Data, creep compliance

Alvarez, M. D., Canet, W., Cuesta, R, Lamua, M. (1998). Viscoelastic characterization of solid foods from creep compliance data application to potato tissues. Z Lebensm. Unters. Forsch. A., 207, 356-362. 

These differences in the mechanical behavior are not reflected, within the experimental error, in the temperature dependence of the mechanical properties. As shown by the examples of Figures 1 and 3, the relaxation modulus and creep compliance data showed very little scatter and could be shifted smoothly into superposition along the logarithmic time axis. The amounts of shift, log Or, required to effect superposition are plotted against the temperature, T, in Figure 5 for the relaxation data, and in... 

The creep-compliance technique has been used extensively by Sherman and co-workers for the study of ice cream, model emulsions, margarine, and butter (Sherman, 1966 Shama and Sherman, 1969 Vernon Carter and Sherman, 1980 Sherman and Benton, 1980). In these studies, the methodology employed was similar to that for ice cream, that is, the creep-compliance data on a sample were described in terms of mechanical models, usually containing four or six elements. Attempts were made to relate the parameters of the models to the structure of the samples studied. However, with increased emphasis on dynamic rheological tests and interpretation of results in terms of composition and structure, the use of mechanical models to interpret results of rheological tests has declined steadily. 

For melted ice cream, the equation for creep-compliance data was ... 

Figure 3-42 Mechanical Models for Creep-Compliance Data of Ice Cream Mix and Melt (Sherman, 1966).

As expected, magnitudes of instantaneous elastic modulus. Go = (l/./o), and of storage modulus G at 1 rad s (Yoo and Rao, 1996). Also, as noted by Giboreau et al. (1994) for a gel-like modified starch paste, the two parameters were of the same order of magnitude. Further, as can be inferred from data in Table 5-E, the other moduli from creep-compliance data (Gi = 1/Ji, G2 = 1//2) and the Newtonian viscosity increased with increase in °Brix. 

The creep-compliance data on the mayonnaises were modeled by means of the six parameter model ... 

The latter procedure is an adaptation of that usually employed to generate creep compliance data a creep yield stress is determined by extrapolating creep-rate data to zero rate, with the corresponding value of applied stress being taken as the yield stress [Lohnes etal., 1972], In addition to its use in yield stress measurement, the vane has foimd application as the basis of... 

The creep data were represented as creep compliance D(t) = e t)/(7, where D t) is the compliance, t is time, and s and (T are the engineering strain and stress, respectively. To minimize scattering, three to five creep curves were measured on different samples at each temperature level. Standard deviations were less than 10%. Averaged experimental creep compliance data are shown by the dots in Figure 12.1. As may... 

Figure 12.2 Experimental tensile creep compliance data in logarithmi. coordinates at the same temperatures as in Figure 12 1 (After [36])...

Averaged experimental creep compliance data are represented by dots in Figure 12.12 as a function of log time. The tests show that even after 14 months the creep continued and deformations kept increasing. After tests of 10000 h the compliance of the materials examined exceeds the instantaneous elastic compliance by a factor varying from 3.8 (for pure PP) to 3.2 (for the 80% PP + 20% PLC blend). This shows that the inelastic strain of these materials manifests itself substantially methods of accelerated testing and prediction have to be subjected to very detailed scrutiny. 

PU (cross-linked) 228.2 12.5 42.5 [56] ar,s of the softening dispersion from creep compliance data. 

This principle applies to all of the viscoelastic functions defined previously for stress relaxation, creep, and dynamic mechanical experiments. A most comprehensive discussion of TTS is provided in the text by Ferry (1980). An example of TTS is shown in Fig. 5.14 for the modulus data of Fig. 5.15, which were determined at various temperatures (Mercier et al. 1965) by both stress relaxation and creep measurements. The creep compliance data were converted to modulus by the relationship E(t) = VJ t). The single curve formed by superposition of the various curves shifted on the time axis to the given reference temperature (Tr) is referred to as a master curve. In this case... 

Typical examples of tensile (isochronous) linear and nonlinear stress-strain diagrams for elastic and viscoelastic materials are shown in Fig, 10.1. For elastic materials, the response is time independent, so there is a single curve for multiple times and the nonlinearity is apparent as a deviation of the stress-strain response from linear. For linear viscoelastic materials, the isochronous response is linear, but the effective modulus decreases with time so that the stress-strain curves at different times are separated from one another. When a viscoelastic material behaves nonlinearly, the isochronous stress-strain curves begin to deviate from linearity at a certain stress level. Fig. 10.2 shows creep compliance data for an epoxy adhesive as a function of stress level for various time intervals after initial loading. 

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