Fatigue Performance of a Thermal Protection Structure with a Composite Stringer-Stiffened Panel

In the thermal protection structure (TPS) of reusable reentry vehicles, replacing the traditional titanium alloy substrate with a composite stringer-stiffened panel (CSP) significantly reduces structural weight. However, the thermomechanical coupling load during reentry can severely degrade the fatigue performance of the CSP, making it essential to investigate its fatigue behavior. Tensile fatigue experiments were conducted to evaluate the fatigue performance of a TPS with a CSP substrate. A nonlinear variable-amplitude fatigue degradation criterion based on equivalent fatigue damage accumulation was proposed to solve the variable-amplitude fatigue issue. With this criterion, the finite element model (FEM) of the TPS was developed and validated. Based on the FEM, the fatigue performance, failure mechanisms, and temperature parametric effects of the TPS were thoroughly investigated. The results show that the fatigue analysis model effectively simulates the fatigue process of the TPS. The primary failure mode of the TPS is delamination failure at the middle layer, typically initiating in stress concentration regions at the peak temperatures. The delamination failure propagation rate increases significantly and then stabilizes. When the peak temperature is reduced from 150 to 85°C, the delamination failure propagation rate decreases by 79.5%, and the fatigue life of TPS increases 5.1 times.