Acoustic Attenuation

We have systematically investigated the elastic properties (ρ, VP, VS, K, μ and σ) of eight SiO2–TiO2 glasses, varying in composition from 1.3 to 14.7 wt% TiO2, as a function of pressure up to 0.5 GPa by the pulse superposition (PSP) ultrasonic technique, and two compositions (1.3 and 9.4 wt% TiO2) up to ~5.7 GPa by Brillouin scattering in a diamond anvil cell. The parameters were also measured after annealing to 1020 °C. Composition–elasticity relationships, except for K and σ, are more or less linear; the annealing simply makes the relationships more uniform (less scatter). There is excellent agreement between the ultrasonic and Brillouin measurements at ambient and high pressure. The pressure-induced anomalous elastic behavior (negative dVP/dP and dK/dP) becomes more negative (more compressible) with the increasing TiO2 content. Correspondingly, the acoustic Grüneisen parameters become more negative with increases in the TiO2 content, reaching a minimum near ~8–10 wt% TiO2. The c...

... Editorial Board Dr. Richard H. Nadolink, Chairman Dr. Ding Lee Dr. James CS Meng Dr. Albert H. Nuttall Dr. Norman L. Owsley Dr. Bruce E ... where s is a general surface coordinate along the generator line of the axisymmetric structure, ani and bni are constants, I = Ix +12 + Is is ...

The paper deals with the determination of geometric parameters for studying the relationship between tire-road noise and texture of road surfaces. The approach was found to be an alternative to classical spectral analyses and numerical simulations of the tire-road contact. Texture parameters were derived from previous works at the Laboratoire Central des Fonts et Chaussées related to the influence of the microtexture of road surfaces on skid resistance. Use of these parameters was justified by consideration of generation mechanisms of rolling noise. Texture, rolling noise, and absorption measurements were performed on 12 road surfaces. The measuring devices and the test methods produced texture profile analyses, including the spectral and geometric approaches. Geometric parameters were defined. Correlation between the noise and texture spectra showed results similar to those published in previous works. Fair tendencies were found between the global noise level at 90 km/h and the geo...

ABSTRACT LEED beam intensities were measured from the freshly cleaved (in UHV) Mg0(001) surface using beam energy modulation to avoid electrical charging. Dynamic LEED analysis of the data indicates: (1) an interlayer relaxation of (1 {plus minus} 2)% and a rumple of the first layer ions of (5 {plus minus} 2.5)%; (2) a new attenuation model containing no adjustable parameters gives fits to the data that are comparable to those using a constant V{sub i}; (3) a weak dependence of the optimum rumpling on the energy range of the data used. The structure determined in this study is compared to others reported in the literature for this surface, and the effects of lattice vibrations, attenuation length and number of surface layers treated exactly are considered. 26 refs., 4 figs.

FELTMETAL® fiber metal acoustic materials function as broad band acoustic absorbers. Their acoustic energy absorbance occurs through viscous flow losses as sound waves pass through the tortuous pore structure of the material. Exhaust gas noise attenuation requirements are reviewed. Their selection process for higher performance materials is discused. A new FELTMETAL® fiber metal acoustic material has been designed for use in gas turbine auxiliary power unit exhaust environments without supplemental cooling. The physical and acoustic properties of mesh supported fiber metal acoustic medium FM 827 are discussed. Exposure testing was conducted under conditions which simulated auxiliary power unit operation. Weight gain and tensile strength data as a function of time of exposure at 650‡ C (1202‡ F) are reported. Fabrication of components with fiber metal acoustic materials is easily accomplished using standard roll forming and gas tungsten arc welding practices.