Effets synergiques de l'exposition à une flamme de kérosène et des comportements mécaniques dans les composites aéronautiques thermoplastiques hybrides en PEEK

Concerning the stringent fire safety regulations for thermoplastic (TP) composites in the aeronautics field, it is imperative to comprehend and determine the thermo-mechanical behavior of laminates in-fire and post-fire scenarios. The objective of this thesis is therefore to investigate the synergistic effects of different critical thermal aggressions and mechanical behaviors in CG/PEEK aeronautical composite laminates: isothermal exposure (from Tm 350℃ to Td 550℃) and kerosene flame exposure (1100 C and 116 kW/m² heat flux, from 300 s to 900 s, in accordance with certification standards). A series of experimental studies, both ex-situ and in-situ, involving a range of mechanical load types (tensile, flexural, fracture and open-hole tensile tests), are supported by various analytical modeling approaches. When subjected to a kerosene flame, the presence of temperature gradients results in heterogeneous degradation mechanisms, in contrast to the isothermal case. The char layer serves as a thermal insulator, thereby preserving the mechanical properties of laminates over extended exposure times. Depending on the pyrolysis degree of each ply, the load-bearing capabilities are gradually reduced from the exposed side to the back surface. Master curves were obtained to emphasize the correlation between porosity ratio and residual flexural properties, providing an efficient criterion to estimate the post-fire mechanical properties. Based on the discretization of the post-fire laminate into multi-layer (char and decomposition/virgin zone), the proposed analytical modeling (adapted to TP-based laminates) has been proven effective in predicting the residual tensile and bending properties. The modeling of the in-situ mechanical properties over multiple phase transition temperatures of the PEEK matrix is applied to characterize and ultimately predict the thermo-mechanical response of laminate under tensile loading in fire.