Mechanism of Rotational Screw Thread Loosening in Bolted Joints Under Repeated Temperature Changes

Abstract

Bolted joints have been used in mechanical structures. However, loosening accidents sometimes happen under several types of loadings. Recently, some studies have been conducted on the screw thread loosening in bolted joints. It is verified that bolted joints are loosened when transverse repeated loadings are applied. Some studies on no rotational loosening in bolted joints under thermal changes have also conducted. However, few studies on rotational screw thread loosening in bolted joints have conducted. In this study, rotational screw thread loosening in bolted joint under repeated temperature changes is examined. Effects of the linear thermal expansion coefficient of clamped parts and number of repeated temperature changes are examined by the measurements and finite element analyses. In the experiments, a bolted joint, which consist of two rectangular plates fastened at room temperature by two bolts and nuts, are put in a furnace and heated by an electric heater. Then, the bolted joint is cooled at room temperature. These thermal cycles are repeated. Bolt temperature and bolt load were measured. Loosening is evaluated from the reductions in the bolt load. Finite element analyses were carried out for clarifying the loosening mechanism. Discussion is made on the mechanism of rotational screw thread loosening in bolted joints under repeated temperature changes. The results show that loosening occurs under repeated temperature changes due to difference in the linear thermal expansion coefficients of the different clamped parts.

Research Progress on Influencing Factors of Bolted Joint Structure Loosening

“…The results show that under the action of high temperature and transverse vibration load, the axial force of the bolt decreases rapidly at first and then decreases at a stable rate. Sawa et al [45,46] investigated the effects of the linear expansion coefficient and the number of cyclic temperatures on the axial force of bolts by experimental and finite element methods. The results show that under cyclic temperature load, due to the difference in thermal expansion coefficient between the connecting piece and the connected piece, the degree of thermal deformation is inconsistent, and relative slippage occurs between the contact surfaces.…”

A Mathematical Model for Temperature Induced Loosening due to Radial Expansion of Rectangle Thread Bolted Joints

“…There are two main modes for relative motions caused by expansion difference: (1) relative motions between clamped parts caused by their expansion difference; (2) slippage between thread contact surfaces while inner and outer threads expand differently. The first one works as transversal load [4,5] on the joints, and transversal load induced loosening has been studied by many researchers. Radial expansion difference between inner and outer thread may cause relative slippage.…”

“…The first one works as transversal load [4,5] on the joints, and transversal load induced loosening has been studied by many researchers. Radial expansion difference between inner and outer thread may cause relative slippage.…”