This grant provides funding for the development of computer models to simulate the behavior of fiber reinforced composite parts during the manufacturing process and to couple the new models with existing commercial compression and injection molding software. During the manufacturing of short fiber reinforced composite parts, mold filling plays a significant role in the quality, reflected by fiber damage, excessive fiber orientation, fiber jamming and fiber matrix separation. Current approaches are based on simulation as well as trial and error techniques. However, in order to properly deal with fiber damage, fiber jamming and fiber-matrix separation, a comprehensive understanding of the physics behind fiber motion is required. Within this project, the fibers are modeled using a mechanistic approach, where their structure is represented as a flexible chain composed of a combination of springs and beads or cylinders.
The final product will allow the process engineer to predict potential defects and optimize the properties of a part before a mold is actually made. Simulation results will include final fiber orientations, fiber attrition and fiber density distributions within a molded part. Furthermore, such a tool will help shed light on phenomena that are not well understood, such as fiber matrix separation, that result in ribs and features with low fiber content and in injection molded parts with a fiber free skin region. With a higher level of understanding of fiber motion phenomena during molding, it will eventually be possible to mass produce polymer composite parts with higher quality and controlled properties, making lightweight polymer composites available to a wider range of applications, at a time when energy efficiency and innovation are needed in the automotive and aeronautical industries. Furthermore, the nature of this project will provide students the unique opportunity to obtain interdisciplinary training in various fields including material science, polymer composites engineering, systems science, and manufacturing.
In some polymer composite manufacturing processes, the number of defective parts can be more than half of the total production. Mold filling phenomena play a significant role in fiber attrition, fiber orientation, fiber jamming and fiber matrix separation. These problems has been approached by simulation as well as trial and error techniques considering that in order to properly optimize these processes, a comprehensive understanding of the physics behind the process is required. The main goal of this work was to model the behavior of flexible fiber suspensions at polymer processing concentrations and to couple the modeling algorithm with existing commercial software, used for the modeling of injection and injection compression molding. Currently, there is no software tool able to predict fiber orientation and density distribution within a molded part. Defects such as fiber jamming and fiber matrix separation are also only corrected by trial and error techniques to yield acceptable parts. As the popularity of molding processes increase and polymer composites become an alternative material in an era where environmental concerns, energy consumption and intelligent materials are the main challenges faced by industry, it is then required to develop the proper tools such as the ones developed along this project to ensure that the full potential of polymer composites is reached. A mechanistic simulation approach was developed at the Polymer Engineering Center (PEC) in UW-Madison was perfected and optimized to be able to simulate industrial size molding problems. In these models, fibers are modeled as chains or rigid beads connected by springs (Figure 1). Parameters such as fiber concentration, fiber length and stiffness can be modified to match specific processing conditions. Simulation results will include final fiber orientations, fiber distributions and also fiber size distribution since the mechanistic model is able to predict fiber breakup (Figure 2). These simulations were validated with experimental measurements conducted at the PEC Laboratories (Figure 3 and Figure 4) and with models that predict fiber orientation distribution. These aid in the understanding of the fiber-fiber and fiber matrix interaction to the mechanical properties, optical properties and general properties of a final product. Specific applications for these types of simulations include processes such as the compression molding of sheet molding compound, and injection-compression molding. Implementation of such simulation tool will allow the process engineer to predict defects, as well as the properties of the final part before a mold is actually made by controlling fiber density distribution and orientation during processing, and by simulating molding processes before they take place in reality. This lead to parts where mechanical properties are tailored depending on the use of the part while also minimizing the weight. With this level of control and the understanding of the molding phenomena it is possible to mass produce polymer composite parts and therefore make them available for a wider range of applications. Once polymer composites have become standard and mass produced, energy requirements in processing will decrease, lightweight parts will result in increased efficiency, and the percent of defective parts will decrease. This will be beneficial to the nation in terms of reduced energy consumption in processing and in terms of weight, reduction of greenhouse effects and most importantly it will provide a technical edge in industries such as the automotive and aeronautical at a time where innovation is needed. Additionally, the outcomes of this project have provided students the opportunity to obtain interdisciplinary training in various fields including mechanical engineering, material science, system science, and statistics.
