Numerical life prediction of unidirectional fiber composites under block loading conditions using a progressive fatigue damage model

Abstract Practical applied components made of Fiber-Reinforced Plastics (FRPs) are usually subjected to cyclic loading with variable load amplitudes and arbitrary load orientation in the course of their service life. For a cost-effective design process of composite structures, it is essential to use computationally efficient and detailed fatigue damage design tools. This contribution focuses on the extension and application of a progressive Finite-Element-based Fatigue Damage Model (FDM) for unidirectional FRPs for lifetime prediction under different block loading conditions. The employed FDM relies on a layer- and energy-based approach, and it is capable of including basic fatigue phenomena such as load sequence effects and stress redistributions. First, the damage evolution laws on which the FDM is based are extended to block loading conditions with arbitrary load sequences. The effects of passive damage, which occur in this context under alternating cyclical tensile and compressive loading, are also taken into account. Secondly, appropriate block loading patterns are defined for the numerical prediction of the lifetime. Finally, the calculation results are presented and critically evaluated based on experimental findings from literature. The comparison of simulations with experiments demonstrates the high predictive capacity of the presented FDM.