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Ultrasonic Velocity Measurements of Engineering Plastic Cores by Pulse-echo-overlap Method Using Cross-correlation
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An automated ultrasonic velocity measurement system adopting pulse-echo-overlap (PEO) method has been constructed, which is known to be a precise and versatile method. It has been applied to velocity measurements for 5 kinds of engineering plastic cores and compared to first arrival picking (FAP) method. Because it needs multiple reflected waves and waves travel at least 4 times longer than FAP, PEO has basic restriction on sample length measurable. Velocities measured by PEO showed slightly lower than that by FAP, which comes from damping and diffusive characteristics of the samples as the wave travels longer distance in PEO. PEO, however, can measure velocities automatically by cross-correlating the first echo to the second or third echo, so that it can exclude the operator-oriented errors. Once measurable, PEO shows essentially higher repeatability and reproducibility than FAP. PEO system can diminish random noises by stacking multiple measurements. If it changes the experimental conditions such as temperature, saturation and so forth, the automated PEO system in this study can be applied to monitoring the velocity changes with respect to the parameter changes.
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We report an evolution of an all-digital ultrasonic pulse technique for measurements of elastic constants of solids. An unambiguous analytical procedure is described for determining the correct time delay of echoes without any need for actual echo overlap. We also provide a simple procedure for making corrections for transducer-bond-induced phase shifts. The precision of a measurement made with this system at ambient temperature exceeds one part in 107 without the use of mixers, gates, time delays, and other complications normally associated with such measurements.
Summary A new improvement of the sing-around technique for the measurement of the speed of ultra-sounds in liquids and solids is presented.
This is accomplished by using a differentiation method in order to stabilize the trigger point of the singing pulse. Measurements
of velocity in bidistilled water are carried out using this technique in order to evaluate its performance. Satisfactory results
are obtained.
A new apparatus for the measurement of ultrasonic speed in compressed liquid was constructed. The reliability of this instrument was confirmed by measuring the speeds in pure benzene in the ranges from 283.15 to 323.15 K and pressures up to near freezing pressure, and by comparing the results with literature values. The isentropic compressibilities κS were also determined using the experimental speeds and densities, and the results κS(u) were compared with those observed directly elsewhere κS(d) and those calculated thermodynamically κS(c) from (p, Vm, T). At atmospheric pressure, the present results, while agreeing with κS(u) reported in the literature, show differences from κS(d) and κS(c), while those for higher pressures close on a simple curve with κS(c).
An improvement of the pulse‐echo‐overlap (PEO) method is proposed to make it accessible for computer control. The modification makes it possible to avoid the systematic and subjective errors of the original PEO method. A digital oscilloscope and a frequency synthesizer is controlled by a personal computer providing a fast automatic method for determination of ultrasonic wave transit times. Description of the method and the computer program, as well as the technical parameters is given. The Panametrics 5053A ultrasonic time intervalometer has been slightly modified to be applicable in the new configuration with a better precision. The 0.5 ppm precision velocity determination in water requires a 0.0003 °C level temperature control and reproducible wettability of the surface of the transducer. For both problems, a practical solution is proposed. Error analysis shows that the reproducibility of measurements is within 0.5 ppm.
A completely stand‐alone pulse‐echo‐overlap system which can be easily built using commercially available integrated circuits is described. The system uses a broadband pulse to excite the transducer. The equipment is relatively cheap and yet the sensitivity of the transit time (and, hence, velocity of sound measurement), is made high by making use of a digital frequency synthesizer of 0.01‐Hz resolution, specially constructed for this purpose. Except for the oscilloscope the instrument does not require any other equipment for its operation.
A new instrument is described which permits the travel time of ultrasonic waves to be measured accurately and conveniently by the pulse‐echo‐overlap method (PEO). The accuracy and versatility of the PEO method are reviewed, and optimal methods of preparing and interrogating samples are presented. Extensive data on a large blank of fused silica are presented. Longitudinal and shear wave velocities were calculated from the wave travel times through measured thicknesses, and the elastic moduli were subsequently calculated from the velocities and the measured density. Error analysis shows that the measurement of travel time contributed less than 20 ppm to the total error of about 400 ppm in the calculated moduli.
Ultrasonic velocity measurements have been used to estimate average grain size in an AISI type 316 stainless steel. For precise ultrasonic transit time measurements, the pulse-echo-overlap technique has been used. Master graphs relating ultrasonic velocity with metallographically obtained grain size have been generated. Using these graphs, grain sizes in new specimen have been obtained. The results indicate that grain size can be predicted with good confidence level using ultrasonic velocity measurements. Shear waves are found to be more sensitive for grain size measurement, as compared to longitudinal waves. The grain size estimated by velocity measurements is found to be more accurate when compared to that obtained by attenuation measurements.
An ultrasonic apparatus for the measurement of the speed of sound in pure liquids is described. To test its performance the speed of sound in several liquids at 298.15 K was measured and the results were compared with literature values. Isentropic compressibilities ks were also calculated from the experimental results and for the n-alkanes the variation with the chain number of atoms was studied.