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Micro mEchanical Characterization of A ThErmoplastic Co-conSolidated / welded joinT for usE in aiRcraft fuSelages

Periodic Reporting for period 1 - MECATESTERS (Micro mEchanical Characterization of A ThErmoplastic Co-conSolidated / welded joinT for usE in aiRcraft fuSelages)

Reporting period: 2019-04-01 to 2020-09-30

The aerospace industry currently has a need for lightweight, complex composite structures to make their way into operational use. Changes in the regulatory landscape and demands for reduced emissions, coupled with the need to optimize Revenue Passenger Kilometers (RPK), have driven research efforts into lighter and more efficient aircraft designs. A key approach to reducing emissions is minimizing weight: by reducing weight, fuel usage drops, leading to a reduction in overall emissions. This requires that traditional materials such as steel, aluminum, and even titanium be replaced with lighter, high-performance materials.
High Performance Thermoplastics (HPTP) are an excellent solution to the issues of recyclability, light weight, high performance, and reparability. HPTP composites offer compelling advantages over metal components: improved working life, lower weight, reduced fuel consumption, and longer service intervals. In comparison to thermoset composites, thermoplastic composites also have several advantages: they can be directly joined using welding techniques, and there is hardly any damage or damage growth in the laminate structure.In addition, their thermoplastic nature also opens up numerous possibilities for rework and repair. The use of thermoplastic composites can reduce manufacturing times by as much as 20-30% as compared with metals or thermoset composites.

MECATESTERS project focus on these kind of materials, especially the welding technology we could use for the futurs assembly.

KVE Composites Group and Rescoll cooperate to create a greater level of understanding of the micromechanical behaviour of the welded interfaces for UD tape based laminates. Issues such as aging, healing, processing parameters, and durability need to be investigated in greater detail in order to develop a coherent approach.

In order to reach this goal, four Key Objectives (KO) have been figured out which will make the overall MECATESTERS project realistic.

- KO1: Evaluate the effect of surface conditions upon interface healing. (WP1)
A detailed examination of different types of surface will provide the Topic Manager with clear guidelines for production, and maintenance with respect to the surface state.

- KO2: Examine the effects of aging on the durability of carbon UD LM-PAEK and PEEK parts (WP1 – WP3)
The evaluation of aging on the durability of carbon UD LM-PAEK and PEEK parts will provide valuable information to the Topic Manager in terms of establishing maintenance intervals, engineering tolerances, and lifetimes for carbon UD LM-PAEK and PEEK parts.

- KO3: Perform a process window comparison for methods for welding (WP2)
Two welding method are selected and further investigated in the MECATESTERS project, in order to provide the Topic Manager with an industrially suitable, high-performance, high-quality solution for thermoplastic welding of carbon UD LM-PAEK and PEEK parts.

- KO4: Perform mechanical testing to validate the performance of the bonds
The MECATESTERS project will provide the Topic Manager with a detailed analysis of the microstructural behaviour of welded thermoplastic assemblies. This will enable the Topic Manager to select and apply the most optimal joining technology.
After a first phase of discussion done at the start of the project in order to specify sharply all requirement needed of both manufacturing and testing phase, work began both in K.V.E and RESCOLL facilities.

In order to prepare the testing phase, which involves specifics tooling and test method, Rescoll took the folowing action :

- Design and manufacture of a tooling dedicated to the test of L-shape profil in pull-off, shear and combined load configuration.
- Development of a specific method with video extensometry for single lap shear test. This method will allow to get the measurement of displacement in a dot cloud on the slice of the specimen and therefore determine the potential rotation and the deformation of the specimen in a global view.
- Development of a specific test method for dynamical fissuration (mode II). Since specific test standards are not available, This method is based on research papers on this field.

K.V.E is on its side manufacturing the test specimen for the incoming test. During RP1, composite plate has been ordered from supliers, and induction welding was performed for single lap shear specimen from working package 2, which focus on the definition of optimal parameters for welding process. Composite plates have been sent as well to Fokker facility to start the conduction welding.
The single lap shear (SLS) welding trials of WP2 are done on the standard coupon welding tool that KVE has designed to assist in the welding of standard test coupons and elements like single lap shear, G1c and pull-off assemblies. During this project, blanks with dimensions of 24” by 5” are used for the SLS welds. The following material types were selected for MECATESTER WP2.
The materials have different polymers and therefore different processing parameters are defined for each material, like temperature and cooldown time, to allow full crystallisation. First, these processing parameters were determined. Afterwards the SLS assemblies were welded according to the test matrix defined.
Manufacturing of all material used for WP 2 is done by KVE. Stacking of the material is performed by KVE. The consolidation of the laminates is performed with the autoclave at Thermoplastic research centre (TPRC). After with the laminates were milled by KVE.

A first batch of SLS inducted plate was sent to Rescoll in 2020, A-scan was performed on all plate to check any potential dammage on futur specimen. All the plate were then machined to get specimen to the test dimensions needed. First SLS test on these batches are expected for March 2021, according with Fokker requirement about video system to use.
The first mechanical results will be available at the beginning of 2021, the biggest impact will be the better understanding of the welded interfaces for UD tape based laminates especially in term of process parameters.
The socio-economic impact and the wider societal implications will be the help to the design of new airplane generation more responsible in terms of CO2 emission.
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Welded test assembly
SLS welded assembly
Autoclave consolidated laminate