On the improvement of thermo-mechanical behavior of carbon/polyphenylene sulfide laminated composites upon annealing at high temperature. (1st July 2021) - Vieille, B.
Abstract: This work consists in investigating the influence of the structural changes induced by annealing, such as the presence of a rigid amorphous fraction (RAF) and crosslinking, on the mechanical properties of polyphenylene sulfide (PPS) and the fracture mechanical behavior (particularly tenacity) of a Carbon/PPS laminated composite. The first part of the study aimed at obtaining PPS samples with different amounts of RAF, and in determining the conditions potentially favoring crosslinking. The results obtained on the matrix alone encouraged to transpose the mechanisms associated with the structural changes in PPS to the polymer phase in C/PPS laminated composites with woven-fibers reinforcement. The laminates have a [(+/-45°)]7 stacking sequence, whose overall mechanical response is controlled by the PPS matrix. The ultimate axial strength is little influenced (about 10% increase) by different annealing conditions with respect to as-received state. The optimum annealing conditions (230 °C under air for 576 h) contribute to the improvement of the axial stiffness (doubled compared to the as-received state). At the same time, the critical translaminar toughness (at initiation) is significantly increased (about 20%) and the translaminar failure is associated with a slower crack propagation. Highlights: The influence of annealing conditions on the mechanical behavior of thermoplastic based laminates was investigated. Annealing conditions are favorable to both the formation of rigid amorphous fraction (RAF) and crosslinking. From annealing, the mechanical properties (tension and fracture toughness) are improved. The optimum annealing conditions (230°C under air for 576h) improve the axial stiffness (twice the initial value). The same conditions result in a significant increase (about 20%) in the critical translaminar fracture toughness. Highlights Once the crack is initiated, the energy required to grow the crack is the same regardless the annealing conditions.