The high quality and the relevance of Saber’s thesis contributed to get significant results as a part of CompinovTP project.
About this thesis
Reducing aircraft weight is one of the major challenges facing the aerospace industry. In order to achieve the ambitious goals of fuel consumption and emission reduction, carbon-fiber reinforced composites have been introduced to the market. These materials are attracting increasing interest, however, they have low electrical conductivity to ensure protection against lightning strick. For this reason, composites filled with conductive particles are the subject of ongoing research activities.
The objective is the development of multifunctional composites with enhanced electrical properties. Actually, the most used thermoplastic matrix is PEEK, but this polymer remains expensive, and its processing temperature is high. For this purpose, thermoplastic matrices, such as PEKK, are again studied. Between the raw material and the final part, the thermoplastic matrix undergoes several thermal steps with high temperature exposure (impregnation, consolidation, forming and assembly processes) during which its ability to crystallize evolves continuously. In order to evaluate the impact of the process and the composite constituents on its properties, crystallization has been the subject of particular attention. Two complementary experimental devices were used to characterize the crystallization. The heating stage, allows to apply a thermal cycle and observe the crystallization in optical microscopy and differential scanning calorimetry.
The influence of carbon fibers and conductive fillers on the crystallization kinetics was evaluated. A decrease in crystallization times was observed through the increase of the nucleation rate. The collected data were used to develop a kinetic model identified through an original approach based on microscopic data. This model makes it possible to predict the crystallization kinetics of PEKK composites.
Nevertheless, it does not make it possible to predict the final microstructure. However, the microstructure has a significant impact on mechanical properties as it has been proven through nano-indentation tests. To predict the final microstructure, a model based on the pixel coloring approach has been developed. The influence of carbon fibers has been introduced through the formation of a transcrystalline phase.
A good correlation is found between the analytical approach, the simulation and the experimental data in terms of crystallization kinetics. Mechanical and electrical characterizations were performed to evaluate the performance of these new materials. On the studied materials, the mechanical response is not homogeneous as observed on tensile tests followed in stereo-correlation.
The study of matter health shows the existence of defects, in particular, at the microstructure level. In order to take this particularity into account, it is thus necessary to describe the microstructure more finely. For this, X-ray tomography was used to characterize the composite. Recent developments in this technique allow, in combination with segmentation tools, to reconstruct a representative geometry of the material. This geometry is used to simulate the mechanical behavior as well as the crystallization.
The numerical simulations of a RVE are able to calculate the properties of a ply, then those of a laminate. This multi-scale modeling could reduce the number and cost of experimental campaigns. Thus, determining the properties of the final structure based on characterizations and simulation at the microstructure scale is a strategic scientific and industrial issue. This work is a contribution towards this approach.
- Gilles Regnier, professor, Arts et Métiers ParisTech – Rapporter
- Fabienne Touchard, research director CNRS, Poitiers Univertisty – Rapporter
- Nicolas Boyard, researcher CNRS, Nantes University – Examiner
- Damien Soulat, professor, Lille University, ENSAIT, GEMTEX – Examiner
- Philippe Olivier, professor, Paul Sabatier University, Clément Ader Institute Director – Examiner
- Olivier De Almeida, lecturer, Ecole Nationale Supérieure des Mines d’Albi-Carmaux, Clément Ader Institute – Examiner
- Jean-Noël Périé, HDR lecturer, Paul Sabatier University, Clément Ader Institute – Thesis Director
- Philippe Marguerés, lecturer, Paul Sabatier University, Clément Ader Institute – Co-Thesis Director
- Jean-Charles Passieux, lecturer, Paul Sabatier University, Clément Ader Institute – Co-Thesis Director
- Alain Vinet, research engineer, Airbus SAS, Central Research & Technology, Material X – Invited
- Bénédicte Reine, research engineer, IRT Saint Exupéry – Invited
S. Chelaghma, O. De Almeida, P. Marguerès, J.-C. Passieux, J.-N. Périé, B. Reine and A. Vinet. (2017) (FR) : ETUDE DE LA MORPHOLOGIE CRISTALLINE DU PEKK ET CARACTERISATION DE LA CINETIQUE DE CRISTALLISATION DES COMPOSITES A MATRICE PEKK. Proceedings of JST AMAC – Mise en Œuvre des Composites à Matrice Thermoplastique, 2017
S. Chelaghma, J.-N. Périé, P. Marguerès, J.-C. Passieux, A. Vinet and B. Reine (2017) (FR) : Prévision du comportement multi-physique élémentaire d’un matériau composite à matrice thermoplastique chargée et renforcée de fibres de carbone : Identification des propriétés en lien avec les paramètres de fabrication du matériau et validation des modèles – Concours Doctorants SAMPE EUROPE 2017 Materials & Processes, 2017.
S. Chelaghma, B. Reine, J.-N. Périé, P. Marguerès, J.-C. Passieux, A. Vinet and O. De Almeida (2017) (EN): Investigation of crystal morphology of PEKK and modelling of the crystallization kinetic of PEKK composites. JNC 20 (Journées Nationales sur les composites), June 28 – 30, 2017, Champs-sur-Marne (France)
S. Chelaghma, O. De Almeida, P. Marguerès, J.-C. Passieux, J.-N. Périé, B. Reine and A. Vinet (2017) (FR) : Etude de la morphologie cristalline du PEKK et caractérisation de la cinétique de cristallisation des composites à matrice PEKK. JST AMAC (Journées Scientifiques et Techniques de l’AMAC), Jan. 26 – 27, 2017, Toulouse (France).
S. A. Chelaghma, J.-N. Périé, P. Marguerès, J.-C. Passieux and A. Vinet. (2017) (EN): Crystallization kinetic modelling of multifunctional thermoplastic composites… First step towards mechanical and electrical optimization. SAMPE Europe Student, Stuttgart, Germany. Oral and Poster presentations. Accepted – Award. 2017