In-situ analysis and degradation modeling of tensile properties in pyrolyzed needle-punched and stitched composites for high-temperature applications

Needle-punched and stitched carbon fiber-reinforced phenolic resin-based (NS-CFRP) composites are widely used in thermal protection systems due to their improved interlaminar bond strength and thermomechanical stability. This study systematically examined the temperature-dependent behavior of NS-CFRP composites through in-situ tensile experiments and finite element simulation calculations. In-situ high-temperature tensile tests combined with synchrotron X-ray micro-CT revealed real-time pyrolysis behavior and damage progression, showing that high temperature ablation pyrolysis significantly lowers the composite’s tensile strength. A new needle-punched and stitched mesoscopic model was developed using the UMAT-UMATHT subroutine in Abaqus to quantitatively assess thermal conductivity between fiber and matrix phases and to predict pyrolysis-induced damage failure. Results indicate that pyrolysis damage fundamentally changes the failure mechanism, causing simultaneous decreases in mechanical strength and thermal conductivity, which greatly affect the thermomechanical properties of the composite.