Study on the improvement method of Goodman-Smith Fatigue Limit Diagrams based on IIW Standard and Unilateral Tolerance Coefficient Method

Abstract

The Goodman-Smith (GS) diagrams are widely used for fatigue strength assessment of bogies as a common method for welded structures. The traditional GS diagrams proposed by the UIC ORE B12/RP17 standard suffer from the problems of too large a safety factor leading to loose assessment results, data scarcity, and low safety margins for low survival rates. Therefore, an improved method of GS diagrams for base metals and welded joints was proposed. The traditional GS diagrams were improved by combining the IIW standard and the unilateral tolerance coefficient method. The design guidelines of the traditional GS diagrams were incorporated into the improved GS diagrams to obtain the improved design guidelines. Within this framework, the improved GS diagrams were validated by applying base metal specimens with three common welded joints. The results showed that the safety factor was reduced to 0.3–0.5 times the original factor for the same survival rate and confidence level. The accuracy of the fatigue strength assessment was improved. Finally, the improved GS diagrams were used for the fatigue strength assessment of the critical base metal and weld region of the bogie frame, which provided a new reference for the fatigue strength assessment research in the field of rail transport.