Deformation time

Figure 9.8. Deformation-time curves, (a) Material showing substantial ordinary elastic, high elastic and viscous components of deformation, (b) Material in which high elastic deformation...

The internal viscosity of the macromolecule is a consequence of the intramolecular relaxation processes occurring on the deformation of the macromolecule at a finite rate. The very introduction of the internal viscosity is possible only insofar as the deformation times are large, compared with the relaxation times of the intramolecular processes. If the deformation frequencies are of the same order of magnitude as the reciprocal of the relaxation time, these relaxation processes must be taken explicitly into account and the internal viscosity force have to be written, instead of (2.26) as... 

Fig. 1. Shear stress versus deformation time when the rotor rpm is 0,05-0 3 min ...

Figures 1,2 show typical curves of shear stress versus deformation time of aminoplastic at 120 °C for different r.p.m. of the plastometer rotor, from 2 = 0.05 to 50 min (i.e. for shear rates from 1.4 x 10 to 1.5 x 10 s ).

As already mentioned (pp. Ill and 112) the deformational mechanism is characteristic of kinetically flexible molecules for which the orientation time to is greater than the deformation time Tj, i.e. the time during which the molecule in solution retains a random conformation (relaxation time of the conformation). 

Figure 3. Deformation-time response of the panel system under sustained lateral pressure of 1.5 kN/m2...

To investigate the long-time deformation of the panels under sustained lateral loading, the panels were kept under a lateral pressure level of 1.5 kN/m2 for a longer time the long-term experiments lasted up to several months. The maximum deflection after 4.5 months under a pressure level of 1.5 kN/m2 remained confined to about 28 mm. Figure (3) shows the deformation-time response of the panel system under sustained lateral pressure of 0.015 bar this would correspond to a wind action of 1.5 kN/m2. 

FIG. 4—Deformation time diagram loaded 20% the compressive strength at the given humidity... 

Additional hardened gypsum was examined with regaid to its creep behavior. Figure 4 shows the deformation time diagram of hemihydrate as a function of the citric acid addition and of the equilibrium humidity. 

The viscosity of the oil plays an important role in the break-up of droplets the higher the viscosity, the longer it will take to deform a drop. The deformation time is given by the ratio of oil viscosity to the external stress acting on the drop,... 

We must point out that all simple Newtonian substances, even such as air, water, and benzene, possess noticeable shear elasticity under very large loadings in the acoustic range of velocities. In this case, the characteristic deformation time must be of the order of 10-8 to 10 10s (these are approximate relaxation times for simple fluids). Under these conditions, all simple fluids can be treated as viscoelastic media. 

The advantages of cone penetration include the simplicity of the test that the test piece can be used without any previous deformation (which would affect the value of cry) and that the deformation time (of the order of a second) is about the same as during the spreading of margarine. Altogether, the test results correlate well with the subjectively evaluated spreadability. 

At a quasi-elastic impact the film thinning velocity is much smaller than the particle velocity. Thus dh/dt is very much less than unity and can be neglected in deriving Eq. (11.5). It is easy to obtain the well-known formula of Evans (1954) for the film deformation time from Eq.(11.6),... 

Lohfink and Kamal [1993] observed that an increase of die gap size yielded fewer, but thicker layers. On the other hand, a smaller die gap size resulted in an increased number of stacked thin layers. Higher screw rpm produced a more pronounced lamellar stracture. In real mixing equipment, such as a SSE, deformation time (residence time) could be limited by the deformation rate (screw speed). Lee and IQm [1997] reported that an increase in screw speed reduced the degree of mixing, because the residence time decreased and the minor phase melting was insufficient. 

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