Using longitudinal critically refracted waves to detect absolute stress of steel members considering the influence of temperature

Longitudinal critically refracted (LCR) waves are widely used to detect the absolute stress of steel members in service. The influence of temperature leads to deviation in absolute stress detection. However, existing methods compensate the detected stress by measuring the variations in the acoustic time at different temperatures in zero-stress specimens, which neglects the influence of temperature under different stresses. This study proposes a new ultrasonic method for detecting the absolute stress of steel members considering the influence of temperature. The most important feature of this method is considering the coupling between temperature and stress. A temperature sensitivity experiment was designed to compare the effects of temperature using a one-transmitter-one-receiver (OTOR) transducer group and a one-transmitter-double-receiver (OTDR) transducer group. The absolute stresses of three steel specimens (Q235B, Q345B, and Q390B) were detected at different temperatures to verify the proposed method. The experiment results indicate that the OTDR transducer group has a lower temperature sensitivity of 2.07 ns/°C compared with 14.16 ns/°C for the OTOR transducer group. Using the OTDR group can effectively reduce the negative influence of temperature and improve detection accuracy. The stress coefficient decreases with increasing temperature, and the temperature coefficient increases with increasing stress, which reflects the coupling of temperature and stress. The deviations of the proposed method are within 10 MPa and far less than the deviation of the traditional method. The proposed method can be used in practical steel structures at different temperatures.