Understanding the Mechanical Behavior of Novel High-Strength Nanoscale Structures

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One application of nanostructured materials is incorporation into solid surfaces, to alter the properties and behavior of these surfaces. These nanostructures, however, often deform very easily under contact stresses encountered in typical applications, which severely limits their durability. A novel nanoscale "core-shell" structure was recently discovered to have unusually high strength and deformation resistance; however, the nanoscale mechanisms that contribute to this unusual mechanical behavior are not currently known. This award supports research to gain a fundamental understanding of the mechanical behavior of the novel high-strength nanoscale structures, in order to design nano-textured surfaces using these structures for optimized mechanical performance. This research will provide valuable information to guide the rational design of nano-textured surfaces employing nanoscale these core-shell structures for micro/nano-electro-mechanical systems (MEMS and NEMS), and provide potential solutions for this multi-billion dollar industry to solve plaguing issues of wear and contact mechanics. The novel nanoscale core-shell structure concept can also be applied to other applications, including magnetic recording, nanoimprinting, surface wetting, and biomedical applications, where mechanical integrity of the nanostructures is of paramount importance. Comprehensive education and outreach activities will be implemented which will significantly stimulate the next generation's interest in nanomaterials and nanomechanics and will improve America's future competitiveness in nanotechnology.This award supports an integrated experimental and modeling approach to bridge material length scales, to (1) perform nanoindentation experiments to investigate the effects of core and shell materials, core size and microstructure, and shell thickness and shell/core volume ratio on the mechanical behavior of nanoscale core-shell structures, including strain hardening and fatigue, (2) to develop and validate molecular dynamics and coupled atomistic-continuum multiscale simulation models to understand the role of the core/shell interface, core/substrate interface, core microstructure, core material, and substrate thickness; and determine the mechanisms contributing to the large recoverable deformation and high strength of the nanoscale core-shell structures, and (3) after model validation, to computationally explore a sufficient core/shell parametric space so that the fundamental understanding provided by the simulations can guide the fabrication of nanoscale core-shell structures with optimal behavior, beyond the original experimental space. The research will result in a fundamental understanding of the unique mechanical behavior of nanoscale core-shell structures attached to substrates and identify the mechanisms that provide the novel mechanical behavior of these structures. The research can also result in molecular dynamics and multiscale models that can be used as design tools for surface engineering with nanoscale core-shell structures.