Numerical investigation on the fracture driving force of laser welds and arc welds
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RESEARCH PAPER
Numerical investigation on the fracture driving force of laser welds and arc welds Chendong Shao 1 & Haichao Cui 1 & Yasuhito Takashima 2 & Fumiyoshi Minami 2 & Fenggui Lu 1,2 Received: 1 October 2019 / Accepted: 19 August 2020 # International Institute of Welding 2020
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 (ε∞) 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 ε∞ = 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 ε∞ = 0.1%, which decreased to 2.5 at ε∞ = 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. Keywords Driving force . Laser welds . Shielding effect . Weld width . Strength mismatch
1 Introduction Laser beam welding (LBW) is being increasingly adopted in recent years due to its advantage of deep penetration, narrow heat-affected zone (HAZ), less distortion, and high productivity efficiency comparing with the traditional arc welding (AW) methods. Due to the high cooling rate of the narrow and deep molten pool, hardened microstructure can be generated in the weld metal (WM) and HAZ, which has much higher yield strength than the base Recommended for publication by Commission X - Structural Performances of Welded Joints - Fracture Avoidance * Yasuhito Takashima [email protected] * Fenggui Lu [email protected] 1
Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering,, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China
2
Joining and Welding Research Institute, Osaka University, Osaka, Japan
metal (BM). Comparing with arc welds, the hard microstructure in the WM of LBW can lead to high susceptibility to brittle fracture, which determines the service properties under different loading conditions [1]. For a welded joint, discontinuities usually exist in the form of welding defect [2], welding hot crack [3], shrinkage porosity etc. Such discontinuities can grow into long cracks during service under complex operating loading conditions or unpredictable forces, where the fracture toughness should be taken into consideration for more accurately assessing the residual
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