Proposition of helical thread modeling with accurate geometry and finite element analysis

Abstract

Distinctive mechanical behaviors of bolted joints are caused by the helical shape of thread geometry. Recently, a number of papers have been published to elucidate the strength or loosening phenomena of bolted joints using three-dimensional finite element analysis. In most cases, mesh generations of the bolted joints are implemented with the help of sophisticated commercial software. Therefore, the mesh patterns thus obtained are not necessarily adequate for analyzing the stress concentration and contact pressure distributions, which are the primary concerns when designing bolted joints. In this paper, an effective mesh generation scheme is proposed, which can provide helical thread models with accurate geometry in order to analyze such important characteristics as the stress distribution along the helix and the contact pressure distributions on the pressure flank. Using the FE models constructed according to the proposed procedure, it is shown how the thread root stress and contact pressure vary along the helix. Also shown is how the imperfect engagement of the mating threads, around the top and bearing surfaces of the nut, affects the circumferential contact pressure distribution at the nut loaded surface and the axial load distribution along engaged threads.