Residual Tensile and Compressive Behaviors of CFRP Composites With Different Controlled Thermal Pyrolysis Damage

ABSTRACT The evaluation of residual mechanical properties in carbon fiber/epoxy composites following pyrolytic damage represents a critical challenge for structural safety design in extreme thermal environments. This study investigates T700/epoxy unidirectional laminates subjected to isothermal pyrolysis at 250°C, 300°C, and 350°C, systematically examining the influence of pyrolysis degree on room‐temperature tensile/compressive performance and failure mechanisms. Through thermogravimetric analysis (TGA), ultrasonic C‐scan, scanning electron microscopy (SEM), and digital image correlation (DIC), the microscopic degradation mechanisms and their evolution are elucidated. Mechanical characterization reveals that compressive strength and modulus exhibit pronounced sensitivity to pyrolysis, whereas the tensile modulus decreases by merely 6.5%, indicating significant load‐path dependence. This dichotomy is attributed to the carbon fiber‐dominated tensile modulus versus the strong reliance of compressive performance on matrix stiffness and interfacial integrity. Microstructural analysis demonstrates that pyrolytic damage at 250°C is confined to surface oxidation and minor delamination; at 300°C, damage propagates inward forming a multiscale damage network; while at 350°C, pervasive through‐thickness cracking develops. A micromechanics‐based model is established, quantitatively correlating mass loss ratio with strength reduction factors, thereby providing a theoretical foundation for safety assessment of composite structures in extreme thermal environments.