Mechanisms and Damage-Based Assessment of Time-Dependent Fatigue Crack Propagation in Polymer Electrolyte Membrane

The time-dependent fatigue crack propagation mechanisms of polymer electrolyte membrane are explored in conjunction with in-situ experiments from both microscale and mesoscale. The results show that decreasing the loading frequency significantly increases the damage level at the crack front while also enhancing the near-tip plasticity deformation. The plasticity-induced micropores development and coalescence is considered as the dominant fatigue crack propagation mode. Then, a cyclic cohesive zone model considering the elastic–viscoplastic mechanical response of the bulk material is established, which further verified that more plasticity deformation is introduced near the crack tip at reduced loading frequency, thus imposing more damage accumulation to the crack tip. Besides, the established cyclic cohesive zone model is proved to be efficient in assessing fatigue crack propagation rate under distinct loading frequencies.