Spot welding thin sheets is an economic and effective joining technique, well-suited to vehicle structure applications. Typically the sheets are in the 0.5 to 3 mm thickness range. The spot welding process tends to harden the sheet material, causing it to warp. This reduces the material's fatigue strength, and may stretch the material as well as anneal it. The physical effects of spot welding include internal cracking and surface cracks.
How to assess spot weld fatigue
The method we implement in our fatigue analyses of spot welds is based closely upon the work of Rupp, Störzel and Grubisic — Computer Aided Dimensioning of Spot-Welded Automotive Structures. [SAE Technical Paper 950711].
The spot welds are modeled by stiff beam elements and the creation of these welds in this form is supported by many leading FE pre-processors. Cross-sectional forces and moments are used to calculate structural stresses around the edge of the weld. Life calculations are made around the spot weld at multiple angle increments and the total life reported includes the worst case.
Beside spot welds, we are also capable to model other joining methods such as rivets or bolts.