Stress Measurement of a Pressurized Vessel Using Ultrasonic Subsurface Longitudinal Wave With 1-3 Composite Transducers.

This article aims to develop a stress-sensing method for a pressurized vessel based on subsurface longitudinal (SSL) waves confined in a specific waveform by using 1-3 composite transducers. Although ultrasonic SSL waves have been commonly utilized for stress sensing, wave excitation under the predefined function using the composite-type transmitter is not well studied. In this article, composite-type transducers having a wide frequency bandwidth (> 60%) and a predominant thickness mode are utilized to enhance the signal intensity of the SSL wave and the accuracy of the sensor by incorporating a specific toneburst waveform. Finite element analysis demonstrates that the signal intensity of the composite-type transducer is up to 45.3% higher than that of a single-phase transducer. Pulse-echo tests reveal that the frequency bandwidth of the developed transducer reaches up to 60.7% and is, therefore, sufficient (> 57.0%) to transmit and receive Hanning-windowed toneburst signals. Results of stress sensing affirm a linear relationship between the time delay of SSL wave and the mechanical stress of a pressurized vessel (0.335 ns/MPa). Accordingly, the regression model is constructed via principal component regression (PCR) under temperature-varying condition. PCR has a less significant degree of error (0.62 MPa) compared to that of a typical least square regression (9.49 MPa).