25. Experimental Observations of Dynamic Delamination in Curved [0] and [0/90] Composite Laminates

Curved composite parts are increasingly replacing metal ribs and box structures in recent civil aerospace structures and wind turbine blades. Delamination of L-shaped composite laminates occurs by interlaminar opening stresses in addition to the interlaminar shear stresses at the curved region. An experimental setup is designed to investigate dynamic delamination in L-shaped composite brackets under quasi static shear loading. The materials are unidirectional [0]₁₇and cross-ply [0/90]₁₇ epoxy/graphite composite laminates. The load displacement curves are recorded and subsequent dynamic delamination is captured with a million fps high speed camera. The failed specimens are analyzed under a microscope. It is seen that layup differences change the failure mechanism in composites. Multiple delaminations in one load drop are observed in failure of unidirectional laminate whereas sequential delamination at each discrete load drop is seen in cross ply laminates. In the [0] laminate single delamination in the center ply followed by symmetric delamination nucleations around the two crack tips are observed. In the 0/90 cross-ply laminate, multiple load drops are recorded and delaminations start near the inner radius by peeling of 0/90 plies sequentially at each load drop. In both layups, first time observation of intersonic delamination speeds up to 2,200 m/s are made.