A Bolt-Nut Loosening Mechanism in Bolted Connections Under Repeated Transverse Loadings (Effect of Inclined Bearing Surfaces on the Loosening)

Abstract

Loosening accidents sometimes occur under several types of loadings such as winds, vibrations, earthquakes, impact loads and thermal changes. Recently, some studies have been conducted on the screw thread loosening in bolted joints under repeated transverse loadings. It is well known that bolted joints are easily loosened when repeated transverse loadings are applied. While, in assembling bolted joints, the contact surfaces between a bolt head/nut and a clamped part are inclined geometrically. However, a lot of researches have dealt with the bolted joints in which the bearing surfaces are perfectly contacted without the inclined surfaces. Thus, it is necessary to examine the incline of the bearing surfaces on the loosening in bolted joint. A lot of parts for preventing the loosening have been proposed and sold at market. Among these parts, the authors have demonstrated that eccentric nuts are especially expected to be the solution for preventing the loosening of the joints under repeated transverse loadings. However, a few studies have been carried out on the loosening and loosening mechanism in bolted joints with inclined bearing surface and the effective solution for preventing loosening of bolted joint with the inclined bearing surfaces under the repeated transverse loadings. Thus, it is necessary to examine the effect of the incline at the bearing surfaces on the loosening and to evaluate the solutions for preventing loosening of the bolted joints with the inclined bearing surfaces. In this study, the effect of the incline at the bearing surfaces on the loosening is examined using FEM calculations. In the FEM calculations, the incline angle at the bearing surfaces is changed as 0, 2 and 3 degree, respectively. The experiments to measure the loosening in bolted joints were carried out using Junker’s testing machine to validities of the FEM calculations for revealing the effect of the loosening in the joints with the inclined bearing surfaces. In addition, nut parts for preventing the loosening in bolted connections with the inclined bearing surface under repeated transverse loadings are examined using the FEM calculations. As the result, it is seen that the loosening increases as the angle of incline increases. In addition, it is observed that bolted joints in which almost nut parts for preventing loosening are applied are loosened easily while the eccentric nut does not loosened. Discussion is made on the loosening mechanism in bolted joints under repeated transverse loadings.

Review of research on loosening of threaded fasteners

“…The relationship between the loosening and load amplitude, the initial preload, and the friction coefficient was discussed. In addition, Sawa and Ishimura [118] studied the effects of the inclination angle of the bearing surface on loosening.…”

Study on Tightening, Anti-Loosening, and Fatigue Resistance Performances of Bolted Joints with Different Anti-Loosening Washers and Nuts

“…Typical products include wedge-locking and variable-diameter nuts. Third, two nuts are employed to be fastened to a bolt to achieve excellent anti-loosening performance [35][36][37], including normal double nuts, eccentric double nuts, and double-thread bolt connections (a double-thread bolt and two nuts). The shapes of internal threads in eccentric double nuts are unchanged, but there is an eccentricity in eccentric double nuts, and the outer structures of the two nuts differ from the properties of normal double nuts.…”

Concept of radial slippage propagation triggering self-loosening and optimisation design of novel anti-loosening structures

“…The latter mainly consists of wedge locking nuts, prevailing torque nuts, eccentric double nuts, and double nuts. They have been demonstrated to provide superior anti-loosening abilities [28][29][30][31]. In the transversal vibration experiment or finite element (FE) simulation, the preloads decrease very slowly or remain almost unchanged with the increase in vibration cycles.…”