Elastic relaxation

A-X With strain maintained gradual elastic relaxation occurs. x-Y instantaous deformation occurs when load is removed. 

Top atom pairing (Schlier-Farnsworth model) with elastic relaxations down several layers... 

It was shown that the stress-induced orientational order is larger in a filled network than in an unfilled one [78]. Two effects explain this observation first, adsorption of network chains on filler particles leads to an increase of the effective crosslink density, and secondly, the microscopic deformation ratio differs from the macroscopic one, since part of the volume is occupied by solid filler particles. An important question for understanding the elastic properties of filled elastomeric systems, is to know to what extent the adsorption layer is affected by an external stress. Tong-time elastic relaxation and/or non-linearity in the elastic behaviour (Mullins effect, Payne effect) may be related to this question [79]. Just above the melting temperature Tm, it has been shown that local chain mobility in the adsorption layer decreases under stress, which may allow some elastic energy to be dissipated, (i.e., to relax). This may provide a mechanism for the reinforcement of filled PDMS networks [78]. 

Helveg S, Li WX, Bartelt NC, Horch S, Laegsgaard E, Hammer B, Besenbacher F (2007) Role of surface elastic relaxations in an O-induced nanopattem on Pt(110)-(1 x2). Phys Rev Lett 98 115501... 

In addition to this overall stress variation, there are local stress variations due to a non-uniform distribution of pores and/or porosity or of network properties (viscosity, visco-elastic relaxation). 

It has been proposed that the absorption of ultrasound energy depends on the thermo-elastic relaxation of ice crystals in food and is affected by ice crystal orientation and size, impurities present in the ice crystals, as well as temperature (Kissam et al., 1981). Miles and Shore (1978) and Shore et al. (1986) found that ultrasound was more attenuated in frozen meats than in unfrozen tissues and that the attenuation increased markedly with temperature, reaching the maximum near the initial freezing points of the foods before decreasing rapidly at higher temperatures, thus making ultrasound particularly suitable for the controlled thawing of foods (Miles et al., 1999 Torley and Bhandari, 2007). 

Figure 13-17. Cross-sectional geometry of wear scars on a spherical ball including the effects of elastic relaxation. (a) Convex scar. (b) Concave scar.

The question of a mechanically normal behaviour has an analogous bearing upon the range of validity of the linear phenomenological flow equations of irreversible thermodynamics. Somewhere between a normal fluid and a gel there must exist systems which are still fluid but where an elastic relaxation dissipation process invalidates the main assumptions used in both approaches, or makes them incomplete. In such systems, Pick s laws may no longer be vahd. ... 

The elastic relaxation of the materials after deformation is faster that the ellipsoidal droplet retraction, that is, a clear separation of the two mechanisms is achieved. 

In summary then, we see that theoretical estimates which take account of the elastic relaxation of the surrounding lattice put the formation energy of a pair of separated l- and D-defects at rather less than i eV. Experimental information from dielectric relaxation studies, which we shall discuss in chapter 9, gives a value of 0 68 eV which, in view of the uncertainties involved in the theory, represents reasonably satisfactory agreement. 

These points can be illustrated by comparing the elastic relaxation modulus ,(0 for crystalline (isotactic), amorphous, and chemically cross-hnked (atactic) polystyrene samples, as shown in Figure 15.9. Crystalhnity has little effect below Tg, but as the molecular motion increases above T, the modulus of the amorphous polymCT drops more sharply. The value of E t) remains high for the crystalline polymer throughout this range until the rapid decrease at the melting temperature is recorded. The cross-hnked sample maintains its modulus level at this temperature as the crosslinks are not thermally labile and do not melt. 

With strain maintained gradual elastic relaxation occurs. 

Subsequent workers, notably Terrell Hill and colleagues [6], extended the model to include back reactions for the chemical processes so that thermodynamic parameters such as efficiency can be calculated. In their analysis the motion of the myosin while attached to actin is modeled as a deterministic elastic relaxation often termed a power stroke. Unfortunately, this treatment of the mechanical motion as a deterministic process is not thermodynamically consistent and leads to incorrect predictions about the importance of the mechanical properties of the myosin. 

Based on the observation that molecular elasticity relaxes quickly, in hundredths of a second, whereas band formation and evolution occurs in times of the order of minutes, it seems clear that texture elasticity is the direct energy source. 

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