Deformation rates

Minimization of the elastic behavior of the fluid at high deformation rates that are present when high molecular weight water-soluble polymers are used to obtain cost-efficient viscosities at low shear rates. 

Extensional flows occur when fluid deformation is the result of a stretching motion. Extensional viscosity is related to the stress required for the stretching. This stress is necessary to increase the normalized distance between two material entities in the same plane when the separation is s and the relative velocity is ds/dt. The deformation rate is the extensional strain rate, which is given by equation 13 (108) ... 

Fig. 14. Shear viscosity, Tj, and extensional viscosity, Tj as a function of deformation rate of a low density polyethylene (LDPE) at 150°C (111). To convert...

A deformation due to slippage of polymer molecules past one another (viscous deformation Dvisc)- H often assumed that such viscous deformation rates do not change with time if the applied stress is constant. However, in long-term deformations chemical and morphological changes may occur which affect the rate of chain slippage. 

Table 2 Average Values of the Modulus, Yield Stress, Yield Strain, and Strain at Break for Three Samples of PTEB Stretched at Different Temperatures and Deformation Rates...

To understand how the dispersed phase is deformed and how morphology is developed in a two-phase system, it is necessary to refer to studies performed specifically on the behavior of a dispersed phase in a liquid medium (the size of the dispersed phase, deformation rate, the viscosities of the matrix and dispersed phase, and their ratio). Many studies have been performed on both Newtonian and non-Newtonian droplet/medium systems [17-20]. These studies have shown that deformation and breakup of the droplet are functions of the viscosity ratio between the dispersity phase and the liquid medium, and the capillary number, which is defined as the ratio of the viscous stress in the fluid, tending to deform the droplet, to the interfacial stress between the phases, tending to prevent deformation ... 

As for the compression test, the lowest stress amounted to 0.314 kp/mm at the lower deformation rate at 503K and to 0.535 kp/mm for the higher rate at the same temperature. For the lower deformation temperatures the values of the flow stress increased sharply and at 373K reached 2.3 and 4.5 kp/mm" for the lower and higher deformation rates, respectively At room temperature they were 9.0 kp/mm and 11.28 kp/mm . 

The backward press forming method was applied to produce the cups from the investigated alloys at temperature 523 K at a small deformation rate. The velocity of the displacement of the stamp was in the range of 1-10 mm/min. 

The average deformation and deformation rate in the wall of a moulded piece in the backward press forming are ... 

The deformation rate in the synchronous press forming is much greater than in the backward press forming... 

For all high-filled polymers, whatever the nature of the matrix and filler, it has been found [297,298] that the Bagley pressure loss at extruder inlet increases sharply in a certain range of temperatures and rates of deformation. What distinguishes composites with PMF is that for them the pressure loss at the inlet begins at lower deformation rates. 

Therefore in many cases, where the behavior of polymer compositions under real technological conditions is of practical interest, i.e. in the region of high deformation rates, the yield stress and the region near it may be neglected and only upper branches... 

Dynamic loading in the present context is taken to include deformation rates above those achieved on the standard laboratorytesting machine (commonly designated as static or quasi-static). These slower tests may encounter minimal time-dependent effects, such as creep and stress-relaxation, and therefore are in a sense dynamic. Thus the terms static and dynamic can be overlapping. 

Since the resistance of solids to deformation does not change very much with moderate changes of deformation rate, the power dissipation by the displacement of compressed priming mixt by a firing pin is nearly proportionate to its velocity (Ref 19)... 

The use of internal viscosity forces permit us to take into account kinetic effects associated with deformation rates which were beyond the scope of most polymer... 

In contrast to rotational shear flow, deformation and breakage occurs over the whole range of viscosity ratio in an irrotational (extension) flow produced, for example, in a 4-roll apparatus (Fig. 23) from which the data shown in Fig. 21 were obtained [76]. Comparing the critical conditions for breakage by shear and by elongation. Fig. 23 shows that for equal deformation rates, irrotational flow tends to be more damaging than rotational flow. 

The samples were tested at a deformation rate of 1 in./min. for the simple tension experiments. In the case of stress-relaxation measurements, the samples were prestrained to 7% elongation at e = 5 in./min. then allowed to stress relax over a 20 minute period. All mechanical testing were carried out at room temperature. 

When there are no distinct bonds crossing a glide plane, there are no distinct kinks. This is the case for pure simple metals, for pure ionic crystals, and for molecular crystals. However, the local region of a dislocation s core still controls the mobility in a pure material because this is where the deformation rate is greatest (Gilman, 1968). 

In general terms, as has already been mentioned, plastic deformation is a transport process analogous with electrical and thermal conductivity. These involve an entity to be transported, a carrier that does the transporting, and a rate of transport. In the case of electrical conductivity, charge is the transport entity, electrons (or holes) are the carriers, and the electron net velocities determine the rate. In the case of plastic deformation, displacement, b (cm) is the transport entity, dislocations are the carriers, N ( /cm2), and their velocities, v (cm/sec) determine the shear deformation rate, d8/dt. In two dimensions, the latter is given by the Orowan Equation ... 

The most widely used model for the SGS stresses is due to Smagorinsky (1963) and involves a SGS eddy viscosity, ve, which is related to the local resolved deformation rate S ... 

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