Towards efficient prediction of buckling-induced delamination growth in composites under compressive fatigue loading conditions

Delaminations can significantly compromise the structural integrity of composite structures by creating regions of reduced bending stiffness that are prone to sublaminate buckling. Such buckling can in turn drive delamination growth and ultimately lead to a loss of load-carrying capacity. This study presents nonlinear finite element analyses of buckling-induced delamination growth in composite laminates under compressive fatigue loading conditions. Delamination propagation is modelled using an established cohesive fatigue zone model, which requires the evolving local stress ratio as input. To this end, a computationally efficient method is proposed, representing a refinement of the simplified cyclic loading approach through its combination with the cycle jump method. Four laminate configurations of varying thicknesses are studied, each with a single through-width delamination near the surface. Depending on thickness, laminates undergo local or mixed local/global buckling under compression, with both mechanisms promoting delamination propagation. Across all configurations, delamination growth is initially unstable, with growth rate increasing up to a peak value at shorter delamination lengths before transitioning to stable growth. The influence of geometric imperfections is investigated in a thick laminate and is found to affect the initial growth rate, with a diminishing influence as the delamination propagates. In the same laminate, a 10% reduction in the applied fatigue strain is shown to reduce the peak growth rate from 0.06 mm/cycle to 0.02 mm/cycle. While thin laminates exhibit higher growth rates at shorter delamination lengths, propagation becomes significantly slower at longer lengths compared to thick laminates, highlighting the important role of sublaminate stiffness ratios in governing the fatigue delamination growth.