Determination of critical energy release rates for discrete damage mechanics analysis in ANSYS

Matrix cracks are the first type of degradation observed in most polymer matrix composites. The Discrete Damage Mechanics (DDM) model has been added to ANSYS® as a user material (UserMAT) to enable prediction of initiation and evolution of matrix cracks in laminated composites. Besides the usual material properties that describe the elasticity and strength of a ply, DDM uses two, in situ, critical energy release rates (GIc and GIIc) to provide accurate predictions of intralaminar cracking. No standard test method exists to determine these properties in situ, in a finished laminate. Therefore, a methodology is proposed herein to evaluate these properties in terms of experimental stiffness-degradation data from specimens made with two different laminate stacking sequences. Experimental data for other stacking sequences of the same material system are used to validate the methodology. Comparison with other model-results are also presented. The objectivity of the constitutive model is evaluated by performing both p- and h-refinement.