Active Research Projects

Plasticity in High Entropy Alloys

High entropy alloys (HEAs) are a new class of metallic materials in which multiple elements are alloyed without a clear distinction of the dominant species. This is in contrast to conventional metallic alloys where a single species is dominant and alloying elements are present only in small concentrations. Recent research indicates that HEAs do not fit seamlessly into the current understanding of plastic deformation in metallic materials. The objective of this work is to provide a fundamental understanding of the role of composition and local chemical disorder on plasticity related mechanisms in HEAs. This includes stacking fault energies, dislocation Peierls barriers and dislocation mobilities.

Students: Yixi Shen, Tatiana Grower (B.S. MSE 2019)


Dislocation - Grain Boundary Interactions

The objective of this research is to develop a multiscale simulation approach to study dislocation – grain boundary interactions and to employ this approach to advance criteria for slip transfer across grain boundaries to consider the grain boundary damage state. In addition, the proposed simulation approach will allow for an analysis of the role of dislocation core structures on slip transfer. The hypothesis of this proposal is that the mechanisms by which dislocations are obstructed, absorbed, and/or transmitted through grain boundaries are sensitive to the damage state of the grain boundary (defined as a departure from equilibrium atomic structure) in addition to slip geometry. Such details are critically important to understand how grain boundaries promote strengthening or act as sources/sinks for damage during high rate plastic deformation. To meet this objective, this proposal introduces a unique approach to integrate classical atomistic simulations (molecular statics and molecular dynamics) and discrete dislocation dynamics (DDD) simulations.

Students: Khanh Dang (Ph.D. ME 2018), Darshan Bamney, Royce Reyes
Collaborator: Laurent Capolungo (Los Alamos National Lab)
Funding: Army Research Office


Combustion Reactions in Nanostructured Materials

Nanostructured Ni/Al reactive systems are a topic of scientific interest due to their highly modifiable exothermic output and unique industrial applications. These systems can be produced in both nanolaminate and mechanically-structured composite forms. This work investigates the role of internal defects and free surfaces on the reactivity of these systems. Initial work has focused on the effects of point defects and grain boundaries in the highly-ordered nanolaminate systems. Later studies will evaluate the relative roles of particle size and bilayer thickness on the reactivity of the mechanically-structured Ni/Al reactive composites and investigate the significance of the multiple diffusion paths available to these systems. The atomistic results will be incorporated into a continuum-level system description for use at higher length scales.

Students: Brandon Witbeck (Ph.D. ME 2020), Darren Tio (B.S. ME 2020)
Collaborator: Eglin Air Force Base
Funding: DOD SMART Fellowship (Witbeck)


Shock Wave Propagation and Dynamic Failure in Hydrogel Materials

Hydrogels consist of a polymer network absorbed in water. Hydrogels are an important class of materials because their properties may be customized to mimic the behavior of many biological tissues. Accordingly, hydrogels are commonly used as tissue simulants for skin, muscles and human organs (lungs, heart, brain, etc.) in experiments to study traumatic injuries. This research will provide an understanding of fundamental physical mechanisms related to the dynamic behavior of hydrogels, such as variation in wave velocity as a function of propagation distance and water volume fraction. Further, this research will provide a first understanding of high rate viscosity in hydrogels as a function of water content, atomic scale stresses and strains during high rate shearing deformation, and the rate of crack growth in hydrogel samples. Experiments will be conducted using a unique polymer split Hopkinson pressure bar customized to study shockwave propagation and dynamic fracture in hydrogel materials. Molecular dynamics simulations will be conducted to study shockwave propagation and viscosity with atomic resolution. Combined, data from experiments and simulation will be used to improve hyperelastic constitutive models for the dynamic mechanical behavior of hydrogels.

Students: Lucas Luo (Ph.D. MSE 2020), Charity Wangari (NSF REU), Amber Moynihan (B.S. MSE 2019), Ashley Foster (B.S. MSE 2020)
Collaborator: Ghatu Subhash (Unviersity of Florida)
Funding: National Science Foundation


Atomistic Modeling of Grain Boundary Embrittlement

This work investigates the relationships between interface properties, interface structure and impurities. MD simulations will be conducted to study crack propagation along grain boundaries with various structures (low angle vs. high angle grain boundaries) and various impurity concentrations, following the methodology proposed by Yamakov et al. (2008) for extracting cohesive zone models from atomistic simulations of crack propagation. The simulation approach used in this study is based on a MD simulation model of crack propagation under time-independent, or steady-state, conditions using a flat grain boundary. The nucleation stress for dislocations and the traction-displacement opening profile for a crack growing in a pre-stressed system will be extracted using MD simulations.

Students: Doruk Aksoy (Ph.D. ME 2020)
Collaborators: Remi Dingreville, Stephen Foiles (Sandia National Labs)
Funding: Sandia National Laboratories


Past Research Projects

Atomistic and Phase Field Modeling of Vapor Deposition Processes

The objective of this project is to elucidate the fundamental nanoscale and mesoscale mechanisms associated with microstructure development and evolution during vapor deposition, through combined use of atomistic and phase-field simulations. Historically, models for microstructure development during vapor deposition are formulated via extensive experimentation and materials characterization. These phenomenological models do not consider atomic or mesoscale material behavior and thus cannot predict microstructure development in complex heterophase material systems, such as alumina. In this work, atomistic simulations will be used to provide an understanding of the role of ion flux on phase evolution and to compute interface energies between solid metastable phases in alumina. This information will be incorporated into a phase-field model to study phase formation and evolution in alumina thin films during simulated physical vapor deposition conditions.

Students: Shawn Coleman (Ph.D. ME 2014), James Stewart (Ph.D. ME 2016)
Collaborators: Matt Gordon (University of Denver), Dave Glocker (IsoFlux Inc.)
Funding: National Science Foundation CAREER CMMI#0954505, National Science Foundation S-STEM DUE#0728636


Mechanical Behavior and Failure of MoS2

Recent focus on energy efficiency has motivated heavy machinery manufacturers to use nanoparticle-based lubricants that respond at different pressure and temperature widows. In this work, environmentally-friendly nanoparticles of molybdenum disulphide (MoS2) are studied as a solid lubricant. To elucidate the ability of MoS2 nanoparticles to be tunable to specific temperature regimes, it is first necessary to understand fundamentally the structure and size-dependent mechanical behavior of MoS2 nanoparticles.

Students: Khanh Dang, James Stewart (MS MicroEP 2012)
Collaborators: Ajay Malshe (University of Arkansas), Susan Sinnott (Penn State University)
Funding: National Science Foundation CMMI CMMI#1000912, National Science Foundation S-STEM DUE#0728636


Diffusion of Atmospheric Penetrates in PDMS

This research focuses on the fundamental processes of corrosion and multi-phase diffusion in metal particle polymer composites with functionalized nano behavior. The knowledge attained by this research will enable a new type of MEMS-based corrosion sensor technology that is small-size, tailorable and smart, ultimately allowing the US to better focus financial investments earmarked for infrastructure repair. Atomistic simulation is used to study the nanoscale details of diffusion in particle polymer composites. The proposed simulations will provide a detailed understanding of the role of the inclusions on the structure of the polymer chains in the matrix and on the transport of corrosive molecules through the composite. Fundamental aspects of diffusion in the composites studied in this work potentially have broad applicability to other sensing technologies.

Students: Alex Sudibjo (MSME 2010), Varun Ullal (MSME 2012)
Collaborator: Adam Huang (University of Arkansas)
Funding: National Science Foundation CMMI#0800718


Plastic Deformation of Nanocrystalline Metallic Alloys

In this work, molecular dynamics simulations are used to study dislocation activity in single-crystal and nanocrystalline copper with low concentrations of antimony (0.0-1.0 at.%Sb). In single crystal models, MD simulations show that the strained regions around substitutional Sb atoms act as sources for partial dislocations and that the dislocation nucleation stress decreases with increasing concentration of antimony. Substitutional Sb atoms positioned at the slip plane lower the intrinsic and unstable stacking fault energies in copper, effectively reducing the barrier for nucleation of partial dislocations. In nanocrystalline models, MD simulations show that very small concentrations of Sb positioned at the grain boundaries increase the flow stress of nanocrystalline Cu, but do not appear to shift the grain diameter associated with maximum strength.

Student: Rahul Rajgarhia (Ph.D. ME 2009)
Collaborators: Ashok Saxena (University of Arkansas), K. Ted Hartwig (Texas A&M), Oak Ridge National Laboratory
Funding: ORAU (Ralph E. Powe Junior Faculty Enhancement Award)


Cyberinfrastructure

Research tasks require the use of advanced cyberinfrastructure resources, including large-scale cluster computers and visualization, maintained by the Arkansas High Performance Computing Center (AHPCC).

A partnership between Arkansas and West Virginia has been established to build on common research in geosciences, virtual environments, and computational sciences while leveraging technical expertise within the two states: WV has expertise in the deployment and operation of shared high performance computing resources while AR leverages expertise in visualization and modeling. This consortium seeks to create a nationally competitive computation and visualization environment, to provide visualization display devices at each partnering institution, and to procure a suite of hardware and software for data capture and content creation that can enable a broad range of research and education activities across science and engineering domains. The consortium seeks to build the needed cyberinfrastructure to advance the frontiers of knowledge in several scientific domains, and to transform information technology services for enabling discovery and innovation. Dr. Spearot serves a critical role in this project as Faculty Campus Champion for Cyberinfrastructure.

Collaborators: Amy Apon (Clemson University), Jackson Cothren (University of Arkansas), et al.
Funding: National Science Foundation EPSCoR EPS#0918970, National Science Foundation ARI OCI#0963249, National Science Foundation MRI CNS#0959124