Local strain for fatigue strength of welded structures

Field criteria, which are usually applied in fracture mechanics to ensure t he structural integrity of cracked components, are extended to the fatigue design of welded joints, whose weld toe can be assimilated to a notch with a small tip radius. In particular, fatigue strength in terms of strain rath er than of stress has been determined by applying stress cycles with differ ent stress ratios R = sigma (min)/sigma (max). Finally, for the evaluation of the fatigue strength of welded joints in structural steel, a strain curv e versus different R ratios is given to be compared with the service measur ed local strain at the weld toe.