Casson body

Fig. 6 Typical rheogram for a shear thinning (a), shear thickening (b), and a Casson body (c).

The Casson body model " is a semiempirical model used to describe shear thinning behavior after an apparent yield stress has been exceeded. It is, in fact, a combination of the apparent yield stress with the power law model, whereby the power law index n is arbitrarily set to 0.5 ... 

Tg and . This is shown in Fig. 7 both for the extrapolated (Bingham) and Casson s yield value. In both cases the linear relationship is maintained indicating that such crude models may be applied to the rheology of the complex system of bentonite clay plus pesticide suspension. It should be mentioned, however, that the elastic floe model is a more realistic description of the system, since the assumption of a maximum of doublets in the floe rupture model is not justified with a concentrated suspension with many body interactions. 

For the Bingham plastic body, a = 1. Many colloidal dispersions which exhibit plastic behavior are well represented by Cassons equation, for which a takes on the value J. 

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