Session: CT-04-01 Assembly of Bolted Joints-1

Paper Number: 151857

151857 - Self-Loosening Behavior of the Nut Due to Inclination Changes of Bearing Surface 

Abstract: 

The loosening of nuts has been a field of researches for a long time, and many papers and presentations have revealed the principles of loosening and methods for preventing it.

The author has used finite element analysis to study the loosening of various nuts due to various loads, and has presented his findings regarding loosening at many previous PVP conferences. It is well known that alternating loads in the direction perpendicular to the axis are generally considered to cause loosening. For loads perpendicular to the axis, we investigated the anti-loosening effects of not only regular hexagon nuts, but also caulking nuts, eccentric nuts, and slit nuts. As a result, it was found that the reason why the nut loosens is that there is always a gap at the contact surface between the bolt and the nut, and the nut loosens by moving in the radial direction by the amount of that gap. In addition, considering this principle, it is thought that the thermal deformation due to alternating thermal loads causes relative movement in the radial direction of the bolt and nut, and simulations have confirmed that this phenomenon actually happens. The movement of the radial direction is thought to be affected by the coefficient of friction on the screw thread surfaces and the friction coefficient on the bearing surface, and we have reported on this effect previously. Furthermore, we know from experience that alternating loads in the axial direction (tension) usually causes less loosening than alternating loads in the direction perpendicular to the bolt axis, but we have shown that load in the axial direction also causes loosening. It became known that the tilt of the seat has a major effect on this loosening phenomenon. In this paper, we used finite element analysis to investigate whether the alternation of the seat inclination itself causes the nut to loosen.

 The motivation for this research is the accident in which the left rear wheel of a large vehicle drops off, which frequently happens in Japan since the nut tightening method was changed from JIS method to ISO method. The number of drop-off accidents has increased remarkably, and it is necessary to identify the cause of the problem. Many users feel that the problem is the large moment applied to the tire, and we considered how that moment is related to the loosening of the nut. The author considered that a large moment would cause the tire wheel to tilt, which would also affect the amount of tension. This phenomenon is particularly considered to occur during sharp left turns, where the tire, especially real left tire, experiences an opposite tilt and changes in tension during one revolution. Therefore, the author believes that if he can show that the nut loosens when the seat inclination alternates and the tension changes at the same time, this will help us investigate the cause of the problem.

In this paper, we report that nut loosening occurs due to alternating seat inclinations, and how the magnitude of the inclination and bolt tension affect this.

Presenting Author: Yasumasa Shoji YS Corporation LLC

Presenting Author Biography: He graduated from Keio University and received BS and MS in 1982 and 1984, respectively. He received PhD from Nagoya University in 1993.
After graduating from Keio University, He worked in 5 companies in plant engineering, mechanical components and systems, and software development for totally 30 years, and he established YS Corporation in 2014 and now he is still the CEO..
His interests in research field are bolted fasteners and other mechanical components.
Based on his carrier, he conducted many analyses and training of younger engineers.
He was the conference chair of the PVP2024.

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