Elastic deformation processes, effect

Figure 2 shows the contact geometry for a pyramid indenter at zero load, at maximum load, and after unloading. The material under the indenter consists of a zone of plastic deformation (a few times the penetration depth distance) surrounded by a larger outer zone of elastic deformation. Several effects can be distinguished during the indentation process ... 

In this chapter studies of physical effects within the elastic deformation range were extended into stress regions where there are substantial contributions to physical processes from both elastic and inelastic deformation. Those studies include the piezoelectric responses of the piezoelectric crystals, quartz and lithium niobate, similar work on the piezoelectric polymer PVDF, ferroelectric solids, and ferromagnetic alloys which exhibit second- and first-order phase transformations. The resistance of metals has been investigated along with the distinctive shock phenomenon, shock-induced polarization. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

Fig. 23. Deformation and recurrent deformation at constant stress as a function of time, (a) total deformation at high stress (nonlinear behavior, relaxation time rai), (a ) deformation at low stress, (b) viscous flow, (b ) viscous flow at low stress, (c) purely elastic deformation for high stress, and for low stress (c ), (d) and (d ) recurrent effects (diffusion process)...

Trials are carried out and described, which proves the method of elastic-deformation dispersion as a technique in making possible the effective processing of waste from various PVC materials to obtain fine-particle recycled product with wide possibilities of practical use. The elastic-deformation dispersion method, is based on the idea of multiple breakdown, when the material is subjected to the combined action of high pressure and shear deformation at elevated temperatures. Elastic-deformation dispersion of roughly ground materials with particle diameter of 1-3 cms. was carried out in a single-... 

The Young equation contains the surface tension of the liquid yi - which can easily be measured, and the difference of the surface tensions of the solid-vapor ysv and the solid-liquid interface ysL That the surface tension enters the Young equation is not beyond doubt. Linford I6 inserted the generalized intensive surface parameter ys, arguing that at the three-phase contact line elastic deformations take place. In accordance with Rusanov [I7 we use the surface tension, because the spreading of a liquid on a surface is a process similar to immersion or adsorption. Immersion is usually considered to effect the surface tension since no extension or contraction of the surface occurs. 

Many materials, particularly polymers, exhibit both the capacity to store energy (typical of an elastic material) and the capacity to dissipate energy (typical of a viscous material). When a sudden stress is applied, the response of these materials is an instantaneous elastic deformation followed by a delayed deformation. The delayed deformation is due to various molecular relaxation processes (particularly structural relaxation), which take a finite time to come to equilibrium. Very general stress-strain relations for viscoelastic response were proposed by Boltzmann, who assumed that at low strain amplitudes the effects of prior strains can be superposed linearly. Therefore, the stress at time t at a given point in the material depends both on the strain at time t, and on the previous strain history at that point. The stress-strain relations proposed by Boltzmann are [4,39] ... 

In all cases in the thermodynamic analysis we considered partial pressures of H2O, CO2, and other volatiles to be independent variables, if they were not related to one another by reactions. In addition the general conclusion was drawn that in thermodynamic calculations of metamorphic reactions it is impossible to assume different isotropic pressures on the solid phases and fluid. Lithostatic (nonhydrostatic) pressure or loading pressure has practically no effect on equilibrium in elastic deformation of rocks. Isotropic pressure equal to fluid pressure in the case of an excess of volatiles should be considered an equilibrium factor in actual natural processes. 

Applying external forces to an elastic body we change the relative position of its different parts which results in a change in body size and shape, i.e. under stressed conditions an elastic body undergoes deformation. As the particles of a body are shifted with respect to each other, the body develops elastic forces, namely stresses, opposing the deformation. In the course of deformation these forces increase and at a certain instant of time they can even counter-balance the effect of the external stress. At this moment the deformation process comes to an end, and the body is in a state of elastic equilibrium. As the stress is removed gradually, the elastic body returns to its initial state however, the abrupt disappearance of the outside force causes the particles inside the body to oscillate. To describe these oscillations, it is necessary to quantify the relationships between the forces arising at each point of the deformed... 

The hysteresis loss mechanism of friction is based on the fact that in real life recovery of a material from elastic deformation on removal of the stressing load is never perfect. The energy lost by this effect can be treated as a frictional loss. The hysteresis loss mechanism is of major importance in explaining rolling friction. Details of the rolling friction process are complex the second volume of the monograph by Bowden and Tabor [23] devotes an entire chapter to various aspects of rolling. 

A mechanical interaction of the abrasive grains with the workpiece usually leads to compressive residual stresses by localized elastic deformation and plastic flow. The predominance of mechanical process effects can be achieved by chip formation with increased ratio of micro-plowing. This usually occurs in grinding with small chip thickness and low cutting speeds (Fig. 2). 

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