Progressive fatigue damage modelling and life prediction of 3D four-directional braided composite I-beam under four-point flexure spectrum loading

This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D (three-dimensional four-directional) braided composite I-beam under four-point flexure spectrum loading. New fatigue damage models of fibre yarn, matrix and fibre–matrix interface are proposed, and fatigue failure criteria and PFDA (Progressive Fatigue Damage Algorithm) are thus presented for meso-scale fatigue damage modelling of 3D4D braided composite I-beam. To validate the aforementioned model and algorithm, fatigue tests are conducted on the 3D4D braided composite I-beam under four-point flexure spectrum loading, and fatigue failure mechanisms are analyzed and discussed. Novel global–local FE (Finite Element) model based on the PFDA is generated for modelling progressive fatigue failure process and predicting fatigue life of 3D4D braided composite I-beam under four-point flexure spectrum loading. Good agreement has been achieved between experimental results and predictions, demonstrating the effective usage of new model. It is shown that matrix cracking and interfacial debonding initially initiates on top surface of top flange of I-beam, and then gradually propagates from the side surface of top flange to the intermediate web along the braiding angle, and considerable fiber breakage finally causes final fatigue failure of I-beam.