Bolt for ultrasonic axial tension measurement

Abstract

Both end surfaces of a head portion and an axial portion of a bolt are formed into a curved surface having a predetermined curvature in order to provide a bolt which allows accurate axial tension measurement without changing various settings of an axial tension detection device. Upon ultrasonic radiation applied from a piezoelectric element into a top surface of a head portion of the bolt, the top surface thereof serves as an ultrasonic lens to allow ultrasonic propagation in convergence within the bolt. If the bottom end surface of the axial portion of the bolt is formed into a curved surface, the bottom end surface thereof will also serve as the ultrasonic lens to allow propagation of the reflection to return to the piezoelectric element in convergence. The ultrasonic propagation path within the bolt is not diffused, which allows the ultrasonic radiation to be reflected from the bottom surface of the axial portion of the bolt so as to be detected by the piezoelectric element. The axial tension, thus, can be measured with great accuracy.

Dependencies are inferred from the claim text.