Investigating the Mechanical performances of PEKK and its ABility to withstand with Loads and the Environment – IMPEKKABLE

The use of composite materials in aeronautical structures has significantly increased in the last decades comparing to metals traditionally used, involving an important reduction of the weight and a decrease of the fuel consumption. If fiber reinforced thermosetting composites have a wide scope in the field of aeronautic applications, the introduction of thermoplastic matrices is however considered as an interesting way to reach better performances under high temperature solicitations and to improve the environmental impact through recyclability.
The ImPEKKable project deals with the use of organic matrix composite materials such as thermoplastic matrix reinforced with continuous carbon fibers for “high temperature” parts. More precisely, it refers to the utilization of a new generation of C/PEKK composite for structural applications around 180°C, that is to say at temperatures above the glass transition of the thermoplastic matrix. The innovative and ambitious aspect of this study remains in the development of models and simulation tools aiming at predicting the thermo-mechanical behavior of these composites for long term solicitations under these temperature levels. Considering such conditions, creep recovering and recrystallization phenomenon as well as chemical evolutions are expected.
The semi crystalline thermoplastic matrix studied belongs to the polyaryletherketone (PAEK) family (the same as PEEK) which exhibits high mechanical performances, as well under high temperatures during continuous solicitations, and offers a good dimensional stability and a strong chemical resistance. Nevertheless, the PEKK is not very used for aeronautical composite applications and the related literature is not very important comparing to the one dealing with PEEK behavior. As a copolymer, different grades of PEKK can also be obtained in changing the ratio of the components introduced during the molecule synthesis. These grades have similar glass transition temperatures but different melting temperatures and the kinetics of crystallization can be optimized in order to meet the requirements of the final end user’s applications.
The scientific objective is to reach a better understanding of the coupled mechanisms of the long term deformation and the ageing of C/PEKK composites for such applications. Main activities revolve around the development of coupled multiphysic models: a multi scale thermos-mechanical model applied to creep-recovering solicitations combined to the evolution of the microstructure; a modeling of the ageing behavior of either the neat polymer and in the presence of carbon fiber in the C/PEKK composite for temperatures above the glass transition. This numerical work will be supported by accelerated experimental tests (by increasing the temperature, the oxygen content or the creep stress), and by a characterization of the evolution of the microstructure of the C/PEKK composite considered. The deep understanding of these phenomena and the predictive simulations of the creep-recovering behavior will contribute to a better prediction of the service life of the considered materials.
To carry out these activities, the ImPEKKable project is built on a collaboration between the experienced research laboratories Pprime from ISAE ENSMA and PIMM from ENSAM and by two industrial partners, the French material supplier ARKEMA and Airbus Group, confirming the strong aeronautical activities of the project. The high level of competences combined with the relevant experimental resources of the partners will enable the definition of the suitable scientific framework and support the French competitiveness in the aeronautical field.