs into prepreg for further production of laminates would enable electrical conductivity enhancement along the “z” axis of the laminate; the project analyses how the addition of CNTs can modify the prepreg processing along the different steps (resin doping, prepregging, storage, handling / lay-up and curing) to understand the processing of three phase composites with CNTs and their influence on final performance.
The prepreg technique requires a high viscosity resin that undergoes minimal flow, which reduces the mobility of CNTs during the curing process and therefore their possible re-agglomeration during this phase. However, the processing side-effects can not be completely ruled out because previously cross-linking is initiated by chemical reaction, the resin undergoes a minimum viscosity level. The influence of CNT content must be evaluated.
Secondly, the multifunctionality concept is approached, which consists of the integration of three main functionalities:
• Increase of electrical conductivity of CFRP laminates for indirect lightning strike protection, static discharge, electrical bonding and grounding, interference shielding and current return through the structure. Standardisation of electrical measurement and assessment procedures.
• Monitoring and optimisation of CFRP curing process by Dielectric Mapping. In order to monitor and optimize the process dielectric sensors will be incorporated in the mould used for CFRP curing. This technology, previously developed under the framework of different R&D projects, has been adapted to the materials and processes to be studied along the project.
• Quality assurance of final component (delaminations, inclusions, etc) by Electrical Resistance Tomography (ERT). This will be achieved by the integration of CNT fibres into the CFRP laminates. More precisely, this technology will be based on PVS/CNT fibres stitched on the standard structural reinforcements; the nano-doped fibre can act as distributed conductivity sensor for NDT using ERT
Description of work
The work breakdown structure defined to meet the main technological challenges and objectives is based on seven work packages, going forward through the main challenging tasks from definition of specifications towards manufacturing issues, testing and evaluation. Six work packages were devoted to technical matters, while the seventh will deal with coordination and managerial issues, as can be seen in the following diagram:
WP1 is devoted to the definition of targeted component types (composite structural part) and their specifications. This constitutes the base for a preliminary selection of materials (polymers and CNTs) and manufacturing processes.
The development of strategies for CNTs incorporation into laminates is approached in WP2. The structures here developed constitutes the basis for further incorporation into composite components. Two main approaches are considered during the first half of the project until month 18, the first one based on the incorporation of CNTs into thermoset resins for liquid technologies (RTM, etc) or prepregs (autoclave), and the second one based on innovative structures like CNT buckypapers, or dry performs based on CNT doped thermoplastic fibres, veils or films.
In this WP, a specific Milestone has been established in Month 18 as a Preliminary Review in order to assess technical achievements regarding electrical conductivity, mechanical performance, etc in order to select the most promising strategy for the applications considered. The second half of the WP and project focuses all the efforts in those most promising materials and technologies.
WP3 deals with nanoreinforced composite production through liquid infiltration technologies, as the main route, and autoclave curing as an alternative short-term manufacturing method (risk reduction).
In parallel to WP2 and 3, the WP4 is devoted to the characterisation of composite laminates produced, mostly for electrical conductivity, and development of the sensing and damage detection approach. Furthermore, parallel structural tests are carried out in order to evaluate how the nanofillers affect to mechanical properties.
Multifunctional composite with electrical conductivity and sensing systems developed in WP4 are validated in WP5. For that, representative scaled structural components incorporating the CNT-structures were designed, fabricated and technically evaluated in order to provide guidelines for optimal design. Moreover, safety and security aspects were considered.
The commercial evaluation of products obtained from previous develop will be carried out in WP6, in order to assess the potentialities to transfer to real applications. The diffusion and exploitation aspects will also be undertaken to address future activities and to establish a roadmap for the quick introduction in the market of the structural concept developed in the project
Project Results:
3. DESCRIPTION OF THE MAIN S&T RESULTS/FOREGROUNDS
WP1. Requirements. Specification of Materials, Processes and targeted Components
The objectives for this WP are:
• To precisely define the input data necessary to manage the whole technical issues: targeted component types (composite structural part) and their mechanical and electrical specifications, materials (polymers and nanomaterials) and manufacturing processes, (prefroming and laminate manufacturing), working program and configurations to be developed and evaluated
• To define a global electrical conductivity test method in order to have a common understanding: Standardisation of electrical measurements and assessment procedures
The technology to be developed in the project to achieve the main goal of developing novel aeronautical multifunctional composite structures with bulk electrical conductivity and self-sensing capabilities for rapid non destructive quality assessment, is the nanoreinforcement of CFRP airframes.
Definition of Target Parts
ELECTRICAL, as FP7 level 1 project, aims at contributing to mature the nanocomposite technologies for electrical application in aeronautical field, to TRL, technology readiness level, 2-3. Therefore, in this project the demonstration is planned at the level of stiffened panels, which will be representative of the selected structures (wing, fuselage).
Wing
• Composite structure: skin, stringers, ribs, ...
Figure 1 – Wing structure
Fuselage section
• Composite structure: skin, stringers, frames, ...
• Low level electrical function ESN parts (metal): frames, cross-beams, race-ways, ...
Figure 2 – Fuselage structure
Requirements
First priority objective of ELECTRICAL project is the improvement of the aeronautical CFRP structure electrical behaviour with the final aim of weight saving. The mechanical behaviour of CFRP structure at least needs to be maintained, being the mechanical enhancement in second place. Therefore, electrical requirements to be met by the nanoreinforced laminates to be developed in this project are key.
The following electrical constraints to be sustained by the aeronautical CFRP structure were identified. A detailed description is compiled within Deliverable D1.1&D1.2
a)Lightning strike: direct and indirect effects
The requirement for the resistance per square of future CFRP fuselages will be between 1 and 6 mΩ per square
b) Edge glow (CFRP edges), sparking (CFRP bolted joints)
During some lightning strike lab tests on coupons made of last generation thermoset matrix like the M21E, some sparking have been observed on the coupon edges. This phenomenon, which is called edge glow, must be avoided in fuel tank areas
c)Electrical bonding: handling of electrical current due to a short circuit inside a system
The electrical bonding is the return of fault, defect currents in the aircraft. The path of the bonding current circulates through structural CFRP elements. Currently a specific metallic network is used for new generation aircrafts with CFRP fuselage to carry out this function. The network is named MBN (Metallic Bonding Network).
This network usually merges with the metallic structural parts like seat-tracks to perform an aircraft mesh which permits to evacuate the function and fault currents of the different systems, the full network in fuselage area is the ESN (Electrical Structural Network).
Nevertheless, it is necessary to add specific components (metallic strips) to each frame and crossbeam of the aircraft to insure the electrical continuity answering to the global specifications of all the systems. The sum of the elements constitutes a complex mesh like the virtual mock-up bellow
For the electrical bonding function, a current of 2000 A for 300 ms needs to be considered
d) Short circuits between wire and CFRP
The short circuit involves the direct contact of an electrical wire with the CFRP.
3 different short circuit issues have been identified:
• Direct on CFRP
• Bundle exploded near the CFRP
• Behavior of CFRP junctions submitted to a failure
e)Electrical grounding: systems functional current return
The electrical grounding is the systems functional electrical current return. Electrical current return refers to the establishment of a low impedance current path between the power supply reference (0 V DC, 0 V AC or AC Neutral) of an electrical component and the aircraft point of voltage reference.
For electrical grounding, the following requirements need to be considered:
- Continuous electrical currents: Low: 10 A, Medium: 20 A, High: 200 A
- This current shall not lead to a resin temperature increase above a temperature at least 28°C below the resin Tg
- Electro-thermal aging
In the following table a raking of the electrical functions to be covered and aimed at by the nanocomposite technology within the ELECTRICAL project is shown. This ranking was performed taking into account the electrical requirements and, then, the probability of success.
Ranking of electrical functions
Materials and Processes
The materials and processes selected for the project are:
Laminate Materials
Thermoplastic preform materials
One of the key research lines of the ELECTRICAL project to obtain nanoreinforced infused laminates is the introduction of CNT in the infusion textile preform thermoplastic materials (veils), with the main aim of avoiding filtering problems associated to the nanodoped bulk resin infusion.
The following requirements need to be met by the nanodoped thermoplastic materials to be introduced in the infusion textile preform:
Key requirements
• No wash-out: poor solubility in the laminate matrix at the infusion temperature (120°C) during the infusion time (120 minutes / 2 hours)
• Good adhesion to the laminate matrix after cure.
• No negative influence on thermo-mechanical properties (hot-wet)
• Binding parameters: Veil target weight: 6 g/m2 for 268 g/m2 UD CFRP layer
A complete compilation of potential thermoplastic materials to be used as nanocarriers was done (refer D1.1&D1.2). From this table the following thermoplastic material was selected: Platamide Copolyamide (Arkema). Two grades: 110ºC and 135ºC melting Temperature. It is important to remark that the selected material should perform both functions: Nanocarrier and binder. Additionally, some basic infusion trials will be done by EADS IW - G with higher melting temperature polyamides, supplied by Arkema: PA6 (210 ºC) and PA12 (176 ºC).
Nanomaterials
The CNT selected for the project are compiled in the following table.
System Selected material
CNT MASTERBATCH:
First priority • PLATAMID (copolyamide): fibers and veil application to be supplied by ARKEMA
• MVR444/EF6809: premixture to be supplied by CYTEC to ARKEMA to produce a masterbacth
• CW245: CMC (carboxymethyl cellulose) based masterbatch to be supplied by ARKEMA
MWCNT
POWDER • ARKEMA-C100: for nanodoped prepreg production by Patras University and for buckypaper production by Tecnalia
Testing
Electrical testing
The proposed electrical test methods are compiled in the table below. As for the electrical conductivity, it is important to remark that it is a goal of this project to develop an appropriate test method. However, as these measurements are needed in the project early phase in order to assess the value of the different techniques before entering the phase of the listed tests, appropriate test methods have been identified to carry out these measurements.
Lightning strike direct effects on fuselage panel
The behaviour of the investigated material under lighting strike shall be compared to the one of the current baseline, i.e. the A350-900 fuselage skin configuration.
The A350-900 baseline for the fuselage skin is the following one:
9 plies of M21E/IMA, FAW: 194 g/m2, RC: 34%, lay-up: [45/0/135/90/0/90/135/0/45]
Expanded copper foil, AW: 195 g/m2, impregnated by 170 g/m2 of surfacing film
Top layers:
The external paint system shall be representative of the A350XWB-900. The targeted external paint system thickness will be about 330 μm. With such a thickness and taking into account around 30 μm of basic primer and 90 μm of surfacing film on top of the ECF, the total thickness on top of the ECF should be around 450 μm.
Sample dimensions:
For lightning strike tests at the LCOE lab (Getafe, Spain) or at Lightning Technologies (Culham, UK), the samples shall have the dimensions presented in figure 12.
For lightning strike tests at the DGA-TA, the dimensions of the samples need to be indicated by the relevant specialists.
Mechanical testing
The proposed mechanical tests in the project are compiled in the following table. These tests should be done at room temperature, that is hot/wet tests will not be carried out, due to the relatively low TRL of the ELECTRICAL project.
Physico-chemical testing
The proposed physico-chemical tests are included in the next table.
Non-destructive ultrasonic inspection of all the manufactured panels / specimens were carried out in order to ensure their quality.
Microscopy evaluation (SEM) was performed to assess the quality of the nanomaterial dispersion in the manufactured panels / specimens. More detail information can be found within D1.1 (definition and requirements of structural parts) and D1.2 (definition of materials and processes).
WP2. Development of Strategies for Incoporation of CNTs
This work package aims at the development of strategies for the incorporation of CNTs into the composite laminates, which constitutes the basis for further incorporation into composite components. Different approaches for CNT incorporation were considered:
• Incorporation of CNT into thermoset resins for liquid technologies (RTM,etc) or prepregs
• Incorporation of CNTs as innovative structures like buckypapers, or dry preforms based on doped thermoplastic fibers, veils or films.
Due to concern related to the use of nanomaterials, health, Environment and Safety issues derived from CNT handling were specially considered in the project. Partners were trained prior to the start of the activities related to the handling and use of nanomaterials in both laboratory and industrial environment since it is considered a major issue in the current development and uptake of these technologies. A security training course for the handling of nanomaterials and in particular carbon nanotubes (CNT) materials was organised. This training course took place during the Electrical meeting organized in France by Arkema at the research center of Lacq (GRL) in october 2011. CANOE organized this training course in collaboration with Arkema. This training course was organized for a day and was composed of 5 parts:
- 1st part : General aspects of nanomaterials and nanotechnologies (by Pr Daniel Bernard) : 8H30-9H00
- 2nd part : Regulation and normalization at international level (by Pr Daniel Bernard) : 9h30-10h00
- 3d part : Health and safety at work station/Metrology and characterization problems (by Serge Bordere, ARKEMA) : 10h00-10h45
- 4th part : Visit of GRL work stations : 10h45 – 12h30
- 5th part : Discussions with partners : 12H30-13H00
The 6M Progress meeting was deliberately held at ARKEMA in order to include the security training ahead of the main scientific programme. Eventhough it was scheduled within WP5 the consortium considered to celebrate the workshop at the earliest possible date (see D5.3).
In WP2 two major technologies are approached. Each of them covers two research lines where different partners took part:
• Bulk resin doping
o 2.1A Liquid technologies (doped resin)
CYTEC, ARKEMA, TECNALIA, BOMBARDIER
o 2.1B Prepreg development
CYTEC, ARKEMA, UoP
• Novel engineered structures
o 2.2A Dry preform development
ARKEMA, CANOE, TECPAR, TECNALIA, EADS-IW-G, BOMBARDIER
o 2.2B Buckypaper development
TECNALIA, UoP, BOMBARDIER
The work carried out in WP2 during the 36 months of the project is contained in the 1st and 2nd periodic reports. The following paragraphs intend to give a general overview of objectives, activities and results obtained in this WP.
BULK RESIN DOPING
Liquid technologies
The activities of Tecnalia have been focused on the development of CNT doped resin to be used in composite laminates manufacturing by liquid technologies. Tecnalia has been working in close cooperation with Cytec for the development and supply of the MVR 444 resin in two parts and with ARkema for the development of CNT masterbatches. In summary the activities related to bulk resin doping answer to three Approaches:
-Approach 1: the MB based on part A of the MVR444 resin (extrusions)
-Approach 2: Two MB based on MVR444 (A+B) containing 25%wt of CNTs, in two formats: pellets (p) and granules (g)
-Approach 3: For this approach, the MB based on part A of the MVR444 resin (approach 1) was converted to pellets by Arkema.
The work performed in the frame of this activity (masterbatches treatment, characterization –rheology, electrical and mechanical- is carefully described in D 2.6. Main conclusions of the work carried out in the doping of epoxy resin with part A based masterbatch in pellet form, it can be summarized as follows: Electrical conductivity of E-6 S/m is obtained with 0.1 wt.% CNT. This conductivity value is similar to that obtained with CNTs in powder form, and approximately 4 orders of magnitude higher than the conductivity obtained with the previous masterbatches. Rheological results reveal that the quality of dispersion is good and carbon nanotubes have an accelerating effect in the curing of epoxy resin. However, the nanocomposites based on this nanomaterial show narrower processing window than that required by BAB.
Prepreg developement
UOP lead this task along with support from CYTEC. Objective of this WP was to develop various strategies for the incorporation of CNTs into the composite laminates, which constituted the basis for further incorporation into composite components.
The Process Development Plan agreed (11/01/2012) that takes into account CYTEC material IP limitations consists of three (3) distinct Routes:
Route 1 (Direct Doping): Direct doping of EF6809 resin system used to produce CYTEC pre-pregs. Part A of EF6809 is shipped to UOP where the CNT dispersion was performed. CNT doped part A of EF6809 is returned to CYTEC where complete EF6809 formulation is created. This CNT-doped EF6809 resin system is used by CYTEC to produce a CNT-doped EF6809 pre-preg.
Route 2 (Resin Film Treatment): CNT- treatment of conventional EF6809 resin films of CYTEC. Fully formulated resin film (EF6809) is shipped to UOP. UOP using various CNT deposition/integration techniques produces CNT treated ELE-EF6809 film.
Route 3 (Prepreg Treatment): CNT-Treatment of conventional EF6809 prepreg materials of CYTEC. Conventional EF6809 pre-preg is shipped to UOP. UOP using various CNT deposition techniques produces the CNT-treated EF6809 pre-preg. Two bacthes were manufactured with the second having improvements over the first
All the activities UoP performed for the development and manufacturing of CNT treated prepreg are compiled within D2.6
NOVEL ENGINEERED STRUCTURES
Dry preform development
Nano-doped fibres
The activities performed by CANOE followed the objectives:
- Fibers fabrication based on thermoplastic and thermoplastics co-polymers (different grades of copolyamide were prepared and doped with CNT by ARKEMA) with different weight fractions CNT,
- Optimization of the fibers processing methods by extrusion process
- Characterization of mechanical and electrical properties of these fibers and TECPAR manufactured fibers
The activities related to CANOE are compiled within D 2.6
CANOE developed and adapted the fabrication line of the fibers for CNT doped fibers. The work carried out by TECNALIA involved the stitching of CNT doped fibres into carbon fibre panels as a means of introducing CNTs into the bulk of the composite. EADS IW Germany performed trials using a tufting robot in order to insert conductive fibres (Polyamide +CNTs) in the transverse direction of the preform to improve the electrical conductivity in the z-direction. Initial basic mechanical testing (manual stretching to assess fibre response) showed that 4 fibres were unsuitable due to fragility and low cross sectional areas. These properties meant that the fibres could not be fed through the stitching rig without breaking. The stitching tests, revealed the doped fibers being developed by CANOE were not suitable for tecnalia’s type of processing. A lower elongation at break and a higher Young’s modulus would be necessary to realize the stitching trials. To obtain these mechanical properties, a higher stretch has to be applied to the fibers during the process. However, a higher stretching implies a higher orientation of CNT in the fiber. Several tests showed that an increase of stretching implies a decrease of electrical conductivities, below the value fixed by EADS IWG and TECNALIA.
In spite of several tests with higher stretching, the combination of electrical conductivity of 10 S/m with a higher young modulus was not achieved for the stitching trials. The activities related to stitching by TECNALIA and tufting by EADS IW G are compiled within D 2.6. CANOE continued the developments with new fibre based on other grades of polyamide with different melting points (i.e.Platamid HX2598). However initial trials suggest CNT % loading will not be sufficient for expected electrical properties. This line was abandoned and not considered to be implemented within the demonstrators
Dry Preform Development (based on non-woven veils)
TECPAR activities have the objective to develop and manufacture CNT doped veils. The objectives are:
- non-woven veil fabrication based on thermoplastic co-polyamide with different weight fractions of MWCNT,
- up-scaling of the veil fabrication method using melt blown technique and adjusting the veil fabrication parameters to obtain required GSM and homogeneous fibres distribution within the veil.
TECPAR started to work with the half-industrial scale machine for veils production – melt-blown process. Additionally, veils from fibers (fabricated by TECPAR as well as received from CANOE) were produced using pressing lab scale method by hot-pressing (details of the technique were reported in the P1 report). Master-batches were produced and supplied by ARKEMA, France. TECPAR succeed in manufacturing good quality veils with required areal weight (below 10g/m2 with 5.5wt.% MWCT from 7 wt.% MWCT MasterBatch. The average areal weight was 7.1 g/m2. Details of the manufacturing and characterization of veils can be found within D2.6 and P3.
The objectives of EADS IW G on dry preform development were the characterization, screening and selection of the Polyamide based materials (with and without carbon nanotubes). The objective was to investigate which new techniques are suitable for the incorporation of CNT into dry fibre preforms to obtain through thickness conductivity in composite laminates manufactured by liquid infiltration technologies. Among the most relevant methods to be investigated the following method was selected by EADS-IWG: the possibility of inserting the CNTs with non-woven veils as carrier in between the layers of structural fibres. After the results being obtained with the different grades of Polyamides, it was agreed on a single thermoplastic material to be used for non-wovens manufacturing: Platamid HX2598. This materials shows a melting domain (based on DSC) between 130-155ºC. EADS IW G set up a measurement protocol in order to measure the electrical conductivity of non-woven veils manufactured by TECPAR
A transverse conductivity of σDC = 5.10-4 S/m was found. Far below the requirements expected for this thermoplastic CNT carrier. The main problem encountered is the insufficient transverse electrical conductivity of the non-wovens materials delivered. This issue has been taken very seriously and is currently investigated by all partners involved in the development of the non-woven materials. All the activities developed by EADS on polyamide binder materials development is compiled within D2.6 and P3.
BAB addressed the theoretical analysis of materials available to achieve that objective (task mainly developed by scientific partners, where BAB has worked as support). Materials were assessed for their manufacturability and how well each can be integrated into the laminate using our standard processes. All materials were tested for their suitability/manufacturing capabilities:
1) The handling/application of the material
2) Preform capabilities (melt/tacking abilities)
3) Possible problems with infusion (incomplete wet-out resulting in washout)
4) Moisture Absorption
Then, the practical manufacturing test of materials identified to assess their suitability to the purpose in terms of range of working temperatures for preforming, infusion, cure and water absorption. These trials were made on three material versions: an extruded fibre veil, a melt-blow veil and granular masterbatch. It proved difficult to evenly spread the supplied granules, which varied in size, over the carbon fabric. In an effort to increase the dispersion, a sieve was used to remove the larger particles from the sample. Due to the nature of the materials it was necessary to vary the areal weight of the granule layers to maintain a network over each ply. Due to this variation in the homogeneity of the delivered materials, it’s difficult to draw a comparison of the preforming performances in between each. What we can say is that most of the materials can be used for preforming within the 150°C range originally specified by BAB for potential industrial use of the material itself with facilities in place at this moment. As a summary; in terms of manufacturing capabilities, all of the screened materials could be used in the manufacturing process of BAB, though; the granules are not recommended by BAB due to the method of application plus the health and safety risks posed by airborne particles and the PA12 would require the addition of a binder material to aid preforming.
Buckypaper development
CNT sheets or “buckypapers” are the last nanostructured preform addressed in the project by TECNALIA focusing the work on its development to be further manufactured in a continuous process pilot line, including design, building and setting up. The lab scale production facility was developed in previous FP7 projects (ADVITAC and LAYSA). During the first stages of ELECTRICAL the BP production at a lab scale was enhanced and adapted to the raw materials being prepared by Arkema. The step forwards to a pilot plant allowed to produce bigger BP with controlled properties (porosity, thickness) and high electrical conductivity.
BPs produced at this pilot plant did give good and promising results to achieve the main objective followed by Electrical: integration of CNT in common CFRP manufacturing processes to enhance the out of plane electrical properties. BP where selected as a technology to be further implemented in the production processes of CFRP laminates by the project partners. The BP dimensions and quality produced in the pilot plant were good enough to further analyse their potential in developing electrical functions. This fact meant that Tecnalia would have to manufacture a big amount of BP that would be introduced in CFRP manufacturing processes by Tecnalia, BAB, AESI and EADS F and combined with doped resin and CNT treated prepreg developed by UoP. Furthermore, an optimization of the dispersion and filtration processes was needed to be carried out at pilot plant scale since the properties of the different batches of the Arkema products presented several changes, causing problems in both steps: the new CNTs presented a higher agglomeration degree, to avoid the dangerous finest particles, therefore providing a reduction in the final properties of the manufactured BPs.
An important effort was also made with regard to provide a safer material to the end users, avoiding the direct handling of the BPs: An encapsulation process has been developed, in which the BP is placed between two CNT doped resin films (developed by Cytec), so the final preform can be handled in a safer way. A modified MSDS was generated for the encapsulated BP, in order to fulfil the requirements defined by BAB and to have their agreement on the delivery of this material (according to their H+S procedures)
This scenario lead to slight change in the project programme: the pilot plant was adopted as the BP manufacturing facility for the whole project. A continuous production equipment was designed but not built as described in D2.5. BP development history, from the lab scale to the plant scale is covered in D2.4
A basic scheme of the continuous pilot line has been established. The manufacturing processes involve three main phases that comprise the parameters to be analyzed:
• Initial phase: For the initial phase related to the manufacturing the BP as such, different parameters will be defined and tested, as the dispersion quality and the stability of the dispersion provided by Arkema, to avoid the powder manipulation. The most suitable filter material will also be assessed. For this purpose, different large scale commercially available filters will be analysed and different trials with different filters materials will be carried out. The quantity of dispersed CNT to be deposited must be optimized also according to the desired final BP thickness and to assure the reproducibility of the final BP. The vacuum system to be applied, the cleaning mechanism and the drying step will be studied as well.
• The second phase of the manufacturing process is related to the preparation and packing of the BP. Different optional parallel lines will be studied, according to the end users requirements and targets. Different final presentation of the BP could be made by different methods, enveloping the BP between resin films, preimpregnated in liquid resin, etc. In this case, the health and safety aspects will be fulfilled also, as the end users could receive the final product in safe conditions for further handling.
• The third phase will consist of the final BP characterization: Different properties as dimensions, thickness, density, porosity, permeability and electrical conductivity will be tested. SEM analyses will be also carried out to characterize the final product. The parameters setting up in each manufacturing stage must lead to have the BP with the final desired properties.
Once the final design is finished, the large scale pilot line will be outlined. Specific equipment will be necessary to use, including the tools that allow the quality control in each step of the product line.
Tecnalia is dedicated to the continued development of the BP manufacturing process and as such has brought together a consortium and coordinated a proposal for the H2020-NMP-PILOTS-2014 call. The proposed project will continue the development of the BP manufacturing line, with the work specifically focused on scaling the process up to a full pilot plant scale. The continuous BP manufacturing system detailed briefly here has been assessed further for the H2020 proposal. If successful, the system will be developed to process larger quantities of BPs whist at the same time offering greater in line control over the BP properties.
Composite Processing Set-up (WP3) and Development of multifunctionality (WP4)
WP3 dealt with nano-reinforced composite production through liquid infiltration technologies, as the main route, and autoclave curing as an alternative short-term manufacturing method. The strategies developed for CNT incorporation into composite laminates constitute the basis for further incorporation into composite components. Next table summarizes the different approaches considered for CNT incorporation into laminates, the level of success reached for the developments based on the ability to integrate CNTs within the carrier, the stability of the hosting matrix-CNT and the resulting properties
Technology Ability for CNT integration Stability matrix-CNT Properties Success
Bulk resin doping CNT doped resin Good Good high
CNT treated prepreg good good high
Novel engineered structures Fibers tufting good good Low
Fibers stitching good good Low
Veils good good high
Buckypapers good good high
The tuning of manufacturing processes is necessary in order to integrate successfully the CNTs. Process parameters such as temperature, pressure and resin curing kinetic will be adapted in order to obtain the required CFRP laminate quality (fibre volume content, good impregnation and CNT dispersion, lack of voids…), as well as to overcome the possible issues associated to the CNT introduction into the process.
The objectives for composite processing set up (WP3) are:
• Development of a manufacturing process to incorporate electrically conductive additives in the CFRP laminates: liquid infiltration of nanoreinforced resin as the main and baseline route, and autoclave technology as an alternative short-term manufacturing methos (risk-reduction)
• Design, fabrication, process optimization and overall characterization of small scale components using engineered multifunctional (Sensing and structural) nanomaterial-based elements
The processing routes for laminate manufactured are summarized in the following table.
Processing routes for the manufacture of functional laminates
Liquid Injection Technologies (RTM and Infusion)
Liquid doped resin and Buckypapers (Tecnalia)
Tecnalia focused its activity in optimizing the integration of CNTs in the CFRP laminates, using Liquid Injection Technologies. One of the proposed approaches in this line is related to the use of, on one hand doped resin, and on the other hand buckypapers as the first layer in the laminate. In the same way, the use of the doped resin and the buckypaper simultaneously in the same laminate was also considered. In every panel manufactured the presence of the filtering effect was carefully evaluated. Manufactured panels were based on the next formulations:
1. Undoped resin + carbon fabric (reference panel)
2. Doped resin (developed in WP2.1) + carbon fabric
3. Undoped resin + carbon fabric + buckypaper (developed in WP2.2)
4. Doped resin (developed in WP2.1) + carbon fabric + buckypaper (developed in WP2.2)
The infusion parameters for the composite manufacturing were established finding the following conclusions: In general a good dispersion can be observed. It is remarkable to see the presence of CNTs in the outlet part of the laminate, in the central area also, which can rule out the possible total filtering effect in the laminate. Regarding the doped resin + BP based laminate, also the BP has been well impregnated and well dispersed CNTs can be found in the central area of the laminate, even in the outlet part, in the central area. With respect to mechanical properties (ILSS) the doped laminate presents slightly higher values with respect to the neat resin laminate. Can be observed also that the BP, as expected, does not affect the mechanical properties, but unexpectedly the doped resin and BP based laminate show a slightly decrease with respect to the neat resin. These small differences can be due to the variability usually found in the infusion process.
In parallel to this study and taking into account that one of the aims of the project is to define and set-up a global electrical conductivity test method in order to have a common understanding, Tecnalia coordinated a cross check taking into account the high influence of the surface treatment in the final electrical conductivity values, especially in the case of X/Y direction. The cross check was performed between partners, in order to assess and compare the different methodologies in surface treatment and EC testing used by EADS-IW-F (applying pressure), AIR-F and TECNALIA (according to the AITM standard). As part of the study different surface treatments for the samples and the partner in charge to perform such treatment were identified
The results of the cross check are detailed in D3.3 and in the P2 report. As a summary: Regarding the EC results, different metallization and testing methods have been compared between different partners: For the X/Y direction, lower results are found for the doped resin based laminates. The electrodeposition type and the testing method affects to the final EC results. Regarding the Z direction results, the different metallization types give the same results except for the silver paste. In the same way as in the X/Y EC results, the CNT presence leads to have lower results than the ones get in the reference panel. The best formulation seem to be the doped resin+BP based laminate where an improvement of 30% has been found in Kz with respect to the neat resin panels, but on the contrary, a 26% decrease is observed for the X/Y direction
Two-Step Infiltration (University of Patras)
Two step infiltration techniques for LRI (TSI-LRI) involve the use of a carrier liquid (aqueous or organic solvent) of very low viscosity in which the CNT's are optimally dispersed. As first step of LRI process the CNT doped carrier liquid is injected into the mold and then drained from it. During this step, the large quantities of CNTs are attached on the fiber pre-form. The treated fiber pre-form is allowed via vacuum application to dry. The second step compromises from the conventional LRI procedure of resin injection. During this process the CNT treated fabric pre-form succeeds to retain most of its sticking CNTs allowing the production of a nano-doped composite FRP plate.
Under the framework of the ELECTRICAL project the TSI-LRI process is decided to be evaluated with CNT products from ARKEMA (CW2-45 Water soluble pellets or C-100 CNT raw powder product), MVR-444 advanced RTM resin system from CYTEC. Glass fiber reinforced composites (GFRP) were evaluated at the beginning in order to facilitate the process development while at final stage also trials with Carbon fiber reinforced composites (CFRP) were planned. All the trials carried out related to this technique are well documented within D3.2.
Final assessment is that TSI-LRI technique is most applicable for GFRP material due to its high potential on transforming electrical insulating materials to conductive. For CFRP materials due to the inherent high conductivity of carbon fibers the CNT “coating” provided with the additional step of TSI technique is not providing any further benefit.
CNT-modified preforms (non-woven Veils)
BAB carried out a series of mechanical (ILSS) and electrical tests (surface conductivity and through thickness conductivity) with the aim of identifying the most promising material(s) to be used in future primary aerospace structures manufactured via Resin infusion processes.
The qualitative and quantitative results of the so called preliminary test campaign for selection of materials are summarized in table below. To evaluate each material, we used a series of screening tests to assess its capabilities both pre and post cure. The areas looked at were;
• The handling/application of the material
• Its preforming capabilities (melt/tacking abilities)
• Possible problems with infusion (incomplete wet-out resulting in washout)
• Homogeneity/dispersion
• Electrical conductivity
• Mechanical properties (ILSS)
electrical mechanical
areal weight and CNT % conductivity ILSS
technology innovation area detailed description TRL surface - no mesh surface - with mesh volume RT H/W
BASELINE BASELINE .020 psf 97.6 gsm in use - 8 100% 100% 100% 100% 100%
thermoset doped carrier MVR444 epoxy powder binder 20 gsm, 25%CNT 2 175% N/A 333% 60% 73%
thermoplastic doped carrier Platamide PA80 115C melt 12 gsm, 7%CNT 2 95% N/A 286% 102% 42%
thermoplastic doped carrier blend of PA80 and PA12 20 gsm, 20%CNT 2 100% N/A 100% 80% 58%
thermoplastic doped carrier Platamide HX2598 12 gsm, 7%CNT 2 175% N/A 400% 90% 36%
thermoplastic doped carrier PA 12 12 gsm, 7%CNT 2 100% N/A 90% 90% 38%
Electrical & Mechanical Properties Matrix
Regarding the manufacturing impact, the materials supplied in granules were not easy to integrate into the carbon preforms with a good dispersion level. Only the panel that was manufactured with the blend of PA80 and PA12 displayed problems with infusion (dryness in the panel).
All of the doped carrier materials with the exception of the doped B-stage epoxy displayed ILSS results similar to that of the baseline when tested at room temperature, although when tested at hot wet, all materials had a negative effect relative to the baseline, with the most promising result coming from the B-stage epoxy, as can be seen in the table.
In relation to electrical conductivity, all materials performed as good as, if not better than the baseline through the thickness, though only the doped B-stage epoxy and the high temp melt Platamid performed better than the baseline on the surface.
Based on results above (compiled in D3.2 and D3.3) the following solutions were developed to be further implemented and characterized:
Material solution 1 Material ARKEMA Platamid TP HX2598 is the only selected thermoplastic carrier, and two routes are recommended to integrate it in veils:
• Between plies: the use of 5-7 gsm veils could help not to affect mechanical properties;
• As multiple layers on top of the laminate: for lightning Strike protection.
Material solution 2 to allocate CNT doped epoxy film (CYTEC-ARKEMA) on the outer layers to impact LSP.
Material solution 3 a layer of buckypaper (TECNALIA) fully encapsulated in two layers of CNT doped epoxy film to impact LSP.
EADS IW G performed preliminary trials mostly with two thermoplastic copolyamide based non-woven veils (unmodified and modified with 7,10%wt. CNT by ARKEMA) with high melting point (PA12), and low melting point (Platamid H106 PA80) manufactured and delivered by CANOE or TECPAR
EADS IW G performed trials to assess the implementation of CNTs in the preform using CNT modified polyamide veil (followed by vacuum assisted infusion) in order to improve the electrical conductivity in the z-direction
The materials were used as interlayers placed between each interlayer of preforms that were infused following vacuum assisted infusion afterwards. In order to evaluate the influence of the use of a polyamide CNT carrier, an investigation on the process-ability of the veils, the quality of the manufactured CFRP panel, water uptake and mechanical properties (ILSS) was done. The conclusion for this study (D3.2) was that an intermediate melting temperature copolyamide could behave better in process-ability and could bring the laminate to better properties. CNT-doped thermoplastic non-wovens veils were specially designed and manufactured for this purpose by Technology Partners, by melt-mixing an intermediate temperature melting (ITM: Platamid HX2598) copolyamide polymer with 5wt% CNTs. For comparison an unfilled Intermediate Temperature Melting veil (Platamid HX2598 without CNT) and a commercially available veil with 12 g/m² Low Temperature Melting Polyamide (Spunfab PA1541A) was used. Manufactured laminates were evaluated in terms of quality. Mechanical (Gic) and Electrical conductivity measurements were measured (D 3.3).
Unfortunately, no increase in conductivity could be observed due to the addition of CNTs, remaining far from the targeted conductivity. One explanation could be the insufficient conductivity provided by the doped non-wovens. Thus far, it was not yet possible to determine the electrical conductivity of the non-wovens themselves with the available equipment, though further trials are planned to determine the electrical conductivity of such non-woven material and explain these results. Moreover the Platamid HX2598 material exhibits a slightly lower conductivity compared to the Spunfab baseline material, which may be explained by varying thicknesses of the veil, causing a thicker insulation layer between the carbon layers, though this remains to be verified.
Prepreg Technology
Incorporation of Buckypapers with undoped prepregs (EADS-IW F)
To study the process-ability of buckypaper EADS IW F manufactured a specific laminate with some area with only prepreg; some area with prepreg and film resin between plies, some area with prepreg and buckypaper between plies and some area with prepreg buckypaper and film resin between plies to verify if the buckypaper could be infiltrated by the resin of the prepreg or if an additional layer of resin film with the buckypaper is needed. Details for the manufacturing and characterization are compiled within D3.2 D3.3 and P3
C-Scan observations on the manufactured panel revealed that the impregnation of the dry buckypaper by the resin of the prepreg is not possible when dry buckypaper are inserted between prepreg plies. Based on the obtained results with high level of porosity in the dry buckypaper, we stopped developing composite prepreg with addition of dry buckypaper between each prepreg layer. But when dry buckypaper is positioned on the top of the laminate as a first ply, the resin of the prepreg can impregnate correctly the dry buckypaper. The addition of a layer of dry buckypaper on the surface of composite laminate is possible at the lab scale. To asses the influence of the presence of BP in the electrical properties of the laminate only the addition of a dry buckypaper layer on the surface of the laminate was investigated for electrical characterization.
CNT doped prepregs
University of Patras developed the up-scaled prepreg treatment setup. Semi-automated hardware pre-preg modification assembly to allow the continuous treatment of higher amounts of EF6809 pre-pregs needed by EADS-IW-F for the envisioned manufacturing and testing. The final assessment for the selection of the nano-treated prepreg:
Processing Technologies CNT carrier Processing ability
Good (g)
Bad (b) Properties improvement:
Yes/no Comments &
GO/NO GO
Process Technology
Electrical
[S/m] Mechanical
PREPREG NANO-DOPED CS1-25 Medium YES ([0]14:KZ=0.01→0.51) NO NO-GO
NANO-TREATED CM2-20 Good YES ([0]16:KZ=0.78→4.55) NO GO
UOP worked on repairs and further upgrading plans for the semi-automated hardware pre-preg modification assembly.
UOP acted as CNT-treated prepreg material provider for EADS-IW-F using EF6809 prepreg material from CYTEC and CM2-20 powder from ARKEMA. EADS IW F assessed the processability of composite with CNT treated prepreg prepared by UoP from CNT doped thermoplastic powder with prepreg manufactured by Cytec.
First results on Electrical conductivity obtained did not show any no-go to continue the evaluation of this technology.
Based on the work performed on composite processing set-up and documented in deliverables D3.1 D3.2 and D3.3 the following technologies were selected to be further investigated for multifunctionality development (WP4)
The objectives for the development of multifunctionality phase were:
• Characterisation of composite laminates produced, mostly electrical behaviour characterisation and correlation with possible applications (static discharge, default current discharge, current return, interface shielding,…)
• Development of quality control technologies: Dielectric Mapping for monitoring and optimisation of CFRP curing process, and Electrical Resistance Tomography ERT for quality assurance of CFRp laminates
• To ensure multifunctional testing towards final user requirements
The manufacturing plan established for the characterization of composite laminates, mostly for electrical conductivity and the development of the sensing and damage detection approach is depicted in the next table
The testing plan:
Following the manufacturing and testing plans composite laminates were manufactured and tested during WP4 to see if they met the requirements in terms of, quality of the material, electrical conductivity, physic-chemical and mechanical properties. For that purpose a test matrix was defined. According to the test matrix BAB and TECPAR were responsible to measure the mechanical properties. BAB, EADS IW F, and AIR F were responsible to measure the electrical conductivity of developed material and performed lightning strike tests with damage expertise on material developed in the project
Liquid technologies
Mechanical properties (D4.3)
Sample Manufactured
by Solution G1C [J/m2] AITM 1.0005 Std. Dev. G2C [J/m2) AITM 1.0006 Std. Dev. DMA-Tg [C]
ASTM D 7028 Std. Dev. Charpy impact test
acu [kJ/m2] ISO 179 Std. Dev.
MVR-I-UD-8-1 TECNALIA
Infusion BASELINE 452 45 670 88 194,3 0,3 100,3 22,6
MVR-BP-A-CNT-0,1-I-UD-8-1 TECNALIA
Infusion 0,1%CNT doped resin+BP on top 373 12 620 64 193,6 0,6 116,3 12,0
13.49.02 Baseline EADS-IW-G
Infusion BASELINE
Non woven veils
Platamide HX2598 787 110 727 65 208,9 1,2 94,3 11,7
13.50.01 +CNTs EADS-IW-G
Infusion Doped non woven veils
(5%CNT) 464 61 974 207 209,4 0,7 93,8 16,6
Mode I fracture toughness (G1C) decreases for laminates with a layer of buckypaper on top of the laminates. This result appears strange as in principle the buckypaper should not affect the delamination of the laminate. For the laminates integrating non-woven veils as an interlayer between each fibre layer, Mode I shows a decrease while mode II fracture remains stable. With respect to impact the presence of the buckypaper increases the impact strength of the laminate as expected.
Looking at the results on CAI performed by BAB (see next figure) the following comments can be taken. The Encapsulated BP panel was very resin rich which is reflected in the results where it was the worst performing in terms of ultimate load. As there is only a layer of enhancement placed on the outside of the e-Buckypaper panel and the doped film panel, the performance is not expected to differ much from the baseline panel – this can be seen with the doped film panels having similar results across the three impact energies.
For the non-woven veils – there is no influence due to the presence of veils on the ultimate load nor on the delamination area
For the doped resin+ BP- BP slightly increases the ultimate load in the CAI testing while the delamination area becomes smaller as a result of the presence of the BP on top of the laminate.
Electrical properties were also measured for each of the configurations (D4.1).
Electrical conductivity measurements have been done on the manufactured composite with the methodology described in the D4.1 and in the P3. The results for EC are far from the requirements set at the beginning of the project. The best values are given by the samples based on the Technology 3 (e-BP), but in general, the nanotechnologies do not show improvement of the conductivity.
AIRF performed the LST on the infused panels manufactured by Tecnalia based on doped resin and a layer of BP (non- encapsulated) on top: The observation of the surface of the panel reveals puncture on the skin. This kind of damages is not acceptable
BAB performed the LST on the panels manufactured by infusion with the three technologies being approached and described in P3. Details of testing, figures and graphs are well presented in D4.1.
The best performing technology selected to be implemented in the demonstrative part was the Technology 3 based on e-buckypaper. The selection was based on the analysis of the different temperatures that were induced by each of the strikes on the panel as this result is indicative of how conductive the laminate is. The buckypaper fully encapsulated displayed the lowest temperature among the three technologies and close to that of the reference panel (including a Cu mesh).
Prepreg Technologies
Sample Manufactured
by Solution G1C [J/m2] AITM 1.0005 Std. Dev. G2C [J/m2) AITM 1.0006 Std. Dev. DMA-Tg [C]
ASTM D 7028 Std. Dev. Charpy impact test
acu [kJ/m2] ISO 179 Std. Dev.
JCI 1058 5557 EADS-IW-F
Prepreg BASELINE 378 32 468 37 218,3 0,4 120,1 10,3
REP 5601
Batch 1 CNTs EADS-IW-F
Prepreg CNT Doped prepreg
Batch1 392 23 2505 361 209,9 0,4 117,9 4,2
Batch 2 TECNALIA
Prepreg CNT doped prepreg
Batch 2 289 23 398 20 220,8 0,9 115,7 12,6
Batch 2 BP TECNALIA
Prepreg CNT doped prepreg batch2+ e-BP on top surface 274 21 417 27 219,9 0,2 118,3 12,0
With respect to the mechanical properties, higher ultimate load and lower delamination area for the CNT treated prepreg(batch 1) in the whole range of impact energies studied. Results are compiled in D4.3
EADS IW F performed LST on the prepreg based laminates:
The addition of a layer of dry buckypaper (during curing, the resin of the prepreg fill the gaps of the buckypaper) seems to improve the lightning strike properties of the composite if we consider the visible surface damage after lightning strike impact. The presence of the buckypaper on the composite surface reduces the delaminated area in the composite of about 25%. But the damage is still important and the buckypaper alone could not be used for lightning strike protection. The mixing of extended copper foil with buckypaper could be investigated in future program to verify if a weight reduction of the extended copper foil could be a possibility. If the buckypaper is embedded between 2 layers of resin film EF2713, the obtained results gives visually a very important damage area on the surface of the impact and also a visible delamination on the opposite face of the composite. The addition of CNT in the prepreg gives visually a more important damage on the impacted surface of the composite compare to the reference sample of composite The lightning strike impact results are very poor.
EADS IWF performed activities to set up the electrical conductivity measurements in x,y and z direction of the UD and QI composite materials manufactured integrating CNT treated prepreg and Buckypapers. The details for the tests and the results are compiled within P3 and D4.1. A summary of results can be seen in the table below:
Electrical conductivity measurement results on composite materials
WP5: Validation of technologies
The objectives of the WP are to validate the multifunctional composite with electrical conductivity and quality control systems developed in WP4 through its application on a macroscale representative aeronautic structure. Through this WP, design and manufacturing of scaled structural technological components will be carried out and the necessary testing and technical evaluations will be performed on the fabricated components. Representative scaled structural components incorporating the technologies developed and matured through the project were fabricated. Three type of demonstrators were manufactured integrating the three technologies. Two demonstrators were manufactured by infiltration and a third one was manufactured by prepreg.
Technology Technology developer demonstrator Manufacturer
Infusion/doped resin and encapsulated buckypaper on top TECNALIA representative aircraft fuselage panel AESI
Infusion/e-buckypaper TECNALIA representative aircraft fuselage panel BAB
Prepreg/CNT treated prepreg UoP representative aircraft fuselage panel EADS IW F
The purpose to assess the developed technologies by the fabrication of representative demostrators was twofold:
- To assess the manufacturability when integrating the technology and also to evaluate the scale up issues
- To evaluate the behaviour of the demonstrator against the lightning strike
All the details related to the manufacturing of the demonstrator can be found within D5.1. AESI and BAB were able to manufacture reference demonstrators as well as demonstrators integrating developed technologies for CNT integration into laminates. EADS IW F was not able to manufacture the demonstrator integrating CNT due to health and security reasons, since working with prepreg containing CNT has been forbidden by Airbus Group Innovation security department without any modification of the working conditions. The last modifications to allow working with prepreg containing CNT should be operational in October 2014. Due to that reason the manufacturing of the composite demonstrator with prepreg including CNT batch 2 from Patras University has been postponed.
The quality control techniques developed by INASCO were implemented during the manufacturing of the demonstrators at AERNNOVA facilities (D5.2)
Demonstrators manufactured by AESI and BAB were subjected to LST. The following conclusions can be drawn below:
Conclusions for AESI demonstrators:
The direct lightning effects on aircraft structures are of great importance nowadays, because of the massive use of composite materials in the new generations of aircrafts. In this project, Aernnova have tested four panels (two reference panels, plain and curved, with expanded copper foil and two panels with a buckypaper layer) under lightning strike test. The test results have shown some differences between the Copper mesh and buckypaper tested panels. The copper mesh performed a little better in resisting damage depth penetration than the buckypaper. The main conclusion is that the use of Buckypaper layer as a lightning strike protection is not suitable compared with copper mesh.
Conclusion for BAB demonstrator:
In terms of manufacturing, there is still some work to be done to reduce the defects that were identified in both of the panels, however it didn’t cause any major issues. At this stage, the encapsulated Buckypaper is not suitable for use as a lightning strike protection
Details for demonstrators testing are carefully explained within D5.2
WP6. Economical Evaluation, Exploitation and Dissemination
During the last stages of the project it was foreseen to develop the economical evaluation of the developed multifunctional systems, to include; material costs, manufacturing costs, operation costs and maintenance costs. These costs will be compared with the current costs of the traditional, ‘state-of-the-art’ systems. A detailed weight evaluation of the developed multifunctional systems will be done in order to determine the savings due to the enhanced electrical and mechanical performances. It was discussed and agreed in the presence of the project officer and co-ordinator at project meeting in Seville (13th June 2014) that devoting time and resources to this detailed evaluation and analysis would not be practical due to the technologies developed not being deemed viable for such application.
With respect to the exploitation plan D6.2 refers to an exploitation plan of the technologies and processes that have been developed within the project. The potential outputs for exploitation include;
• Innovative solution for bulk electrical conductivity with an important aircraft weight saving. This can be considered as the main outcome of the activity with potential applications in composite structures in different aeronautical products.
• An innovative solution for the control of manufacturing processes (proper resin curing status) and quality assurance of final component (delamination, inclusions etc.), with an important maintenance cost reduction.
• Innovative CNT engineered structures and CNT doped resin formulations
• Innovative solution for nano-reinforcements integration in CFRP
• Based on all partner inputs, the exploitation plan will be developed. The plan will establish the steps to bring the technology closer to an industrialized scheme.
Though there was no optimised multifunctional nanocomposite material developed within this project, there was a lot of knowledge and experience gained in areas such as doping methods, manufacturing procedures and developments in the screening of composite materials for electrical properties. The materials, with some further developments within the framework of, for example Horizon 2020, have potential application opportunities, as identified above, even beyond that of the aerospace industry
Within this framework, the consortium had the aim to disseminate and share, for financial and scientific reasons, the non-confidential, publishable information developed within the project, through media streams such as scientific and trade magazines and conferences. There was a lot of activity from all partners to write papers, organise and deliver presentations at various events throughout Europe. The work towards this deliverable started in month 24 when it was agreed with the organising committee of SETEC ’13 that there would be two sessions based around the work that was being carried out within the ELECTRICAL Project. The two sessions took place on the afternoon of Thursday 11th September and contained 6 papers consisting of inputs from all partners of the ELECTRICAL Consortia. The conference was attended by representatives from industrial and research communities.
When the 9 month extension in the project was granted, it was identified that there was an opportunity for further dissemination activity as a group and so papers were submitted during the call for ECCM16 to take place in Seville in June 2014. A session entitled ‘Electrical Properties of Continuous Fibre Reinforced Composites’ was organised and chaired by partners from Tecnalia and the University of Patras. Six out of the eight papers presented at this session came directly from the work within the ELECTRICAL project. Alongside these two group events, partners individually submitted papers, delivered presentations and submitted posters to various events to diffuse the work within the project, all of which are contained in D6.3.
Final remarks
The project for the first time allowed the transition from improved nanoreinforced resins to the exploitation of their enhanced electrical and mechanical properties in full laminates manufactured by automated process.
During the project, different strategies to incorporate carbon nanotubes in composite laminate using the common manufacturing process (infusion, RTM and/or prepreg) have been successfully investigated. The strategies supposed the study and understanding of the mechanisms that govern the behaviour of the doped resin during the infusion process, the development of dry engineered structures such as buckypapers to be implemented in infusion and prepreg, the exploitation of the thermoplastic interlayers commonly used as toughening materials as potential carbon nanotubes carriers to be implemented in infusion and prepreg and the development of specific treatments for commercial prepregs with carbon nanotubes. The three technologies further matured up to the end of the project: buckypapers, doped veils and CNT treated prepreg have been well adapted to the common composite manufacturing routes. The first goal of the project is that the technologies can be implemented in current manufacturing processes for composite laminates. The objective of the enhancement of the through the thickness electrical properties has been partly reached as the technologies allow to enhance the electrical conductivity in the z direction but none of them reach the conductivity values initially set in the project. With respect to lightning strike performance the technologies do not pass the minimum requirements as the surface impacted is damaged. However, the presence of the technologies diminishes on the lightening impacted surface and reduces lightly the total delaminated area the damage when compared to the panel with no Cu mesh on it. Therefore, the combination of the technologies with a lighter Cu mesh could be the basis for future activities. With respect to mechanical properties,
The fact that the CNT doped composite systems did not perform as well as existing solutions for the aggressive lightning strike tests, does not exclude them from use in other less aggressive electrical and thermo-electrical applications within the aircraft structure. These uses might include applications for edge glow, anti-icing and de-icing in which the inherent performance of the current solutions are more closely suited to the requirements of these systems. Further development and enhancement of doped composite structures, or the use of hybrid solutions, could enable the properties of these composite solutions to approach the requirements needed for LST protection.
WP7. Management and Coordination
The coordinator and the partners involved in project management have normally dealt with all the day to day administrative aspects:
• Management of funding
• Distribution of information from the EC to the consortium
• Organisation of consortium progress review meetings
• Preparation of periodic report
• Distribution of project reports and further deliverables to the EC
• Resolving of problems occurring between the partners during the project
More in detail, management activities are listed:
• Website of the project www.electrical-project.eu with the update information of the project. The website is divided in two different areas, one for public dissemination of the project and, the second one, only for project members.
• Organization of progress project meetings (KOM, 6 months, 12 months, 18 months and 24 months, 30months, 36 months and final meeting (45 months)
• Organization of the 36M PM in parallel to SAMPE Congress in Wuppertal (Germany) and 45M PM in parallel to ECCM16 in Sevilla (Spain).
• Organization of several technical teleconferences
• Preparation of the official reporting documents.
• Distribution of the funding between partners.
• Coordination of the diffusion actions in different forums (Aerodays 2011, SAMPE SETEC 2013, ECCM16, JEC Composites Show 2013)
• Preparation of two Amendments to the Contract (July 2011 and July 2013)
Potential Impact:
This project will increase the competitiveness of an important group of European Aeronautical companies, being the aeronautic sector one of the most innovative sectors with high R&D investments in Europe. Without this project, the parity situation with US manufacturers will not be maintained due to rapid developments at Boeing. Against Brazilian, Canadian, Russian and Chinese manufacturers Airbus leads by one generation (CFRP fuselage). With the work conducted within ELECTRICAL, this lead can be maintained. Without ELECTRICAL, these manufacturers will rapidly close the technological gap.
Targeted markets of ELECTRICAL are mainly the following:
- Primary market: composite fuselage parts for the next generation of large aircrafts. AIRBUS and EADS are the main beneficiaries of the products among the partners. AERNNOVA, as large composite structures manufacturer, either for AIRBUS and BOEING, will also benefit from the project outcomes.
For AIRBUS ELECTRICAL represents one of the major milestones of its internal Nanocomposite roadmap for the further development and implementation of Nanocomposites into commercial aircrafts. This foresees TRL2 to be reached in Q2 2010 and TRL3 in 2012. The implementation of ELECTRICAL is the key stepping stone for achieving this goal as well as the advancement to TRL4 post 2012
EADS strategy is to develop a full composite fuselage. ELECTRICAL will give potential solution to overcome the problem of poor electrical conductivity of composite materials.
- Second market: wings for business, regional and small commercial jet aircrafts. BAB as main end-user, and AERNNOVA as composite parts are the main beneficiaries of ELECTRICAL. The strategic importance to BAB is that it contributes to keep technological leadership with respect to other non-european major players. BAB is expecting a time-to-market of materials and technologies developed in a medium term to be implemented in future aircraft production
- Third market: Composite fuselage parts for helicopters. EADS group is the main end-user represented in the consortium (Eurocopter) and Aernnova a composite parts manufacturer for the main helicopter producers worldwide.
- Another important market, and fully in line with product development and market strategies of the company CYTEC, is related to advanced composite materials for aircrafts and other related markets where the new materials (prepregs, films, etc) developed in ELECTRICAL are to be applied (space, automotive,rail).
- Finally, related to nanomaterials, an important market addressed in the present project is referred to CNTs and new CNTs based resin formulations, with a big economic impact not only for the aerospace sector, but also for other sectors such as rail, automotive, sport and goods. ARKEMA, as one of the main European CNTs and CNTs based products manufacturers, is specially interested to participate in Electrical due to the expected economical benefit from the commercialization of the new products developed.
The main expected outputs for potential exploitation are summarised:
- Innovative solution for bulk electrical conductivity, with an important aircraft weight saving. This can be considered as the main outcome of the activity with potential applications in composite structures in different aeronautical products.
- Innovative solution for control of manufacturing process (proper resin curing status) and quality assurance of final component (delaminations, inclusions,.), with an important maintenance cost reduction.
- Innovative CNT engineered structures and CNTs doped resin formulations.
- Innovative solution for nanoreinforcements integration in CFRP and out-of-autoclave manufacturing methods for composites
