Failure of resistance spot welds: tensile shear versus coach peel loading conditions

Abstract

This paper aims at investigating the failure behaviour of resistance spot welds under tensile shear (TS) and coach peel (CP) loading conditions. A failure mechanism was proposed to describe both interfacial and pullout failure modes in each loading condition. The mechanisms were confirmed by SEM investigations, examining the cross-sections of the fractured welds to detail the fracture path. The experimental results showed that in the pullout failure mode during TS testing, necking is initiated at the nugget circumference in the base metal, and then failure propagates along the nugget circumference in the sheet, leading to the final fracture, while pullout failure during the CP test occurred by crack initiation and propagation near the weld nugget/heat affected zone boundary. The interfacial failure to pullout failure mode transition in the TS and CP tests was also studied. The critical weld nugget size required to ensure the pullout failure mode was obtained for each loading condition. The critical fusion zone size to ensure pullout failure mode during the TS test was larger than that of the CP test. It was found that the load bearing capacity of the spot welds under CP is significantly lower than that of the TS test.

Failure mode of HSLA/DQSK dissimilar steel resistance spot welds

“…Figure 9 represents a simple stress analysis of the spot welds during the tensile-shear test. 20 Failure is a competitive phenomenon, i.e. spot weld failure occurs in a mode that needs less force.…”

“…Indeed, even though the loading condition is nominally shear, the pullout failure is predominantly tensile through rotation and preferential necking in the soft region of the nugget circumference. 10,[20][21][22] Therefore, the driving force of pullout mode is the tensile stress at the nugget circumference (see Fig. 9).…”

Small-scale resistance seam welding of 304 stainless steel with capacitor discharge welding machine

“…Failure mode and failure mechanism, largely depend on the complex interplay between the weld geometry and the material properties of the fusion zone (FZ)/HAZ, HAZ/base metal (BM) as well as the test geometry and the stress state in each weld. 39 Figure 11 shows typical failure paths during the mechanical testing of a spot weld.…”

“…As shown in Figure 12(a), in RSW, the shear stress at the sheet/sheet interface is the driving force of the IF mode along the path A which shown in Figure 11, and the tensile stress at the nugget circumference is the driving force for PF mode. 39…”

Effect of Double Pulse Resistance Spot Welding Process on 15B22 Hot Stamped Boron Steel

“…In Figure 16d, the crack initiated at the joint of the two plates adjacent to the weld nugget. Stress concentration caused by the notch effect plays an important role in crack initiation [32]. Figure 18 is the schematic illustration of the failure mode that occurred on the AHSS.…”