EFFECT OF STRESS RATIO ON THE FATIGUE OF UNIDIRECTIONAL GLASS-FIBER EPOXY COMPOSITE LAMINAE

Fatigue behaviour of unidirectional glass fibre/epoxy composite laminae under tension-tension and tension-compression loading is investigated. Stress/life experimental data were obtained for fibre orientation angles, theta, of 0, 19, 45, 71 and 90 degrees. These tests were performed under stress ratios, R (= sigma(min)/sigma(max)), of 0.5, 0 and -1. A fatigue failure criterion is proposed based on the input strain energy. This criterion takes into account both the fibre orientation angle and the value of the stress ratio. A non-dimensional form of this criterion collapses all data points, obtained from different combinations of fibre orientation angles and stress ratios, Onto a single curve.