Measurement and mechanisms of elastic deformation in amorphous solids

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Non-technical summaryAmorphous solids are materials in which the atoms or molecules are not arranged in a regularly repeating pattern. Ordinary window glass and many plastics are amorphous, but there are more exotic examples such as metallic glasses. Our interest is in understanding how the structure of amorphous materials change when they are deformed by being placed under mechanical stress. In this program we use computer models to study how the atoms and molecules in an amorphous material rearrange themselves when the material is deformed. The results from the models are compared with experiments in which we examine how x-rays and neutrons are scattered by the material as it is deformed, providing information about the how the atomic and molecular structure evolves. One goal is to develop these scattering techniques into reliable routine tools for measuring the deformation which could then be used by researchers interested in a wide range of applications, including studies of residual stresses in glasses and the mechanical behavior of complex materials such as bone.The primary educational objective of this program is to develop rigorous, validated tools for assessing student learning in a core undergraduate Structure of Materials course. These tools will be disseminated for use by other instructors and provide a template for how to develop similar assessment instruments for undergraduate materials science courses, and engineering courses more generally.Technical summaryRecent experimental and computational results clearly demonstrate that nominally elastic (recoverable) deformation in amorphous solids is considerably more complex that the simple bond-stretching picture invoked in describing elastic deformation of crystalline solids. The first objective of this program is to understand fundamental mechanisms of elastic deformation in amorphous solids using metallic glasses and linear amorphous homopolymers as model systems. This will be investigated using molecular dynamics simulations, paying particular attention to inhomogeneous, non-affine atomic and molecular rearrangements now believed to be responsible for several unusual phenomena observed during nominally elastic loading. The second objective is develop x-ray and neutron scattering into reliable tools for quantitative, non-destructive measurement of elastic strains from non-crystalline solids. This will give researchers a powerful new ability to explore the mechanical behavior of a wide range of complex materials with amorphous constituents. Potential applications include investigation of internal residual stresses due to processing of oxide and polymer glasses and in situ studies of load transfer in polymer matrix composites and hard biological materials such as bone.The primary educational objective of this program is to develop rigorous, validated tools for assessing student learning in a core undergraduate Structure of Materials course. These tools will be disseminated for use by other instructors and provide a template for how to develop similar assessment instruments for undergraduate materials science courses, and engineering courses more generally.