Improvement in Sensitivity of Thin Plate Sensor for Bolt Loosening on Early Stage

Abstract

Bolted joints sometimes suffer bolt loosening and may sometimes induce accidents. Therefore. bolt loosening detection technologies are essential for many machines and structures having bolted joints. Authors have proposed a new bolt loosening detection sensor using a natural frequency change of a thin plate and validity of the sensor is shown by experimental results. However, it is difficult to detect the bolt loosening on early stage because the sensor is not so sensitive in high axial tension condition. In this paper. the mechanism of natural frequency change of the sensor induced by axial tension change of bolt is investigated with numerical and experimental results and two sensitivity improvement methods, using conical spring washers and size change of the sensor are examined. The results show that size change of the sensor is not effective for improvement of the sensitivity on early stage of bolt loosening and that conical spring washers change the contact area on each sensor surface and can improve the sensitivity on early stage of bolt loosening.