Fatigue of Seam Welds

The seam weld fatigue analysis method we use is based on that originally proposed by Volvo Car Corporation and Chalmers University of Technology, and developed in cooperation with nCode. The method was developed particularly for automotive components welded from thin steel sheets (typically 1-3 mm), and most of the industrial applications of this method have been to this type of structure. However, the structural stress-based approach it uses is of quite general applicability and an approach based on the ASME Boiler & Pressure Vessel Code VIII, Division 2 for thicker parts using solid elements is also being used. The method is basically quite similar to the standard S-N method, but with some special features to deal with welds.

Fatigue of seam welds

We offer fatigue analysis of seam welded joints, including fillet, overlap and laser welds. The method used is based on the approach developed by Volvo (SAE paper 982311) and validated through years of use on vehicle chassis and body development projects. Seam weld analysis can be carried out with all load types including vibration. Stresses can either be taken directly from FE models (shell or solid elements) or calculated from grid point forces or displacements at the weld. The approach is appropriate for weld toe, root and throat failures.

Thick welds are assessed using the stress integration method outlined in ASME Boiler & Pressure Vessel Code VIII (Division 2) standard. Corrections are also accounted for sheet thickness and mean stress effects. The structural stress at the weld toe, the hot-spot stress, can be also be estimated by the extrapolation of the surface stress at points near the weld. The BS7608 welding standard is also supported, together with required material curves.

Seam weld analysis from crack initiation to final failure

A unified theory of fatigue analysis developed by Prof. G. Glinka is used to improve the accuracy of analysis of thick welds. It uses an integrated approach for modeling fatigue over the entire lifetime of a component - from the very early stages to final fracture - to give more accurate determination of weld lives particularly for complex geometries.

The method uses the through thickness stress distribution for the geometry and can include the effect of a known residual stress profile. Although this is primarily a CAE based analysis, the same method may also be applied to measured stress data.