Flexural fatigue characteristics of two different types of glass fiber/epoxy polymeric composite laminates with statistical analysis

Flexural fatigue tests have been conducted on unidirectional glass fiber/epoxy, [U]5 and random glass fiber/epoxy, [R]5 composite laminates with a constant fiber volume fraction (Vf) = 37% and average thickness = 5.5 ± 0.2 mm. The laminates were manufactured using hand lay-up technique. Flexural fatigue tests were performed on standard specimens at zero mean stress, i.e. a cyclic stress ratio = Smin/Smax = −1. A 20% reduction of the initial flexural stiffness was taken as a failure criterion. The specimens’ surface temperature increase was investigated. To construct the S–N curve for each composite type, four stress levels have been considered using five specimens for each one. The failure modes of the test specimens were investigated. Two-parameter Weibull distribution function was used to analysis statistically the fatigue life results. Also, it has been employed to incorporate failure probability into S–N relationships.