A Practical Approach to Rheology and Rheometry

Rheology
9.8 Mathematical treatment of test results in retrospect
For those who still remember using pocket slide-rules for calculating the shear
stress, the shear rate and the viscosity, modern computerization still has the
aura of a “miracle”. We can do now-a-days much more – see the WLF-Superposition
– and much faster. Computers allow us to evaluate dynamic data and
thus establish the interdependence of viscosity and elasticity, and provide a
long-time differentiation between elastic and viscous responses in creep and
recovery tests. We can present data in tabulated and graphical form and we
can evaluate the significance of data to allow a better interpretation of results.
But results are still dependent on the operator’s ability to provide optimum test
conditions. One must be aware of the pitfalls of turbulence, non-linear viscoelasticity
or of plug flow. While tests using computers can be so fully automated
that one could think of reading a newspaper while the rheometer and computer
do their work, it is still correct procedure to keep an eye on the extrudate at the
die or the sample sheared in a cone-and-plate sensor system – at least when
establishing a quality control test procedure for the first time for samples or
batches which are known not to differ too much in the long-term.
243