Carbon fiber thermoset composites with architected thermoplastic lattice interlayers: Topology- and density-driven enhancement of interlaminar and flexural properties

Abstract

Introducing compliant interlayers is a common strategy for enhancing the damage tolerance of carbon fiber–reinforced polymer (CFRP) laminates; however, continuous elastomeric layers often severely degrade interlaminar stiffness and strength. Inspired by natural segmented architectures, such as nacre, where discrete compliant domains are embedded within a stiff load-bearing framework, we demonstrate that interlaminar performance is governed not solely by material compliance, but critically by the spatial architecture, topology, and relative density of the interlayer. CFRP laminates incorporating architected thermoplastic polyurethane (TPU) lattice interlayers are fabricated and compared with baseline CFRP and laminates containing continuous TPU sheets. Short-beam shear and flexural tests, combined with digital image correlation and Ashby-style stiffness–energy design-space mapping, were used to evaluate the laminates. The results reveal that discretizing the compliant phase into isolated TPU pockets embedded within a predominantly epoxy-controlled interlaminar network preserves nearly the full baseline interlaminar stiffness, while increasing flexural energy absorption by up to fourfold relative to baseline CFRP and twofold relative to continuous TPU interlayers. In contrast to continuous elastomeric layers, architected lattices mitigate the stiffness–toughness trade-off and promote stable, distributed damage mechanisms. Finite-element simulations employing heterogeneous cohesive interfaces provide mechanistic insight into damage initiation, strain redistribution, and post-initiation stability, reproducing key qualitative experimental trends. These results establish architectural design of the interlaminar region as an effective pathway for enhancing damage tolerance in CFRP laminates without incurring the severe mechanical penalties associated with continuous elastomeric interlayers.