Finite Element Analysis of the Cyclic Stress Amplitude of Wheel Bolts for Large Vehicles

Abstract

Tire coming-off accidents from large vehicles are primarily caused by the fatigue failure of wheel bolts, by which the tire wheels are clamped to the hubs of the shaft. In the previous study, stress amplitudes occurred in wheel bolts were measured using a full-scale test equipment, which was constructed utilizing an actual trailer. In the experiments, the thread ridges of the wheel bolts were partly removed and the portion was machined into cylindrical shape in order to attach strain gauges. To examine the fatigue mechanism in more detail, it is necessary to evaluate the stress amplitudes at thread root, where the fatigue failures of threaded fasteners usually occur. In this study, the stress amplitudes at thread root are analyzed using three-dimensional FEM. Threaded portions are modeled using fine meshes to evaluate the stress amplitudes generated in both wheel bolts and inner nuts with sufficient accuracy. The magnitudes of the live loads, which exert alternating external forces on the wheel bolted joints, are varied so as to cover from the normal condition to the over-loaded ones. It has been found that the maximum stress amplitudes at the threat root significantly increase when the initial clamping force decreases as low as 30% of the prescribed value, which is also exaggerated with larger friction coefficient at contact surfaces around wheel bolted joints. The validity of the numerical analysis is confirmed by comparing the numerical results of the stress amplitudes on the wheel bolt surface with those by experiments.