Overcuring-assisted mechanical interlocking of metal–polymer composites fabricated by vat photopolymerization

Metal–polymer hybrid structures offer significant potential for lightweight and high-performance applications; however, achieving robust interfacial joining between dissimilar materials remains challenging. In this study, a novel metal–polymer joining strategy based on overcuring-assisted mechanical interlocking is proposed using vat photopolymerization (VPP). Dovetail-shaped grooves were machined on a steel substrate, and liquid photopolymer resin was intentionally overcured inside the grooves to form a strong mechanical interlock without adhesives or additional fastening elements. Experimental results showed that the maximum cured depth increased logarithmically with UV exposure time and saturated at approximately 700 μm, enabling full curing even in undercut regions. Tensile tests demonstrated that the maximum tensile load increased nearly linearly with the number of grooves (3, 6, and 10), while decreasing the groove angle from 90° to 29° significantly enhanced joint strength; in contrast, the polymer root width (1.6–2.5 mm) had a negligible effect. Finite element analysis revealed pronounced z -direction stress concentration at the groove nose for smaller angles, which correlated well with experimentally observed fracture modes. These results demonstrate that overcuring, traditionally considered a defect in VPP, can be effectively exploited as a reliable joining mechanism for fabricating high-strength metal–polymer composites with high geometric freedom.