Proposition of Helical Thread Modeling With Accurate Geometry and Finite Element Analysis

Distinctive mechanical behavior of bolted joints is 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 software. The mesh patterns so obtained are, therefore, 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 a helical thread model with accurate geometry in order to analyze such important characteristics as stress concentrations and contact pressure distributions along the thread helix. Using the FE models with accurate thread geometry, it is shown how the thread root stress and contact pressure vary along the helix and nut loaded surface and how the chamfering of the top threads of the nut mitigate the stress concentration concerned.