The Research On Fatigue Strength For Round Bar Specimen With Double Notches

In order to realize certain functions, multi notches are designed to enhance the mechanical components in that in recent years emerges the trend of the complication in the design of mechanical components. Lots of experiments and researches on the effect of single notch on fatigue limit have been conducted domestic and abroad in the past years; however, researches on the effect of multi notches on fatigue limit are rarely seen. In addition, since the categories of multi notches are increasingly complex, the current researches on multi notches are comparatively insufficient. As a result, researches on the effect of multi notches on fatigue limit are of great significance for the fatigue strength design and the prediction of the fatigue life of the mechanical components.Choosing the double-notch shape which combines the stepped shaft and the round hole, this paper uses the mainstream material used in mechanical engineering, structural steel, as its object of investigation. The fatigue specimens are divided into 20 groups:plain, the single stepped shaf(t 1 chanfers),the single round hole(3 diameters), and the double notches ( 5 notch distances). The experiments study the interactions between the stepped shaft and the round hole from different distances and the effect on fatigue limit. Based on the experiments and researches, the traditional estimating method of fatigue limit and the rationality of the recent research results are analyzed and compared, and certain corrections are attempted. Meanwhile, the stress concentration factors of multi notches are analyzed with the application of the FEM(finite element method) analysis and a conclusion is drawn on the relationship between the fatigue notch factor and the stress concentration factor.