ひずみ勾配パラメータによる疲労寿命評価手法の開発

Welded structures are widely used for construction machines, automobiles, railway vehicles, etc. In these structures, the welded parts are generally the weakest points. In particular, the toes of welding and the tops of non-welded portion become causes of fractures because these are stress concentration points. Thus, a method is required for evaluating fatigue life by analyzing these stress concentration points in a lump. In this study, a new evaluation method was developed for welded parts using strain gradient parameters. The conclusions were as follows: (a) Comparing strain approximation equation Δε = Hε/rλε (Δε: Strain range, r: Distance from strain concentration point, Hε: Magnitude of strain concentration, λε: Slope of strain concentration) to the strain distribution of the aluminum alloy specimens calculated by using elasto-plastic analysis, the strain gradient parameters Hε and λε were derived. A fatigue-life surface was derived using the parameters and fatigue life data that were obtained from the fatigue testing of the test specimens. The equation of the surface was logN = －5.2logHε－3.5λε＋21.7. (b) The fatigue life calculated by the fatigue-life surface equation had approximately good agreement with the fatigue life derived in the test.