Читать книгу The Rheology Handbook - Thomas Mezger - Страница 198

Here, a straight line is fitted through the entire range of measuring points of the logarithmic stress/deformation diagram with best fitting to the measuring points as well in the lower as well as in the upper shear stress range. Then the location is determined at which the distance between the measuring points and this straight line shows its maximum value. The corresponding shear stress value is then taken as the yield point. An advantage of this method is that also the whole deviation function can be presented versus the shear stress τ showing the distinctness of the bend of the logarithmic tau-gamma function. Another advantage is that several bends may be determined if occurring.

Note: Yield point and flow point

Beside the methods described above, there are existing further methods for yield point determination: in Chapter 3.3.4 using flow curves obtained by rotational tests, in Chapter 6.4 via creep curves, and – as already mentioned – in Chapter 8.3.4. The latter method is more meaningful in a scientific sense, since here are determined both the yield point and the flow point (oscillatory tests, amplitude sweeps). An overview on diverse methods for yield point determination is also given in Chapter 12.4.1a (guideline) and in the Index, as well as in [4.16].

End of the Cleverly section