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Extension of the Method of Ellipses to Determining the Orientation of Long, Semi-flexible Fibers in Model 2- and 3-dimensional GeometriesHofmann, John 23 October 2013 (has links)
The use of fiber-reinforced polymer composites formed via injection molding is of increasing interest due to their superior mechanical properties as compared to those of the polymer matrix alone. These mechanical properties, however, are strongly dependent on the fiber length and orientation distributions within a molded part. As such, there is a need to understand and model the orientation evolution of chopped fibers in flow in order to accurately simulate the final fiber orientation distribution within injection molded parts. As a result of this, accurate and reliable experimental measurement of fiber orientation is needed.
Within this research, the application and validity of the Method of Ellipses for determining the orientation of long, semi-flexible glass fibers within injection molded composites has been investigated. A fiber suspension with an average length of approximately 3.9 mm was the focus of this study and assumed to be representative of commercial distributions. A novel method to quantify fiber curvature was developed and utilized to show that flexibility in center-gated disc and the end-gated plaque samples was minimal on average for the selected fiber length distribution. Thus, it was determined that the Method of Ellipses was applicable when utilized to obtain reliable orientation data for the selected long glass fiber suspension and within the chosen geometries that exhibit 1-, 2-, and 3-dimensional velocity fields. However, a modified image analysis width was found to be necessary in regions of highly aligned fibers, due to the increase in ellipse size and the need to reduce the number of partial objects and thus minimize error. This allowed for a direct comparison of the experimental orientation behavior of short and long glass fibers within the center-gated disc and the end-gated plaque, as well as the effect of the orientation distributions on the global modulus of the part. / Ph. D.
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Experimental Evaluation and Simulations of Fiber Orientation in Injection Molding of Polymers Containing Short Glass FibersVelez-Garcia, Gregorio Manuel 22 May 2012 (has links)
Injection molded short fiber reinforced composites have generated commercial interest in the manufacturing of lightweight parts used in semi-structural applications. Predicting these materials’ fiber orientation with quantitative accuracy is crucial for technological advancement, but the task is difficult because of the effect of inter-particle interactions at high concentrations of fiber found in parts of commercial interest.
A complete sample preparation procedure was developed to obtain optical micrographs with optimal definition of elliptical and non-elliptical footprint borders. Two novel aspects in this procedure were the use of tridimensional markers to identify specific locations for analysis and the use of controlled-etching to produce small shadows where fibers recede into the matrix. These images were used to measure fiber orientation with a customized image analysis tool. This tool contains several modifications that we introduced in the method of ellipses which allow us to determine tridimensional fiber orientation and to obtain measurements in regions with fast changes in orientation. The tool uses the location of the shadow to eliminate the ambiguity problem in orientation and characterizes non-elliptical footprints to obtain the orientation in small sampling areas.
Cavitywise measurements in two thin center-gated disks showed the existence of an asymmetric profile of orientation at the gate and an orientation profile that washed out gradually at the entry region until disappearing at about 32 gap widths. This data was used to assess the prediction of cavitywise orientation using a delay model for fiber orientation with model parameters obtained from rheometrical experiments. Model predictions combining slip correction and experimentally determined orientation at the gate are in agreement with experimental data for the core layers near the end-of-fill region.
Radialwise measurements of orientation at the shell, transition and core layer, and microtextural description of the advancing front are included in this dissertation. The analysis and assessment of the radial evolution of fiber orientation and advancing front based on comparing the experimental data with simulation results are under ongoing investigation. / Ph. D.
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