Collaborative Research: Controlling the Microstructure for Improved Mechanical Properties of Large-scale Polymer Composite Structures Made by Big Area Additive Manufacturing

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This grant supports research that contributes to new knowledge related to a manufacturing process, thus promoting the progress of science, national prosperity, and national defense. Additive manufacturing, more commonly known as three-dimensional printing, is a method of making virtually any shape from a digital computer model. Although desktop three-dimensional printers have become quite popular, they are often limited to smaller objects without sufficient strength for structural applications. This research focuses on a relatively new class of additive manufacturing that is capable of making large-scale structures such as full-size cars and houses. This project conducts fundamental research to better understand big area additive manufacturing (BAAM) of extruded carbon-fiber reinforced polymer materials to produce higher strength components that can be used in the automotive, aerospace, energy, construction and defense sectors. This is a collaborative research effort between two universities that exposes a wide and diverse group of students, including women and minorities, to new manufacturing technologies and provide opportunities to engage in hands-on activities that encourage them to pursue a career in STEM-related fields.While the development of big area additive manufacturing (BAAM) of large-scale polymer structures has moved quickly, a basic understanding of the unique microstructure within an extruded fiber-reinforced polymer composite has not kept pace. The majority of recent efforts to improve the mechanical performance of 3D-printed materials has focused on interfacial properties and addressing meso-structural defects, such as voids between beads due to incomplete filling. However, there are significant opportunities for improving the mechanical performance of 3D printed structures by controlling the internal microstructure of the extruded bead. Specifically, the goal of this research is to maximize the mechanical performance of an extruded polymer composite by controlling the size, orientation, and distribution of reinforcing fibers and voids that define its internal microstructure. This is accomplished by altering the flow path and resulting shear strain fields within the single-screw extruder and optimizing processing parameters such as flow rate, pressure, and temperature profile. Research tasks seek to establish new finite element models for deposition flow as polymer melt passes through the screw and nozzle, in addition to constitutive models defined by differential equations that provide unique insight into fiber orientation, void formation, fiber breakage and particle migration during processing. The resulting knowledge and database of material properties enable the printing of tailored microstructures within BAAM parts and components.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.