Fatigue lifetime of glass fabric/epoxy composites

Monotonic and fatigue tests were carried out in four-point bending on a glass fabric/epoxy composite, using two different stress ratios. Ultimate failure both in monotonic tests and in fatigue was precipitated by microbuckling phenomena happening at the compression side of the specimens. The experimental results were evaluated adopting a fatigue model statistically implemented, based on the hypothesis of a two-parameter Weibull distribution of the 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 classical S-N curve. By the model, the virgin strength for each specimen failed in fatigue was evaluated, and the distributions of the measured and calculated monotonic strength were compared. Some discrepancies between the two distributions, resulting in poor agreement in the tail portions of the curves, were noted. It is shown that the inconsistencies found are probably attributable to the inadequancy of a two-parameter Weibull curve to describe the actual material trend. Better results were obtained by using a three-parameter Weibull distribution. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.