Structural Evaluation of Hybrid Double-Lap Shear Bolted Connections Incorporating Additively Manufactured 316L Stainless Steel Inner Plates

This study investigates hybrid double-lap shear bolted connections incorporating additively manufactured 316L stainless steel inner plates, alongside conventionally produced reference plates, in single- and double-bolted configurations with different geometric design variables. The additive manufacturing technologies considered are wire arc additive manufacturing and selective laser melting. The tests were designed to invoke failure at the inner plates, while additive manufacturing-related material properties, surface undulations and thickness variation can further influence the failure mechanism. The study integrates experimental testing with analytical, numerical, and machine learning assessments to build a comprehensive evaluation framework. First, coupon tests were used to characterise the mechanical response of all manufacturing methods, while double-lap shear tests were used to identify failure modes observed in the inner plates. The additively manufactured specimens were examined under different extraction angles relative to the printing direction, including 0°, 45°, 60° and 90°, and under both machined and as-built conditions. The measured response is then compared against design code-based strength estimations to evaluate the extent to which conventional design equations remain applicable when the inner plates are additively manufactured. These estimations are also compared with literature-based equations to identify which method provides better agreement with the test results. A stress-based prediction technique is subsequently examined by applying the Theory of Critical Distances using linear elastic finite element stress fields to estimate static failure in the tested joints. Finally, machine learning models are evaluated to predict failure load and failure mode using a dataset collected from the literature, which is later expanded using results from the present tests and additional literature data on additively manufactured inner plates. Ultimately, this study evaluates whether additively manufactured plates can be used safely and beneficially in structural bolted connections, and it provides experimentally supported and validated prediction methods as practical alternatives for structural integrity assessment.