Fractal dimension analysis via μCT for failure behavior of C/SiC composites under rapid heating to 1600 °C

Computed tomography (CT) images are typically employed to quantify the volume fraction of defects or to track the evolution of internal microcracks in materials, yet they are seldom utilized from alternative perspectives for analyzing material failure behavior. In this study, fractal theory is used to assess the complexity of microcrack networks after heating. A multiscale experimental framework combines ohmic rapid heating, in-situ tensile testing at 1600 °C, and three-dimensional micro-CT (μCT) imaging. A wide range of heating rates, from 3 °C/s to 350 °C/s, simulates different thermal loading conditions. The results show clear differences in failure behavior across thermal histories. High heating rates cause a drop in tensile strength and fractal dimension, and lead to an increase in macroporosity and fiber-matrix debonding. The damaged network becomes more irregular and less connected, producing brittle fracture and poor energy absorption. At lower heating rates, gradual temperature increase enables thermal stress relaxation and interface healing. This creates a more uniform and connected damage structure, resulting in higher strength and mesoscale fractal dimension. Extended high-temperature holding partly restores the interface and matrix, but irreversible damage from rapid heating remains. A strong quantitative relationship is found between mesoscale fractal dimension and tensile strength in these composites. This relation provides a practical metric for predicting internal damage and mechanical performance with different thermal histories. These findings represent an advance in connecting microstructural detail to composite properties. Overall, this work offers guidance for designing C/SiC composites with improved reliability in applications where they face rapid thermal changes.