The effect of staggered matrix crack induced delamination growth on the mechanical properties of cross-ply laminates

Matrix cracking in composite laminates is a common sub-critical damage mechanism that forms under thermomechanical loading and may induce delamination, which is a prevailing critical damage mechanism. Previous studies have considered induced delamination stemming from a symmetric pattern of matrix cracks despite observations revealing matrix crack patterns are staggered. In this study, delamination cracks induced from staggered matrix cracks in [90_n/0_m/90_n]_s cross-ply laminates is investigated analytically for the first time. A new energy-based analytical model is developed within the framework of classical lamination theory, where distinct zones along the induced delamination cracks are defined in the unit cell and a crack closure technique is employed. The laminate stiffness and strain energy release rate (ERR) are predicted for increasing induced delamination crack length. The analytical results were in excellent agreement with that of a finite element analysis (FEA) of the unit cell, demonstrating the accuracy and robustness of the developed model.