Evolution of ply cracks in multidirectional composite laminates

This paper treats evolution of ply cracks in multidirectional composite laminates subjected to a quasi-static tensile load in the longitudinal direction. Starting with pre-existing ply cracks in off-axis plies, the formation of additional cracks is analyzed by an energy-based approach. A critical laminate energy parameter associated with formation of these cracks is defined and is evaluated using experimental data for a reference cross-ply laminate. The modeling approach requires crack surface displacements, which are calculated by a three-dimensional finite element (3-D FE) analysis performed on a suitable representative volume of the given cracked laminate. The model predictions agree well with experimental data for [ 0 / ± θ 4 / 0 1 / 2 ] s and [ 0 / 90 / ∓ 45 ] s laminates. A parametric study is conducted to evaluate effects of ply thickness and ply stacking sequence on damage evolution in [ 0 m / 90 n / ∓ θ p ] s laminates.