Fracture Performance Evaluation of Laser Beam Welded Joints Based on the Weibull Stress Criterion

This paper examines the fracture performance of laser beam welded joints of a high strength steel with a notch in the weld metal (WM). The standard fracture toughness specimen (3-point bend specimen, 3PB) and tension panel (edge through-thickness crack panel, ETCP) are tested at a low temperature in the brittle fracture range. The focus lies on the difference between near crack-tip plastic constraints for the standard fracture toughness specimen and the tension, and on the very narrow and highly hardened WM shielding high strain in the weld metal from external loading. The ETCP has presented a higher critical CTOD at brittle fracture initiation than the 3PB specimen. The fracture performance of ECTP is predicted from CTOD fracture toughness test results by means of the Weibull stress criterion with the consideration of the shielding effect of the weld metal. The results show an advantage of the Weibull stress criterion for the fracture transferability analysis of toughness results. Furthermore, the influence of very narrow and highly hardened weld metal of laser beam welded joints on the toughness requirement has been analyzed by means of the Weibull stress criterion. The effect of the distinctive strength mismatch of laser beam welded joints on required CTOD fracture toughness of laser beam welded joints in 3PB necessary to meet design requirement of joint performance is discussed taking into account the shielding effect on crack opening behavior and toughness collection due to constraint loss between ETCP and 3PB specimen. The required CTOD in 3PB is a little bit lower than arc welded joints. Therefore, it should be noticed that the very narrow and highly hardened WM does not necessarily lead to poor fracture performance of the welded joints.