Abstract
Bolted joints sometimes suffer bolt loosening and may sometimes induce accidents. Therefore, bolt loosening detection techniques are essential for many machines and structures having bolted joints. Authors have proposed a new bolt loosening detection sensor using a natural frequency of a thin plate and validity of the sensor is shown by experimental results. However, the sensor is not sensitive in high axial tension condition in other words, early stage of bolt loosening. In this paper, the mechanism of natural frequency change of the sensor induced by axial tension change of the bolt is considered with numerical and experimental results and two sensitivity improvement methods, using conical spring washers and size change of the sensor are studied. As a result, conical spring washers change the contact condition on sensor surfaces and improve sensitivity in early stage of bolt loosening.
