Strength improvement and failure analysis of dissimilar FDM printed single-lap joints with tailored interface geometry

Fused deposition modelling (FDM) offers design flexibility for thermoplastics tailored to specific structural optimization. Hybrid joints, combining adhesive bonding and mechanical interlocking, are effective in joining dissimilar thermoplastics. This study aims to strengthen dissimilar FDM-printed single-lap joints (SLJs) by understanding failure mechanisms and delaying damage initiation and propagation. Asymmetric stress due to differences in adherend stiffness concentrates higher stress on the lower stiffness adherend, justifying the need for geometric grading to improve joint strength and prevent premature failure. This study introduces a novel approach by incorporating positive and negative mechanical interlocking teeth on the bond-layer interface to enhance the performance of FDM-printed dissimilar SLJs using Polylactic acid (PLA) and Polyamide (PA). Dogbone samples of PA and PLA were FDM printed to characterize their tensile properties experimentally. A detailed parametric analysis investigates the influence of key geometrically graded tooth parameters on strength and failure behavior. Computational models, including cohesive zone modelling and ductile damage methods, are utilized to predict SLJ performance. Three distinct SLJs were manufactured with consistent printing parameters and orientations, each exhibiting a comparable overall geometric configuration. Uniaxial tensile tests were conducted to validate computational strength and failure modes experimentally. Results demonstrate a significant ≈59 % strength increase and ≈143 % improvement in failure strain for the optimized configuration compared to non-tailored SLJs.