Study on Unified Fatigue Strength Assessment Method for Welded Structure

Abstract

There has been proposed several methods to evaluate hot spot stress (HSS), which is an effective parameter to assess fatigue strength of various fillet welded structures. One is 2-points extrapolating method in which HSS is evaluated by linear extrapolation of stress at two specified points distant from weld toe and the other is 1-point representative method in which HSS is defined as stress at a specified point distant from weld toe.In these methods, specified point (s) to estimate HSS is defined as a function of plate thickness t. But, generally, the specified point (s) should be defined as a function of not only plate thickness t but also weld leg length l.First, in order to investigate a universal method to evaluate HSS for various combinations of t and l in fillet welded joints, stress analysis in the vicinity of weld toe has been carried out for 2-dimensional fillet welded joint models, by means of boundary element method (BEM). As a result, the authors propose the following new equation to estimate HSS σhs for various fillet welded joints.σhs = σ (Xhss) This means that HSS is defined as stress at xhss the specified point distant from weld toe. And Xhss/t is the function of l/t and is expressed as follows.Xhss/t=f (l/t) =c·a· (l/t) +b· (l/t) 2/a+ (l/t) 2where a, b, c are constants.Second, in order to verify the validity of the proposed HSS evaluating method, the fatigue tests of fillet welded joints in thick plate structures have been carried out and other fatigue test data has been refered. As a result, each S-N data based on HSS range evaluated from the new proposed method has gathered within a narrow band respectively, independent of structural stress concentration factors. And, it has been confirmed that the new proposed method to evaluate HSS is applicable for unified fatigue strength assessment of fillet welded structures.