Fatigue lifetime of glass fabric/epoxy composites

Monotonic and fatigue tests were carried out in four-point bending on a gla ss fabric/epoxy composite, using two different stress ratios. Ultimate fail ure both in monotonic tests and in fatigue was precipitated by microbucklin g phenomena happening at the compression side of the specimens. The experim ental results were evaluated adopting a fatigue model statistically impleme nted, based on the hypothesis of a two-parameter Weibull distribution of th e monotonic strength, previously assessed for random glass fibre reinforced plastics failed in tension. The fatigue model was able to account for the effect of the stress ratio on the fatigue life, accurately predicting the c lassical S-N curve. By the model, the virgin strength for each specimen fai led in fatigue was evaluated, and the distributions of the measured and cal culated monotonic strength were compared. Some discrepancies between the tw o distributions, resulting in poor agreement in the tail portions of the cu rves, were noted. It is shown that the inconsistencies found are probably a ttributable to the inadequancy of a two-parameter Weibull curve to describe the actual material trend. Better results were obtained by using a three-p arameter Weibull distribution. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.