Internal friction direct measurement

The viscosity coefficients at dislocation cores can be measured either from direct observations of dislocation motion, or from ultrasonic measurements of internal friction. Some directly measured viscosities for pure metals are given in Table 4.1. Viscosities can also be measured indirectly from internal friction studies. There is consistency between the two types of measurement, and they are all quite small, being 1-10% of the viscosities of liquid metals at their melting points. It may be concluded that hardnesses (flow stresses) of pure... 

Intrinsic resistance to dislocation motion can be measured in either of two ways direct measurements of individual dislocation velocities (Vreeland and Jassby, 1973) or by measurements of internal friction (Granato, 1968). In both cases, for pure simple metals there is little or no static barrier to motion. As a result of viscosity there is dynamic resistance, but the viscous drag coefficient is very small (10" to 10" Poise). This is only 0.1 to 1 percent of the viscosity of water (at STP) and about 1 percent of the viscosity of liquid metals at their... 

Measurements of <5 yield direct information about the magnitude of the energy dissipation and the phase angle. 0 measures the fractional energy loss per cycle due to the anelasticity and is often termed the internal friction. According to the discussion above, 8 will be a function of the frequency, to should approach zero at both low and high frequencies and will have a maximum at some intermediate frequency. The maximum occurs at a frequency that is the reciprocal of the relaxation time for the re-population of the point defects. 

The effective angle of internal friction of the powder, 5. This property is a measure of the friction between particles of a bulk solid and can be determined directly in a shear cell (Fig. 5.6a) containing the powder. 

The angle of internal friction can be measured indirectly, in shear cells for example, or directly, by the grooved plate method. There... 

Fig. 19 shows the principle of the direct method of measuring the angle of internal friction. An open-ended ring similar to that used... 

It has been possible, for metals and ceramic materials, to demonstrate by direct observation the existence of lattice defects called dislocations, using the techniques of transmission electron microscopy. These studies have shown that it is often adequate to assume that dislocation motion is responsible for the observed plastic, or permanent, deformation, and that this motion is negligible at stresses below the yield stress. Although very refined microstrain measurements and internal friction experiments have failed to define a stress range in which dislocation motion is completely absent, there is still a clear distinction for these materials between elastic and plastic strain, both on a macroscopic level, in terms of permanency of deformation, and on a microscopic level in terms of large scale dislocation motion. 

The angle of internal friction can be measured directly by the "grooved plate" method. The base of the Jenike shear cell is replaced by a metal plate in which a number of saw-toothed grooves are cut (Figure 2.15). These... 

From a microscopic point of view, damping is directly related to internal frictions that absorb the vibrations of the atoms in the crystal lattice (i.e., phonons). In practice, internal frictions are usually measured by a system that is set in motion with a certain initial amplitude Aj and then allowed to decay freely at an indiscernible amplitude. Then the amplitude follows the exponential equation listed below ... 

Viscosity is a measure of fluid friction and is proportional to the force required to move a layer of fluid over another layer. Highly viscous materials are those that possess a great deal of internal friction when layers are in relative motion — they cannot be spread or poured as easily as less viscous materials. Consider figure 3.1 in which two parallel planes of fluid of equal area A, separated by a distance d, are moving in the same direction but at different speeds. The force F which is necessary to maintain this difference is given, for many fluids, by the following equation which was introduced by Sir Isaac Newton ... 

It is best to measure the lateral pressure ratio K directly (see Chapter 1), but it has long been common to estimate it from the measured angle of internal friction (pi. Accounting for the above effects, the European standard EN 1991-4 (2007) defines the filling value of Kt for design purposes as... 

The use of more direct measurements of strength properties for the detailed design (such as cone penetration values, angle of internal friction) or the state parameter Vr as a measure of in situ state (Jefferies and Been, 2006) is, however, strongly advised, see section 8.6.2. 

It is the particle-particle frictional properties, in particular the "angle of internal friction" (p of the powder, which determine the initial length Lgs of a solid slug. A number of standard methods for measuring p are reported by Zenz and Othmer (1960), two of them relating directly to solid slug formation. 

Since dynamic friction of polymers has a large contribution from internal viscoelastic dissipation, plots of the friction force, determined, e.g., by AFM, vs./D are qualitatively similar to plots of tan<5 vs. fa. Hence, by measuring dynamic friction forces under well-controlled conditions, the dynamics of a given polymer can be directly probed at the free surface of a sample specimen. Thereby surface vs. bulk properties can be probed as well as confinement effects. 

To evaluate the oscillation model, the components of its equations ought to be measured experimentally. Some parameters such as, and N can be easily estimated. However, for some internal parameters such as, yam-to-yam friction coefCfcient and normal load in the crossing points, there are no empirical approaches. These parameters are related to the internal mechanical properties of the plain woven fabrics, have not been meastrred directly yet. As an alternative, the force balance model, which has been introduced by Valizadeh et al, is errrployed to estirrtate these parameters [10]. 

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