Coupled residual stiffness and strength model for fatigue of fibre-reinforced composite materials

The fatigue behaviour of fibre-reinforced composite materials is complex and present knowledge is far from complete. Several classes of models attempt to predict the fatigue life and/or fatigue degradation of fibre-reinforced composites. Two major classes are the residual stiffness models and the residual strength models. This paper presents a phenomenological residual stiffness model which predicts both the stiffness degradation and the final failure of the composite component. The reserve to failure has been evaluated by means of a modified use of the Tsai–Wu static failure criterion. The fatigue damage model has been applied to displacement-controlled bending fatigue experiments of plain-weave glass/epoxy specimens. The damage and stress (re)distribution, as well as the force-cycle history have been simulated and compared to experimental results. Because of the consistent integration of continuum damage mechanics and the residual stiffness approach, the implementation of the fatigue model in a commercial finite element code has been possible, which allows for an accurate simulation of the successive damage states during fatigue life.