Viscoelastic region

At very small strains within the viscoelastic region (e<0.5%), deformation within the PP solid is confined to disordered amorphous regions [97,98) due to their inherently low stiffness at temperatures above their Tg (-10 °C). In this deformation region, spherulites undergo affine deformation on the whole. Inside the spherulites, rotation of lamellae occurs [101]. The resulting orientation of lamellae depends on their position within the spherulite in respect to the orientation of the external deformation [102-104],... 

For shear strains greater than approximately 2 the ratio cr(r)/> 0 for a concentrated polystyrene solution was reduced at all observable times. For the large strains, relaxation proceeded more rapidly at short times, but at longer times the residua] stress decayed with about the same time dependence as that in the linear viscoelastic region. 

Number-average relaxation time of the terminal viscoelastic region,... 

LVE region, see Linear viscoelastic region Lyase, pectic characterized, 342 PGase assay, interference in,... 

Figure H3.2.4 Linear viscoelastic region as determined by the strain dependence of G (storage modulus) and G (loss modulus).

Real (viscoelastic) materials give an intermediate response that is an exponential curve. The exponential time constants associated with the curve are used to approximate the relaxation times of the material itself. Thus, the shape of the output curve is analyzed to give viscoelastic information, although this model fitting is only strictly legitimate in the linear viscoelastic region. Workers have shown that the mechanical parts of the models (springs and dashpots) can be associated with specific parts of a food s makeup. 

Stress relaxation master curve. For the poly-a-methylstyrene stress relaxation data in Fig. 1.33 [8], create a master creep curve at Tg (204°C). Identify the glassy, rubbery, viscous and viscoelastic regions of the master curve. Identify each region with a spring-dashpot diagram. Develop a plot of the shift factor, log (ax) versus T, used to create your master curve log (ot) is the horizontal distance that the curve at temperature T was slid to coincide with the master curve. What is the relaxation time of the polymer at the glass transition temperature ... 

Butter and milk fat exhibit viscoelastic behavior at small stresses (Chwiej, 1969 Pijanowski et al., 1969 Shama and Sherman, 1970 Sherman 1976 Shukla and Rizvi, 1995). To probe this behavior, a very small stress or deformation is applied to a sample and the relationships between stress, strain and time are monitored. Viscoelastic testing is performed in the linear viscoelastic region (LVR) where a linear relationship between stress and strain exists and where the sample remains intact. Depending on the material, this region lies at a strain of less than 1.0% (Mulder and Walstra, 1974) or even less than 0.1% (Rohm and Weidinger, 1993). Figure 7.10 shows the small deformation test results for milk fat at 5°C. 

The derivation of fundamental linear viscoelastic properties from experimental data obtained in static and dynamic tests, and the relationships between these properties, are described by Barnes etal. (1989), Gunasekaran and Ak (2002) and Rao (1992). In the linear viscoelastic region, the moduli and viscosity coefficients from creep, stress relaxation and dynamic tests are interconvertible mathematically, and independent of the imposed stress or strain (Harnett, 1989). 

The Contribution of the Linear Viscoelastic Region to the Impact Properties of Thin Polymer Films... 

Although the difficulty in correlating dynamic mechanical and impact data has been noted (J, 2) because the former is measured in the linear viscoelastic region and the latter is measured presumably in the nonlinear region, it is nonetheless well documented (2-8) that various types of correlations do exist between these two measurements. 

As both referees pointed out, other reasons have been offered for energy dissipation during impact. In each case however some energy dissipating mechanism must be provided. The present work indicates that, at least for the samples used, this mechanism is provided by the dynamic mechanical dissipation factor. This in turn is attributed to the fact that at the high strain rates of impact the linear viscoelastic region is the largest, if not the only, contributor to the dissipation process. 

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