Stress concentration at the root of a screw thread (Effects of root radius and friction coefficient)

Abstract

In general, the stress at the first root of the ridge in a bolt seems to be beyond the yield stress. But the fastened parts which are made of ductile material have generally enough strength, since the regions deformed plastically may be limited around the root. In the case of evaluating the strength for dynamic load and cyclic load (fatigue strength) or the strength of the bolt made of high strength material, however, the stress concentration factor at the root of the ridge must be estimated correctly. In this paper, an analysis is carried out with a high accuracy for the case of bolt being both tensioned and fastened in order to obtain elementary knowledges concerning the stress concentration of the screw thread. The effects of the root radius and the friction coefficient of the contact surfaces upon the stress concentration at the root of screw thread are examined on the basis of the results by an axi-symmetric FEM which can deal with a three-body elastic contact problem.