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Decreasing the notch root ñ the theoretical stress concentration factor Ktincreases and the fatigue limit of a notched component decreases. Below a givencritical value for ñ, the fatigue limit is no longer controlled by Kt and the notch behaveslike a crack of equal depth. In the welded joints the conventional welding proceduresresult in a small value of the weld toe and the weld root radius. The influence of theradius can be considered negligible for as-welded joints and the highly stressed regionsare modelled as sharp V-notches. Then fatigue life assessments should be performed onthe basis of the Notch Stress Intensity factors (NSIFs), which quantify the intensity ofthe asymptotic distributions.A synthesis of fatigue strength data in terms of NSIF needs the constancy of the V-notchangle. Fatigue data from failures originated from weld roots or weld toes can besummarised in a single diagram by using the mean value of the strain energy density ina well defined volume (area) surrounding the fatigue crack initiation points. The strainenergy density is a function of the relevant NSIFs.In view of practical applications of the NSIF approach, a simplified calculationprocedure based on finite element analyses can be defined. A mesh patterncharacterised by a constant element size must be used close to the critical point andthen the elastic peak stress can be adopted to assess the fatigue life of the joint. Despiteits simplicity, such a method fully includes the scale effect, differently from othercommonly adopted engineering methods.