The Peak Stress Method for fatigue analysis of welded details

In fatigue design of welded joints according to the notch stress intensity factor (NSIF) approach, the weld toe profile is assumed to be a sharp V-notch having tip radius equal to zero, while the root side is assumed to be a pre-crack in the structure. The Peak Stress Method (PSM) represents an engineering, simplified method which allows a rapid calculation of the NSIFs on the basis of the singular linear elastic peak stresses evaluated at the notch tip by means of FE analyses with coarse FE meshes. The advantages of the PSM can be summarized as follows: (i) coarse meshes can be adopted, the required FE size being some orders of magnitude larger than that necessary to evaluate the NSIFs from the local stress distributions; (ii) only a single stress value is sufficient to estimate the NSIFs instead of a number of stress-distance numerical results. First, the PSM has been calibrated by analysing several mode I and mode II problems with Ansys FE code. Recently, the PSM has been also calibrated by adopting six commercial FE packages other than Ansys, taking advantage of a Round Robin between some Italian Universities. After having recalled the calibration of the method, the paper presents some applications of the PSM relevant to partial-penetration butt joints made of aluminum alloys as well as load-carrying cruciform joints and tube-to-flange joints made of structural steels under uniaxial fatigue loadings. Because of the relatively coarse FE analyses required and simplicity of post-processing the calculated peak stresses, the PSM might be useful in the everyday design practice.