Multi-Axial Failure Models for Fiber-Reinforced Composites

Combined in-phase tension/torsion loading was applied to 8-ply 45° 4 E-glass/epoxy composite shafts under monotonic and fatigue conditions to determine the effects of multi-axial loading on its failure. A damage criterion for multi-axial monotonic loading was proposed considering the contribution of both normal and shear stresses on the plane of failure. The experimental data showed an excellent agreement with the proposed model for various loading conditions. Several multi-axial fatigue failure models were proposed considering mean and cyclic normal stress and shear stress at the plane of failure, as well as the mean and cyclic normal strain and shear strain at the plane of failure and their capability for predicting the fatigue life of the composite under study was examined. In addition to the fatigue damage model based on the plane of failure, a multi-axial fatigue failure model was proposed considering the mean and cyclic energy in the fatigue experiments. The experimental data showed a reasonably good correlation with some of the proposed damage models.