CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Stress and Deformation Analysis Based on ANSYS Secondary Development
Literature Overview
This 2016 study published in the Journal of Tianjin University (Science and Technology) by Deng Caiyan, Zhao Junmei, Wang Dongpo, and Gong Baoming from the School of Materials Science and Engineering, Tianjin University, presents a weld overlay stress and deformation analysis system developed through ANSYS secondary development. The research addresses the need for accurate prediction of residual stresses and distortions in weld overlay processes, which are critical for ensuring the structural integrity and dimensional accuracy of clad components.
Core Technical Points
Residual stress and distortion prediction in weld overlay processes is a complex multiphysics problem involving thermal-mechanical coupling, phase transformations, and plastic deformation. Traditional analytical methods are inadequate for capturing the nonlinear behavior of weld overlay processes, making finite element analysis (FEA) the preferred approach. However, standard FEA software requires significant programming expertise to implement the specialized constitutive models and boundary conditions needed for accurate weld simulation.
| Analysis Parameter | Typical Value | Method |
|---|---|---|
| Thermal conductivity of overlay | 15–50 W/(m·K) | Temperature-dependent |
| Thermal conductivity of base | 40–60 W/(m·K) | Temperature-dependent |
| Specific heat of overlay | 450–550 J/(kg·K) | Temperature-dependent |
| Specific heat of base | 460–520 J/(kg·K) | Temperature-dependent |
| Yield strength (overlay, room temp) | 200–600 MPa | Stress-strain curve |
| Yield strength (base, room temp) | 235–500 MPa | Stress-strain curve |
| Thermal expansion coefficient | 12–18 × 10⁻⁶/K | Temperature-dependent |
| Heat input | 1–10 kJ/mm | Process-dependent |
The ANSYS secondary development approach allows engineers to create specialized analysis modules that incorporate the unique features of weld overlay processes, including moving heat sources, sequential layer deposition, and phase transformation effects. This customization capability is essential for capturing the complex thermal and mechanical behavior that occurs during multi-pass overlay welding.
Methodology and Model Development
The analysis system developed in this study incorporates several key modeling approaches:
- Moving heat source model: The heat input from the welding arc is modeled as a moving Gaussian or double-ellipsoidal heat source that traverses the weld path. The heat source parameters (power, efficiency, and geometry) are calibrated against measured thermal profiles to ensure accuracy.
- Sequential layer activation: The overlay is modeled as a series of material layers that are sequentially activated as each pass is deposited. This approach captures the thermal history of previously deposited layers as subsequent passes are added.
- Thermal-mechanical coupling: The thermal analysis provides temperature fields that drive the mechanical analysis through thermal strain and temperature-dependent material properties. Phase transformation effects are incorporated through the Koistinen-Marburger equation or similar models.
- Plasticity model: An elasto-plastic constitutive model with kinematic hardening is used to capture the Bauschinger effect observed in weld metals. The stress-strain curves are temperature-dependent, reflecting the significant reduction in yield strength at elevated temperatures.
- Boundary conditions: Realistic boundary conditions are applied to simulate the restraint conditions of the actual welding setup, including fixture constraints, backing plate effects, and gravity loading.
Analysis Results and Validation
The study presents analysis results for typical weld overlay configurations, including single-layer and multi-layer overlays on flat plates and cylindrical shells. The predicted residual stress distributions show the characteristic pattern of high tensile stresses in the overlay and compressive stresses in the base metal near the weld. The peak residual stresses typically reach 300–500 MPa in the overlay, depending on the welding parameters and restraint conditions.
| Configuration | Peak Residual Stress (MPa) | Maximum Distortion (mm) | Analysis Time |
|---|---|---|---|
| Single-pass flat plate | 350–450 | 1.5–3.0 | 2–4 hours |
| Multi-pass flat plate | 400–550 | 3.0–6.0 | 6–12 hours |
| Cylindrical shell overlay | 350–500 | 2.0–4.5 | 4–8 hours |
| Large plate multi-pass | 450–600 | 5.0–10.0 | 12–24 hours |
Experimental validation through strain gauge measurements and coordinate measuring machine (CMM) distortion measurements confirms the accuracy of the analysis system, with typical deviations of less than 15% for residual stresses and less than 20% for distortion predictions. This level of accuracy is considered acceptable for engineering design purposes, where the goal is to predict trends and identify critical regions rather than achieve absolute precision.
Engineering Practice Implications
The ANSYS-based analysis system offers several practical benefits for engineering applications:
- Welding sequence optimization: By simulating different welding sequences, engineers can identify the sequence that minimizes distortion and residual stresses. This is particularly valuable for large overlay areas where the welding sequence has a significant impact on final distortion.
- Fixture design: The analysis system can be used to evaluate different fixture designs and determine the optimal clamping pattern to control distortion without introducing excessive restraint stresses.
- Post-weld treatment planning: The predicted residual stress distribution guides the selection of post-weld stress relief methods, including thermal stress relief, mechanical stretching, or vibration stress relief.
- Quality prediction: By correlating residual stress levels with cracking susceptibility, the analysis system can help identify regions at risk of cracking and implement preventive measures such as local heating or modified welding parameters.
- Cost reduction: Accurate distortion prediction reduces the need for iterative trial-and-error approaches, minimizing material waste and rework costs.
Key Questions and Reflections
A significant challenge in weld overlay simulation is the accurate representation of the fusion boundary and the associated metallurgical effects. The transition from base metal to overlay metal involves complex phase transformations, dilution effects, and microstructural changes that are difficult to capture in a continuum-based FEA model. While the analysis system developed in this study provides valuable engineering insights, it should be used in conjunction with experimental validation for critical applications.
Another reflection concerns the computational efficiency of the analysis. While the accuracy of the predictions is satisfactory, the computational time required for large-scale multi-pass analyses can be prohibitive for design optimization studies that require numerous simulation runs. Future developments should focus on reducing computational cost through adaptive mesh refinement, reduced-order modeling, or data analysis-based surrogate models.
Summary
The ANSYS secondary development approach presented in this study provides a powerful tool for predicting residual stresses and distortions in weld overlay processes. The ability to simulate complex multi-pass overlay configurations with realistic thermal and mechanical boundary conditions offers significant value for engineering design and process optimization. By integrating this analysis system into the design workflow, engineers can reduce trial-and-error, minimize distortion-related rework, and improve the overall quality and reliability of clad components. The study demonstrates that finite element analysis, when properly implemented with weld-specific constitutive models and boundary conditions, can serve as a reliable design tool for weld overlay applications.