Vibrational rheometry
The vibration rheometry deals with unsteady, d. H. oscillatory , rheological measurements. In contrast to the stationary measurement, the sample is not exposed to a continuous, but to a sinusoidally oscillating deformation . This enables rheological measurements on solids that can only be deformed to a limited extent.
evaluation
In contrast to rheological rotation tests, rheological oscillation tests have two linearly independent default values: amplitude and frequency . They result in two equally linearly independent response quantities: response amplitude and phase shift . Typical rheological measurements that they are used to evaluate are the amplitude and frequency sweeps .
Response amplitude and phase shift can be mathematically converted into the storage modulus and the loss modulus , each in Pascal (Pa) , using complex numerical calculations . The two modules stand for the elastic and for the viscous (i.e. frictional ) part of the material in the complex shear module . They can be used to characterize viscoelastic material behavior in more detail, assign the sample to a rheological model and determine its parameters. As sums parameter of the two variables is often also the amount of the complex viscosity indicated that a measure of the analog dynamic viscosity toughness is a mass.
practice
One advantage of vibration rheometry is that, with low vibration amplitudes, the sample is hardly sheared and any structures in the material are not destroyed. This is e.g. B. helpful when investigating effects such as thixotropy or gelling processes . Due to a significant improvement in measurement technology in recent years, modern air or magnetically levitated rheometers deliver reliable measured values from a torque of 0.02 µ Nm and a deflection angle of 0.1 µ rad . However, the actual realizable measuring range also depends on the sample to be tested and the moment of inertia of the measuring system .
In practice, no more than one of the physical quantities amplitude, frequency, normal force or temperature is varied simultaneously per test section.