Micromechanics of Cracked Laminates under Uniaxial Load: A Comparison between Approaches

Abstract

This paper compares stiffness degradation models of cross-ply glass fiber/epoxy laminates based on four of the most commonly used approaches to micromechanical modelling: shear-lag, variational, McCartney, and synergistic damage mechanics (SDM). All of these include the process of defining [0/90] s laminate unit cell, from which governing differential equations and corresponding boundary conditions are stated. Afterwards, these boundary value problems (BVP) are solved in order to obtain a stress function which couples the initial and perturbation stresses, the latter being in function of crack density, thus related to material stiffness reduction. When compared against experimental results, shear-lag model presented accurate results however, additional differentiation and integration steps were required in order to obtain the final stress field. Hashin's variational method predicts correctly the boundary conditions at crack surfaces and gives out the complete stress field. McCartney's approach shows further improvement over the previous two models, taking into account thermal strains and stresses. Finally, SDM, which is designed for numerical experimentation, implying a more economical alternative in comparison to traditional physical experimentation, also presented very good agreement with experimental results and can be extended to arbitrary laminate stackings, going beyond the classical cross-ply.