Numerical Investigation of the Influence of Ultimate-Strength Heterogeneity on Crack Propagation and Fracture Toughness in Welded Joints

Yueqi Bi; Xiaoming Yuan; Mingrui Hao; Shuai Wang; He Xue

doi:10.3390/ma15113814

Numerical Investigation of the Influence of Ultimate-Strength Heterogeneity on Crack Propagation and Fracture Toughness in Welded Joints

Materials (Basel). 2022 May 27;15(11):3814. doi: 10.3390/ma15113814.

Authors

Yueqi Bi^{1

2}, Xiaoming Yuan^{2

3}, Mingrui Hao², Shuai Wang⁴, He Xue⁴

Affiliations

¹ National Engineering Laboratory for Coal Mining Machinery and Equipment, Taiyuan 030000, China.
² Taiyuan Research Institute of China Coal Science and Engineering Group Co., Ltd., Taiyuan 030000, China.
³ School of Mechanical and Electrical Engineering, China University of Mining and Technology, Beijing 221008, China.
⁴ School of Mechanical Engineering, Xi'an University of Science and Technology, Xi'an 710054, China.

Abstract

The mechanical properties of dissimilar metal-welded joint materials are heterogeneous, which is an obstacle to the safety evaluation of key welded structures. The variation of stress-strain conditions at the crack tip caused by mismatch of material mechanical properties in dissimilar metal-welded joints is an important factor affecting crack propagation behavior. To understand the influence of uneven distribution of ultimate strength of the base metal and the welded metal on the crack propagation path, fracture toughness, as well as the mechanical field at the crack tip in the small-scale yield range, the user-defined field variable subroutine method is used to express continuous variation characteristics of welded joint ultimate strength in finite element software. In addition, the J-integral during crack propagation is calculated, and the effect of the ultimate strength on the J-integral and the stress field at the crack tip are analyzed. The results show that as the crack propagation direction is perpendicular to the direction of ultimate strength, the gradient of ultimate strength increases from |G_y|= 50 to |G_y|= 100 MPa/mm, the crack deflection angle increases by 0.018%, and the crack length increases by 1.46%. The fracture toughness of the material decreased slightly during crack propagation. Under the condition that the crack propagation direction is the same as the direction of ultimate strength, the crack propagation path is a straight line. As the gradient of ultimate strength increases from G_x = 50 to G_x = 100 MPa/mm, the crack propagation length decreases by 5.17%, and the slope of fracture toughness curve increases by 51.63%. On the contrary, as the crack propagates to the low ultimate strength side, the crack propagation resistance decreases, the ultimate strength gradient increases from G_x = -100 to G_x = -50 MPa/mm, and the slope of the fracture toughness curve decreases by 51.01%. It is suggested to consider the relationship between crack growth behavior and ultimate strength when designing and evaluating the structural integrity of cracks at the material interface of dissimilar metal-welded joints.

Keywords: crack propagation path; fracture toughness; uneven distribution of ultimate strength; user-defined field variable subroutine.

Grants and funding

This research was financially supported by the National Key R&D Program of China (2020YFB1314003) and the Enterprise youth science and technology project (grant number M2022-QN08). This research was also funded by the National Natural Science Foundation of China (grant number 52075434). The APC was funded by M2022-QN08.