Geometry-dependent mechanical behavior of mechanically interlocked metal–polymer structures fabricated by hybrid PBF–VPP additive manufacturing

This study investigated the effect of interlocking geometry on the curing behavior and tensile performance of metal–polymer hybrid interfaces fabricated by infiltrating and over-curing a photocurable resin within additively manufactured metal structures. Four unit-cell geometries—Cone, Pillar, Reversed cone, and Pawn—were compared through microhardness measurements, tensile tests, finite element analysis (FEA), and fracture observations. The tensile results showed strong geometry dependence: the Pawn geometry exhibited the highest maximum load (1268 N), whereas the Cone geometry showed the lowest value (732 N) because of straightforward metal–polymer separation. Although the Pillar geometry had no macroscopic undercut, it exhibited a high maximum load (1174 N), suggesting that micro-scale mechanical interlocking provided by the rough PBF surface significantly enhanced interfacial resistance. The Reversed cone geometry showed a slightly lower load (1089 N), which was attributed to localized stress concentration near the undercut edge. FEA further showed that the interfacial geometry controlled both stress transfer and stress localization, while fracture observations confirmed geometry-dependent crack paths and polymer retention behavior. In particular, the Pawn geometry promoted broader stress distribution, more uniform curing near the interface, and a more tortuous fracture path. These results demonstrate that the performance of metal–polymer hybrid interfaces is governed by the balance among geometric confinement, curing uniformity, micro-scale anchoring, and stress redistribution, rather than by undercut volume alone.