Three-dimensional stress measurement for structural steel plates using ultrasonic T-waves and P-waves

Ultrasonic technology has been widely used in uniaxial stress measurement for key components of steel structures. However, multi-dimensional stresses are described by the combination of unidirectional stresses of multi-directions, failing to reflect the true stress field inside the material. In this study, we proposed a measurement method theoretically and experimentally for average three-dimensional stresses on the cross-section of steel plates. We used ultrasonic T-waves and P-waves for stress separation and deduced the stress-acoustic relation for each stress component. The required phase velocity information was measured by the echo phase spectrum. The acoustoelastic coefficients (AECs) of eight steel specimens were experimentally calibrated. The center frequency of the transducer was selected as the optimal frequency based on calibration experiments, and the thicker the steel plate, the higher the fitting rate. Experimental verifications proved that the proposed method has good reliability on the laboratory scale.