Abstract

This study investigates the behaviour and tensile performance of multi-material additive manufacturing (MMAM) by fused deposition modelled (FDM) laminates composed of polylactic acid (PLA) and thermoplastic polyurethane (TPU). The work aims to establish the relationship between layer configuration, material sequence, and deformation mechanisms in rigid–compliant polymer systems. Single-material PLA and TPU specimens were first characterised to establish baseline mechanical behaviour, followed by six laminate architectures combining PLA and TPU in alternating layers. Tensile testing was conducted with apparent stiffness values derived from crosshead displacement and failure modes documented through post-fracture imaging. Results show that PLA exhibited brittle fracture with minimal necking, while TPU demonstrated extensive elongation and stress whitening prior to rupture. The laminates displayed intermediate mechanical properties, achieving improved ductility compared with pure PLA and higher strength than TPU. The strongest configuration, a PLA/TPU/PLA laminate with thinner layers (0.1 mm), reached an average ultimate tensile strength (UTS) of 33.5 MPa and elongation of 7.7%, reflecting effective stress transfer across the interface. Fracture analysis revealed mixed brittle–ductile morphologies and limited delamination, indicating partial interlayer adhesion despite the intrinsic surface-energy mismatch between PLA and TPU. The findings highlight the feasibility of combining dissimilar thermoplastics within a single FDM build to achieve tuneable mechanical response. However, the results also highlight the need for interfacial improvement through diffusion optimisation or compatibilisation to fully exploit the potential of multi-material polymer additive manufacturing for high-performance structural and flexible systems.