Abstract
It is considered that contraction deformation of bolt is one of the causes of loosening in a boltnut unit. In this paper, radial deformation of bolt shank which consists of the mating thread portion and the other, is examined analytically and experimentally. First, a method is proposed to analyze the deformation of the bolt shank in a bolt-nut unit under the axial load, and the radial deformation of bolts shanks is calculated by this method. Second, the validity of the numerical analysis is confirmed by some experiments with strain gauges. As a result, it is revealed that mating thread of bolt shank contracts in a radial direction by the force acting on mating thread ridges and Poisson's ratio under tensile load. Especially, its contraction deformation is large at the part of bearing surface for concentration of load, while the rest of bolt shank contracts almost uniformly with Poisson's ratio.
