Thin-shell thermoplastic composites with tunable out-of-plane properties: The interplay of layer thickness and cooling rate

Abstract

This study explores how layer thickness and cooling rate influence crystallinity and flexural properties in cross-ply carbon fiber-reinforced polyamide 6 thin-shell composites ($672\mu m$ total thickness). By varying layer thickness and cooling rate during consolidation, the matrix microstructure and resulting flexural behavior were significantly affected. Reduced layer thickness and increased cooling rate lowered crystallinity due to restricted chain migration, while thinner layers also decreased stiffness per classical lamination theory. This enables tailoring of the strength/stiffness ratio. Notably, a thin-layer laminate ($42\mu m$) achieved a similar strength to the thick-layer composite ($168\mu m$) but exhibited 40% enhanced flexibility, 35% higher failure onset strain, and 20% improved damage tolerance. This highlights the enhanced tunability for thin-ply thermoplastic composites, surpassing the limitations of thermoset and conventional thermoplastic composites.