ボルト締結体の締付けおよびゆるみ機構の三次元有限要素法解析

抄録

Bolted joints are widely used in mechanical structures since the disassembly for maintenance is easy without much cost. However, vibration induced loosing due to dynamic loading has been unsolved subject over past six decades. In this paper, we have investigated the mechanisms of bolted-joint tightening process and loosening process due to shear loading in the framework of the three-dimensional finite element method (FEM). Results are compared with the previous theory based on the material mechanics and experimental results. We found some new aspects for bolted-joint theory. Previous theory overestimates the tightening torque in the relation between axial forces and tightening torque. Since the previous theory ignores the extrusion of bolt from nut and the stiffness of jointed material, the load distribution of 1st pitch decreases and that of 4th pitch turns to be minimum. Good qualitative agreement is observed between FEM and experiments with respect to behavior of loosening process subjected to shear loading, such as hysteresis loop of transverse displacement and transverse load and critical slipping distance for gross slip at the head contact surface. It is found that loosening has started when complete thread contact slip has occurred prior to the gross slip at the head contact, which has been considered as an initiation point of loosening. Therefore, the modification of the design of bolted joint is needed.