Statistical analysis of bending fatigue life data using Weibull distribution in glass-fiber reinforced polyester composites

The bending fatigue behaviors were investigated in glass fiber-reinforced polyester composite plates, made from woven-roving with four different weights, 800, 500, 300, and 200 g/m2, random distributed glass-mat with two different weights 225, and 450 g/m2 and polyester resin. The plates which have fiber volume ratio Vf ≅ 44% and obtained by using resin transfer moulding (RTM) method were cut down in directions of [0/90°] and [±45°]. Thus, eight different fiber-glass structures were obtained. These samples were tested in a computer aided fatigue apparatus which have fixed stress control and fatigue stress ratio [R = −1]. Two-parameter Weibull distribution function was used to analysis statistically the fatigue life results of composite samples. Weibull graphics were plotted for each sample using fatigue data. Then, S–N curves were drawn for different reliability levels (R = 0.99, R = 0.50, R = 0.368, R = 0.10) using these data. These S–N curves were introduced for the identification of the first failure time as reliability and safety limits for the benefit of designers. The probabilities of survival graphics were obtained for several stress and fatigue life levels. Besides, it was occurred that RTM conditions like fiber direction, resin permeability and full infiltration of fibers are very important when composites (GFRP) have been used for along time under dynamic loads by looking at test results in this study.