Exploring the Iosipescu method to investigate interlaminar shear fatigue behavior and failure mechanisms of carbon fiber reinforced composites

Iosipescu method, commonly adopted to determine the static shear properties of composite material, is extended to analyze the shear fatigue properties of carbon fiber reinforced epoxy composites. Following the results of the ultimate shear strength (τ) and interlaminar shear modulus (G₁₃) in the static tests, this work conducted interlaminar shear fatigue tests with two stress ratios and four stress levels to obtain the S-N and stiffness degradation curves. The S-N curves of the stress level versus logarithmic fatigue life exhibit a good linear relationship, and the specimens display a better fatigue performance at the stress ratio of 0.1 than −1. A significant three-stage cumulative damage evolution characteristic was found in the fatigue stiffness degradation process. In addition, the damage evolution, dominated by the propagation of matrix microcracks along the fiber direction inside the material, that is, debonding and delamination of the interface, was captured and analyzed via microscopic observation of the damaged zone on the specimen surface. Understanding the revealed processes of shear fatigue failure is crucial for ensuring the safe utilization of composite structures.