Evaluation on fatigue crack growth behavior with microstructure and multiscale-failure characteristics of perfluorinated sulfonic-acid ionomer

Fatigue crack growth (FCG) is a critical mode of performance degradation and failure in perfluorinated sulfonic-acid ionomers. However, the underlying damage mechanisms associated with microstructure and failure characteristics are not yet well understood. To address this gap, the FCG behavior of a PFSA membrane was investigated through a combined theoretical, numerical, and multiscale experimental approach, encompassing microscopic fracture morphology, mesoscopic crack tip stress distribution, and macroscopic FCG rate. The results show that FCG exhibits a progressive failure mechanism, primarily characterized by features such as microvoid nucleation and coalescence in high-stress regions, as along with step-like morphology on the fracture surface. Analysis of the mesoscopic crack tip strain field revealed distinct strain gradient effects and butterfly-shaped plastic zone, both of which intensify with increasing stress ratio. An anisotropic viscoelastic-plastic constitutive model, incorporating stress status, was integrated with a cyclic cohesive zone model to establish a progressive fatigue damage framework. This model effectively captured strain distribution near the crack tip and reproduced the observed FCG rates. Finally, a multiscale validation method established the correlation between macroscopic mechanical response and microscopic damage evolution. These findings reveal the multiscale characteristic of fatigue failure in PFSA ionomers and contribute to a more comprehensive framework for understanding their fracture mechanisms.