Fatigue behaviour of unnotched and notched woven glass/epoxy laminates

Abstract

Unnotched and notched rectangular specimens of three E-glass/epoxy woven laminates (two orthotropic and one quasi-isotropic) have been cycled, with a stress ratio of 0·1 and a frequency of 20Hz, under load control at room temperature. The fatigue strengths for these laminates are determined. The influence of the hole and the stacking sequence on the fatigue behaviour have been studied. The results show that the unnotched and notched laminates have the same ratio of the fatigue strength to the monotonic ultimate tensile strength (UTS); that the fatigue strength ratios of notched and unnotched laminates are, respectively, equal to the ratios of their monotonic notched and unnotched strengths (strength reduction factor); and that at the same ratio of maximal fatigue stress to UTS the notched laminates have a slightly longer fatigue life than the unnotched laminates. The results also show that the orthotropic and quasi-isotropic laminates are of different fatigue strengths but have the same ratio of fatigue strength to UTS; that the different stacking sequences in the two orthotropic laminates can influence fatigue damage development although there is no significant fatigue strength difference between the two different orthotropic laminates; and that the fatigue strength for the quasi-isotropic laminate is the most insensitive to the hole effect among the three laminates.