A Continuum Damage and Discrete Crack Approach for Fatigue Damage Prediction of Laminated Composites

Abstract

This study is focused on the development and demonstration of a continuum damage and discrete crack (CDDC) approach for fatigue damage characterization and post-fatigue residual strength prediction of notched composite specimens subjected to tension. In order to capture both the fatigue cycle driven material degradation and discrete damage induced stress concentration and redistribution, an overlapped element approach is developed based on a combined user-defined material and element formulation. An Abaqus element coupled with UMAT for fatigue damage and failure characterization is used to detect the location of failure initiation while the discrete crack network (DCN) based UEL is applied to insert a crack without remeshing. The intensified stress field induced by the newly inserted matrix crack is used for the evaluation of failure initiation and stiffness degradation. A stress-life (SN) approach is applied to perform the strength degradation prediction associated with the intraand interply damage mode. To demonstrate the applicability and validity of the CDDC based toolkit for Abaqus, a blind followed by a re-calibrated fatigue failure prediction is performed for a notched coupon of [30, 60, 90, -60, -30]2S followed by its postfatigue residual strength prediction. The predicted fatigue failure progression and its stiffness drop against cycle curves are compared with the test data provided by the Air Force Research Lab (AFRL).