Validation of Fiber Breakage in Simple Shear Flow with Direct Fiber Simulation

This study aims to use particle level simulation to simulate the breakage behavior of glass fibers subjected to simple shear flow. Each fiber is represented as a chain of rods that experience hydrodynamic, interaction, and elastic effects. In order to validate the approach of the model, the simulation results were compared to simple shear flow experiments conducted in a Couette Rheometer. The excluded volume force constants and critical fiber breakage curvature were tuned in the simulation to gain a better understanding of the system. Relaxation of the fiber clusters and a failure probability theory were introduced into the model to solve the fiber entanglement and thus, better fit the experimental behavior. The model showed agreement with the prediction on fiber length reduction in both number average length and weight average length. In addition, the simulation had a similar trend of breakage distribution compared to a loop test using glass fibers.

pvT-Behavior of Polymers under Processing Conditions and Implementation in the Process Simulation

The development of high performance products at lowest possible product development-time and costs is the demand of the plastics industry today. A successful use of process simulation to describe the behavior of complex structures and to minimize the technical and economic risks for companies requires application and process-relevant material data.The pvT-behavior of polymers is an essential parameter for process simulations. Especially the dependence of the specific volume of pressure and temperature [1, 2] under process conditions is not mapped to the existing measurement methods.In this study pvT measurements were performed on selected amorphous and semi-crystalline polymers (PP, HDPE, POM, PBT, and ABS) with a Pirouette pvT device, a combination of a dilatometer and Couette rheometer. The specific volume was determined as a function of temperature (25-300°C) and at pressures ranging between 200-1000 bar. On top of that, the influence of the cooling rate was also investigated by pvT measurements performed at cooling rates of 0.1°C/s, 1°C/s and 100°C/s.The coefficients for the 2nd domain Tait pvT-model, which is implemented in the software Autodesk Moldflow, were determined by fitting the experimental pvT data and comparing them with the measured curves. As a result, the semi-crystalline polymers show a shift of the transition temperature to lower temperatures and a reduction in the specific volume in the melt is observed. For validation, in a case study shrinkage results in real were compared with the simulation.

Formulas for Calibration of Rheological Parameters of Bingham Fluid in Couette Rheometer

We propose simple formulas for calibration of rheological parameters of Bingham fluid using a co-axial cylinder rheometer, in which the inner cylinder rotates at a constant speed, and the outer cylinder is stationary. A critical rotational speed exists due to existence of yield stress. If rotation speed exceeds the critical value, all fluid is fully sheared between the concentric cylinders. Plug flow exists only when rotation speed is less than the critical value. The effects of radius ratio and Bingham number are discussed. The rheometer with radius ratio very close to unity is discussed as a limiting case, and the result confirms previous research. Formulas for calibration are derived using Least Squares and perturbation methods for all values of radius ratio, based on measured rotation speed and torque. Two sets of experimental data are used for verification. The validation shows that the formulas derived here yield reasonable and accurate estimates of rheological parameters.