Mechanical performance of hybrid metal-composite joints reinforced with additive-manufactured stainless steel pins: a comparative study of pin geometry and fabric architecture

The design of robust hybrid joints between metal and composite parts is critical in multi-material structural applications. This study investigates the mechanical performance of single-lap joints reinforced with additively manufactured stainless steel pins featuring two geometries—spike (Type S) and ball-head (Type B)—embedded in unidirectional (UD) and twill (TW) carbon fiber-reinforced polymer (CFRP) laminates. Under quasi-static shear loading, ball-head pins increased peak load by up to 44% and failure energy by up to 66% compared to spike pins, with the Type B TW configuration achieving the highest energy dissipation. Microscopy revealed that fiber architecture and pin geometry jointly influenced failure mechanisms: TW laminates promoted distributed damage and bridging, while UD laminates exhibited localized fiber fracture and matrix splitting. These findings demonstrate that additive pinning strategies can be tailored to enhance strength and toughness in hybrid joints, and provide insight for the future design of durable metal–composite interfaces in aerospace and automotive applications.