Buckling behaviour and delamination growth in impacted composite specimens under fatigue load: an experimental study

Impact-damaged carbon-fibre/epoxy composite laminates have been tested in fatigue under constant-amplitude loading with emphasis on studying mechanisms leading to delamination growth and fatigue failure. The shapes of the buckles have been measured with an optical whole-field measurement technique, while the extension and depth of delaminations was measured several times by ultrasonic C-scanning during testing. It was observed that the delamination growth occurs mainly in transverse direction to the load and that buckles on the backside usually have the same shape as some of the delaminations. This indicates that the buckling which takes place during the compressive part of the load cycle drives delamination growth. In specimens run to the fatigue limit, buckling and delamination growth occur only in the outer 2 or 3 layers on the backside while a specimen that failed before the fatigue limit buckled through the whole specimen.