Stress Analysis of a Bolt-Nut Joint by the Finite Element Method and the Copper-Electroplating Method : (2nd Report, Stress at the Root of a Bolt Thread under a Tensile Load)

Abstract

This paper presents a stress analysis at the root of a bolt thread by the finite element method and the copper-electroplating method which were used for the stress analysis of V-groove in the 1st report. Firstly, as a three dimensional axially symmetrical problem, the load distribution at the bolt thread which is screwed in a nut thread, is computed by the finite element method combined with the point matching method. Then, the stress concentration factor under this load distribution is computed. Secondly, a measuring method of the stress concentration factor by the copper-electroplating method presented in the 1st report, is applied to the bolt threads with three.root radii. The obtained results are as follows : (1) The numerical solution of the stress concentration factor by the finite element method shows a fairly good agreement with the experimental value by the copper-electroplating method; (2) the deviation of the maximum stress point at the root of a thread toward the loaded flank becomes larger with an increase of the root radius; (3) even if the root radius is increased over the range which is specified in ISO Standard, the stress concentration factor is scarcely improved.