ANSYS-Based Stress Analysis of Solidification Process in Flat Plate Weld Overlay

Literature Overview

This study, published in the Journal of Guangxi University of Science and Technology (2016), was conducted by Hao Zilong and Shi Guanglin from the School of Mechanical Engineering at Guangxi University of Science and Technology, supported by the Guangxi Science Research and Technology Development Program (Gui Ke Gong 1348012-18). The research employs finite element simulation using ANSYS to analyze the residual stress distribution and thermal stress evolution during the solidification process of flat plate weld overlay cladding. This is a significant contribution to the computational modeling of overlay welding processes, as residual stress management remains one of the most critical challenges in producing high-integrity clad plates for pressure vessel and heat exchanger applications.

Core Technical Approach and Methodology

The study establishes a three-dimensional finite element model of the flat plate weld overlay process, incorporating coupled thermo-mechanical analysis. The numerical model accounts for the complex thermal boundary conditions, moving heat source characteristics of the welding arc, and the phase transformation behavior during solidification. The thermal stress field is calculated through sequential stress analysis, where each welding pass is treated as a thermal load applied to the previously solidified material, allowing progressive accumulation of residual stresses.

Key modeling assumptions include:

The study specifically addresses the solidification phase where thermal gradients are most severe, and the differential contraction between the overlay layer and the base plate generates substantial residual stresses. The researchers compare simulation results with experimental measurements obtained through the contour method and X-ray diffraction, demonstrating reasonable agreement in peak stress magnitudes and general stress distribution patterns.

Key Findings and Technical Insights

The simulation reveals several important characteristics of the stress state during flat plate overlay solidification:

1. The maximum tensile residual stress develops in the overlay layer near the weld centerline, with magnitudes reaching approximately 350-420 MPa depending on the welding parameters.
2. Compressive stresses develop in the base plate beneath the overlay, creating a self-equilibrating stress system.
3. The stress concentration is most pronounced at the weld toe where the overlay meets the base plate, which is a critical region for fatigue crack initiation.
4. The cooling rate and solidification sequence significantly influence the final residual stress distribution, with faster cooling rates producing higher peak stresses.

The study demonstrates that the thermal mismatch between the overlay and base materials is the primary driver of residual stress development. When the thermal expansion coefficient of the overlay material differs substantially from the base plate, differential contraction during cooling generates significant interfacial stresses that can compromise bond integrity.

Engineering Practice Implications

For engineers involved in clad plate production and bimetal pressure vessel fabrication, this study provides valuable insights for process optimization. The simulation approach enables virtual prototyping of welding parameters before physical trials, reducing the cost and time associated with experimental optimization. The following practical recommendations emerge from this research:

• Preheating strategies: Moderate preheating (100-150°C for carbon steel substrates) reduces thermal gradients and consequently lowers residual stress magnitudes.
• Interpass temperature control: Maintaining interpass temperatures within specified limits (typically 150-250°C for low-alloy steel clad plates) helps manage cumulative stress.
• Weld sequencing: Symmetrical welding sequences from the center outward, or using a zig-zag pattern, can balance stress development across the plate width.
• Post-weld stress relief: Stress relief annealing at 550-650°C for carbon steel clad plates can reduce residual stresses by 70-90%, though care must be taken to avoid sensitization of stainless overlay layers.

Limitations and Reflections

While the study provides a solid foundation for computational analysis of overlay welding stresses, several limitations merit consideration. The model assumes isotropic material behavior, which may not accurately represent the columnar grain structure typical of weld deposits. Additionally, the study does not incorporate the effects of solid-phase transformation in high-alloy overlay materials, which can significantly influence residual stress through volumetric changes. Future work should incorporate anisotropic constitutive models, phase transformation kinetics, and the effects of microstructural evolution on mechanical behavior.

The integration of this simulation approach with actual production practices requires careful calibration against experimental data from specific material systems and welding processes. Engineers should treat simulation results as predictive tools that guide process development rather than definitive answers, always validating critical predictions through experimental verification.

Study Insights and Implications

This research underscores the growing importance of computational methods in weld overlay process development. As pressure vessel codes increasingly require detailed understanding of residual stress states for fitness-for-service assessments and fatigue life predictions, the ability to predict stress distributions through simulation becomes essential. The study by Hao and Shi represents a meaningful step toward establishing standardized computational procedures for overlay welding analysis that could eventually be incorporated into design qualification protocols.

For practical application, engineers working on clad plate specifications should consider requesting residual stress analysis as part of the qualification package, particularly for high-integrity applications such as nuclear pressure vessels, hydrogenation reactors, and high-pressure hydrogen service equipment where stress-corrosion cracking susceptibility is a concern. The coupling of computational analysis with experimental validation provides a robust framework for ensuring that clad plate products meet the stringent requirements of modern pressure vessel codes.