Rx-FEM Modeling of Fatigue Damage Growth in Composites with Local R-Ratio by Using Strength Tracking Method

Abstract

A computationally efficient fatigue methodology is proposed that uses automatic cycle jump step selection algorithm within implicit framework to predict fatigue damage accumulation in laminated composites. Stress state scan within a specified load profile such as one or more cycles is performed to determine local stress ratio (R-ratio) in each integration point. S-N ply level-based strength criterion was applied for matrix Mesh Independent Crack (MIC) insertion in each ply as well as within respective Cohesive Zone Model (CZM) formulation at the damage initiation stage. Paris Law based propagation was utilized for MIC and delamination opening within CZM. The local R-ratio is implemented within CZM for initiation and propagation stages. In addition to the matrix failure modes fatigue degradation in the fiber direction under compression loading was implemented. The concept is based on shear strength degradation in the misalignment frame and LaRC failure criterion. Finite element simulations of [45/0/−45/90]3?? open hole laminate under tension-tension (T-T) and compression-compression (C-C) fatigue were performed. Fiber damage, delamination, and matrix cracks are seen to be the appropriate size and location compared with the experimental result.