Prediction of Buckling Deformation in TIG Overlay Welding of Thin Plates

Literature Overview

The paper by Guo Nan, Yu Yongjian, Yin Xianqing, and Yang Fang, published in Welding Journal (2019, Vol. 40, No. 10, pp. 116–120), addresses a practically significant challenge in overlay welding: the prediction and understanding of buckling deformation in thin plates subjected to TIG (Gas Tungsten Arc) overlay welding. Funded by the Henan Provincial Major Science and Technology Program (161100210900) and Henan Provincial Key Scientific Research Project (17A460012), this study combines finite element analysis with Digital Image Correlation (DIC) experimental validation to develop a reliable predictive model for buckling behavior.

Technical Approach

Finite Element Model Components

The authors developed a thermo-elastoplastic finite element model that incorporates:

Model Component	Description	Key Parameters
Heat source	Gaussian double-ellipsoidal model	Heat input, travel speed, arc radius
Thermal boundary conditions	Non-linear transient heat conduction	Convection coefficient, radiation coefficient, temperature-dependent
Material properties	Temperature-dependent elastic and plastic properties	Young's modulus, yield strength, thermal expansion coefficient
Constitutive model	Thermal-elastoplastic	Bilinear kinematic hardening
Geometry	Thin plate with overlay weld bead	Plate thickness, bead geometry

Experimental Validation Method

Digital Image Correlation (DIC) was employed as a non-contact full-field deformation measurement technique. The authors designed a dedicated thin plate welding deformation detection apparatus that enables:

Real-time, full-field displacement measurement during welding
Three-dimensional deformation tracking
Dynamic temperature field correlation with deformation data
High spatial resolution measurement of local buckling patterns

Core Findings and Buckling Mechanism

Saddle-Shape Deformation Pattern

The study confirms that thin plate TIG overlay welding produces a characteristic saddle-shaped (hyperbolic paraboloid) buckling deformation after cooling. This is distinct from the simple angular distortion or longitudinal bowing observed in butt welds of thin plates.

Mechanism Interpretation

The saddle-shape buckling arises from the interaction of:

Compressive residual stresses — The overlay weld creates compressive stresses in the surrounding plate material due to the constrained thermal expansion of the weld zone.
Buckling instability — When the compressive stress exceeds the critical buckling stress of the thin plate, elastic-plastic buckling occurs.
Asymmetric thermal field — The traveling heat source creates an asymmetric temperature distribution that drives the buckling mode in a specific direction.
Geometric non-linearity — The large deflections associated with buckling require non-linear geometric analysis, which the elastoplastic model captures.

Model Accuracy Assessment

Validation Metric	FEM Prediction	DIC Measurement	Deviation
Maximum out-of-plane displacement	Within 10%	Measured value	Acceptable
Buckling mode shape	Qualitative match	Qualitative match	Good
Peak location	Within 2 mm	Measured position	Good
Dynamic deformation history	Captures trend	Captures trend	Reasonable

Engineering Practice Applications

Relevance to Pipeline and Vessel Manufacturing

For engineers in the piping and pressure vessel industry, this research has several practical implications:

Overlay welding of thin-walled piping: When applying corrosion-resistant overlay welds to thin-walled pipes (such as 2–5 mm wall thickness CRA pipes), buckling deformation can compromise dimensional accuracy and affect subsequent fit-up for assembly.
Repair welding of thin plates: In the maintenance of heat exchanger tubesheets, boiler tubes, and thin-walled pressure vessels, understanding the buckling behavior allows for better planning of weld sequences and backing support arrangements.
Process optimization: The model can be used to predict the optimal welding parameters (heat input, travel speed, bead width) that minimize buckling while maintaining adequate dilution control.

Comparison with Conventional Distortion Prediction

Aspect	Conventional Angular Distortion	Buckling Deformation
Governing mechanism	Differential thermal contraction	Compressive stress exceeding critical buckling stress
Applicable plate thickness	All thicknesses	Primarily thin plates (t/L < 0.05)
Deformation type	Linear/angular	Non-linear geometric instability
Predictive difficulty	Moderate	High (requires non-linear analysis)
Mitigation strategies	Backing bars, clamping, reverse weld	Reduced heat input, backing support, pre-camber

Key Questions and Reflections

The saddle-shaped buckling pattern is particularly interesting because it represents a fundamentally different failure mode from conventional welding distortion. The transition from stable equilibrium (no buckling) to unstable equilibrium (buckling) is governed by the critical buckling stress, which depends on:

Plate thickness and material properties
Restraint conditions at the plate edges
Magnitude and distribution of residual compressive stresses
Weld geometry and heat input

For engineering practice, the critical question is: at what heat input level does buckling initiate? The authors' model provides the framework to answer this question quantitatively, but the transition from elastic buckling to plastic buckling represents a significant non-linearity that requires careful numerical treatment.

Study Insights and Conclusions

This paper successfully demonstrates that a thermo-elastoplastic finite element model, validated by DIC experiments, can accurately predict the buckling deformation of thin plates during TIG overlay welding. The saddle-shaped deformation pattern is a characteristic response that should be anticipated in any overlay welding operation on thin sections. For engineers involved in the manufacturing and repair of thin-walled piping systems, heat exchangers, and pressure vessels, this research provides both a predictive tool and a mechanistic understanding that can guide process optimization and quality assurance decisions.