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

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.

A Numerical Approach to Analyze Detail Mechanical Characteristic at the Crack Tip of SCC in Dissimilar Metal Welded Joints

“…e accuracy and reliability of the subroutine are verified by numerical simulation and experiment. Xue et al [19] have established the continuous transition model of the welded joint based on the User-Defined Material Mechanical Behavior (UMAT) subroutine in the ABAQUS and found that the stress field at the crack tip of the continuous transition model deflects to the low yield strength zone. However, the writing progress of UMAT subroutines is complicated.…”

Interaction of Mechanical Heterogeneity and Residual Stress on Mechanical Field at Crack Tips in DMWJs

“…A sudden change in the mechanical properties at the material interface is produced, and it cannot accurately describe the mechanical heterogeneity of the DMWJ. us, structural integrity assessment has certain limitations by using the "Sandwich" model [15][16][17]. More detailed characterization of the DWMJ mechanical properties will greatly help the research of the crack tip mechanical field.…”

Cracking Driving Force at the Tip of SCC under Heterogeneous Material Mechanics Model of Safe-End Dissimilar Metal-Welded Joints in PWR

“…Nevertheless, the mechanical field and driving force at the tip of SCC in different positions of the welded joint are analyzed by the "Sandwich" model has been unable to meet the requirements [20][21][22]. To characterize the distribution of mechanical properties in the DMWJ more accurately, some scholars [23,24] tried to use some subroutines in ABAQUS to realize the uneven distribution of mechanical properties varies along with the spatial position. Xue et al [23] have established the "Sandwich" model and the heterogeneous material model of the DMWJ based on the user-defined field (USDFLD) subroutine, and the results illustrate that the heterogeneous material model compensated for the sudden change of the mechanical properties of the Sandwich model at the interface.…”