Progressive fatigue damage modeling of laminated composites using strain-based failure criteria

The progressive fatigue damage (PFD) model is a well-known approach for simulating the fatigue behavior of laminated composites. In the PFD model, stress-based failure criteria detect failure modes in a unidirectional (UD) ply of laminated composites. Using stress-based failure criteria requires performing numerous UD ply characterization tests. The present research presents a series of strain-based failure criteria for the unidirectional ply under fatigue loading conditions. Using the current criteria, the need for strength degradation tests was eliminated, and the number of characterization tests was reduced drastically. Using a user-defined material behavior (UMAT) subroutine code, stress-based failure criteria were replaced by the present strain-based failure criteria in the PFD model. To evaluate the results of the model, a comprehensive experimental program was conducted to characterize the mechanical properties of UD ply and laminated composites (with/without hole) under static and fatigue loading conditions. Moreover, the PFD model was also evaluated by the available experimental data of pin-loaded composites under fatigue-loading conditions. Compared to the stress-based criteria, the present criteria improved the accuracy of the predicted fatigue life by up to 63% and reduced the cost of testing by about 50%.