Perfluorosulfonic-acid membranes have long been used as the typical electrolyte for polymer-electrolyte fuel cells, which not only transport proton and water but also serve as barriers to prevent reactants mixing. However, too often the structural integrity of perfluorosulfonic-acid membranes is impaired by membrane thinning or cracks/pinholes formation induced by mechanical and chemical degradations. Despite the increasing number of studies that report crack formation, such as crack size and shape, the underlying mechanism and driving forces have not been well explored. In this paper, the fatigue crack propagation behaviors of Nafion membranes subjected to biaxial loading conditions have been investigated. In particular, the fatigue crack growth rates of flat cracks in responses to different loading conditions are compared, and the impact of transverse stress on fatigue crack growth rate is clarified. In addition, the crack paths for slant cracks under both uniaxial and biaxial loading conditions are discussed, which are similar in geometry to those found after accelerated stress testing of fuel cells. The directions of initial crack propagation are calculated theoretically and compared with experimental observations, which are in good agreement. The findings reported here lays the foundation for understanding of mechanical failure of membranes.

长期以来，全氟磺酸膜已被用作聚合物电解质燃料电池的典型电解质，它不仅传输质子和水，而且还充当防止反应物混合的屏障。然而，全氟磺酸膜的结构完整性经常由于膜变薄或由于机械和化学降解而引起的裂纹/针孔形成而受到损害。尽管报告裂缝形成的研究数量不断增加，例如裂缝的大小和形状，但尚未深入研究其潜在机理和驱动力。本文研究了Nafion膜在双轴载荷条件下的疲劳裂纹扩展行为。特别是比较了扁平裂纹在不同载荷条件下的疲劳裂纹扩展速率，阐明了横向应力对疲劳裂纹扩展速率的影响。此外，还讨论了在单轴和双轴载荷条件下倾斜裂纹的裂纹路径，其几何形状与燃料电池加速应力测试后发现的相似。理论上计算了初始裂纹扩展的方向，并与实验观察结果进行了比较，两者吻合得很好。此处报道的发现为理解膜的机械故障奠定了基础。理论上计算了初始裂纹扩展的方向，并与实验观察结果进行了比较，两者吻合得很好。此处报道的发现为理解膜的机械故障奠定了基础。理论上计算了初始裂纹扩展的方向，并与实验观察结果进行了比较，两者吻合得很好。此处报道的发现为理解膜的机械故障奠定了基础。