Compilation and Application of UMAT for Mechanical Properties of Heterogeneous Metal Welded Joints in Nuclear Power Materials

He Xue,Shuai Wang,Yueqi Bi,Siyu Gou,Jianlong Zhang

doi:10.1155/2019/3151823

Abstract

For the problem of mechanical properties of heterogeneous dissimilar metal welded joints, when analyzed by the finite element method, it is usually simplified into a “sandwich” material structure model. However, the mechanical properties of materials in different regions of the “sandwich” material mechanics model are different, and there will be mutations at the material interface. In order to accurately describe the mechanical properties of welded joints, the constitutive equations of dissimilar metal welded joint materials were compiled, and the constitutive equations of inhomogeneous materials whose material mechanical properties were continuously changed with space coordinates were established. The ABAQUS software was used to establish the “sandwich” model and the continuous transition model. The model is used to compare and analyze the crack tip stress distribution of different yield strength mismatch coefficients. The results show that the continuous transition material model eliminates the mutation of the “sandwich” model at the material interface and achieves the continuous change of the mechanical properties of the material. For the longitudinal crack, under the influence of different mismatch coefficients, the crack tip stress field of the transitional material model is deflected toward the low yield strength side. The compilation of constitutive equations for continuous transition materials of dissimilar metal welded joints provides a basis for the safety evaluation of dissimilar metal welded joints.

Highlights

Damage and defect problems are important factors affecting material processing and structural life [1,2,3]. e welded joint is a complex heterogeneous structure composed of the base material, weld material, the weld fusion zone, and the heat affected zone. e welding process is a very complicated metallurgical process. e material of the structure, the temperature, and other dramatic changes are very likely to cause pores, cracks, and complex residual stress fields [5,6,7]
Yang et al [7, 8] investigated the effect of the elastic response of austenitic behavior of austenitic stainless steel, the orientation of crystal orientation, and the grain boundary (GB) dip angle under constant displacement by means of numerical simulation. e results showed that the larger the difference in the orientation of the twin crystal, the greater the strain inconsistency of the twin crystal
Subramanian et al [9] performed a number of experiments to investigate the effect of the mechanism of premature failure of bimetal welds, which are caused by the close proximity of the ferrite (BCC) and austenite (FCC) interfaces. e results revealed that premature failure depends on the initial carbide distribution of the zone

Summary

Introduction

Damage and defect problems are important factors affecting material processing and structural life [1,2,3]. e welded joint is a complex heterogeneous structure composed of the base material, weld material, the weld fusion zone, and the heat affected zone. e welding process is a very complicated metallurgical process. e material of the structure, the temperature, and other dramatic changes are very likely to cause pores, cracks, and complex residual stress fields [5,6,7]. When using the finite element method to study the mechanical properties of dissimilar metal welded joints, the dissimilar metal welded joints are mainly simplified into the “sandwich” material structure model [15], that is, the welded joints are partitioned, and the material parameters of various parts are different but constant parameters, that is, just like a sandwich. Is model has certain limitations on the structural integrity safety evaluation of heterogeneous metal welded joints on nuclear power safety terminal. In order to accurately describe the complex mechanical field of heterogeneous metal welded joints on nuclear power safety terminal, the effects of different yield strength mismatches on crack tip stress-strain distribution law are analyzed, and the problem of material property mutation at the boundary of different materials of “sandwich” material structure model is solved. Compared with the “sandwich” material structure model, the cracked tip stress field distribution of different yield strength mismatch coefficients of dissimilar metal welded joints is analyzed. Compared with the “sandwich” material structure model, the cracked tip stress field distribution of different yield strength mismatch coefficients of dissimilar metal welded joints is analyzed. e regular influence provides basic material performance data for the subsequent integrity assessment of the heterogeneous metal welded structure at the safety terminal

UMAT Compilation

Static Crack Model Establishment

Results and Discussions

Conclusions