Parameters affecting growth of local delaminations at transverse crack tips in [0m,90n]s cross-ply laminates

Abstract

Transverse cracks in the 90-layers in cross-ply laminates have singular stress state at the crack tips. This causes formation of fiber/matrix debonds which coalesce into a local delamination along the 0/90-layer interface. Various studies in the literature have predicted onset strains for local delaminations at transverse crack tips using energy-based criteria such as critical strain energy release rate (ERR) and critical generalized stress intensity factors. Although similar ERR-based analyses have been carried out to predict the delamination growth as well, a systematic parametric analysis is lacking. Such systematic analysis of parameters that can affect the growth of local delaminations including geometrical parameters, elastic constants and transverse crack density is necessary to predict delamination growth under complex thermo-mechanical loading conditions. In the present work, FEM is used to carry out ERR-based analysis of the growth of local delaminations with different shapes in carbon-fiber epoxy and glass-fiber epoxy [0_m,90_n]s cross-ply laminates with the help of virtual crack closure technique and J-integral method. Firstly, the ratios of elastic constants and geometrical parameters that can prominently affect the ERR values are identified by a simple analytical routine. Then, the analytical predictions are verified using FEM for local delaminations growing symmetrically (I-shaped and C-shaped) or non-symmetrically (T-shaped and S-shaped) with respect to the laminate midplane. It is shown that a non-symmetrical I-shaped crack would always transition into a symmetrical I-shaped crack before any further delamination growth, if energetically viable. Finally, a simplified strategy to calculate ERR values for local delaminations growing under combined thermo-mechanical loading is presented.