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The creep and recovery curve of this model is given in Figure 3b. Again, there is some resemblance between this curve and the behavior observed with cheese. The deformation and the recovery are not instantaneous in this case and this is more in line with practical experience, but the model predicts a complete recovery, which is not always observed.

The student of electric circuit theory will be aware of some familiarity with the Voigt and Maxwell models. If one replaces the spring with a capacitor and the dashpot with a resistor, the two models become the two alternative rep-

Figure 3. Creep recovery curve: (a) Maxwell body; and (b) Voigt body.

Figure 3. Creep recovery curve: (a) Maxwell body; and (b) Voigt body.

resentations of a leaky dielectric. Just as in electrical network theory these binary combinations can be built up into more complicated networks by adding more elements, so the Voigt and Maxwell bodies can be extended. One popular combination is of a Voigt body placed end-to-end with a Maxwell body. This is known as a Burgers body and it does indeed give a creep and recovery curve in which both the deformation and the recovery are retarded to different degrees and in which the recovery is incomplete.

Although the process of building up more complicated models may be continued indefinitely, the expressions for the behavior rapidly become cumbersome. As the number of elements increases it becomes disproportionately difficult to analyze the data, and the accuracy of the parameters extracted decreases (8). Indeed, the precision of any experimental measurements made on cheese may well be insufficient for more than two or three parameters to be identified with any pretensions of accuracy. Only if the rheological behavior can be linked unequivocally to the structure of the sample may the use of complex models be justified. Otherwise, the model should be kept as simple as possible.

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