Electromagnetic ultrasonic measurement method for axial force of bolts with non-uniform temperature distribution

This paper proposes a method for compensating bolt axial force measurement in high-temperature non-uniform temperature fields based on equivalent temperature. The method is founded on the principle that the propagation time of ultrasonic wave in a non-uniform temperature field is equal to the propagation time in an equivalent uniform temperature field. By analyzing the sensitivity of longitudinal wave, trailing wave and shear wave to temperature and axial force, the longitudinal wave and trailing wave are used to measure bolt axial force, while the shear wave is used to determine the equivalent temperature. Experimental results show that the proposed method can effectively compensate for the influence of non-uniform temperature distribution and significantly improve the accuracy of bolt axial force measurement. Compared with the uncompensated method and the traditional temperature compensation method, the maximum measurement error is reduced to 4.11 kN, and the maximum relative error is controlled below 7%.