Failure investigation of hybrid double-lap shear bolted connections with additively manufactured 316L stainless steel inner plates

The growing body of research on additive-manufactured components in structural engineering highlights the importance of assessing their potential, particularly in understanding how key manufacturing and design parameters influence performance. In this context, alongside conventional inner plates, this study investigates the failure behaviour of additive-manufactured inner plates of 316L stainless steel as hybrid component in double-lap shear bolted configurations. Two distinct printing methods were considered: wire arc additive manufacturing and selective laser melting. The study considered different surface conditions (as-built and machined) and extraction/print direction (θ=0°,45°, 60° and 90°). By evaluating the actual failure mode and cracking behaviour, this study explores the influence of the manufacturing process and variations in geometrical design parameters, treated as key variables affecting the failure mechanism of the inner plates. The findings indicate that while the test coupons exhibited significant variations in stiffness and ductility, the failure behaviour of conventional and additively manufactured inner plates remained largely similar when accounting for surface condition and printing direction. Differences in load capacity across manufacturing methods were found to be limited when thickness was controlled. However, distinctly different crack propagation paths were observed in as-built wire arc additive-manufactured inner plates extracted at θ=45° and 60°, attributed to the effect of diagonal printing layers. These insights contribute to understanding overall connection integrity and highlight both the challenges and opportunities of integrating additive manufacturing into bolted connections.