An Analytical Study on Reduction of Stress Concentration at the Underhead Fillet in High-Strength Bolts

Abstract

Fatigue fracture or delayed fracture often occurs at the threaded portion or the underhead fillet of high-strength bolts where the stress concentrates. In order to reduce the stress-concentration at the threaded portion, we have already proposed the improved thread shape. In this paper, the cone shape head is proposed to reduce the stress-concentration at the underhead fillet. The efficiency of this shape is analyzed by the FEM in which the parameters are the radius of the fillet and the angle of the bearing surface at the underhead.