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Manufacturing of high temperature composite parts for air cooling unit (e.g. cyanate ester / carbon fibres) by filament winding

Final Report Summary - HITEMCOMFIL (Manufacturing of high temperature composite parts for air cooling unit (e.g. cyanate ester / carbon fibres) by filament winding)

Executive Summary:
Project HiTemComFil covers the development of a composite sleeve for an aircraft cooling unit, including process and methodology development. Due to the extremely high thermal and structural requirements, Cyanate ester resin is utilized in a filament winding process. As this resin poses high demands for the control of moisture and heat generation during the winding process, a methodology was developed and the winding process was optimized for achieving the desired laminate quality. In-depth analysis of the chemical and physical processes during curing and utilization of these findings for process optimization lead to a reduction of the void rate of the laminate by 78 % during the project. As a result of this optimization, high quality composite parts with superior properties at elevated temperatures are available for the current application as well as for various high-technology applications in other fields.
In order to achieve a design with minimum weight while fulfilling all mechanical requirements, finite element simulation was performed alongside with experimental validation, resulting in two alternative designs for the sleeve, based on two different manufacturing methods. The commonly used press-fit design, requiring the assembly of several individually produced components, was compared to a novel, one-step production process using pre-strained filaments in a winding process. During the project, this latter method emerged as a highly efficient, reproducible manufacturing method for the given part as well as for general components subjected to high-speed rotation or internal pressure, e.g. pressure vessels, pressure lines or fly-wheels.
The development of the manufacturing alternatives allows for a significant reduction in production time. When the manufacturing efficiency for press fit solution using conical glass fibre inner layer and carbon fibre sleeve with conical inner shape is set to 100%, manufacturing effort using direct winding solution is about 40%. In other words the manufacturing efficiency for the developed direct winding would be about 60% more efficient than the press fit solution mentioned before.
As a result of the simultaneous optimization and adaption of the component design as well as the process control, the utilization of cyanate ester resin with its demanding processing properties was established in the series-production- worthy filament winding process. The unique adaption of the filament winding process with introduction of high pre-stress values in the fibers by an especially developed brake allows for the systematic adjustment of built-in stresses in the cured laminate.
The project success was demonstrated by successful manufacturing and application-related testing of five demonstrator parts. The project results were presented at various exhibitions, among them Composites Europe and JEC, and were received with interest by potential customers across industries.

Project Context and Objectives:
Project HiTemComFil deals with the introduction of composite materials to a component of an aircraft cooling unit. Components of aircraft cooling units have to withstand highly variable environmental conditions, including temperatures in the range of 0 °C to 240 °C. A sleeve which is part of a rotor assembly is analyzed in project HiTemComFil. In addition to varying temperatures, this sleeve is subjected to high rotational speeds and the consequentially arising centrifugal forces. Previously being made of metallic alloys, the introduction of fiber reinforced polymer promises advantages in the mechanical properties, but also imposes high demands on the thermo-mechanical behavior of the composite material. Due to the high expected temperatures, traditional resins such as epoxy are not applicable. Therefore, the usage of Cyanat ester resin is intended in project HiTemComFil. Cyanat esters are highly sophisticated thermoset polymer resins suitable to be used in high temperature environment with highly desirable properties and encompass characteristics of epoxy resins. However, during processing, Cyanate ester resins are sensitive to ambient conditions (reaction with moisture before curing, oxidation degradation during post-curing) causing the need for a sophisticated management of moisture contact and specific adaptations of the process. Filament winding is used as manufacturing process in this project due to its ability to produce circular parts with appropriate fiber orientation for the sleeve to be designed.
The sleeve is part of an assembly consisting of several parts made of different materials, including a steel core and magnets. Due to the differing coefficients of thermal expansion, stresses are introduced by thermal expansion. Therefore, thermo-mechanical calculations have to be undertaken to optimize the design of the sleeve. The stresses arising in the sleeve are calculated and analyzed using failure mode concepts.
In order to ensure the achievement of a low void rate, a methodology for monitoring the filament winding process is developed, including the assessment of gelation and curing. Prototypes are manufactured and mechanically tested. The process is further optimized by identifying relevant process parameters and optimizing them based on an optimization matrix using weighing factors. The achievement of the desired quality is ensured by implementing a quality assessment plan. Finally, technology demonstrators are manufactured in order to document the achievement of technology readiness level 5.

Project Results:
During project HiTemComFil, knowledge has been built in the fields of simulation of wound composite parts, analysis methods and manufacturing of parts from Cyanate ester resins.
During the design and simulation work packages, valuable knowledge concerning the mechanical properties and laminate quality of wound composite parts was gained thanks to the combination of simulation and experimental validation. Special emphasis was put on modelling and measuring the residual stresses that form in the sleeve after winding. The interaction between manufacturing parameters such as fiber straining during winding and the properties of the finished part has been studied and valuable insight has been gained.
For the analysis of laminate quality and the chemical processes during curing, several physical and chemical analysis methods have been utilized and judged for their applicability. As a result, best practice methods for the evaluation of cyanate ester composite parts have been identified, allowing for the accurate measurement of all relevant properties. These methods are easily applicable for future manufacturing processes, thereby reducing the effort needed to achieve the desired part properties.
Finally, relevant influence factors on laminate quality have been identified during the process optimization and manufacturing of prototypes and demonstrators and strategies for controlling these factors have been developed and successfully applied.

Potential Impact:
The project partners will benefit from results of project HiTemComFil both commercially and scientifically. CirComp and Liebherr will use the knowledge generated in the development and implementation of new products. Especially the feasibility of wound parts using Cyanate ester resins demonstrated in project HiTemComFil will allow for the usage of composite materials in a wider field of application due to the superior thermal stability. The combined utilization of cyanate ester resins and pre-straining of the filament during winding in one process qualifies this manufacturing method for the manufacturing of a variety of products under special loading conditions, among them pressure vessels, pressure lines, fly-wheels and engine housings. This enables the partners to broaden their range of products and provide composites parts in new fields of application.
The scientific exploitation of the results will be realized in three domains:
1. Publications and Conference presentations:
A publication of the project results in an conference presentation at the Euro Hybrid (April 2016, Kaiserslautern, Germany) and journal article is under preparation. The results have been shown at recent exhibitions like Composites Europe, JEC, CCeV summit and have been received with great interest by attendants. Additionally, the project was presented on the IVW website and was featured in the IVW Annual report. Furthermore, the Project Results will be presented by CirComp in a booklet to highlight the manufacturing know-how generated.
2. Utilization of the results in education:
The project results will be used in courses for the education of students and for the academic training of scientific staff. IVW (Institut fuer Verbundwerkstoffe - Institute for Composite Materials) is involved in the teaching program of the Technical University Kaiserslautern with three chairs, focusing mainly on novel materials. The findings of project HiTemComFil will be used as an example for results of recent research and for the application of composite materials under elevated temperatures.
3. Non-commercial follow-up projects:
The knowledge obtained through project HiTemComFil will serve as a basis for further research in the areas of manufacturing process development and design of wound composite parts. Several interesting areas of research have been identified during the project, among them being the application of pre-straining in filament winding and the analysis of residual stresses in wound sleeves by non-destructive testing. At the moment, the state of strain in the sleeve can only be validated by destructive testing, thereby limiting its application in serial production to statistical tests. Further research should be concentrated on the validation of the level of pre-stress by means of non-destructive testing.
Due to the change in the state of stress during cure of the directly wound laminate, the relation between geometry and manufacturing parameters is complex. In a succeeding project, dependencies between geometry, e.g. rotor diameter and state of stress in the cured part could be analyzed experimentally and the possibility of representation in a parametric finite element model could be investigated.
Furthermore, future projects would be to research more detailed parameter influence of manufacturing process on pre-stress of the magnets in combination with development of quality assurance systems and strategies.
Extensive investigation of these topics is planned within the framework of further research projects.

List of Websites:
There is no project public website. Contact Details of the contact persons of the project partners are given below:

IVW (Institut fuer Verbundwerkstoffe):
Florian Rieger
Institut für Verbundwerkstoffe GmbH
Erwin-Schrödinger-Straße, Gebäude 58
67663 Kaiserslautern
Germany
florian.rieger@ivw.uni-kl.de

CirComp:
Dr. Ralph Funck
CirComp GmbH
Marie-Curie-Str. 11
67661 Kaiserslautern
Germany
funck@circomp.de

LIEBHERR AEROSPACE:
Elodie Herail
LIEBHERR-AEROSPACE TOULOUSE SAS
408, avenue des Etats-Unis - BP 52010
31016 Toulouse Cedex 2
FRANCE
elodie.herail@liebherr.com