The primarily focused of our research group is to develop a fundamental understanding of the underlying deformation mechanism in materials. Our goal is to enhance the field of Materials-by-Design, by moving from empirical, trial-and-error development techniques of materials, to a combination of state of the art multiscale computational methods and experimental techniques that can result in expediting the process of developing reliable materials with superior performance.

Atomistic and Discrete Dislocation Dynamics Modeling of Mechanical Twinning and Plasticity in Magnesium

   The Center for Materials in Extreme Dynamic Environments
   U.S. Army Research Laboratory
P.I. Jaafar El-Awady
Project Dates: 04/16/2012-04/15/2017
Post-Doc: Haidong Fan

Due to its light weight and its abundance in the earth crust, magnesium alloys are being used in a number of applications (e.g. automobile, aerospace, armors, etc.). The objectives of this research are to study dislocation and twinning plasticity in magnesium using a combined approach utilizing molecular dynamics simulations and discrete dislocation dynamics simulations.

Micro-Mechanics Modeling of Surface Roughness Evolution and Subsequent Crack-Initiation under Thermo-Mechanical Fatigue

   Young Faculty Award
   Defense Advanced Research Projects Agency
P.I. Jaafar El-Awady
Project Dates: 06/25/2012-06/24/2015
Graduate Students: Ahmed M. Hussein, and Quan Jiao

The need to develop and formulate reliable fatigue damage life prediction methods for metals used in civil and military aerospace applications is ever-growing. Fatigue damage is manifested in the initiation of short-cracks near regions of high stress concentrations due to localized surface-slip, and dislocation pileups at inclusions and grain boundaries. The lack of knowledge on how localized plastic flow translates to the accumulation of internal stress concentrations remains a fundamental problem in developing fatigue-life prediction models. This research utilizes the discrete dislocation dynamics technique coupled with crystal plasticity as a platform to correlate surface roughness evolution and crack nucleation with the evolving dislocation microstructure parameters under thermo-mechanical loadings.

Center of Excellence in Integrated Materials Modeling (CEIMM): Coarse-Graining Simulations of Plasticity and Fracture of Epoxy Polymers

   Air Force Office of Scientific Research
   Air Force Research Laboratory
PI: Jaafar El-Awady
Project Dates: 09/01/2012-08/31/2015
Graduate Student: Amin Aramoon

The Center of Excellence on Integrated Materials Modeling (CEIMM) provides a collaborative, multidisciplinary research and educational environment to foster foundational advances in computational and associated experimental methodologies, supporting the Integrated Computational Materials Science and Engineering (ICMSE) theme. The primary opjective of this task is to develop an equivalent three dimensional coarse-grained discrete polymer chain-network dynamics model for highely entagled epoxy polymers. The model will significantly reduce the number of degrees of freedom in highly entangled polymer networks. This model will allow to model the free volume evolutions in epoxies as a function of strain to formulate a microstructurally-based constitutive representation of plasticity in these highly cross-linked polymers.

Discrete Dislocation Dynamics Simulations of Size Effects in Nickel Superalloys

Sponsor: Air Force Research Laboratory
P.I. Jaafar El-Awady
Project Dates: 11/18/2014-06/30/2015
Graduate Student: Ahmed M. Hussein

Extrinsic size-effects in metals and alloys have been a rich topic of research over the past decade, and continue to grow with numerous new challenges and questions emerging at the micro- and nano-scales. We utilize atomistic simulations, discrete dislocation dynamics simulations and microscale experiments to identify the mechanisms governing size-scale effects.

In Situ Experiments and Multiscale Modeling of the Thermo-Mechanical Properties of Ultra-High Strength Micro-Architectured Tungsten Coatings

Sponsor: Air Force Office of Scientific Research
P.I. Jaafar El-Awady
Project Dates: 01/15/2015-01/14/2018
Graduate Students: Quan Jiao, and Steven Lavenstein PostDoc: Gi-Dong Sim

Designing strong materials is of extreme importance for a number of applications. This research utilizes advances in micro-mechanical testing and characterizing to investigate a number of micro-architectured materials having ultra high strength. The Figure shown is of a new refractory metal developed by “Ultramet” in Pacoima CA.

Dislocation Based Multiscale Modeling of Hydrogen-Induced Intergranular Fracture

Sponsor: National Science Foundation
P.I.: Jaafar El-Awady
Project Dates: 02/01/2015-01/31/2020
Students: To be determined

The primary research objectives of this CAREER project are to fundamentally identify the influence of H-diffusion on dislocation microstructure evolution, damage accumulation, and subsequent H-induced intergranular fracture of Ni crystals. We hypothesize that, unlike conventionally presumed, dislocation plasticity plays a major role in controlling material response and subsequent failure even in high-pressure H environments. We will perform unprecedented large scale 3D discrete dislocation dynamics (DDD) simulations coupled with finite element method to study dislocation evolution in H-charged single, bi, and poly-crystals. Details of the dislocation-H interactions, dislocation grain boundary interactions, and H pipe/bulk diffusion will be identified through molecular dynamics (MD) simulations, then hierarchically informed into DDD. In particular, this work will address two fundamental questions: (1) How does H influence dislocation multiplication/evolution? and (2) What is the role of H-diffusion on the evolution of the dislocation microstructure? The MD simulations will: (1) quantify H effects on the activation parameters of cross-slip; and (2) quantify H-diffusion coefficients and dislocation grain boundary interactions. Coupled H-diffusion/DDD simulations will be used to identify effects of H concentration and grain size on: (1) flow strength, and slip-morphology; and (2) dislocation evolution ahead of H-induced intergranular cracks. Simulations will be validated by comparisons with key experimental results from literature.

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