Welding Residual Stress Simulator

The core driver of all welding effects is the heat input per unit length, which determines how much metal melts and subsequently contracts.

Where $Q$ is the heat input (J/mm), $V$ is voltage (V), $I$ is current (A), $\eta$ is the arc thermal efficiency, and $v$ is the travel speed (mm/s). This is the primary parameter you control in the simulator. Higher $Q$ means more heat, leading to greater shrinkage and stress.

The resulting deformations are often empirically related to heat input and geometry. Angular distortion (bending) depends heavily on plate thickness, while longitudinal shrinkage depends on the cross-sectional area resisting the contraction force.

Here, $\theta$ is the angular distortion (radians), $t$ is plate thickness (mm), $\delta_L$ is longitudinal shrinkage (mm), $E$ is Young's modulus, $A$ is the weld cross-section area, and $C_1, C_2$ are empirical constants. The simulator solves these instantly when you adjust thickness or joint type.

Shipbuilding & Offshore Structures: Massive welded panels are prone to buckling distortion (a type of angular distortion). Engineers use simulators like this to optimize welding sequence and heat input before production, saving millions in rework. Preheating thick high-strength steel joints is standard to prevent cracking.

Pipeline Construction: Longitudinal shrinkage in long pipeline welds can accumulate, causing the pipeline to shorten beyond allowable tolerances. The travel speed and heat input are carefully controlled based on calculations similar to this tool's output to ensure fit-up for the next pipe section.

Pressure Vessel Fabrication: High residual stress at welds can combine with internal pressure stress, leading to premature failure or reduced fatigue life. Post-Weld Heat Treatment (PWHT), which you can model with the "PWHT hold time" parameter, is often mandated to relax these stresses and ensure safe operation.

Automotive Frame Assembly: Distortion in chassis components from welding can misalign mounting points for engines or suspensions. CAE engineers use this physics to simulate welding during virtual prototyping, adjusting clamp positions (modeled by "Restraint Condition") to minimize warpage before building physical tools.

First and foremost, keep in mind that this simulation is not an "all-knowing oracle." If you put in arbitrary input parameters, the output will be "garbage in, garbage out." For example, material property data. Many people use catalog values for room temperature data as-is, but in welding simulations, properties like Young's modulus and yield stress at 600°C or 800°C significantly influence the results. The room temperature Young's modulus for SUS304 is about 193 GPa, but at 800°C, it drops to less than half, around 90 GPa. If you get this data wrong, both the deformation and residual stress results will be way off the mark.

Next, errors in constraint condition settings. In reality, the workpiece is firmly fixed by jigs, but if you apply a fully fixed condition (constraining all degrees of freedom) in the simulation, it can sometimes calculate unnaturally high residual stresses. Conversely, if the constraints are too loose, the deformation may appear larger than in reality. For instance, for long butt joints, settings that imagine the actual jig—like constraining only certain directions to allow for thermal expansion-induced "snaking"—are essential.

Finally, don't overlook mesh dependency. Sharp temperature gradients occur around the weld bead, so if you don't use a fine mesh there, you won't accurately capture the temperature or stress fields. However, making the entire mesh too fine will cause computation time to explode. A standard practice is "graded mesh refinement"; for example, using a 1mm mesh near the weld line and a 5mm mesh farther away for a 20mm thick joint. If doubling the mesh density doesn't significantly change the results, you can be reasonably confident.