Tensile-Shear Forces and Fracture Modes in Single and Multiple Weld Specimens in Dual-Phase Steels

Abstract

In this article, weld fracture criteria based upon low strain rate (i.e., ε̇∼10−3-10−2s−1) tensile-shear tests of spot welds in dual-phase (DP) steels DP600, DP780, and DP980 are developed. Three empirical equations are inferred from least-squares root-fitting analyses of tensile-shear testing data. Building upon existing results in the literature, the first equation relates the tensile-shear force to the weld diameter. The second and third equations relate, respectively, a critical weld diameter and a critical tensile-shear force for interfacial fracture to the sheet thickness and hardness extrema in the heat-affected zone. These idealized equations can serve as the basis for further development of fracture criteria resembling material flow laws that account for higher strain rates and more complicated deformation paths. The effect of spot-weld placement in specific patterns or arrays on deformation and fracture behavior was also investigated to explore underlying effects from deformation field interactions between adjacent spot welds.

3D modelling of plug failure in resistance spot welded shear-lab specimens (DP600-steel)

“…This change of the microstructure in the weld region results in a non-homogeneous variation of the mechanical properties. Especially the hardness and thereby the yield stress has been shown to increase significantly in the weld nugget when applying RSW to the DP600 steel (Tong et al 2005;Song et al 2005;Marya et al 2006;Long and Khanna 2007).…”

“…This is also reflected in a number of empirical relations proposed in the literature, to estimate the tensile shear force (TSF) of a spot weld. Based on experimental observations these relations typically relate the weld diameter to the TSF and the associated displacement, u T SF (Marya et al 2006). Neglecting interfacial failure, a strong connection at the weld interface is here normally assumed.…”

Welding Defects Occurrence and Their Effects on Weld Quality in Resistance Spot Welding of AHSS Steel

“…Tensile residual stress at the weld nugget was believed to promote through-thickness cracking. Marya et al 9) showed that solidification cracks can adversely affect the overall bonded area in DP600 spot welds. Pouranvari et al 2,10) suggested that the high tendency to shrinkage void formation during AHSS resistance spot welding was one of the main reasons for its high susceptibility to interfacial failure.…”

Finite Element Method Based Modeling of Resistance Spot-Welded Mild Steel

“…2003a;Chao. 2003b;Zuniga et al 1997;Lin et al 2003;Marya et al 2006;Lin et al 2002). For example, Chao (2003a) studied the ultimate tensile strength of resistance spot welds in mild steel subjected to combined loading tension and shear loads, and verified that a spot weld under cross-tensile loading fails at a lower load than a spot weld subject to lap-shear loading.…”