Impact damage reduction by structured surface geometry

Repeated impacts can cause damage to not only a surface but also inside the material. Mechanisms include stress-wave propagation into the material, reflection of the waves at the back surface, and subsequent repeated reflections in the vicinity of the impact and the back surface. Impact damage performance was observed for polyurethane-coated fibre composites with structured geometries at the back surfaces. Repeated impacts by rubber balls on the coated side caused damage and delamination of the coating. The laminates with structured back surfaces showed longer durability than those with a flat back surface. The in-situ acoustic measurement indicates that the acoustic power within the pulse duration was 25-40% lower using the structured back surfaces. The observed effect can be attributed to scattered reflection at the back surface to reduce the high intensity duration of the acoustic waves.