A New Detecting Method of Clamping Force of Bolted Joint

Loss of the clamping force of bolted joints in service causes fatigue failure. Accurate detection of the clamping force by existing methods is not easy. In this study, a new method of detecting the clamping force of bolted joints in service after tightening is proposed. In the proposed method, the clamping force is detected by pulling the bolt threads with protruded through the nut. During the pulling process, the nut is pressed to the opposite direction and the variation of the apparent spring constant of the bolted joint is measured. At the moment, when the pulling force reaches the clamping force of the bolted joint, the apparent spring constant varies drastically. The clamping force of a pre-tightened bolted joint was detected experimentally by the proposed method and the value was compared with those obtained by an existing method. It is shown that the accuracy of the present method is much better than other method and the error was estimated to be less than ± 10%.