Verification of Anti-Loosening Performance of Super Slit Nut by Finite Element Method

Abstract

We have developed a new nut named 'super slit nut (SSN)′, which realizes anti loosening performance without complicated tightening procedures. In this study, tightening behavior and loosening behavior caused by shear load are analyzed by mean of three-dimensional finite element method. It is found that SSN has a prevailing torque of 15 to 19 Nm, which closely agrees with experimental data. The load distribution of thread depends on the rotation angle of nut. At the angle of 24.6 degree, the distribution of 1st pitch turns to be 10% larger than that of conventional nut, reflecting the decrease in the thread at slit region. It is also found that the antHoosening performance cas be realized by the thread contact force at the slit region. Since its contact force does not depend on the tightening force, the effect of antHoosening performance drastically increases as the tightening force is decreased. Shear fracture would initiate not at slit region but at the bottom of 1st thread, whose stress is about 10% larger, as compared with conventional nut. Moreover, by mean of tensile and fatigue experiments, it is concluded that SSN involves sufficient strength in practical use. © 2005, The Japan Society of Mechanical Engineers. All rights reserved.