Non-uniform absolute stress field detection of H-shaped steel beam based on multi-acoustic path and multi-frequency longitudinal critically refracted waves

Abstract

The internal stress field of steel members exhibits spatial distribution in multiple dimensions under complicated boundaries and loads. However, the existing ultrasonic detection method only considers the variation of parallel stress on acoustic velocity and neglects the effects of multi-dimensional stress. Meanwhile, the existing methods measure the average stress along the propagation path. Due to sensor size and propagation path limitations, existing ultrasonic methods fail to detect non-uniform stress fields accurately. A modified method based on multi-acoustic paths and multi-frequency LCR waves for detecting non-uniform stress fields in H-shaped steel beams is proposed. The main innovations in response to the shortcomings of existing methods are as follows. Firstly, by considering the coupling effect of plane stress components on the acoustic time of LCR waves, a new non-uniform absolute stress field detection equation containing three components of plane stress is derived. Then, by moving the position of the second receiver sensor of the one-transmitter-double-receiver (OTDR) sensor group, the acoustic time difference between two different paths of LCR waves is calculated, thereby shortening the acoustic path length of LCR waves and improving the spatial resolution. Finally, a detection model for stress distribution in the thickness direction is established. By changing the center frequency of LCR waves, the propagation of LCR waves at different depths can be controlled, thereby achieving the detection of stress distribution in the thickness direction of steel plates. A non-uniform absolute stress field of the H-shaped steel beam is detected to verify the proposed method. The experimental results demonstrate that the relative deviation between the proposed method and the strain gauge method is less than 15 %, which is lower than the existing ultrasonic methods. The proposed method has higher accuracy and spatial resolution in non-uniform absolute stress field detection than existing ultrasonic methods.