The notch effect of geometric stress raisers in fatigue

The effect of a notch on the fatigue strength of a component varies considerably with the notch geometry. An analytical method is suggested to assess the notch geometry effect on the fatigue strength reduction factor, K_f. It is shown that a proper analysis of the notch effect must consider the stress distribution around the notch as well as the stress state in the neighborhood of the notch. The elastic stress distribution around the notch is determined by employing either the Finite Element Method or some universal relationships available in the literature. The biaxial state of stress is accounted for using von Mises equivalent stress which were averaged up to the cupic point position. The average von Mises equivalent stress is used to obtain the fatigue strength reduction factor. A material parameter (K_f/K_t′), is introduced. A number of notch geometries in four different types of steels were analyzed. The K_t values of these notches ranged from 1.9 to 3.5. It is found that the method could be satisfactorily used when the material parameter dependence on the notch geometry is small. It is also found that the method performs satisfactorily for low K_t values where the notch stress field can be considered elastic.