抄録
Yoshimoto had been presented a hypothesis concerning the fatigue strength of a bolt in bolt/nut assembly based on Ishibashi's hypothesis on the relationship between the fatigue notch factor and the local stress distribution. By using Yoshimoto's hypothesis, the fatigue behavior of bolt in bolt/nut assembly taking into account the effect of the axial residual stress at the first thread root of a bolt can be explained. However, this has not yet been verified quantitatively since the local stress and the axial residual stress which may exist locally around the thread root can neither be measured nor estimated with sufficient accuracy. This study aims to quantify the relationship between the axial residual stress and the fatigue strength. In this report, 3-D elastic-plastic FE simulation was performed to calculate the axial residual stress distribution by using precisely determined material property and the interim FE model through the thread rolling process of the leadless SG (thread rolled after heat treated) bolt specimen. Calculated result shows that the axial compressive residual stress about 940 MPa level is generated at the thread root of the depth ε_0=30μm of leadless SG bolt. The difference of fatigue strength of SV (heat treated before thread rolled) bolt and SG leadless bolt assembled with threaded adapter can be explained by using the residual stress estimated.
