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

Abstract

A material model is developed that predicts the plastic behavior of fully hardened 22MnB5 base material and the heat-affected zone (HAZ) material found around its corresponding resistance spot welds (RSWs). Main focus will be on an accurate representation of strain fields up to high strains, which is required for subsequent calibration of the fracture behavior of both base material and HAZ. The plastic behavior of the base material is calibrated using standard tensile tests and notched tensile tests and an inverse FEM optimization algorithm. The plastic behavior of the HAZ material is characterized using a specially designed tensile specimen with a HAZ in the gage section. The exact location of the HAZ relative to the center of the RSW is determined using microhardness measurements, which are also used for mapping of the material properties into an FE-model of the specimen. With the parameters of the base material known, and by assuming a linear relation between the hardness and the plasticity model parameters of base material and HAZ, the unknown HAZ parameters are determined using inverse FEM optimization. A coupon specimen with HAZ is used to validate the model at hand.

Plasticity and fracture modeling of the heat-affected zone in resistance spot welded tailor hardened boron steel

“…9a, will be used for calibration of the strain hardening and fracture behavior of the CHAZ. The extended specimen shoulder causes strain localization to occur only on one side of the HAZ, resulting in a well-defined strain field suited for comparison with simulation results (Eller et al, 2015). In the central hole tensile specimen the nugget was completely removed with wire EDM, see Fig.…”

“…Similar to the approach used in Eller et al (2015), the measured force-displacement curves and strain fields of the asymmetric uniaxial tensile tests will be used for calibration of the CHAZ strain hardening models. The material in the gauge section of the specimen is inhomogeneous, featuring a weld nugget, a CHAZ, base material and two corresponding transition zones: the inter-critical and sub-critical heat-affected zones.…”

Development of mechanism-based models for resistance spot weld failure simulation of multi-material advanced high strength steel sheets

“…State of the art localization or necking in base material. This type of failure occurs in AHSSs for some loading cases, such as in-plane conditions where the joints fail in SHAZ [18,39]. However, due to the local properties distribution of AHSS spot welds, these joints fail due to semi-brittle fracture of the nugget due to stress/strain concentration around the notch tip when they are loaded under out-of-plane conditions [6,10,17].…”

“…To model the material properties changes, some authors introduced simple rules, where the plasticity hardening curves of the multiple weld zones are scaled using hardness measurements as a scaling factor [13,[53][54][55][56]. A second approach consists on experimentally obtaining the mechanical properties of the weld zones using Gleeble 3500 thermomechanical simulator specimens, where the thermal evolution that is suffered by the HAZ is applied to a base material tensile specimens [10,16,29,39,57]. A third alternative is to use welded micro specimens, that are designed to develop high strains just in the weld heat-affected zone or the nugget.…”

“…A third alternative is to use welded micro specimens, that are designed to develop high strains just in the weld heat-affected zone or the nugget. Two sheets are welded, one of them is separated using a non-thermal process and the other sheet is trimmed in such a way that the HAZ have the most reduced section of the specimen [16,39,57,58]. A particular case of this characterization procedure is the use of miniature tensile bars extracted from the welding zones [59,60].…”