Enhancement to the Interfacial Element Formulation for the Prediction of Delamination

The effect of through-the-thickness compressive/tensile loads on the strength and response of textile composite blocks loaded in an off-axis configuration with respect to the stack direction is investigated using interface elements. Published data suggests that the composite blocks fail primarily by delamination. Thus, to predict the strength of the blocks, interface elements are placed between adjacent lamina. Recently postulated interfacial constitutive laws utilize a simple quadratic strength-based failure criterion that is shown to significantly underpredict the compressive strength of a composite block loaded 25-degrees off-axis with respect to the stack direction. The generally-used failure criterion is inadequate because it does not consider the apparent increase in shear strength when a composite is subjected to through-the-thickness compressive stress. An empirical failure criterion that considers the increase in shear strength due to the compressive stress and produces excellent correlation with experimental data was adopted and incorporated into the interfacial constitutive law. Strength predictions obtained from numerical simulations using the enhanced constitutive law were in reasonable agreement with published test data for rectangular specimens loaded in tension and compression. The numerical simulations captured the rapid delamination growth and catastrophic failure of the test specimen configurations. The predicted structural response is in good agreement with the measured response in compression when the finite element models consider the transverse nonlinear shear constitutive behavior.