This study is aimed at comparing the response of TS-based (epoxy) and TP-based (PPS or PEEK) laminates subjected to low velocity impacts. C-scan inspections showed that impact led to diamond-shaped damage resulting from different failure mechanisms: fiber breakages in warp and weft directions, more or less inter-laminar and intra-ply damage, and extensive delamination in C/PEEK and C/epoxy laminates. The permanent indentation can be ascribed to specific mechanisms which mainly depend on many factors including the ultimate out-of-plane shear strength, and the interlaminar fracture toughness in modes I-II-III. In TP-based laminates, the matrix plasticization seems to play an important role in matrix-rich areas by locally promoting permanent deformations. Fiber-bridging also prevents the plies from opening in mode I, and slows down the propagation of interlaminar and intralaminar cracks in modes II-III. Both mechanisms seem to reduce the extension of damages, in particular, the subsequent delamination for a given impact energy. In epoxy-based laminates, the debris of broken fibers and matrix get stuck in the cracks and the adjacent layers, and create a sort of blocking system that prevents the cracks and delamination from closing after impact.

International audienceThis study was aimed at comparing the residual compressive strength and behavior of TS-based (epoxy) and TP-based (PPS or PEEK) laminates initially subjected to low velocity impacts. Provided that the impact energy is not too low, the permanent indentation is instrumental in initiating laminates local buckling under compressive loadings. CAI tests revealed that matrix toughness is not the primary parameter ruling the damage tolerance of the studied materials. However, matrix ductility seems to slow down the propagation of transverse cracks during compression thanks to plastic micro-buckling which preferentially takes place at the crimps in woven-ply laminates. It could therefore justify why the matrix toughness of TP-based laminates does not result in significantly higher CAI residual strengths. Finally, the compressive failure mechanisms of impacted laminates are discussed depending on matrix nature, with a particular attention paid to the damage scenario (buckling and propagation of 0° fibers failure)

Could thermoplastic-based composites be used to replace thermosetting-based composites in high-temperature secondary aircraft structures ? The purpose of this work is to establish the ability of a material system to be used in aircraft engine nacelles when subjected to static loadings, with a key upper temperature of 120°C. In order to provide answers to this question, the thermo-mechanical behaviors of carbon fiber fabric reinforced PPS or epoxy laminates have been compared specifically within the temperature change with 120°C at the upper bound. The temperature-dependent ductile behavior of laminates is more or less exacerbated, depending on polymers' glass transition temperature, and laminates' stacking sequence. For both materials, the degree of retention of tensile mechanical properties is quite high in notched and unnotched quasi-isotropic laminates. A Digital Image Correlation technique has been used in order to understand the influence of temperature and matrix ductility on the mechanisms of overstresses accommodation near the hole. In fabric reinforced laminates, the hightemperature results suggest a competition between the mechanisms of damage, and the mechanism of plasticization, enhanced in angle-ply lay-ups. Thus, the highly ductile behavior of TP-based laminates, at temperatures higher than their T g , is very effective to accommodate the overstresses near the hole.

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Impact damage tolerance of hybrid carbon and glass fibers woven-ply reinforced PolyEther Ether Ketone (PEEK) thermoplastic (TP) laminates obtained by consolidation process is investigated. Service temperature being one of the most important parameters to screen TP or thermosetting matrix for aeronautical purposes, impact testing at room temperature (RT) and near the glass transition temperature (Tg) has been conducted. From the results, it turns out that temperature has little influence on the impact behavior in terms of maximum force developed or maximum deflection, though it reduces the dissipated energy especially at lower impact energy. However, temperature has a strong effect on the internal and external damages caused to the plate, as it increases the permanent indentation and it limits the projected delaminated area. As for the influence of temperature on the compressive residual strength of the laminates, it also appears that the classical experimental setup for CAI tests is not completely appropriate to draw a clear cut conclusion. At last the obtained results show that the considered TP-based laminates are characterized by a very good impact behavior and a high-degree of damage tolerance.

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