Local, Semilocal and Nominal Approaches to Estimate the Fatigue Strength of Welded Joints

This paper is concerned with the analysis and the comparison of several so-called "local approaches" to estimate the fatigue strength of welded joints. The considered approaches are based on numerical analyses or strain gauges evaluations of the stress or strain state in the vicinity of the weld toe. The notch stress intensity factor (NSIF) approach applied to fillet-welded joints, as far as the opening angle between the weld and the main plate surface is constant (e.g. 135 degrees, typical for many fillet welds), is able to rationalise the fatigue strength data both for different joint geometries and absolute dimensions. The NSIF approach has been previously developed as an extension of the Linear Elastic Fracture Mechanics (LEFM) to open V notches and is based on the exponential local stress field around the V-notch tip. Several proposed "local approaches", although simpler to use than the NSIF approach, are based on the stress (or strain) field beyond the exponential local one. To distinguish such approaches from the NSIF-based one, we define the former ones as semilocal approaches while the latter is a local approach. The paper underlines that the ability to unify fatigue strength data in a single scatter band is not the same for the semilocal approaches if compared to the local approach.