Evaluation of Fatigue Lifetime and Fracture Mechanisms of Short Fiber‐Reinforced Composites Under the Influence of the Self‐Heating Effect

ABSTRACT This study analyzes the thermomechanical fatigue behavior of short fiber‐reinforced composites (SFRCs) under different loading frequencies, focusing on the relationship between thermomechanical coupling and fatigue damage evolution. The results showed fatigue strength below 45 MPa and a pronounced dependence on loading frequency. A bilinear thermographic approach based on the stress–self‐heating temperature relationship enabled rapid fatigue life estimation, with predictions differing by less than 13% from those obtained using conventional S–N curves. Fatigue degradation was governed by complex fracture mechanisms sensitive to thermomechanical loading conditions. As demonstrated, even a slight increase in loading frequency intensified the self‐heating effect, accelerated degradation, and altered damage evolution. X‐ray computed tomography revealed that higher frequencies promoted direct fracture of reinforcing fibers, while lower frequencies led to matrix cracking and crack coalescence prior to fiber failure. Analysis of self‐heating temperature evolution and hysteresis loops further confirmed enhanced thermomechanical coupling and accelerated structural deterioration with increasing frequency. The results demonstrate that the principal effect of thermomechanical coupling is not the increase in self‐heating temperature but its influence on the evolution of fatigue degradation mechanisms, providing important implications for fatigue testing and lifetime assessment of composite structures used in automotive and aerospace applications.