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A Quantitative Assessment of Debonding in Unidirectional Composites Under Long-Term Loading

Transverse tensile fatigue behavior of unidirectional E-glass/epoxy and E-glass/ vinyl ester composites with 48-50 volume percent glass fiber was evaluated using a strain-controlled test condition. Analysis based on Weibull statistics shows that there is a significant difference in performance between E-glass/epoxy and E-glass/vinyl ester composites. At all strain amplitudes, the moduli of the composites were retained until final failure occurred. This is related to the development of a single dominant crack and the absence of multiple cracking which leads to the final separation in the test specimen. This behavior is similar to homogeneous materials such as metals. Fatigue life in these composites is found to be initiation dominated and, correspondingly, the propagation life is negligible. This study provides an overall insight into the fatigue behavior and damage in unidirectional composites subjected to long term transverse tensile loading. Also, it is useful in materials selection for controlling longitudinal split ting in unidirectional composite structures in fatigue loading.