Stress in bolt and nut (Effects of contact condition at the first ridge)

Abstract

Effects of the contact condition at the first ridge on mechanical behaviors of threaded portions are analysed by an axi-symmetric FEM which can deal with the three-body elastic contact problem including the effects of friction on two contact surfaces between threads of bolt and nut, and between fastened plate and nut. Since the cross sectional shape of nut at the first ridge changes circumferentially due to the lead angle of thread, it causes non-symmetric mechanical behaviors concerning the ratio of flank load and the stress concentration at the root of bolt. Four types of models are used to estimate these non-symmetric properties approximately. Each of them represents the cross section rotated one fourth revolution around the axis. The analytical object is composed of bolt, nut and fastened plate, and only the shape of nut is changed. The analysis is done by the axi-symmetric FEM ignoring the effects of lead angle. The ratio of flank load and the stress concentration at each cross section show some remarkable effects of the non-symmetric behaviors.