| 摘要 |
PURPOSE:To improve the accuracy of measuring axial force by ultrasonic waves so as to facilitate the control of the axial force and to improve the reliability of tightening by applying prestrain attaining 105-130% of the target tightening axial force to a lock bolt body made of an austenitic stainless steel. CONSTITUTION:The lock bolt 1 made of the austenitic stainless steel is set between jigs 5a and 5b by using a nut 2 and the tensile force as shown by arrows is loaded to the jigs 5a, 5b to apply the prestrain attaining 105-130% of the target tightening axial force to the bolt. Such bolt a1 is inserted into bodies b1, b2 to be fastened and is tightened and fastened by screwing down of the nut c. A sensor to transmit and receive the ultrasonic waves is set to one end face of the lock bolt before and after such bolt tightening and the propagation time of the reflection wave reflected from the other end face is measured. The difference of the propagation time before and after the tightening is measured, by which the axial force F is determined.
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