Xianggang Li

Dynamic displacement control error of multifunction and all-electric rheometer

A new multi-function and all-electric rheometer (MAR) is designed by the authors. A sine vibration displacement is superimposed on the steady-state displacement of the piston in parallel. In order to study the dynamic displacement control error of MAR, its frequency and amplitude was obtained through decomposing the measured resultant displacement into steady-state displacement and the dynamic displacement, and transforming the time-domain signal into frequency-domain presentation. The results show that both the frequency and amplitude control errors of MAR are small enough for the test requirement. However, the repeatability of measured values of amplitude is not as well as the frequency. And they are always smaller than the set values. The mean values of amplitude relative errors are about 2%, so it may be a useful way to set the amplitude 2% higher than the wanted values. The relative errors of amplitude in 5Hz are slightly larger than the errors in the other cases. It may caused by the reason that 5Hz is closed to the lower limitation of the vibration table rated frequency.

Method of Calculation of Instantaneous Shear Stress of Polymer Melts Extruding Through a Capillary under Vibration

A calculation method for the instantaneous shear stress of polymer melts extruding through a capillary under vibration is developed. Although directly applied to a multifunction and all-electric rheometer (MAR) designed by the authors, it is believed to be generally applied. The method of determination of each parameters value is given. The influence of compressibility is discussed. A quantitive determination method is given to judge whether the influence of compressibility can be ignored or not. According to the magnitude range of the three terms of the shear stress formula, the gravity effect can be ignored when the polymer melt rheological behavior is studied with MAR, and the inertia effect can normally be ignored under certain conditions. Therefore, the formula can be reduced to two terms normally or to one term under certain conditions. The application example indicates that this calculation method is convenient and feasible. The instantaneous shear stress can be further analyzed by the methods that are used to analyze the nonlinear behavior in oscillatory experiments, such as Fourier-transform rheology (FT-rheology) and general stress decomposition (GSD). The further analyzed results can be related to some information of the polymer melts at high shear rate. The factors that depend on the shear rate and influence the viscoelastic properties can be studied by this method.

Development of multi-function and all-electric rheometer

A new multi-function and all-electric rheometer (MAR) is designed by the authors. Functional requirements and technical index was presented from the practical need. Oscillation superposition onto a high rate steady shear is realized. It can be seen as a traditional rheometer without vibration to test the temperature and shear dependent viscosity, and polymer elasticity indicated from the die swell of the extrudate and the phenomenon of melt fracture. It can be used to simulate the steady-state and dynamic extrusion and injection processing to evaluate theoretical results analysis results. And it is also useful in studying the dynamic rheological properties of polymer melts at high shear rate.