Damping measurements

Chemical, Physical, and Mechanical Tests. Manufactured friction materials are characterized by various chemical, physical, and mechanical tests in addition to friction and wear testing. The chemical tests include thermogravimetric analysis (tga), differential thermal analysis (dta), pyrolysis gas chromatography (pgc), acetone extraction, liquid chromatography (lc), infrared analysis (ir), and x-ray or scanning electron microscope (sem) analysis. Physical and mechanical tests determine properties such as thermal conductivity, specific heat, tensile or flexural strength, and hardness. Much attention has been placed on noise /vibration characterization. The use of modal analysis and damping measurements has increased (see Noise POLLUTION AND ABATEMENT). 

The analogy between the mechanical and the electrical damping measurements is also borne out by the effect of plasticizer concentration on the temperature of maximum damping as shown in Figure 14 (31, 32, 33). 

This paper summarizes different methods of pulsation dampening in high pressure plants, and shows how to control and optimize the effectiveness of damping measures by numerical pulsation analysis. 

In order to test the predictions of the model, plates were made up from selected formulations and tested in air. The thicknesses of the various layers were as stated previously, while the length was one meter and the width was one-third meter. Damping measurements were made by two different methods. In both cases, the plates were suspended in a shock chord and accelerometers placed at different locations on the plate. The first used a reverberation meter and the half-power method (16). In the second, an impact hammer was used to tap the structure and the outputs of the accelerometers fed into a Fourier transform based spectrum analyzer to examine the envelope of vibration (17). The results presented here are based upon the second method. 

The authors would like to thank Mr. Douglas Noll of David Taylor Research Center for performing the plate damping measurements. 

The first to perform wave-damping measurements in a kind of Langmuir trough, i.e., under different compression status of the monolayer, was Agnes Pockels (1891). Ironically, she described for the first time an apparatus that was... 

Note, that previous wave damping measurements were conducted for monomolecular films at surfactant concentrations which usually were smaller or comparable with the concentrations representing a completely covered water surface. It follows from measurements by a Langmuir... 

Here we present an extended study of wave damping due to films of insoluble ordinary surfactants and a polymer substance for a wide surfactant concentration range. Retrieval of the film elasticity from the damping measurements has been performed, and compared with static film elasticity. 

Impulse generation not appropriate in liquid applications Limited range for precise frequency and damping measurement... 

Mechanical relaxation behavior of poly(n-butyl acrylate) was studied using a freely oscillating torsional pendulum at frequencies of about 1 cycle/sec in the temperature range of 100 to 300 K. Two damping measurements were made every 5°. 

Mechanical Damping. The elastic energy behavior of resins at low temperatures was determined from the stress-strain relation. Small inelastic contributions, not detectable with that method can be determined by damping measurements using a free torsion pendulum. The mechanical loss, tan 8m, is plotted vs. temperature in Fig. 10. Low-temperature values were similar for the resins considered. No major structural dependence is indicated. (It is not within the scope of this paper to consider the relaxation maxima of resins.)... 

Common Methods for Damping Measurement Logarithmic Decrement and Bandwidth Method... 

One of the first fundamental studies illustrating the effects of fillers on modulus was described by Nielsen et al. (1955), who showed that the shear modulus of polystyrene in the glassy state was increased by the incorporation of from 20 to 60 vol % of mica, calcium carbonate, or asbestos. The magnitude of the increase depended on the filler, about eightfold for mica, but less for asbestos. In addition, as shown by damping measurements, the apparent glass temperature was increased by the presence of the filler, by up to 15°C. 

In any case, we see that measurement of the damping rate for capillary waves at high frequencies yields information on ro f-dy/dTj). This value can be used with similar damping measurements at low frequencies to calculate the diffusivity D if the adsorption isotherm is known. Or if ) is known from separate experiments, the damping rate can be used to obtain information about dT /dc as a fimction of surfactant concentration, and hmee to determine the adsorption isotherm. 

Patch damp Measurements On-Chip, Rgure 2 Four configurations of patch clamp... 

The equation below summarizes the relationship between each of these damping measurements ... 

A damping measure that is commonly used is the logarithmic decrement A. It is defined as... 

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