Morphology of ply drops in thermoplastic composite materials manufactured using laser-assisted tape placement

Mechanical properties of composite laminates can be tuned by either tailoring ply orientations or by using ply drops to change thickness profiles. The latter cause resin-rich pockets to form in thermoset composites that are autoclave cured after lay-down. This paper focuses on the morphology of ply drop regions with carbon fibre thermoplastic composites manufactured using in-situ consolidation with laser-assisted tape placement. Our work shows that when laying a 0° ply (parallel to the ply drop) over a ply drop then the ply readily conforms to the shape of the ply drop, eliminating voids. However, when a 90° ply covers a ply drop, the processing direction affects behaviour. When the ply ascends a ply drop, a void is created. On the other hand, when the ply descends a ply drop, the substrate changes its shape due to combined laser heat and roller pressure, leading to significantly smaller voids.