Acoustic damping

The temperature for the acoustic damping capacity change from Nitinol was found to be different for alloys that were prepared at different laboratories (even though both alloys have identical composition). Further, the shape memory response to temperature change, such as how fast and how much force, also varied a great deal from one alloy to another. 

A number of unique physical property changes such as memory effect and acoustic damping capacity changes etc. associated with Nitinol transition have been known [47,48]. Here are some additional observations that are not well known [49] but show once again the support for the model presented for the Nitinol transition. 

Hartmann B, "Relation of Polymer Chemical Composition to Acoustic Damping" In Corsaro RD and Sperling LH (Eds), "Sound and Vibration Damping with Polymers", ACS Symposium Series 424, ACS Press, Washington DC, 1990, Chap. 2. 

Relation of Polymer Chemical Composition to Acoustic Damping... 

Acoustic damping in polymers is shown to be dominated by the glass transition occurring in the amorphous portions of the polymer. 

Measurements of acoustic damping have been reported in the literature for numerous polymers under a variety of temperature and frequency conditions. Based on a study of these results, a number of conclusions have been reached ... 

In this report we demonstrate the utility of the procedure for multiplexed data. The usefulness of the procedure for resonant data was the topic of previous publications (ii8). Using data for typical samples of amorphous polymers, poly(methyl methacrylate) (PMMA) and polycarbonate (PC), the procedure is shown to be well suited to the transition region. A Poly(vinyl chloride) (PVC) acoustical damping material is used to demonstrate the ability to change the data reduction equation (the WLF equation) parameters and their subsequent effects on the fit of the superposed data. 

Finally, a proprietary poly(vinyl chloride), (PVC) based acoustical damping material was characterized using the DMA 983. Frequencies tested were 0.033, 0.10, 0.320, and 1.0 Hz at temperatures ranging from -80 to 80 C. The sample dimensions were 17.22 x 14.13 X 3.17 mm. 

The utility of empirically determined WLF equations was investigated using DMA data obtained on the PVC acoustical damping material. Using a separate software package (available from DuPont Intruments), E, E" and tan 8 were empirically fit using the time-temperature superposition procedure. A reference temperature is first determined by the computer software. The data are then shifted manually and the WLF equation is fit to the resulting temperature shift factors. Values for and calcu-... 

Figure 7. Master Curves of PVC Acoustical Damping Material...

With a sensitive pump-probe technique, possibly within a common-path interferometer, one can detect the acoustic vibrations of an individual gold nanoparticle [36]. This measurement directly gives the vibration s damping time, a parameter inaccessible to measurements on ensembles of nanoparticles, because of the inhomogeneity in sizes and shapes of populations of nanoparticles. The damping of vibrations of a nanoparticle depends critically on the acoustic impedance mismatch between particle and substrate materials, as well as on the mechanical contact area between them. Acoustic damping is therefore a probe of this contact, which may often be limited to a few nanometers only in diameter. 

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