Definition of hot spot Stress in welded structure for fatigue assessment (2nd Report)

Abstract

In design of a large structure, the assessment of fatigue strength is one of major design considerations. In evaluation of fatigue strength of welded toes, the development of FE analysis and detailed model tests have enhanced the use of “Hot Spot Stress” or “Peak Strain” concepts.In the first report, the hot spot stress definition for plate type structures was discussed, using the experimental data of the model tests by SR202.In this paper, fatigue strength assessment in the use of “Peak Strain” concept is presented. Fatigue strength assessment methods with the peak stress are shown in ASME Boiler and Pressure Code Sec. III and NK rule Part P.For the short of TMCP steel low cycle fatigue data and the short of application for model tests data in the peak strain concept application, in this research, low cycle fatigue tests of round bars with notch were done and analysis based on the peak strain concept for the model tests by SR202 have been made.In the analysis, the NK method with some choice of detailed assessment process have been investigated.Finally, detailed calculation method for the peak strain with the object of assessing low to high cycle fatigue strength of welded structures is proposed, that is the use of Neuber rule for plastic strain concentration and Manson method for stable stress strain relation.