Delamination suppression in tapered unidirectional laminates with multiple ply drops using a tape scarfing technique

Composite laminate thickness tapering is essential for weight efficient structures. This is achieved by terminating specific plies, but these can in turn act as sites for delamination initiation. One area of importance is the spacing between adjacent ply drops, which can have a significant impact on the delamination stress. In this work, a novel tape scarfing method that applies a tapered profile to dropped ply ends was used on unidirectional tapered laminate specimens with multiple ply drops. The effect of ply drop spacing on the delamination stress of both conventional and scarfed plies in tension was studied experimentally. The results showed that the scarfed ply drop configurations can completely suppress delamination in certain configurations. The scarfed ply drops also retained higher performance with smaller ply drop spacings. This indicates that in using scarfed plies, conventional laminate design rules could be relaxed and the weight of the structure could be further reduced. The underlying failure mechanisms were also investigated using both analytical and numerical methods. A simple stress-based formula for estimating the delamination stress of scarfed plies was introduced and shown to be consistent with both experimental and numerical results, which could be used (and further developed) to make tapered laminate design easier