Atomistic Simulations of Deformation and Fracture Mechanisms in Nanotwinned Nanowires and BiomaterialsYin, ShengcreatorKim, Kyung-SukReaderKumar, SharvanReaderGao, HuajianAdvisorBrown University. Engineering: Mechanics of Solidssponsor2017xiv, 127 p.born digitalThesis (Ph. D.)--Brown University, 2017thesesOver the past decade, nanotwinned metals have attracted considerable attention due to their exceptional mechanical properties, such as ultra-high strength, good tensile ductility, high fracture toughness and remarkable fatigue resistance. Besides metals, in biological materials, some aragonitic mollusk shells, such as Strombus gigas conch shell, are found to contain a high density of {110} growth twins in its third order aragonite lamellae, the basic building block of the material. Nanoscale twins have also been incorporated into polycrystalline ceramics such as cubic boron-nitride (cBN), diamond, boron-carbide (B4C) and boron-suboxide (B6O) during the last few years. One-dimensional (1D) nanostructures, such as nanowires are widely regarded as among the most important building blocks for a broad range of applications. The deformation mechanisms in nanowires with different twin boundary structure have also received much interest. In this thesis, I investigate the contribution of the inherent nanoscale twins in the conch shell to its fracture toughness at the basic building block level. I report an unusual time-dependent deformation behavior in penta-twinned Ag nanowires, with stress relaxation upon loading and complete strain recovery upon unloading. A tensile detwinning mechanism in bi-twinned nanowires which will lead to superplastic deformation is discovered. I also studied the hydrogen embrittlement behavior in penta-twinned Ag nanowires.BiomechanicsMolecular dynamics--Computer simulationNanowiresPlasticityDislocations in metalsMetals--Hydrogen embrittlementEnglishRPB2017061610.7301/Z07D2SN5In CopyrightCollection is open for research.dissertations