EAGER: Dispersion and Selective Positioning of Reinforcement in Polymer Matrix Composites

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Composite materials made with ceramic reinforcements in a polymer matrix offer features of high strength-to-weight ratio, flexibility, and flaw tolerance. One advantage for discontinuous (short) fiber-reinforced composites is the ease of manufacturing complex shaped parts. One disadvantage, however, is reduced strength as compared to continuous (long) fiber-reinforced composites, due to stress concentrations at the fiber ends in the composite during use. This stress localization at the ends of fibers can lead to bond failure between the matrix and fiber reinforcement causing cracks that lead to material failure. The novelty of this project's process is the ability to selectively position a range of particle sizes near the fiber ends to help reinforce and distribute the stress in that zone. This will result in higher strength for composite parts made with discontinuous fiber reinforcement, helping to enable low cost manufacturing of parts with intricate geometries.This EArly-Grant for Exploratory Research (EAGER) project will investigate the homogeneity, stability and reproducibility for fabricating and dispersing suspensions of colloidally-assembled hierarchical ceramic fillers for discontinuous fiber composites. These new materials are predicted to push discontinuous fiber composites toward the holy grail of increased strength and ductility, a combination that is not attainable in most material systems. When these hierarchical assemblies are incorporated into a polymer matrix, the polymer will infiltrate the near-interface of the assemblies to form an interphase region of enhanced mechanical stiffness that encompasses the even stiffer ceramic particles. This new perspective offers a material independent methodology for increasing the properties and performance of discontinuous fiber composites, while maintaining compatibility with bulk, economic, and facile manufacturing techniques such as injection molding, tape-casting or hot-pressing. This research project will answer several fundamental questions associated with stress transfer and failure mechanisms for materials consisting of dissimilar components, and also take advantage of emerging technologies that enable processing of composites with hierarchical morphology (i.e., stepping between macro- micro- and nano- regimes). The work will also provide insight toward the challenges associated with fabrication (i.e., dispersion and preparation) as well as reproducibility and reliability of the composite manufacturing process.