The University of Tokyo Department of Mechanical Engineering,Fracture Mechanics Laboratory.SAKAI & IZUMI group.


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Finite Element Analysis for bolt-nut joint system

Threaded fasteners 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. We have investigated the mechanisms of 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 conventional theories based on the material mechanics and experimental results. We found some new aspects for threaded fastener theory. Good qualitative agreement is observed between FEM and experiments with respect to the behavior of loosening subjected to shear loading, such as hysteresis loop of transverse displacement and shear load and critical slip width for complete bolt-head slip. It is found that loosening initiates when complete thread slip has occurred prior to the head slip, which has been considered as an initiation point of loosening. Therefore, the modification of the design of threaded fastener is needed.

Bolt-nut loosening simulation (contour indicates horizontal displacement)

Bolt-nut tightening simulation (contour indicates axial stress)

Bolt-nut loosening simulation

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