Читать книгу The Rheology Handbook - Thomas Mezger - Страница 197

If the transition from the linear-elastic (LE-) range to the flow range occurs quite gradually, the two yield point values τ1 (as limit of the LE-range) and τ2 (as tangent crossover point) may differ clearly when determined by use of the two methods described above (Figure 4.5). The determined two parameters correspond approximately to the two values which are obtained by an amplitude test (oscillatory test) as yield point τy and as flow point τf (see Chapter 8.3.4 and Figure 8.12). Here, this counts approximately on the one hand for the shear stress values of τ1 und τy and on the other hand for the values of τ2 und τf.

However, if for brittle break behavior the transition from the linear-elastic (LE-) range occurs immediately, and therefore the measuring curve shows a clear kink, then τ1 and τ2 (or τy and τf respectively), both will meet together in one point (Figure 4.6). Correspondingly, also with an amplitude sweep, as yield point τy and flow point τf the same point would be obtained (see Chapter 8.3.4 and Figure 8.13).

Figure 4.5: The logarithmic tau-gamma diagram shows that two different yield point values may result when applying the two different evaluation methods (limit of the LE-range, tangent crossover method)

Figure 4.6: For brittle break behavior of the

sample, the logarithmic tau-gamma diagram shows that for the two different yield point

methods the result will be the same point