Weld Stress in SOLIDWORKS Simulation

Written by: Shaun Bentley, Application Engineer, DASI Solutions

How do you simulate welds in SOLIDWORKS Simulation? Many times when people ask this, they want to try to determine stresses. This is a complicated subject since there are a many approaches, each with their own time vs. accuracy trade-offs, and no method seems to tell the full story. I’ve suggested two popular approaches, but both should be considered conservatively/cautiously.

1.) Model the Geometry of the Weld and Connected Components and Mesh with Solid Elements (tedious and difficult)

Creating a highly detailed accurate representation of a real weld is impractical, and I’ve never seen it done. There can be so much variability in weld size and shape.

[Figure 1 – Weld Shape Variation]

Instead, to construct an approximate version of the weld, a tool like Fillet Bead allows you to add a separate body of weld material.

[Figure 2 – Fillet Bead]

Once this is modeled, it can be strategically bonded to the surrounding material inside of SOLIDWORKS Simulation using Component Contacts. Frequently, the results end up looking like this with a large stress in the root and toe of the weld:

[Figure 3 – Low average stress across weld throat]

[Figure 4 – Large peak stress at the root of the weld where there is a sharp discontinuity. Large stresses are at the toe of the welds as well]

[Figure 5 – Cross section of weld throat showing a relatively low average stress of around 50MPa]

Is the weld going to pass or fail? Under a single load at this stress magnitude, it seems this weld will be ok. The average stress of 50MPa along the smallest cross-section of the weld (the weld throat) is much less than the ultimate strength of 400MPa.

However, the peak stress predicted by my current mesh size seems to be more than 800MPa (actually the stress is singular and will continue to grow with finer meshes). This likely means there may be some local yielding of the material at the root and toe, and it could be a bad sign for fatigue (small cracks could develop and grow with each repeated cycle). Running this as a nonlinear study (which allows for material yielding) reveals more realistic behavior of the stresses, but still cannot be trusted due to limitations in my geometric model.

[Figure 6 – Sharp discontinuity seems to vanish when local plastic deformation is allowed]

Conclusion

This method can help to determine the average stress through your weld, and with this you can approximate a weld size needed to withstand these stresses. Appropriate safety factors should be considered to account for variables that are beyond our control in the FE model.

2.) Mesh with Shells – for Plate-Like or Sheet Metal Geometry Only – and Use the Edge-Weld Connector (relatively easy and quick)

SOLIDWORKS Simulation Professional offers a special connector type called the Edge-weld connector. This connector allows you to bond a terminated shell to a shell or solid body.

With this method, SOLIDWORKS Simulation simply bonds the selections together along an “intersecting edge”. Then it calculates the forces required to keep the connection consistent and uses these forces to estimate a weld size. If you look at some of the equations (American or European) for the estimated weld size, you’ll see that they are simply using averaged stresses across the throat. This is similar to the method from the above, except the extraction of the weld size is automated.

Conclusion

The Edge-Weld Connector speeds up the process for modelling welds for single load cases, but both methods fall short when it comes to predicting fatigue life since we cannot model the weld accurately to predict localized stresses and crack initiation. Other approaches would need to be considered such as the so-called hot-spot method.

If you have questions or would like more details on these methods, check the SOLIDWORKS Simulation Help, search on YouTube, or contact us.

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