7. Fatigue of lap-welded joints

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...