Ultrasonic measurement on axial force of high-strength bolt in service

In order to reduce the effect of delayed fracture of high-strength bolts on train operation and structural safety, a non-destructive testing method for axial force of high-strength bolts in railway steel bridges is studied to identify and replace over-twisted bolts in time, so as to reduce the probability of delayed fracture caused by external factors. Based on the acoustic-elastic effect theory, considering the uneven internal stress distribution of bolts in service, in this paper, the bolt force area is differentiated into three regions: the nut, the screw and the thread; the author calculates the ultrasonic flight-time in different bolt stress areas and revises the impact of bolt elastic deformation and temperature by external force on sound speed and puts forward a more precise measurement method of axial force of bolt in service. According to the results of the test, the relative error between the ultrasonic measurement result and the displayed value of pressure sensor is less than 10%.