Effects of layer waviness on the compression fatigue performance of thermoplastic composite laminates

The influence of layer waviness on the compression fatigue response of carbon/polysulphone composite laminates was studied. Specimens with a moderate level of layer waviness as well as wave-free control specimens were cycled to failure at a variety of maximum stress levels to establish S-N curves. A one and a half decade loss of compression fatigue life was observed for moderate layer wave specimens as compared with the control specimens. Brooming failure, characterized by through-the-thickness splaying of the layers and by numerous delaminations, was the common failure mode. The stress level corresponding to the 106 cycle run-out for these layer wave specimens was reduced to approximately 45% of the static compression strength of the wave-free laminate, as compared with a reduction to 75% for the control specimens. Moderate layer were specimens cycled to the 106 cycle run-out showed no evidence of delamination in the vicinity of the layer wave. Specimens with a mild layer wave failed in the grips away from the wave and exhibited fatigue life comparable to the wave-free specimens.