We investigate the mechanisms of fatigue behavior in nano-crystalline metals at the atomic scale using empirical force laws and molecular level simulations. A combination of molecular statics and molecular dynamics was used to deal with the time scale limitations of molecular dynamics. We show that the main atomistic mechanism of fatigue crack propagation in these materials is the formation of nano-voids ahead of the main crack. The results obtained for crack advance as a function of stress intensity amplitude are consistent with experimental studies and a Paris law exponent of about 2.

Nanocrystalline (NC) materials, defined structurally by having average grain sizes less than 100nm, exhibit a number of enhanced mechanical properties such as ultrahigh strength, improved wear resistance and greater resistance to fatigue crack initiation compared to coarser grained polycrystalline (PC) materials. NC materials exhibit these improved properties, in part, due to the increased grain boundary (GB) volume fraction. NC materials strength increases with decreasing grain size, known as the Hall-Petch (HP) effect often resulting in a peak strength between 10-20nm. Studies have shown that NC materials strength decreases due to the shift from dislocation-dominant to GB-dominant deformation mechanisms in the plastic flow regime as average grain size decreases below 10-20nm. While the potential improved properties are of interest, the application of NC materials are hindered due to microstructural instability i.e., grain growth to reduce the total energy of the system, thus degrading desired mechanical properties. Numerous studies have looked at avenues to stabilize NC microstructure, namely through thermodynamics and kinetics, alloying has been one significant strategy used to stabilize NC materials. As these processes are used to stabilize NC microstructures to thermally-induce grain growth, they add additional uncertainty as the deformation and GB behavior of pure NC materials are still not fully understood. Experimental work on NC materials is difficult due to the length scale being investigated as it is difficult to manufacture and can be time consuming to analyze with current technology. Atomistic simulations have shown the potential to investigate fundamental behavior at the nanoscale and provide important insight in the mechanisms that drive the mechanical behavior of NC materials. This thesis will use atomistic simulations to study the structure-property relationship of face-centered-cubic (fcc) metals by focusing on GBs to investigate the strength of NC nickel. During the course of this thesis, four aspects that govern NC behavior will be studied, yielding, plasticity, thermal effects, and GB disorder to elucidate deeper insight into the underlying deformation mechanisms that control the strength of FCC NC metals i.e., flow stress, in the grain size regime 6 to 20nm.

Providing in-depth information on how to obtain high-performance materials by controlling their nanostructures, this ready reference covers both the bottom-up and the top-down approaches to the synthesis and processing of nanostructured materials. The focus is on advanced methods of mechanical nanostructuring such as severe plastic deformation, including high pressure torsion, equal channel angular processing, cyclic extrusion compression, accumulative roll bonding, and surface mechanical attrition treatment. As such, the contents are inherently application-oriented, with the methods presented able to be easily integrated into existing production processes. In addition, the structure-property relationships and ways of influencing the nanostructure in order to exhibit a desired functionality are reviewed in detail. The whole is rounded off by a look at future directions, followed by an overview of applications in various fields of structural and mechanical engineering. With its solutions for successful processing of complex-shaped workpieces and large-scale specimens with desired properties, this is an indispensable tool for purposeful materials design.

This book describes the main approaches for production and synthesis of nanostructured metals and alloys, taking into account the fatigue behavior of materials in additive manufactured components. Depending on the material type, form, and application, a deep discussion of fatigue properties and crack behavior is also provided. Pure nanostructured metals, complex alloys and composites are further considered. Prof. Cavaliere’s examination is supported by the most up-to-date understanding from the scientific literature along with a thorough presentation of theory. Bringing together the widest range of perspective on its topic, the book is ideal for materials researchers, professional engineers in industry, and students interested in nanostructured materials, fracture/fatigue mechanics, and additive manufacturing. Describes in detail the relevance of nanostructures in additive manufacturing technologies; Includes sufficient breadth and depth on theoretical modelling of fatigue and crack behavior for use in the classroom; Identifies many open questions regarding different theories through experimental finding; Contextualizes the latest scientific results for readers in industry.

Nanostructured materials are one of the highest profile classes of materials in science and engineering today, and will continue to be well into the future. Potential applications are widely varied, including washing machine sensors, drug delivery devices to combat avian flu, and more efficient solar panels. Broad and multidisciplinary, the field includes multilayer films, atomic clusters, nanocrystalline materials, and nanocomposites having remarkable variations in fundamental electrical, optic, and magnetic properties.Nanostructured Materials: Processing, Properties and Applications, 2nd Edition is an extensive update to the exceptional first edition snapshot of this rapidly advancing field. Retaining the organization of the first edition, Part 1 covers the important synthesis and processing methods for the production of nanocrystalline materials. Part 2 focuses on selected properties of nanostructured materials. Potential or existing applications are described as appropriate throughout the book. The second edition has been updated throughout for the latest advances and includes two additional chapters.

State-of-the-technology tools for designing, optimizing, and manufacturing new materials Integrated computational materials engineering (ICME) uses computational materials science tools within a holistic system in order to accelerate materials development, improve design optimization, and unify design and manufacturing. Increasingly, ICME is the preferred paradigm for design, development, and manufacturing of structural products. Written by one of the world's leading ICME experts, this text delivers a comprehensive, practical introduction to the field, guiding readers through multiscale materials processing modeling and simulation with easy-to-follow explanations and examples. Following an introductory chapter exploring the core concepts and the various disciplines that have contributed to the development of ICME, the text covers the following important topics with their associated length scale bridging methodologies: Macroscale continuum internal state variable plasticity and damage theory and multistage fatigue Mesoscale analysis: continuum theory methods with discrete features and methods Discrete dislocation dynamics simulations Atomistic modeling methods Electronics structures calculations Next, the author provides three chapters dedicated to detailed case studies, including "From Atoms to Autos: A Redesign of a Cadillac Control Arm," that show how the principles and methods of ICME work in practice. The final chapter examines the future of ICME, forecasting the development of new materials and engineering structures with the help of a cyberinfrastructure that has been recently established. Integrated Computational Materials Engineering (ICME) for Metals is recommended for both students and professionals in engineering and materials science, providing them with new state-of-the-technology tools for selecting, designing, optimizing, and manufacturing new materials. Instructors who adopt this text for coursework can take advantage of PowerPoint lecture notes, a questions and solutions manual, and tutorials to guide students through the models and codes discussed in the text.