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 (V-f) = 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 = S-min/S-max = -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. (c) 2012 Elsevier Ltd. All rights reserved.