Loosening Lifetime and Residual Clamping Force Prediction Method on Bolted Joints and Evaluation Criterion of Clamping Force Level for Prevention of Loosening Failure

To secure the reliability of bolted joints, high clamping force (axial tension) is required to prevent fatigue breakage or loosening failure, and so on. In this paper, at first, we observe the behavior of the initial clamping force decrease tendency (loosening phenomenon) obtained by tightening the bolt used in the actual machine (large forklift) during operation. Based on our previous research, there is a strong linear relationship on log-log paper of loosening phenomenon between decrease tendency of clamping force and distance travelled (or passage of time). By utilizing its properties, we show estimation method of residual clamping force such as "How much the clamping force is remaining after the tens of thousands of hours (kilometers)?" Also, a method for estimating loosening lifetime with respect to residual clamping force level is shown. Finally, we examine evaluation criteria such as "Is the residual clamping force sufficient for prevention of loosening failure?" The limit surface pressure is examined as the upper limit clamping force. As the lower limit clamping force, the allowable value of the external transverse force is examined.