Abstract: Ceramifiable FRP composites have attracted considerable attention due to their exceptional properties and extensive potential applications as thermal protection materials. However, the service temperature significantly affects their mechanical properties and failure behaviors. To date, systematic studies on the internal damage evolution and failure mechanisms of ceramifiable FRP composites under mechanical loading at elevated temperatures are lacking. In this study, in-situ synchrotron X-ray computed tomography (XCT) is used to obtain the 3D morphology evolution of ceramifiable FRP composites under compressive loading from room temperature to 1000 °C for the first time. The internal damage was classified into four kinds (including warp-weft fiber debonding, matrix crack, interfiber failure, and delamination), and identified by a convolutional neuronal network model. At the same time, a detailed and in-depth study was conducted on the internal damage evolution of these four kinds of cracks with the changes in load levels and temperatures. It is found that the main damage types and degrees are highly correlated with temperature. Additionally, the evolution of 3D strain was calculated by digital volume correlation technology, and the correlation between the high-strain region and the fracture location was analyzed. This study provides a new and practical way to quantitatively analyze and automatically track the micro-crack evolution behavior inside ceramifiable composites in 3D view.

Key words: Ceramifiable composites, Internal damage evolution, High-temperature properties, In-situ XCT, Damage mechanisms