Evolution of strain-rate dependent compressive failure behavior of ceramifiable FRP composites at high temperature conditions

Fiber-reinforced polymer (FRP) composites modified with ceramic fillers have excellent thermal stability at high temperatures and are applied in aeronautical and aerospace fields. The effect of strain rate on their mechanical behavior at different temperatures (corresponding to different states of FRP composites) is of interest. In this study, dynamic and quasi-static compressive tests of a kind of ceramifiable polymer composites, B₄C-talc modified high-silica/boron-phenolic (B₄C-talc_HS/BPh) composites, were examined at 25–1000 °C. A high-temperature split Hopkinson pressure bar with a double-synchronous assembled system was employed to carry out dynamic tests. During the tests, high-speed camera was employed to monitor the progressive failure process, and the failure morphology was examined using an optical microscope. The tests show that the compressive strength decreases with increasing temperature to 600 °C at both low and high strain rates. However, it is found for the first time that the compressive strength increases obviously at 800–1000 °C due to the ceramifiable transition at a high strain rate. Moreover, the influence of temperature and loading rate on the compressive failure behavior of B₄C-talc_HS/BPh composites was systematically investigated. Shear force dominates the failure under dynamic load at 25–1000 °C, while it is 25–450 °C under quasi-static load. Piece-wise models are developed to describe the temperature and strain-rate dependent evolution behavior of the compressive strength. This research provides basic experimental data on the mechanical properties of B₄C-talc_HS/BPh composites, which can inform the design, evaluation of integrity, and reliability of thermal protection structures.