A multi-axial fatigue model for fiber-reinforced composite laminates based on Puck's criterion

A new multi-axial fatigue model for fiber-reinforced composite laminates based on Puck's criterion is proposed in this article. In the fatigue model, fatigue master curves from the ATM are used to determine the uniaxial ply fatigue strengths and the multi-axial fatigue failure is then determined by Puck's criterion with the fatigue strengths at the ply level. The fatigue master curves from ATM are generated with limited uniaxial fatigue tests and can be applied to fatigue loading conditions with various frequencies and stress ratios. Both uniaxial and multi-axial S-N curves can be derived from the fatigue model. Fatigue failure envelopes are also generated from the model to better interpret the multi-axial fatigue failure in multi-axial stress spaces. The proposed multi-axial fatigue model is based on ply-level predictions, but it can be extended to laminate-level predictions with the CLT or numerical methods such as the FEM. Multi-axial fatigue failures caused by either local or global multi-axiality can be predicted by the model. Both uniaxial and biaxial fatigue experiments were carried out to provide test data for establishing and validating the proposed fatigue model. The application of the proposed multi-axial fatigue model is demonstrated with predictions of S-N curves and fatigue failure envelopes of unidirectional laminates and multi-directional laminates with typical lay-up configurations. The predictions from the proposed fatigue model are also compared with various experimental results and reasonably good agreement is observed.