抄録
In this study, loosening-fatigue tests under small transverse vibrations have been performed to understand bolt behavior for the long life region. The results show that if a bolt has loosened within 10^3〜10^4 vibration cycles, damage such as crack nucleation at a root of the bolt thread is not observed, and loosening is due to bolt rotation. However, if loosening does not occur until approximately 10^5〜10^6 cycles, then a crack is observed at the root of the bolt thread in the all experiments. Loosening occurs due to loss of axial stiffness caused by crack propagation which then leads to bolt rotation. The results also show that the initial clamping force of bolted joint does not greatly influence the loosening-fatigue life. The amplitude of the transverse vibration force is the most significant influence on the loosening-fatigue life. This indicates that re-tightening a bolt during maintenance is not useful if the bolt has a crack.
