Deformation and fracture of miniature tensile bars with resistance-spot-weld microstructures

Abstract

Plastic deformation of miniature tensile bars generated from dual-phase steel weld microstructures (i.e., fusion zone, heat-affected zone, and base material) was investigated up to final rupture failure. Uniaxial tensile true stress-strain curves beyond diffuse necking were obtained with a novel strainmapping technique based on digital image correlation (DIC). Key microstructural features (including defects) in each of these three metallurgical zones were examined to explore the material influence on the plastic deformation and failure behavior. For weld fusion zones with minimal defects, diffuse necking was found to begin at 6 pct strain and continue up to 55 to 80 pct strain. The flow stresses of the weld fusion zones were at least twice those of the base material, and fracture strains exceeded 100 pct for both materials. The heat-affected zones exhibited a range of complex deformation behaviors, as expected from their microstructural variety. Only those fusion zones with substantial defects (e.g., shrinkage voids, cracks, and contaminants) failed prematurely by edge cracking, as signaled by their highly irregular strain maps.

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

“…3a, that a significant increase of the hardness is found in the nugget of the weld. This agrees well with the observations by Tong et al (2005); Marya et al (2006) and Long and Khanna (2007). The measurements along the two straight lines, shown in Fig.…”

“…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).…”

Microstructure and Mechanical Properties of Resistance Spot Welded Advanced High Strength Steels

“…For example, Marya et al 7) examined the effects of RSW process parameters on the failure mode during tensile shear testing of DP steels. Similarly, Tong et al 8) examined the mechanical properties of spot welded DP steels and their influence on failure behavior. The current literature, however, fails to critically compare the microstructure and mechanical properties of spot weldments in various different grades of AHSS.…”

Identification of Plasticity Model Parameters of the Heat-Affected Zone in Resistance Spot Welded Martensitic Boron Steel

“…Some authors have used an instrumented indentation test [8,9], converting measured forceindentation depth curves to local stress-strain curves. Another direct method for nugget and HAZ parameter identification is to use miniature specimens taken from actual RSWs [10,11], which then requires specialized testing equipment. A popular indirect characterization method is to use a Gleeble thermomechanical simulator, which is able to simulate the HAZ temperature history on larger specimens [12].…”