Fatigue of lap-welded joints
MAG welding in carmakers

The fatigue strength of steels, in the limited and unlimited endurance ranges, increases with grade. A logarithmic relationship has in fact been established between endurance limit and fracture toughness for the load ratio (S_min/S_max) R_s = 0.1 and R_s = – 1. This relationship is an interesting tool to use with a view to service life prediction, lightening and sizing of parts in service.

Nevertheless, steels are rarely used as such in industry. More often than not, they undergo operations such as cutting, drilling, punching, bending, stamping, assembly, etc., or a combination of some of these. These operations introduce local variations in geometry and/or mechanical properties, concentrating stresses that can lead to premature failure of the part in service.

MAG clinch-welded joints have a lower fatigue strength than the base metal. Fatigue...