Damage evolution in cross-ply laminates revisited via cohesive zone model and finite-volume homogenization

The classical phenomenon of progressive cracking of 90° plies in polymeric matrix cross-ply laminates, and potential or subsequent delamination along the 0°/90° ply interface, is critically revisited using a finite-volume homogenization theory with damage evolution capability. Progressive separation of adjacent phases or subdomains as well as crack evolution may be simulated with this capability within a unified framework that employs discontinuity functions in conjunction with the cohesive-zone model. The finite-volume simulations of evolving damage in graphite/epoxy cross-ply laminates on the fly and its effect on the homogenized axial stress–strain and transverse Poisson's responses, as well as crack density, are compared with available experimental results, taking account of residual stresses, interfacial resin-rich region and variable strength of the 90° plies. The comparison demonstrates the theory's ability to capture the dramatic effect of transverse cracking on the homogenized transverse Poisson's ratio that increases with increasing 90° ply thickness, and the damage mode bifurcation from transverse cracking to interfacial delamination. Moreover, the finite-volume simulations indicate that many features observed in the transverse and through-thickness Poisson's response of graphite/epoxy cross-ply laminates may be related to the underpinning damage modes more readily than in the axial response. The developed finite-volume framework offers a unified methodology for simulating damage evolution in a class of composite laminates due to cracking and/or progressive interfacial degradation, and for identifying features observed in the homogenized response that reflect the underpining local failure mechanisms.