Welds are often the weakest points in a structure when it comes to fatigue performance. During welding, residual tensile stresses are introduced, which can accelerate crack initiation. In addition, weld material typically exhibits lower fatigue resistance than the base metal, and the geometric features of welds create stress concentrations that make them ideal locations for fatigue cracks to start.
To address these challenges, engineers rely on advanced durability analysis tools such as Ansys Design Life. This tool enables engineers to predict fatigue life accurately and identify critical weld locations early in the design stage, helping ensure safer and more reliable vehicle structures.
This method is typically used when structures are modeled with shell elements, which are common for thin sheet metal components. The approach is particularly suitable for sheets with thicknesses around 1–3 mm, such as automotive body panels.
One major advantage of this method is that it does not require highly refined meshes or detailed weld geometry. Instead, fatigue damage is evaluated at the weld toe and weld root, considering both membrane and bending stresses acting on the structure.
When the structure is modeled with solid elements, particularly for thicker plates, the solid seam weld method becomes more appropriate.
In this method, stress linearization techniques are used to recover structural stresses within the weld region. This approach is relatively mesh-insensitive, making it reliable even when the mesh density varies. It also enables fatigue evaluation at several critical regions, including the weld toe, weld root, and weld throat.
Automotive assemblies frequently contain spot welds, especially in thin sheet structures. The spot weld fatigue method evaluates durability based on cross-sectional forces and moments acting around the weld.
Fatigue calculations are performed at multiple angular increments around the weld edge, and the worst-case fatigue life is reported. In addition, Python scripting capabilities allow engineers to extend the methodology to simulate other joining techniques such as rivets or bolts.
Fatigue analysis can also be categorized based on the fatigue regime:
Stress-Life (S–N) methods are typically used for high-cycle fatigue, where stresses remain largely elastic.
These methods support several advanced fatigue considerations, including mean stress effects, temperature influence, stress gradients, and surface finish corrections.
Now that the available analysis methods are understood, let’s explore how the weld fatigue analysis of a vehicle subframe is performed using Ansys tools.
In this case study, the Shell Seam Weld method is used because the subframe components are sheet metal structures modeled using shell elements.
The image above illustrates the generated weld lines. Let’s move on to the workflow.
Next, the prepared model is imported into Ansys Mechanical, where the welds are generated using the Weld Mesh feature.
A structural analysis is performed to determine the stress and strain distribution within the subframe under loading conditions.
This step is critical because the fatigue simulation relies on these stress results as input data
Once the structural analysis is completed, the solution is connected directly to an embedded Design Life system within the Ansys Workbench environment.
This integration allows stress results from the structural analysis to be automatically transferred to the fatigue module without additional preprocessing.
Within the fatigue analysis setup, the Shell Seam Weld method is selected.
The next step is to define the loading history using the Load Mapper tool in Design Life.
Several load types are available depending on the nature of the input data.
The different types of the load are described below.
In this example, a time-step loading event is used. The structural analysis results are applied at three discrete time points (1, 2, and 3), and the loading cycle is repeated 2000 times to simulate repeated operational conditions.
After defining the loading events, the fatigue simulation is launched in Ansys Design Life.
The results are then displayed using contour plots, which highlight regions of high fatigue damage and identify the most critical weld locations within the subframe.
These insights allow engineers to quickly determine whether design modifications are required to improve durability.
Fatigue failure in welded structures is a critical concern in the automotive industry, particularly for components such as vehicle subframes that experience repeated dynamic loading throughout their service life.
This integrated workflow not only helps identify potential fatigue failures early in the design process but also enables engineers to optimize weld locations, improve structural reliability, and reduce the risk of costly failures in the field.
Ultimately, adopting such advanced simulation-driven design approaches allows manufacturers to build stronger, safer, and more durable vehicles while accelerating product development cycles
As an authorized Ansys channel partner, CADFEM supports customers throughout their simulation journey by providing expert technical guidance, customized workflows, advanced training, and hands-on implementation support. From model setup and parameter calibration to validation and optimization, CADFEM helps organizations fully leverage Ansys wear simulation capabilities to achieve reliable, high-quality engineering solutions.
