抄録
The residual stress at the thread root of a bolt induced by thread rolling is one of the major factors influencing the fatigue strength, and the method (hypothesis) to predict the fatigue strength has been investigated. However, the effect of the residual stress has not been verified quantitatively since we cannot measure the residual stress with sufficient accuracy, and there are many other variables affecting the fatigue strength data. This study aims to clarify the relationship between the fatigue strength and the local stress distribution at the first thread root including the effect of the residual stress. For this purpose, a method is proposed where the residual stress is induced on the thread root by preloading of a bolt/nut assembly. FEM analysis and fatigue test were done for the preloaded bolts, and the results show that the fatigue strength of bolts could be evaluated from the local stress by using Ishibashi's hypothesis and Yoshimoto's hypothesis although there are some uncertainty left for the effect of nut thread run-out.
