Mechanical performance of bi-material FDM rigid–flexible joints: effects of alternate deposition and mechanical interlocking

The mechanical performance of joints between rigid and flexible materials significantly impacts the engineering applications of multi-material structures, though the effects of joint types and parameters remain uncertain. This study explores the tensile and shear behaviors of alternate deposition and mechanical interlocking joints in FDM-fabricated PLA/TPU (PT) and PLA/Soft PLA (PSP) systems, focusing on key geometric parameters such as deposition width (D) and interlock depth/angle (h/θ). Findings reveal that joint performance is highly influenced by the flexible filament’s properties and material compatibility. In mechanical interlocking joints, the PT system exhibits superior tensile strength at a depth of 2 mm, with maximum values of 6.58 ± 0.33 MPa for PT and 5.91 ± 0.25 MPa for PSP, both at a 45° angle. Maximum shear strength occurs at a 22.5° angle and 4 mm depth, with PT at 24.47 ± 1.99 MPa and PSP at 18.12 ± 0.85 MPa. In alternate deposition joints, tensile strengths increase with D, plateauing at 7.42 ± 0.33 MPa for PT (D ≥ 6 mm) and 5.29 ± 0.01 MPa for PSP (D ≥ 4 mm). The PT system demonstrates a 12.77% higher tensile strength in alternate deposition compared to mechanical interlocking joints, while PSP exhibits 11.72% higher tensile strength in mechanical interlocking joints. These insights offer guidance for selecting joint types and parameters in multi-material applications, advancing the engineering of metamaterials and flexible devices.