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Simulation of ultrasonic measurement on a bolt in a shear joint

An instrument called the ultrasonic extensometer is used to measure tensile preload in bolts used in structural joints. In this paper, the same instrument is used in a different way to measure change in the ultrasonic measurements due to bending in the bolts. A theory and numerical model for the ultrasonic measurements are developed. The bending load results in a rotation and translation of the ultrasonic pulse reflecting face. The load also creates a stress gradient in the bolt. This results in a phase variation (or gradient) in the received ultrasonic beam across the face of transducer. The load also results in a physical shift in the received beam relative to the ultrasonic transducer. The phase gradient and shift in the beam cause a change in the pulse transit time. A numerical example chooses a bolt whose experimental preload characteristic had been published previously by the author. The example displays simulated ultrasonic waveforms before and after subjecting the bolt to bending loads. The simulated preload characteristic was compared to the experimental characteristic. The two characteristics indicate some agreement.