Abstract: Along with research aimed at understanding and improving liquid metal embrittlement (LME) resistance, the effects of LME cracks on mechanical performance should also be considered. Literature studies of tensile-shear and cross-tension tests with LME cracks did not indicate significant property degradation due to cracks smaller than 300 μm at room temperature. In the present work, the quasi-static strength of spot welded specimens from a galvanized advanced high strength steel was tested using tensile-shear and cross-tension with weld crack lengths near 480 μm. Each configuration was tested at room temperature and temperatures as low as -10°C. The peak load decreased with decreasing temperature for both test configurations, but there was no correlation of peak load with crack size or location. The failure modes of the cross-tension tests were consistent between test temperatures. However, tensile-shear tests showed predominantly button pull-out failure at low temperatures and interfacial failure at room temperature. Finite element models were also developed for a 2D tensile-shear configuration to provide insight on critical crack geometries that affect performance. The highest stress near the crack tip exists for crack angles of approximately 60° with respect to the surface sheet surface, and stresses increase with increasing crack length. However, these stresses near the crack tip are significantly smaller than those at the weld edge; therefore, the models predict that LME cracks would have no influence on the tensile-shear failure mode.
Authors: Kayla M. Molnar, Matthew L.S. Zappulla, John G. Speer, and Kip O. Findley
Keywords: Liquid Metal Embrittlement, Advanced High Strength Steel, Spot Weld, Finite Element Analysis