Immersed interlaminar fatigue of glass fiber epoxy composites using the I-beam method

Exposure to marine environment causes a degradation of the interlaminar shear performance of composites. This effect has been reported in several studies, but the mechanisms that lead to failure in composites subjected to cyclic loading under water exposure are still not fully understood. In this work a novel test method, the I-beam short beam shear, was used to determine shear properties and accelerate fluid saturation in glass fiber epoxy specimens. The interlaminar shear performance of the material was studied experimentally. From the analysis of the cyclic parameters recorded during the test and from optical micrographs it was possible to observe a change in failure mode between dry samples and conditioned samples. The failure of dry samples was a creep dominated effect, which led to inter-ply cracks, while the failure of conditioned samples was a damage growth dominated effect, which led to intra-ply failure. Optical micrographs showed that fiber/matrix debonding occurs in conditioned samples prior to mechanical loading, which are potential damage onset spots