Demonstration of low-frequency vibration tests to evaluate bolt loosening

This study proposes a simple and cost-effective method to detect bolt loosening on the basis of low-frequency vibration signals as low as several hertz. Laboratory tests were conducted using M16 bolts connecting two SS400 plates. The bolts were vibrated by external impulse using a test hammer, and their vibrations were measured using accelerometers attached to the nuts holding the bolts. The accelerometers had the lowest measuring frequency of 0.5 Hz, and no high-pass filter was used. The results of the tests show that one can confirm whether or not bolts have been tightened to the rated torque quite clearly in time domain signals. Subsequent field tests were conducted to evaluate the M42 anchor bolts in a factory, and the results demonstrate the effectiveness of the method.