Suppression of Delamination at Ply Drops in Tapered Composites by Ply Chamfering

ABSTRACT: The design of structures is often optimized by gradually decreasing the thickness as the load carrying requirement on the components decreases. Such structures in composites are made of tapered laminates involving dropping of plies. However, these structures are often prone to early delamination initiation, which leads to premature failure of the component and therefore limits its useful life. In the past, many routes to circumvent this problem have been evolved, such as the use of adhesive film layers or interleaving the dropped plies between continuous ones. In this work, a novel technique of ply edge chamfering has been developed and employed in the specimen fabrication. Comparisons have been drawn between similarly configured specimens, with and without chamfered ply drops. Static and fatigue test results have shown remarkable improvements, both in terms of complete suppression of delamination around ply drops and in realizing 14.5–77.6 % higher strength levels in tapered composite test coupons. The experimental data along with their comparative cases are presented. KEY WORDS: helicopter flexbeams, tapered laminates, ply drops, interleaving, delamination, terminating plies, ply drop-offs, chamfering, processing