Strategies for stiffness analysis of laminates with microdamage: combining average stress and crack face displacement based methods

Abstract

Many approximate analytical models have been developed to calculate stress state between intralaminar cracks with the aim to predict the degradation of certain elastic property (most often axial modulus or shear modulus) of cross‐ply laminate. Often they are plane stress solutions and laminate constants like Poisson's ratios cannot be considered. On the other hand the so called GLOB‐LOC approach, presented in WWFE III, allows calculation of any thermo‐elastic property of a general symmetric laminate with an arbitrary number of cracks in each layer provided that two local parameters – average and normalized crack opening displacement (COD) and crack face sliding displacement (CSD) are known. In this paper relationships are derived expressing these two parameters (COD and CSD) with average value of transverse stress and in‐plane shear stress perturbation between cracks. Expressions are exact and independent on the approximations in the stress model. As examples, average perturbation functions for two shear lag models and Hashin's variational model are used to calculate damaged laminate properties that would not be available in original formulation: Poisson's ratio and thermal expansion coefficients. Predictions are compared with test data for GF/EP laminates and with more accurate predictions based on FEM calculations.