Abstract

A Study on the Self-Loosening Mechanism of Bolt-Nut Joint and Optimal Design of Anti-Loosening Nut using Finite Element Method

Noo-Ree CHOI
Department of Aeronautical & Mechanical Design Engineering
Graduate School of Korea National University of Transportation
Advisor : Joon HWANG, Ph.D.

This paper outlines the Taguchi optimization methodology, which is applied to optimize the anti-loosening nut design parameters in order to reduce self-loosening rotation angle of bolt-nut joint.
The assembly of bolt and nut is the element most widely used for connecting mechanism and structure. However, if the vibration or shock load or repeated load on the bolt in the early stages of the coupling occurs, it can be loosening occurs tensile force of the bolt coupling portion is reduced. This study developed finite element model to simulate mechanism of the loosening process of bolt-nut joint due to shear loading. In this study, using the hex nut of M10XP1.25, was implemented using the structural analysis to the mechanism of loosening of the nut about cyclic loading.
The parameters evaluated the protrude face length, overall height, side hole radius, overall width for anti-loosening nut geometry design to enforce locking compressive force between bolt and nut threads. The appropriate orthogonal array, signal to noise (S/N) ratio and analysis of variance (ANOVA) are employed to analyze the effect of the mentioned parameters on the rotation angle reduction. The optimized anti-loosening nut design result was obtained with 3.76% mass reduction, 12.85% self-loosening rotation angle reduction, 12.7% equivalent stress reduction which is compared with initial anti- loosening nut design. Using Taguchi method for the design of experiments (DOE), it is investigated the significant influence and the parameters interaction effect with minimum number of trials as compared with a full factorial design.