Measured loss factor

The KK relation can also be used to check the consistency of experimental data. Lack of agreement between the measured loss factor and that calculated from the modulus is an indication of some experimental error. 

Figure 9. Measured Loss Factor of Segmented Constrained Layer Damping for Various Segment Lengths on a 36-in.-Long Bar (The curve for 3 segments may actually be for 2.) (Adapted from ref. 22)...

The time-temperature superpositioning principle was applied f to the maximum in dielectric loss factors measured on poly(vinyl acetate). Data collected at different temperatures were shifted to match at Tg = 28 C. The shift factors for the frequency (in hertz) at the maximum were found to obey the WLF equation in the following form log co + 6.9 = [ 19.6(T -28)]/[42 (T - 28)]. Estimate the fractional free volume at Tg and a. for the free volume from these data. Recalling from Chap. 3 that the loss factor for the mechanical properties occurs at cor = 1, estimate the relaxation time for poly(vinyl acetate) at 40 and 28.5 C. 

By monitoring the insulation condition of the windings during maintenance, at least once a year, which can be carried out by measuring (a) the polarization index (Section 9.5.3) and (b) the dielectric loss factor, tan S (Section 9.6) and making up the insulation as in Section 9.5.2, when the condition of the insulation is acceptable and only its level is less than permissible. 

For lower voltage systems, say. 2.5 to lU kV, measurement of dielectric loss factor tan 5. along similar lines, to those recommended... 

Figure 22. Relative Changes in Plate Temperature with Column Flow, Measured in Units of -vil for Different Values of Heat Loss Factor (P)...

An alternative method of studying the molecular motions of a polymeric chain is to measure the complex permitivity of the sample, mounted as dielectric of a capacitor and subjected to a sinusoidal voltage, which produces polarization of the sample macromolecules. The storage and loss factor of the complex permitivity are related to the dipolar orientations and the corresponding motional processes. The application of the dielectric thermal analysis (DETA) is obviously limited to macromolecules possessing heteroatomic dipoles but, on the other hand, it allows a range of frequency measurement much wider than DMTA and its theoretical foundations are better established. 

The specimen may be a sheet of any size convenient to test, but should have uniform thickness. The test may be run at standard room temperature and humidity, or in special sets of conditions as desired. In any case, the specimens should be preconditioned to the set of conditions used. Electrodes are applied to opposite faces of the test specimen. The capacitance and dielectric loss are then measured by comparison or substitution methods in an electric bridge circuit. From these measurements and the dimensions of the specimen, dielectric constant and loss factor are computed. 

The loss factor is the product of the dielectric constant and the power factor, and is a measure of total losses in the dielectric material. 

A definite correlation of the results of the measurements can be achieved by using the adiabatic compressor power per unit volume of reactor according to Eq. (10) which is shown in Fig. 15 [27]. The experimentally determined loss factor is required in Eq. (10). The measured data for spargers with holes dL= 0.2 - 2 mm can be correlated with Eq. (24). 

In order to determine the efficiency of the screens, the front-to-back ratio (F/B) of activities and a loss factor (SL) by which one multiplies to correct for loss in the screens (the alpha particles absorbed in a screen that cannot be detected either during the front or back measurements, see figure 1) have to be determined. Experimentally, this was accomplished by two methods ... 

However, because measurements are kinetically determined, this is a less accurate form of the equation. Very often it is observed that the measured shift factors, defined for different properties, are independent of the measured property. In addition, if for every polymer system, a different reference temperature is chosen, and ap is expressed as a function of T — rj, then ap turns out to be nearly universal for all polymers. Williams, Landel and Ferry believed that the universality of the shift factor was due to a dependence of relaxation rates on free volume. Although the relationship has no free volume basis, the constants and may be given significance in terms of free volume theory (Ratner, 1987). Measurements of shift factors have been carried out on crosslinked polymer electrolyte networks by measuring mechanical loss tangents (Cheradame and Le Nest, 1987). Fig. 6.3 shows values of log ap for... 

The electrical properties of materials are important for many of the higher technology applications. Measurements can be made using AC and/or DC. The electrical properties are dependent on voltage and frequency. Important electrical properties include dielectric loss, loss factor, dielectric constant, conductivity, relaxation time, induced dipole moment, electrical resistance, power loss, dissipation factor, and electrical breakdown. Electrical properties are related to polymer structure. Most organic polymers are nonconductors, but some are conductors. 

C. G. Sandler, "An Acoustic Technique for Measuring the Effective Dynamic Bulk Modulus of Elasticity and Associated Loss Factor of Rubber and Plastics", NavOrd Rept 1524(1950)... 

For many applications low-temperature flexibility of the plasticized composition is also important. Plasticizers of low viscosity and low viscosity-temperature gradient are usually effective at low temperature. There is also a close relationship betv/een rate of oil extraction and low-temperature flexibility plasticizers effective at low temperature are usually rather readily extracted from the resin. Plasticizers containing linear alkyl chains are generally more effective at low temperature than those containing rings. Low-temperature performance is evaluated by measuremen t of stiffness in flexure or torsion or by measurement of second-order transition point, brittle point or peak dielectric loss factor. 

For description of an apparatus used by Philipoff Brodnyan, see Ref 3, and of that used by McKinney et al, see Ref 4 Refs l)E.Meyer K.Tamm, AkustZeitschr 7, 45 50(March 1942), "An Accustic Method for Determining the Dynamic Compressibility and Loss Factor of Elastic Substances 2)C.S. Sandler, NAVORD Rept 1524(Sept 1950), "An Accoustic Technique for Measuring the Effective Dynamic Bulk Modulus of Elasticity and Associated Loss Factor in Rubber and Plastics 3)W.Philipoff J.Brodnyan, JApplPhys 26, 846-9(1955), "Preliminary Results in Measuring Dynamic Compressibilities 4)J. E. McKinney et al, JApplPhys 27, 425-30(1956), "Apparatus for the Direct Determination of the Dynamic Bulk Modulus 5)W.S.Cramer, NAVORD Rept 4380(Sept 1956), "Bulk Compressibility Data on Several Explosives 6)J.Alster, PicArsn, Dover, NJ private communication(1961)... 

---