Insights into advanced rheological testing methods using a dual motor device

A rheometer platform based on a combined motor transducer (CMT) rheometer equipped with an electrically commutated synchronous motor on the upper side facilitates the use of a second motor on the bottom side. The second motor could either be a rotational or a linear drive. By using a rotational drive the device is turned into a separate motor transducer (SMT) rheometer by using one motor as drive and the second as a torque transducer. In addition it can operate in a counter rotational mode, where both motors rotate in opposite directions and thus enabling the creation of a stagnation line in the sample at which it is sheared but not moved from its position. A SMT mode has some advantages in sensitivity under certain measurement conditions and allows the use of special tools such as for example a cone-partitioned-plate (CPP), which enables measurements even if edge fracture would hinder them in standard geometries. Counter rotation is especially useful for the investigation of Tayler-Couette instabilities or for rheo-microscopy, since the structures under investigation are not moving out of the field of view when shear is applied. Combining the upper rotational motor with a linear drive in the bottom permits new testing capabilities. The linear drive itself provides force and linear movement information and can it this respect be called a CMT device. By solely using the linear drive Dynamic Mechanical Analysis (DMA) testing on more solid like samples with various geometries like tension, three-point bending, cantilever, or in compression is possible. Using a geometry for solid bars DMA in tension by the linear drive and DMA in torsion by using the upper rotational drive are possible on the same specimen, thus allowing to extract not only the DMA parameters but also the Poisson ratio. In another application fast linear movements lead to a rapid extension of for example low viscous samples. From the relaxation and the capillary thinning process extensional rheological properties can be extracted.


Dr. Jörg Läuger (English)