Extensional viscosity biaxial

Extensional viscosity that results purely from shear deformation seems to be of less interest, but has been measured (108). The theology of several different polymer melts in terms of shear viscosity and uniaxial and biaxial extensional viscosity has been compared (231). Additional information on the measurement of extensional viscosity are also available (105,238—240). 

Analyze lubricated squeezing flow to determine biaxial extensional viscosity (T)R), which is calculated from biaxial stress (cB) and biaxial extensional strain rate (eB). 

The biaxial extensional viscosity ( b) was defined as the ratio of the normal stress difference and the radial extension rate assumed to be half the strain rate ... 

For an unvulcanized polydimethylsiloxane, the biaxial viscosity was approximately six times the shear viscosity over the biaxial extensional rates from 0.003 to 1.0 s (Chatraei et al., 1981), a result expected for Newtonian fluids, that is, the relationship between the limiting value of biaxial extensional viscosity (j, ) at zero strain rate and the steady zero-shear viscosity (i o) of a non-Newtonian food is ... 

Furthermore, when this flow is looked upon as biaxial stretching, it is thought of as being generated by a radial, tensile stress rather than an axial, compressive stress. Thus, the biaxial extensional viscosity is defined as... 

Doughs with different protein contents (13.2, 16.0, and 18.8% based on 14%MB) showed different biaxial extensional viscosities (Huang and Kokini, 1993). Figure 31 shows that the biaxial extensional viscosity approached 6tj at an extensional rate of 7.3 x 10 sec . Strain thinning behavior was observed in dough during biaxial extension. 

FIG. 31. Biaxial extensional viscosity and shear viscosity vs extension and shear for wheat flour dough with 16.0% protein content (Huang and Kokini, 1993). tjb is biaxial extensional viscosity, ij is shear viscosity. 6 ij superimposed with tjb indicate that the biaxial extensional viscosity are about five times larger than shear viscosity at the equivalent shear rate. 

Huang, H., and Kokini, J. L. (1993). Measurement of biaxial extensional viscosity of wheat flour doughs. J. Rheol. 37, 879-891. 

Elongational or tensile viscosity Biaxial extensional viscosity Biaxial stress growth coefficient Biaxial stress decay coefficient Scattering angle... 

Biaxial extensional viscosity Tbmperature, time, strain rate... 

Reactive viscosity of thermosets Uniaxial extensional viscosity Biaxial extensional viscosity First normal stress difference 6721-10 6721-10 A slit die rheometer according to ISO 11443 can also be used. 

By the same token, the biaxial extensional viscosity ri can be defined... 

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