Creep Failure and Pyrolysis Damage Mechanism of CFRP Under Thermo‐Mechanical Coupling

ABSTRACT

A key challenge in airworthiness of composite aircraft is understanding the thermo‐mechanical response and failure of carbon fiber reinforced polymer (CFRP) in in‐flight fire. A sequentially coupled thermal‐stress analysis with a three‐dimensional thermal response model incorporating anisotropic thermal conduction, matrix pyrolysis, and gas diffusion via user subroutines UMATHT and USDFLD was developed. Experiments were conducted under heat fluxes of 35 and 50 kW/m ² and tensile loads of 20%~80% ultimate strength. It was investigated that the pyrolysis, creep, and failure of CFRP under one‐sided heat flux and tensile loading. Results show the temperature, creep displacement, and failure time of CFRP from simulations agree well with experiments. Significant temperature and pyrolysis gradients occur through the thickness, with the pyrolysis front advancing from the heated zone. Higher heat flux accelerates pyrolysis and expands the pyrolyzed range. Creep rate increases substantially with load and heat flux: at 35 kW/m ² , the steady‐state creep rate at 80% load is over seven times that at 20% load; at 50 kW/m ² , this factor is nearly seven. Three distinct failure modes were identified: high stress‐short time failure dominated by fiber fracture, intermediate stress‐long time failure governed by coupled mechanical and thermal damage, and low‐stress failure associated with complete resin pyrolysis.