Evaluation of Constitutive Laws for the Computer Simulation of Fatigue Driven Delamination in Composite Materials

Abstract

A simple mathematical model (cylinder model) is proposed and used to evaluate various constitutive laws used in finite element codes to simulate fatigue-driven delamination in composite materials. The cylinder model has one degree of freedom and allows the evaluation of several parameters of the constitutive laws in an ffcient and accurate way without worrying about the complex interactions that may arise while using a nite element code. This cylinder model enabled a large number of analysis to be performed in a relatively short time and made possible parametric studies with tens of thousands of dfferent sets of parameter values of the constitutive laws. Different fatigue degradations strategies have been implemented into the cylinder model and investigated. A systematic comparison of the different strategies has been performed and it was found that the behaviour of the different strategies is similar but with some variations in the sensitivity to the spacing of the springs and to the size of the increment in the number of loading cycles. The results confirm that the more accurate results are found for smaller values of these two variables. A new fatigue degradation strategy is also proposed. It is based on the construction of a 3-D surface that represents the behaviour of the interface under fatigue loading. This surface has been incorporated into the cylinder model and its performance has been evaluated.