Effect of matrix and fibre cracks on static and fatigue strength of composite laminates

The effect of matrix and fibre cracks on the static strength and stiffness of uni-directional plies and cross-ply laminates under tensile loads was examined with the goal of understanding the main damage mechanisms. The size of matrix cracks emanating from cracked fibres was determined and found to be in excellent agreement with test results. This was used to predict static tensile failure of uni-directional laminates and was shown to be in good to excellent agreement with test results for six different materials. The approach was extended to fatigue loading by determining the number of cycles for the plastic zone ahead of a matrix crack tip to fail. It was combined with an approach to quantify the effect of matrix cracks under any in-plane loading previously developed by the authors to predict changes in laminate stiffness as a function of cycles. Comparisons with test results showed good to excellent agreement between predicted and measured laminate stiffness as a function of fatigue cycles.