Fatigue behaviour and life assessment of composite laminates under multiaxial loadings

A thorough analysis of fatigue of composite laminates under multiaxial loading is presented. A large body of experimental data taken from the literature is examined to delineate the influence on the fatigue strength of factors such as biaxiality ratios and off-axis and out-of-phase angles. The data are found to clearly suggest that the ply-level shear biaxiality ratio, defined as the ratio of the shear stress amplitude to the largest normal stress amplitude, is the governing factor. The multiaxial fatigue criteria are examined next. The empirical method proposed by Ellyin and co-workers, based on the assumed log-linear fatigue life relationship, is compared with data. The Tsai–Hill and Smith–Pascoe quadratic polynomial criteria are also scrutinised. Finally, a mechanisms-based approach to multiaxial fatigue is outlined and proposed as the way to developing a reliable life prediction methodology.