Role of Pre-Straining on the Mechanical Behaviour of Resistance Spot Welded Ultrahigh Strength Steel

Any automotive component undergoes deformation before joining in the assembly lines. The prior deformation may alter the mechanical properties of prestrained and welded components under cyclic and static loading. Thus, it becomes vital to study the effect of prior deformation on the mechanical properties of resistance spot welded joints. In this study, DP 980 (dual phase) steel samples were pre-strained to 2, 4 and 6 pct of their total elongation at an initial strain rate of 0.03 min⁻¹. Welding was performed on pre-strained and unstrained samples. Microstructural observations were made on the cross-section of the welded sheets in pre-strained and unstrained conditions. Tensile testing was performed on the unstrained and pre-strained specimens in lap-shear mode. Enhancement in the weld strength and failure energy were observed in the welds made by 6 pct pre-strained sheet compared to the welds made by the unstrained sheet. The effect of pre-straining on the fatigue strength of welded joints was investigated by conducting fatigue tests on the pre-strained and unstrained specimens in lap-shear mode at various stress levels (5 to 40 pct of weld strength) at a load ratio of 0.1. No significant effect of pre-straining was observed on the fatigue strength of the welded joints.