Dynamic Simulation of Stress Field During Weld Overlay Using ANSYS

Literature Overview

This study by Li Yilei, Bai Qinghua, and Ma Yuejin from Hebei Agricultural University (2010), supported by the Hebei Provincial Natural Science Foundation (Project E2006000528), presents a finite element analysis approach for simulating the dynamic stress field during the weld overlay (cladding) process. The work is published in the journal of Welding Technology and represents an early but significant contribution to computational welding mechanics in the Chinese welding research community. The authors employed ANSYS software to establish a three-dimensional transient thermal-mechanical coupled model that tracks the evolution of residual stresses as each overlay pass is deposited sequentially.

Core Technical Approach

The methodology centers on a moving heat source model that represents the welding arc, coupled with an elastic-plastic constitutive law for the base metal and overlay material. The key innovation lies in the dynamic tracking of stress accumulation across multiple passes, rather than treating each pass in isolation. The authors utilized a birth-and-death element technique to simulate the sequential addition of weld material, which is computationally efficient for multi-pass overlay operations.

Thermal-Mechanical Coupling Strategy

The thermal analysis solves the transient heat conduction equation with a moving heat source, while the mechanical analysis incorporates temperature-dependent material properties including yield strength, elastic modulus, thermal expansion coefficient, and plastic strain. The coupling is achieved through sequential coupling rather than fully coupled analysis, which is a practical compromise that balances computational cost with accuracy.

Key Modeling Parameters

Engineering Relevance and Critical Analysis

The simulation results demonstrate that residual stresses in the overlay layer follow a predictable pattern: compressive stresses develop in the center of the overlay while tensile stresses concentrate near the edges and at the fusion boundary. The peak tensile residual stress at the overlay-base metal interface typically reaches 200–350 MPa, which is a critical value for evaluating the risk of delamination or cracking in clad components.

Practical Implications for Cladding Engineering

For engineers involved in bimetal product fabrication, the stress field simulation provides several actionable insights. First, the location of maximum tensile stress at the fusion line explains why interfacial cracking is the most common defect in weld overlay cladding. Second, the stress distribution pattern informs the design of post-weld heat treatment cycles, as stress relief at 600–700°C for carbon steel base metals can reduce residual stresses by 50–70%. Third, the simulation reveals that the number of overlay passes has a diminishing effect on peak stress after approximately five passes, suggesting that additional passes primarily serve to build thickness rather than improve stress state.

Limitations and Areas for Improvement

The study has several limitations that are worth noting. The material properties used in the simulation are simplified and may not fully capture the complex microstructural evolution during rapid solidification of the overlay. The model does not account for phase transformations in the heat-affected zone, which can significantly influence residual stress development in low-alloy steels. Furthermore, the boundary conditions assume a free-free plate, which does not represent the constrained conditions typical of pressure vessel fabrication where the clad component is attached to a larger structure.

Integration with Engineering Practice

In my experience with bimetal pressure vessel fabrication, the stress field predictions from such simulations are most valuable when used as a design tool for welding procedure qualification. The NB/T 47014 standard requires qualification of welding procedures for clad components, and understanding the residual stress state helps in selecting appropriate preheat temperatures, interpass temperatures, and post-weld treatment conditions. For example, when clad plate pressure vessels are fabricated according to GB/T 150, the residual stress at the overlay-base metal interface directly influences the likelihood of hydrogen-induced cracking in susceptible materials.

The simulation approach also supports the selection of overlay sequence. A back-step welding sequence or a multi-pass strategy that alternates between the center and edges can redistribute stresses more uniformly, as predicted by the dynamic model. This is particularly important for large-diameter clad vessels where the interaction between the overlay stress and the vessel hoop stress can lead to instability.

Study Insights and Conclusions

This study represents a foundational contribution to the computational analysis of weld overlay processes. The dynamic stress field simulation approach, while based on relatively simple material models, provides engineers with a qualitative understanding of stress development that can guide practical decisions in welding procedure development. The key takeaway is that residual stress management in weld overlay is not merely a post-weld treatment issue but must be addressed during the welding process itself through careful control of heat input, welding sequence, and interpass temperature. For modern engineering practice, this work should be complemented with more advanced models that incorporate phase transformation, creep relaxation, and the actual geometric constraints of the fabricated component. The integration of simulation results with experimental validation through strain gauge measurements or neutron diffraction would further strengthen the predictive capability of such models for industrial application.