Critical Excitation of the Fundamental Quasi-Shear Mode Wave in Waveguide Bars for Elevated Temperature Applications

Abstract

The safety of critical pressure equipment in elevated temperature is increasingly important. Moreover, the on-line monitoring method is potentially useful to improve their safety. A waveguide bar system can enable monitoring of critical equipment working in elevated temperature using reliable ultrasonic technology. Among the waveguide bar system, the matching mechanism of the transducer and the waveguide bar is crucial to propagate the pure fundamental quasi-shear mode (shorten for SH0*) wave. In the present research, the loading line sources that can excite pure SH0* wave are investigated and the anti-plane shear loading source is selected. The critical values about the geometric dimensions of the junctions between the piezoelectric transducer and the waveguide bar are explored by simulation and experiments. On the condition that the excitation sources satisfy the critical values, the loading can be approximated to an anti-plane shear one to excite the pure SH0* wave. Some waveguide bar systems are designed based on the simulated critical values and some experiments at high temperature are carried out. The experimental results verify that the designed waveguide bar systems can excite the pure SH0* wave at elevated temperatures, which verify the reliability of the simulated critical results.

Optimal Design Methodology of Tapered Waveguide Transducers for Thickness Monitoring

“…A tapering waveguide unit can be defined by four parameters. The length depends mainly on the temperature of the specimen, the width and thicknesses of the thin end, and the thick end will affect the dispersion of waves [20,24]. In this section, our focus concentrates on the propagation of the SH0* mode wave, while the temperature was not considered in the present research.…”

“…Moreover, if the wafers are mounted on the side surface of the waveguide units, the A0* and S0* modes will be excited, accompanying the SH0* wave [16]. However, the pure SH0* wave can be excited when the wafers are installed on the end side of the units [20]. Therefore, in order to excite pure SH0* mode wave, a specially engineered tapered waveguide transducer is proposed in the present research.…”

Brazing Coupling Performance of Piezoelectric Waveguide Transducers for the Monitoring of High Temperature Components

“…Lawren advised the fusion welding of the metallic bar onto the test piece for high temperature monitoring [ 23 ], but Cegla proved by experiments that the welding will diffuse the waves [ 24 ]. Dry-coupling has been verified as a useful method for waveguide transducers [ 25 ], but the wave transmission efficiency cannot meet the needs for the thickness measurement of some important equipment [ 26 ]. In order to find a reliable coupling method to monitor critical equipment working in harsh environments, several brazing materials were tested by experiments in the present research.…”