An XFEM-based methodology for fatigue delamination and permeability of composites

A methodology for the simulation of thermal fatigue delamination in composites and prediction of delaminated crack opening displacement (DCOD) and composite laminate permeability is presented. This is critical for the safe design of composite cryogenic fuel tanks. The methodology, which is based on an extended finite element method for simulation of crack growth, does not require a priori definition of initial crack (delamination) length or crack propagation path. In contrast, previous work required estimation of delamination length and corresponding number of thermal cycles based on experimental measurements. The methodology is validated against measurements from standardised static and fatigue delamination test methods. Prediction of delamination crack growth in a quasi-isotropic laminate under cryogenic fatigue loading is used to establish the effect of initial interlaminar defect length on subsequent crack growth, as well as the effect of delamination length on DCOD and permeability. A key additional benefit is that the proposed method can simulate both inter- and intralaminar crack growth in two- and three-dimensional geometries.