Estimation of sound velocities from resonance measurements on tungsten carbide calibration spheres
| Autor: | J.R. Dunn, D.N. MacLennan |
|---|---|
| Rok vydání: | 1984 |
| Předmět: |
Materials science
Acoustics and Ultrasonics business.industry Mechanical Engineering chemistry.chemical_element Resonance Condensed Matter Physics Computational physics chemistry.chemical_compound Optics Amplitude chemistry Mechanics of Materials Tungsten carbide Calibration SPHERES Target strength business Cobalt Temperature coefficient |
| Zdroj: | Journal of Sound and Vibration. 97:321-331 |
| ISSN: | 0022-460X |
| Popis: | Tungsten carbide spheres have been used as reference targets to calibrate echosounders. The target strength depends upon the longitudinal and transverse stress wave speeds, c1 and c2, in the sphere. These may be estimated from the resonance frequencies, which can be measured precisely given two or more resonances whose coupling characteristics are sufficiently different to provide well conditioned equations for these wave speeds. The resonance frequencies may be measured by sampling the echo amplitude or by spectrum analysis. The latter method is more accurate but requires more sophisticated equipment. The measurements have been corrected to remove the bias resulting from the finite bandwidth of the apparatus. Experimental results are given for 11 spheres 38·1 mm in diameter containing a nominal 6% of cobalt binder, procured in two batches from different production runs. Both stress wave speeds are significantly different between but not within the batches, and likewise the sphere density which indicates variation of the cobalt content. For a density of 14 900 kg m−3 (6% cobalt) and at 11°C, c1 and c2 are estimated to be 6853 ± 19 and 4171 ± 7 m s−1, respectively, within 95% confidence limits. Empirical equations are presented for the speeds as functions of density. The temperature coefficient of c2 is estimated to be −1·3 ± 0·6 m s−1°C−1. These results demonstrate the high accuracy of the resonance technique for estimating the stress wave speeds in spheres. The small differences observed between the spheres would have a negligible effect on the target strength at 38 kHz. |
| Databáze: | OpenAIRE |
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