Failure loads of multiple spot-welded and weld-bonded joints

The design of experiments (DOE) approach was used to determine the factors that affect the load capacity of multiply spot-welded and weld-bonded joints made of a mild hot-dip galvannealed steel (265 MPa ultimate strength) and a hot-dip galvannealed dual-phase steel (640 MPa ultimate strength). A total of 548 specimens were tested. The DOE parameters were the weld spacing, weld size, edge distance, loading mode (tensile shear and cross tension), the material, and the addition of adhesive in the joint.; The tensile-shear test results show that the weld size, sheet thickness, and the material had strong positive correlation to the joint load capacity. The adhesive addition also increased the joint load capacity, but weld spacing decreased the joint load capacity when the welds were close together. For cross-tension joints, the edge distance had a large influence on the load capacity because of the specimen geometry. The adhesive and the material ultimate strength showed little or no influence on the load capacity of these joints. For most of the two weld joints, load capacity was less than twice than that of single-weld joints because of interactions between the two welds. Microstructural analysis for selected joints was completed. Microhardness profiles were obtained across the weld zones.; Partitioning the data indicated a potential correlation among the factors with the failure load and corroborated the results of DOE analysis. The ratios of the weld to spacing and the weld size to edge distance were modeled by a linear relation with the failure load. Based on the DOE and partitioning data analysis, semi-analytical strength models for multiple spot-welded and weld-bonded joints were determined that incorporated the weld size, spacing, edge distance, sheet thickness, and the ultimate strength of the materials.