Investigation of frequency-dependent fatigue crack growth behavior in perfluorosulfonic-acid membrane: In-situ experiment, constitutive modeling and crack growth prediction

Fatigue crack growth behavior of perfluorosulfonic-acid membrane is investigated under distinct loading frequencies. The evolution of cyclic plastic zone (CPZ) is traced based on in-situ optical microscopy testing and digital image correlation (DIC) technique. The crack tip deformation process is directly observed by in-situ scanning electron microscope (SEM). The experimental results show that fatigue cracks experiencing a higher loading frequency display a comparatively reduced propagation rate. The CPZ can be solely used to interpret the fatigue crack growth rate variation under different loading frequencies. The crack-front microspores are easily formed under lower loading frequency due to the enhancement of near-tip plasticity deformation. Then, a cyclic elastic-viscoplastic constitutive model is developed, which successfully capture the mechanical behavior of the membrane. Finally, based on the plastically dissipated energy, a numerical method incorporated with the developed material's constitutive relationship is established, which gives reasonable prediction of fatigue crack growth under various loading frequencies.