Fracture modeling of resistance spot welded ultra-high-strength steel considering the effect of liquid metal embrittlement crack

Zinc-coated ultra-high-strength steel (UHSS) sheets are highly susceptible to liquid metal embrittlement (LME) during resistance spot welding. However, systematic understanding on LME cracks in the pullout fracture of UHSS welds is still lacking. This study employs artificially created pre-cracks on bare DP980 steel welds to simulate the LME cracks, allowing accurate control of the crack shape and location. To investigate the fracture initiation and propagation behavior of welds with various pre-crack characteristics, a combined experimental and computational approach, which incorporated tensile tests on newly designed miniature specimens for detailed mechanical property measurement and fracture parameter calibration of different weld zones, was proposed. Results indicate that external pre-cracks in a highly strained region accelerated damage accumulation at the fracture onset region and deflected the fracture propagation path to pass through the pre-crack, causing a 12.1% loss of tensile-shear peak load. Conversely, internal pre-cracks vary the fracture initiation site and exhibit a more detrimental influence, with 24.1% loss of tensile-shear strength. The effects of the pre-crack length, orientation, and depth on the tensile-shear performance were quantified. Results show that the negative effect of the LME crack on the weld performance can be mitigated or avoided by controlling the crack location and geometry. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigates the fracture initiation and propagation behavior of welds with different pre-crack characteristics. External pre-cracks accelerate damage accumulation, while internal pre-cracks have a more detrimental influence on weld performance. The negative effects of LME cracks on weld performance can be mitigated by controlling the crack location and geometry.