Bolt Loosening Behavior of Bolted Joints Under Repeated Transverse Loads

Abstract

The objective of the paper is to examine bolt loosening behavior in a bolted joint under transverse loading both experimentally and numerically. Bolt loosening tests were carried out using Junker’s type loosening machine. In the Junker’s loosening tests, repeated transverse displacements (displacement range S = ±0.35mm were applied to a bolted joint with a M10 hexagon bolt and nut, and then a reduction in the axial bolt force was measured. In the FEM calculations, bolt loosening behavior was examined for a model of Junker’s type loosening machine. In addition, the effects of the flatness and the surface roughness at the bearing surfaces in a clamped part on the reduction in the axial bolt force were examined in the FEM calculations. As a results, it was found that the nut rotation occurred when a glider plate moved toward to the center of the joint from the right and the left dead points. In addition, bolt loosening mechanism was elucidated using the change in the contact stress distribution at the engaged screw threads. The reduction in axial bolt force was found to be the largest for the first 1 cycle loading and then it decreased gradually as the loading cycles increased. An amount of the reduction in the axial bolt force was predicted in the FEM calculation taking account of the flatness (inclined of clamped part) and the surface roughness (contact surface ratio) in 10 loading cycles. The contact surface ratio (surface roughness) was found to significantly affect the reduction in axial bolt force. The predicted results were in a fairly good agreement with the experimental results. Furthermore, the effects of the grip length and the nominal bolt diameter were examined on the bolt loosening behavior experimentally.

Finite Element Analysis of the Load Factor and New Design Method for Bolted Joints Consisting of Dissimilar Hollow Cylinders Under Tensile Loads

“…In an actual design of bolted joints, it is important how to determine the nominal diameter d of bolt, the bolt strength grade (classification), and the bolt preload under given conditions such as an external tensile load W, the material of joint members, required interfacial contact stress r c , and a tightening coefficient Q (scatter in preloads) [1,17]. In designing bolted joints, the following items should be satisfied for achieving the joint function and integrity.…”

“…As an external tensile load increases, the contact stress at the interfaces between the joint members decreases, and then a separation of the interfaces starts. When the interfaces start to separate, a possibility of bolt loosening occurs [17]. Bolted joints in practice of which the interfacial contact stress is reduced under external axial tensile loads are sometimes subjected to some unexpected external loads such as transverse loads, impact loads, and thermal loads.…”

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