Three-dimensional finite element analysis for prevailing torque of bolt-nut connection having slight pitch difference

Abstract

In a vast industrial field, the bolt-nut connection is widely used and unitized as an important machine component. In order to improve safety and for cost reduction, cheap bolt-nut connections with excellent anti-loosening performance are always needed. In this paper, the slight pitch difference is considered between the nut and bolt threads to improve the anti-loosening by focusing on the prevailing torque Tp. In the first place, during the nut screwing process, the bolt axial force Fa caused by the pitch difference is examined because previously Fa was studied by the axisymmetric FEM simulation as a substitute of the prevailing torque Tp. Next, the prevailing torque Tp is directly analyzed by changing the pitch difference through the 3D FEM simulation. The obtained prevailing torque needed for the nut rotation is in consonance with the measured value experimentally. By considering manufacturing error sometimes included, finally, the real pitch difference or of the nut is identified from the number of nut thread in contact with the bolt thread, which is measured experimentally. Then, the correctness of this α is confirmed through the prevailing torque obtained by 3D FEM simulation.