Multiscale Modeling of Water Absorption and Mechanical Strength of Polymer Matrix Composite Materials Containing Voids

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This award supports an investigation into water transport in composite materials containing voids due to direct contact with liquid water, and the associated degradation of the performance of the material. The potential degradation of the matrix polymer and the interface will be measured and the test data will be used to calibrate models for such degradation. Polymer matrix composite materials are used in structural applications exposed to water. As polymer matrix composite materials are gaining wide acceptance for several important structures, there has been concern about possible degradation of the performance from exposure to moisture in the form of humid air. Less considered is the influence of direct contact of the composite with liquid water. Such exposure under the presence of voids in the composite may allow water transport in the form of capillary flow. Capillary flow represents a very rapid mechanism of transport which will elevate diffusion into the polymer, and cause increased rate of degradation of the organic polymer and fiber/matrix interface. A substantial fraction of the US export and economy relies on the automotive, aircraft and ship building industries, and results from this research will benefit the US economy and society. This research involves multiple disciplines such as microfluidics, materials science and solid mechanics. The multi-scale approach outlined will involve students from underrepresented groups in science and engineering, and is expected to impact the engineering education program in a very positive manner.Voids and porosity are detrimental structural imperfections in polymer matrix composite materials, not only due to strength reduction, but they provide extra paths for water absorption and filling beyond moisture diffusion in matrix. This project specifically addresses the fundamental problems of the interferences between structural defects, moisture uptake, and mechanical strength and fracture mechanisms of underwater composite materials. Specific objectives are: (1) quantify structural defects in composite materials using scanning electron microscope and micro-computed tomography methods, establish a reliable water uptake model and validate with microfluidics testing; (2) characterize the fiber/matrix interface strength of dry and water-aged composite materials, using in situ scanning electron microscopy on miniature transverse single-fiber and composite tensile specimens; (3) establish a multiscale micromechanical model for prediction the strength of a macroscopic composite exposed to water aging. Predictions will be compared to and validated by the experimental measurements for water-aged glass/vinylester and glass/epoxy composites.