Numerical investigation on the fracture driving force of laser welds and arc welds

Abstract

The brittle fracture driving forces of laser beam welds (LBWs) and arc welds (AWs) are investigated and compared numerically with a center through-thickness cracked panel (CTCP) and a standard fracture toughness specimen (3-point bending specimen, 3PB). The effects of hard zone width (H) and strength mismatch ratio (Sr) were systematically studied at global strain (e∞) of 0.1% and 0.2%. It was found that the peak opening stress near the crack tip decreased with narrower H for LBW at e∞ = 0.2%, which can be ascribed to the better shielding effect provided by the softer base metal (BM) on hard zone welds. The peak normalized opening stress σyy/σY,WM was found nearly to be 3.0 for different Sr at e∞ = 0.1%, which decreased to 2.5 at e∞ = 0.2% due to more plastic deformation in the BM. The shielding effect ΔσW increased with higher Sr or narrower H. The effect of H and Sr on required CTOD fracture toughness in 3PB was also discussed basing on Weibull stress criterion. The required CTOD in 3PB of LBW can be decreased to be much lower than the AW with sufficiently narrow H. The harm effect of higher Sr on required toughness is less compared with the influence of lower H.