Читать книгу The Rheology Handbook - Thomas Mezger - Страница 185

The following section uses the Two-Plates model in order to define further rheological parameters (see also Chapter 2.2). The lower plate is fixed (deflection s = 0). The upper plate with the (shear) area A is deflected by the (shear) force F and the resulting deflection s is measured (see Figure 4.1). Between the plates there is the constant distance h, and the sample is sheared in this shear gap. It is assumed that the following shear conditions are given:

1 The sample shows adhesion to both plates without any wall-slip effects.

2 The sample is deformed homogeneously throughout the entire shear gap, i. e., no inhomogeneous “plastic deformation” is occurring (see also Chapter 3.3.4.2c and Figure 2.9, no. 4).

Accurate calculation of the rheological parameters is only possible if both conditions are met.

The real geometric conditions in rheometer measuring systems are not as simple as in the Two-Plates model. However, if a shear gap is narrow enough, the necessary requirements are largely met and the definitions of the following rheological parameters can be used.

Figure 4.1: Two-Plates model for shear tests to illustrate deformation of a material in the shear gap