Aerospace and Mechanical Engineering
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Ryan S. Elliott

Russell J. Penrose Faculty Fellow
Associate Professor

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Distinct Reseach Projects in My Group


* Branch-following and bifurcation (BFB) methods to identify active materials for tomorrow's sensors and actuators

Support: NSF CMMI (Dr. Shih-Chi Liu, Program Director) CAREER grant


A critical problem currently limiting the technological use of active materials for novel sensor/actuator applications is the lack of accurate analysis and design tools. The overall objective of this project is to develop and validate a branch-following and bifurcation computational methodology capable of systematically mapping out the active behavior of new sensor materials.

New atomistic material models will be developed for active material behavior and computational branch-following and bifurcation (BFB) methods, adapted specifically for studying crystalline materials, will be created. These models and methods will be capable of revealing the lattice-level mechanisms responsible for active behavior. The new techniques will be validated against recently obtained experimental data for the shape memory alloy NiTi and its ternary alloys. The results of this project will include the creation of new computational methods for accurately modeling and interrogating the free energy landscape of active materials and will ultimately result in the development of a mature and robust technology for the design of active materials.


* Three dimensional atomistic models for shape memory alloys (SMAs)

Collaborator: N. Triantafyllidis and J. A. Shaw

Support: NSF CMMI (Dr. Shih-Chi Liu, Program Director) CAREER grant


Martensitic solid-to-solid phase transformations are responsible for the remarkable properties of SMA. This project aims to understand the existence of temperature-induced and stress-induced transformations in SMAs by studying an atomistic model using bifurcation and path-following (BFB) techniques. These techniques provide a wealth of detailed information that helps to explain the presence of these transformations and could eventually be used to design new SMAs that have dramatically improved properties.


* Free energy landscape models for active materials


Standard methods of modeling a material's free energy landscape, such as Finite-Temperature DFT (using the quasi-harmonic approximation) and Effective-Hamiltonian Molecular Dynamics, are not accurate enough for design purposes. This is because these techniques are not able to capture the nonlinear effects of the atomic motion at finite-temperatures in sufficient detail. Thus, new finite-temperature free energy models that explicitly incorporate the nonlinear configurational dependence of the atomic force fields is being developed. These methods will more fully capture the finite-temperature dynamics, and thus, achieve the goal of accurately predicting the material's active properties as functions of temperature.


* Multilattice quasicontinuum methods

Collaborator: E.B. Tadmor


A new multiscale technique, called the quasicontinuum method with cascading Cauchy-Born kinematics (QC/CCB), is being developed that will allow, for the first time, the study of phase transforming multilattice materials subjected to highly nonuniform loading and deformation. A one-dimensional version of this technique has proven very effective and preliminary results indicate great potential for the general three-dimensional method currently under development.


* Quasicontinuum Branch-Following and Bifurcation Investigations

Collaborators: E.B. Tadmor and T. Sendova


This projects aims to develop a better understanding of discontinuous instabilities that occur in finite atomistic systems. These include defect formation (such as dislocations) and solid-to-solid phase transformation. The project couples Prof. Tadmor's Quasicontinuum software package with my BFBSymPack branch-following and bifurcation with symmetry software package. The combined packages provide the never-before-available ability to carefully map out the multitude of equilibrium configurations possessed by discrete atomistic systems. The use of symmetry and group-theory methods has proven to be critical to obtaining a clear and complete description of a system's behavior.


* Alloy modeling and exploration via homogenization and BFB techniques


Many material properties are known to exhibit extreme sensitivity to alloy composition. This is especially true of active materials. Currently, computational alloy modeling techniques are able to predict the behavior of alloys with no more than two types of atoms. However, it is already common for real alloys to contain four or more types of atoms. Thus, a new theory of composition effects in alloys is critical in order to realize a computational materials design methodology. This project is applying the mathematical theory of "homogenization" to develop a new methodology for predicting the effects of an alloy's composition on its properties. The goal of homogenization theory is to predict the behavior of a "composite material," a complex material made up of several other simpler materials. This is achieved by using only a knowledge of the behavior of the simple materials and a small amount of information about how these materials are combined, such as the relative amounts of each simple material contained in the final composite material. Homogenization methods are commonly used with traditional materials modeling techniques (like Elasticity Theory and Plasticity Theory), but they have not been applied to the atomic level materials modeling techniques that are required to perform truly predictive materials design. In order to achieve this goal and ultimately develop a computational materials design methodology, this project aims to adapt these homogenization methods for use with atomic level models.


* Knowledge-base of interatomic models

Collaborators: E.B. Tadmor, J.P. Sethna

Support: NSF CDI grant


Atomistic simulations such as molecular dynamics and multiscale methods are playing an increasingly important role in realistic scientific and industrial applications from materials science to biology. The predictive capability of these approaches hinges on the accuracy of the interatomic model used to describe atomic interactions. Modern models are optimized to reproduce electronic structure estimates for the forces and energies of representative atomic configurations deemed important for the problem of interest. However, no standardized approach exists yet for comparing the accuracy of interatomic models, or estimating the likely accuracy of a given prediction. The result is that interatomic models suffer from a limited, uncontrolled capacity to predict phenomena outside the fitting database.

Recent developments in computational thinking tied to the extraction of knowledge from vast databases, together with the capacity of the Internet to create a virtual organization from disparate groups, have created the opportunity to revolutionize the manner in which interatomic models are designed, tested and accessed. Rather than the current paradigm, where research groups work with interatomic models in isolation, this project aims to develop the Knowledge-base of Interatomic Models (KIM). KIM will be an online virtual organization bringing together all researchers working in the broad field of atomistic simulation, as well as all known data and computational tests they have generated that are relevant to the fitting and selection of interatomic models. This comprehensive, user-extendible framework will create an unprecedented resource for users of atomistic models by ensuring easy, reliable and standardized access to models and tests. Moreover, KIM will couple this database with sophisticated, novel methods for evaluating the accuracy and predictive capacity of fitted models. We believe the result will be a new paradigm, where predictive, accurate interatomic models are designed using the collective knowledge of the entire atomistic modeling community at a fraction of the time currently necessary.


* Design and behavior of nano-structures

Collaborators: K. Dayal, R.D. James


A new theory of "objective structures" is being developed and explored. This theory provides a novel framework for describing of a wide range of atomistic structures. Examples include carbon nanotubes, C_{60}, viral capsids and many viral parts (necks, tails, baseplates), many of the common proteins (actin, GroEL, hemoglobin, potassium channel), bilayers (staggered and unstaggered), and various kinds of molecular fibers. This project aims to apply this new framework to study the behavior of these important structures and to search for new atomic scale structures that are capable of exhibiting "active behavior."

Last Modified: 2014-12-29 at 10:46:12 -- this is in International Standard Date and Time Notation