CLADDING TECHNOLOGY SHANXI CO., LTDDynamic Stress Field Simulation of Cladding Process Using ANSYS
Literature Overview
This study employs finite element analysis (FEA) using ANSYS software to simulate the dynamic evolution of the stress field during the cladding welding process. The research addresses a critical gap in cladding technology—the prediction and control of residual stresses that develop during multi-pass overlay welding. Residual stresses are a primary driver of cracking, distortion, and reduced fatigue life in clad components, and their accurate prediction is essential for process optimization and design validation.
Core Technical Findings
The study develops a three-dimensional transient thermal-mechanical coupled FEA model that captures the moving heat source, phase transformation effects, and plastic deformation during multi-pass cladding welding. The thermal model uses a double-ellipsoidal heat source to represent the welding arc, with parameters calibrated against experimental thermocouple measurements. The mechanical model incorporates temperature-dependent material properties, elastic-plastic behavior, and the effect of solidification shrinkage and thermal expansion.
The following table summarizes the key modeling parameters and assumptions:
| Modeling Aspect | Parameter/Assumption | Justification |
|---|---|---|
| Heat source | Double-ellipsoidal (Goldak model) | Captures arc shape and energy distribution |
| Thermal conductivity | Temperature-dependent | Accounts for phase changes |
| Specific heat | Temperature-dependent | Includes latent heat effects |
| Yield strength | Temperature-dependent | Captures plastic deformation |
| Phase transformation | TTT/CCT diagram-based | Accounts for martensite formation |
| Boundary conditions | Symmetry + convection/radiation | Simplifies computation |
| Element type | 3D 8-node brick (SOLID90/95) | Standard for thermal-mechanical coupling |
| Time step | Adaptive (0.01–0.5 s) | Resolves transient thermal gradients |
Stress Field Evolution Analysis
The study reveals that the residual stress field in the cladding weld develops in three distinct stages: (1) initial stress accumulation during the first pass, (2) stress redistribution and relaxation during subsequent passes, and (3) final stress state after cooling to room temperature. The maximum longitudinal residual stress in the cladding layer reaches approximately 350–420 MPa, which is close to the yield strength of the deposited material at room temperature. The transverse residual stress is lower, typically 150–250 MPa, and the hoop stress (in circumferential cladding) follows a similar pattern.
The study demonstrates that the stress field is highly sensitive to the following process parameters:
- Travel speed: Increasing travel speed from 200 mm/min to 400 mm/min reduces the peak residual stress by approximately 20% due to reduced heat input and faster cooling.
- Interpass temperature: Maintaining interpass temperature below 200 °C limits the accumulation of thermal stress and reduces the risk of cracking.
- Welding sequence: A balanced welding sequence that alternates between opposite sides of the component reduces angular distortion and hoop stress by up to 40%.
- Preheat temperature: Preheating to 200–300 °C reduces the peak thermal gradient and consequently reduces residual stress by 15–25%.
Comparison with Experimental Results
The study validates the FEA model by comparing predicted residual stresses with experimental measurements obtained using the hole-drilling method (ASTM E837) and X-ray diffraction. The agreement between predicted and measured longitudinal residual stresses is within ±15% for most locations, with larger deviations observed near the weld toe where stress gradients are steepest. The transverse residual stress predictions show slightly larger deviations (±20%), which the study attributes to the simplification of the heat source model and the neglect of phase transformation effects in some regions.
The following table presents the comparison between FEA predictions and experimental measurements:
| Location | FEA Longitudinal Stress (MPa) | Experimental Longitudinal Stress (MPa) | Deviation |
|---|---|---|---|
| Weld center | 380 | 360 | 5.6% |
| 1 mm from center | 320 | 340 | 5.9% |
| 3 mm from center | 200 | 220 | 9.1% |
| Dilution zone | 280 | 300 | 6.7% |
| Base metal (5 mm) | 50 | 60 | 16.7% |
Engineering Practice Integration
The residual stress predictions from this study have direct implications for the design and fabrication of clad pressure vessels and other critical components. The following engineering practices are recommended based on the study's findings:
- Stress relief heat treatment (SRHT): Post-weld stress relief at 620–650 °C for 2 hours per 25 mm of wall thickness is recommended to reduce residual stresses to below 100 MPa. However, SRHT must be carefully controlled to avoid sensitization of austenitic stainless steel cladding layers, which can lead to intergranular corrosion.
- Welding sequence optimization: The study's findings support the use of balanced and staggered welding sequences to minimize distortion and residual stress. For cylindrical components, a spiral or helical welding sequence is preferred over a single-direction circumferential sequence.
- Preheat and interpass temperature control: The study recommends preheat temperatures of 150–250 °C and interpass temperatures below 200 °C for most cladding applications. For high-carbon base metals or thick components, higher preheat temperatures may be necessary to prevent cracking.
- Post-weld inspection: Residual stress measurement should be incorporated into the quality assurance program for critical clad components. The hole-drilling method or X-ray diffraction can be used for spot checks, and the results should be compared against FEA predictions to validate the fabrication process.
Key Questions and Reflections
The study acknowledges several limitations that are worth reflecting upon. First, the FEA model does not fully capture the complex metallurgical transformations that occur during cladding welding, particularly the formation of martensite in high-carbon dilution zones and the precipitation of carbides in the deposited layer. These metallurgical effects can significantly influence the residual stress field and should be incorporated into future models.
Second, the study focuses on a single welding configuration and does not explore the effects of different welding processes (e.g., ESW, SAW, PTA) on the residual stress field. In practice, the choice of welding process is often dictated by the component geometry and cladding thickness, and the residual stress field will vary significantly between processes. A comparative study of residual stress fields for different cladding processes would provide valuable guidance for process selection.
Third, the study does not address the effect of residual stresses on the long-term performance of clad components under cyclic loading or in corrosive environments. Residual tensile stresses at the coating-substrate interface can significantly reduce fatigue life and promote stress corrosion cracking. Future work should couple the residual stress analysis with fatigue and corrosion modeling to provide a more comprehensive assessment of component performance.
Study Insights and Implications
The most valuable contribution of this study is the demonstration that FEA can provide accurate predictions of residual stress fields in cladding welds with a reasonable level of modeling effort. The agreement between predicted and measured stresses validates the modeling approach and provides confidence in using FEA for process optimization and design validation. The study also highlights the critical role of welding sequence, interpass temperature, and preheat in controlling residual stresses, which are practical parameters that can be adjusted during fabrication to improve component quality.
For engineers involved in the design and fabrication of clad pressure vessels, this study provides a quantitative framework for understanding and controlling residual stresses. The FEA model can be adapted to specific component geometries and welding procedures to predict residual stress fields and identify potential problem areas before fabrication begins. This proactive approach to residual stress management can reduce the risk of cracking, distortion, and premature failure, ultimately improving the reliability and service life of clad components.
Summary
This literature provides a rigorous FEA-based approach to predicting and controlling residual stresses in cladding welds. The validated thermal-mechanical coupled model offers engineers a powerful tool for process optimization and design validation, and the study's recommendations for welding sequence, preheat, and stress relief are directly applicable to industrial fabrication. The study also identifies important limitations and directions for future research, including the incorporation of metallurgical effects and the extension to multi-physics analysis that includes fatigue and corrosion. For the cladding and bimetal pressure vessel industry, this work represents a significant step toward more predictive and reliable fabrication practices.