Workshop on Multiscale Materials Prediction:

Fundamentals and Industrial Applications

September 14 - 16, 1997, MIT

Supported by the Center for Materials Science and Engineering*, MIT, the Institute of Theoretical Physics and the Materials Research Laboratory at UC Santa Barbara, and ETH Zurich, with additional support from the Industrial Liaison Program and the Materials Processing Center, MIT.

*A National Science Foundation Materials Research Science and Engineering Center (MRSEC)


Participants will assess current capabilities for addressing critical problems in industrial materials technology through theory and simulation across the length scales characteristic of electronic-structure, atomistic, and microstructure modeling. Workshop is the third in a coordinated series aimed at fostering collaborations between universities and industry, with the participation of government laboratories.

Workshop Format and Venue

Plenary and two Invited Poster Sessions will be held at the Cambridge Center Marriott Hotel, Kendall Square, Cambridge. A block of rooms, under designation "MIT Multiscale Materials Prediction", has been reserved at the Marriott for September 13-15 at $155 per night; these will be released on August 24.


All sessions are held at the Cambridge Center Marriott Hotel, Kendall Square, Cambridge

September 14 (Sunday)

9 AM Opening Remarks

9:10 Session I: Methods and Applications (Chair:J. Joannopoulos)

M. Cohen (UC Berkeley) , "Predicting Properties of Materials"
K. Kremer (MPI-Mainz, Germany), "From Microscopic to Semi-Macroscopic Polymer Simulations"
(Break, 10:30-11:00)
J. F. Harris (MSI, San Diego), "Some Issues in Industrial Materials Modeling"
G. Olson (Northwestern Univ), "Systems Design of Hierarchically-Structured Materials: Advanced Steels"

(Lunch, 12:20-2:00)

2 PM Session II: Microstructures and Kinetics (Chair: G. Ceder)

O. Richmond (ALCOA), "On the Need for Chemicomechanical Modeling and Experiments in Alloy Development"
G. Martin (Saclay, France), "Modelling Configurational Kinetics in Driven Alloys"
C. Gandin (EPFL, Switzerland), "Modeling Dendritic Structures by Means of Cellular Automata"
Invited Posters (Presentations, 4:00, Viewing and Refreshments, 5:30-7:00) - see separate listing for titles and authors

September 15 (Monday)

9 AM Session III: Mechanical Behavior (Chair: A. Needleman)

J. R. Rice (Harvard Univ), "3D Elastodynamics of Cracking through Heterogeneous Solids: Crack Front Waves and Growth of Fluctuations"
F. Abraham (IBM-Almaden), "Instability Dynamics in Rapid Fracture: Studying Materials Failure Using Millions of Atoms"
(Break, 10:20-10:50)
L. Kubin (CNRS-ONERA, France), "Mesoscopic Simulations of Dislocations and Plasticity"
U. W. Suter (ETHZ, Switzerland), "Atomistic-Level Modeling of Mechanics of Polymer Solids"

(Lunch 12:20-2:00)

2 PM Session IV: Interfacial Phenomena (Chair: F. Spaepen)

K. Binder (Univ Mainz, Germany), "Simulation of Interfaces between Coexisting Phases in Materials"
D. Wolf (Argonne National Lab), "Interfacially Controlled Atomic Structure and High-Temperature Behavior of Polycrystalline Microstructures"
A. Sutton (Oxford Univ), "Electrical and Mechanical Properties of Metallic Nano-Contacts"

September 16 (Tuesday)

9 AM Session V: Special Materials (Chair: E. Kaxiras)

D. Vanderbilt (Rutgers Univ), "Ferroelectric Instabilities in Perovskites"
M. Boyce (MIT), "Microstructure and Mechanical Performance of Polymeric Materials: Toughening Semi-Crystalline Polymers"
(Break, 10:20-10:50)
S. Suresh (MIT), "Coupled Effects in Layered Structures, Thin Films and Piezoelectric Solids: Modeling and Experiments"
J. Joannopoulos (MIT), "Microphotonic Materials and Structure"

(Lunch, 12:10-1:40)

1:40 PM Session VI: Processing and Performance (Chair: R. A. Brown )

G. Gilmer (Lucent Tech), "Simulation of Silicon Device Processing Using Atomistic Models"
K. Jensen (MIT), "Multiscale Simulations of Thin Film Growth - Linking Quantum Chemistry, Monte Carlo and Finite Element Predictions of Semiconductor Growth Processes"
Concluding Discussions (3:00-3:30)

Notes: Plenary talks are each 30 min, plus 10 min discussions. All sessions will be in Salon III to the right of the escalator, upper level, and Posters in the adjacent room, Salon IV. Registration will be outside of Salons III/IV.

Registration and Invited Posters

Workshop attendance will be limited to 130 participants. Registration Fee: $150. All posters are invited. Interested contributor should give title and brief abstraction on Registration Form. Further information and update:

Workshop Organization

Local Organizing Committee: L. Anand, T. Arias, M. Bawendi, M. Boyce, G. Ceder, J. Clark, G. Dresselhaus, K.Jensen, E. Kaxiras, G. Rutledge, M. Spearing, J. R. Williams

External Advisory Committee: J. S. Langer (UCSB), A. K. Cheetham (UCSB), U. W. Suter (ETH Zurich), J.C.Williams(GE Aircraft Engines)

Coordinators: R. A. Brown, J. Joannopoulos, S. Suresh, S. Yip (chair)

Application Form

PS file

EPS file

List of Invited Posters

  1. The design of cathode oxides for rechargeable Li batteries using the first-principles pseudo potential method
    G. Ceder, M.K. Aydinol and A. Van der Ven, Department of Materials Science and Engineering, MIT

  2. Predicting effects of alloying on ductility of MoSi2 from first principles
    U. V. Waghmare and E. Kaxiras, Department of Physics, Harvard Univ., V. Bulatov, Department of Mechanical Engineering, MIT, and M. S. Duesbery, Fairfax Materials Research, Inc.

  3. Thermoelastic modeling of complex ceramics: A non-empirical DFT approach
    A. V. G. Chizmeshya, G. H. Wolf, and W. T. Petuskey, Materials Research Science and Engineering Center, Arizona State University

  4. First-principles study of a nanoscale friction using local orbitals in adaptive real-space coordinates
    G. S. Smith, N. A. Modine, U. Waghmare, E. Kaxiras, Department of Physics, Harvard Univ.

  5. Test of Herring's scaling laws at the nanoscale
    P. Zeng, P. C. Clapp and J. A. Rifkin, Center for Materials Simulation, Institute of Materials Science, University of Connecticut

  6. Can micron-scale sintering and grain growth theories be applied at the nanoscle?
    P. C. Clapp, P. Zeng, S. Zajac and J. A. Rifkin, Center for Materials Simulation, Institute of Materials Science, University of Connecticut

  7. Nanoporous semiconductors
    A. Demkov, Predictive Engineering Laboratory, Motorola, Inc. and O. Sankey, Department of Physics, Univ. of Arizona

  8. Initial stages of oxidation of silicon (001) surfaces: A case study in managing multiple scales within the DFT
    N. A. Modine, G. Zumbach, G. Smith, and E. Kaxiras, Department of Physics, Harvard Univ.

  9. Modeling quantum effects in the Raman spectra of carbon nanotubes
    E. Dresseelhaus, National Magnet Laboratory, MIT

  10. Models for low dimensional thermoelectricity
    M. Dresselhaus, MIT

  11. Intrinsic crossover mechanism for thermal conduction in rare-gas crystals
    H. Kaburaki, Japan Atomic Energy Research Institute, Tokai

  12. Tight-binding simulation of the amorphous-crystal interface in silicon
    N. Bernstein, E. Kaxiras, and M. Aziz, Division of Engineering and Applied Science, Harvard Univ.

  13. Atomistic simulation of sigma3(111) grain boundary fracture in tungsten containing various impurities
    M. Grujicic and H. Zhao, Department of Mechanical Engineering, Clemson Univ., and G. L. Krasko, U.S. Army Research Laboratory, Aberdeen Proving Ground

  14. Environment-dependent interatomic potential for bulk silicon
    M. Z. Bazant and E. Kaxiras, Harvard Univ., J. Justo, V. Bulatov and S. Yip, MIT

  15. Atomistic simulation of materials using environment-dependent tight-binding potentials
    C. Z. Wang, Department of Physics, Iowa State Univ.

  16. Toughening of ceramic composites by transformation weakening of interphases
    W. Kriven, Department of Materials Science and Engineering, Univ. Illinois

  17. On the role of length-scale in the prediction of failure of composite structures: Assessment and needs
    S. M. Spearing, P. A. Lagace, and H. L. N. McManus, Technology Laboratory for Advanced Composites, Department of Aeronautics and Astronautics, MIT

  18. Multiscale atomistic-continuum modeling of crack propagation in 2D metallic plates
    H. Rafir-Tabar, School of Mathematical Sciences, Univ. Greenwich, UK

  19. Study of the plasticity of silicon at a mesocopic scale by numerical 3D simulation
    A. Moulin, Laboratoire de Metallurgie Structurale, Univ. Paris Sud

  20. Application of the fast multipole method to micromechanics
    G. Rodin, Department of Aerospace Eng and Eng. Mechanics, Univ. Texas Austin

  21. Micromechanical modeling of the mechanical behavior of composites
    S. Schmauder, Univ. Stuttgart

  22. Crystallography of dislocation kinks
    V. V. Bulatov, Department of Mechanical Engineering, MIT, J. F. Justo, W. Cai, S. Yip, Department of Nuclear Engineering, MIT

  23. A mesoscopic approach to dislocation mobility and the mechanical response in bcc single crystals
    M. Tang, Physics Division, Lawrence Livermore National Laboratory

  24. Why L12 intermetallics are brittle and how to make them ductile?
    J.-S. Wang, Div. Eng. and Applied Sciences, Harvard Univ.

  25. Quantitative measures of crack nucleation
    S.-Y. Wu, Department of Physics, Louisville Univ.

  26. Molecular modeling of self-assembling peptide materials in biology and engineering
    S. Zhang, Department of Biology, MIT

  27. The size and shape of self-assembled micelles
    P.H. Nelson, T.A. Hatton, G.C. Rutledge, Department of Chemical Engineering, MIT

  28. Coupling continuum to molecular dynamics simulation: Reflecting Particle Method, Field Estimator, and the Effective Particle Controller
    J. Li, D. Liao, S. Yip, Department of Nuclear Engineering, MIT

  29. Title TBA
    B. Bergstrom and M. C. Boyce, Department of Mechanical Engineering, MIT

  30. Title TBA
    R. Phillips, Engineering Division, Brown Univ.

  31. Time and strain dependence of the mechanical behavior of elastomers
    J. S. Bergstrom, M. C. Boyce , Department of Mechanical Engineering, MIT

  32. Molecular dynamics simulation of boundary lubricated interfaces
    S. Yim, N. Saka, N. Sonwalkar , Department of Mechanical Engineering, MIT

  33. Materials Processing Center (MPC) and Industry Collegium: The industry and government link to materials research at MIT
    L. C. Kimerling, G. B. Kenney, C. Reif, Materials Processing Center, MIT

  34. Lattice Monte Carlo simulations as link between ab-initio calculations and macroscopic behavior of dopants and defects in silicon
    Marius M. Bunea* and Scott T. Dunham**, *Physics Department and Department of Electrical and Computer Engineering**, Boston University


Abraham, Farid
Senior Scientist, IBM Almaden research, <>

Allen, Samuel
Professor of Materials and Engineering, MIT, <>

Baca, Adra
Member of Tech. Staff/Materials Research, AMP, Inc., <>

Binder, Kurt
Professor, University of Mainz, Germany, <>

Boyce, M.
Professor of Mechanical Engineering, MIT, <>

Breedis, John
Materials Engineer, AMP, Inc., <>

Cassenti, Brice
Senior Principal Engineer, United Technologies Res. Ctr., <>

Chang, Jim C.I.
Director, Aerospace & Mat Sci Directorate, AFOSR, Bolling AFB, DC, <>

Chizmeshya, Andrew
Research Scientist, Dept. of Physics, Arizona State University, <>

Cohen, Marvin
Professor of Physics, UC Berkeley, <>

Condat, Marc
Vice Manager, Chemical Sciences Dept., Centre National de la Recherche Scientifique, <>

Coronell, Dan
Section Manager, Equipment Stimulating Group, <>

Demkov, Alex
Dr. Sr Staff Scientist, Predictive Eng. Lab., Motorola Inc., <>

DePristo, Andrew E.
Dr., Interim Program Manager, Materials Science Div., DOE

Derby, James
R&D, Materials, EG&G, <>

Fitzsimmons, Timothy
Div. of Materials Sciences, US DOE, <>

Fossey, Stephen
Materials Res. Eng., US Army Natick RD&E Center, <>

Gandin, Charles André
Postdoctoral Fellow, Ecole Polytechnque Federale de Lausanne, <gandin@epfl.ch5>

Gilmer, George
Member of Technical Staff, Bell Laboratories, <>

Grujicic, Mica
Prof., Mech. Eng., Clemson Univ., <>

Harris, John F.
Research Director, Molecular Simulations Inc., <>

Heaney, Michael B.
Sr. Staff Scientist, Raychem Corp., <>

Jensen, Klavs
Professor of Chemical Engineering, MIT, <>

Joannopoulos, John
Professor of Physics, MIT, <>

Kaburaki, Hideo
Principal Researcher, Group Leader, Ctr for Promotio n of Computational Sci & Eng., Japan Atomic Energy Resear ch Institute,

Kai, Zhang
Development Eng., Parker Hannifin.

Kniazzeh, Alfredo
Polaroid, Waltham, <>

Kohn, Robert V.
Professor, Courant Institute, New York University, <>

Kremer, Kurt
Director, Max-Planck Institute, Mainz, <>

Kriven, Waltraud (Trudy)
Professor, Mat Sci & Eng, U Illinois Urbana-Chanpaign, <>

Kubin, Ladislas
Research Director, CNRS-ONERA, France, <>

Lipton, Robert
Professor, Dept. of Material Sciences, Worcester Polytechnic Inst., <>

Mailhiot, Christian
Division Leader, Physics Dept., Lawrence Livermore Nat. Lab., <>

Martin, Georges
Research Director, CEN-Saclay, France, <>

Marx, Klaus
FV/FLT, Robert Bosch GmbH,

Monette, Liza
Program Leader, Advanced Composite, Exxon R&E, Annan dale, NJ, <>

Moulin, Antoine
Laboratoire de Metallurgie Structurale, Universite P aris Sud, <>

Olson, Greg
Professor of Materials Science, Northwestern Univ., <>

Rafii-Tabar, Hashem
Head of Res., Nano-Sci Simul Grp, Schl Math Sci, Uni v Greenwich, UK, <>

Rice, James R.
Professor of Engineering Sciences, Harvard Univ.,

Richmond, Owen

Research Director, ALCOA Technical Center, <>

Rodgers, Brendan
Chief Engineer, Goodyear Tire & Rubber Co., <>

Rodin, Gregory
Assoc. Prof., Aeorspace Eng. & Eng. Mechanics, Univ. Texas at Austin, <>

Schmauder, Siegfried
Professor Dr. rer. nat., MPA Stuttgart, University of Stuttgart, <schmauder@mpa.uni-stuttgart-de>

Suresh, Subra Professor of Materials Science and Engineering, MIT, <>

Suter, Ulrich W.
Professor of Polymer Science, ETH Zurich,

Sutton, Adrian
Department of Materials, Oxford Univ., <>

Tadmor, Ellad
Postdoc, Div. of Eng & Applied Sci, Harvard, Gordon McKay Laboratory, <>

Tang, Meijie
Physicist, H-Div./P&ST, Livermore NL, <>

Tasaki, Ken
Ph.D., Chief Scientist, Mitsubishi Chemical America, <>

Tewary, Vinod
Physicist, Materials Reliability Div., NIST, <>

Thomas, Edwin
Professor, DMSE, MIT, <>

Vanderbilt, David
Professor pf Physics, Rutgers Univ., <>

Visintainer, Jim
Dr., R&D Assoc., Goodyear Tire & Rubber Co.

Wang, Cai-Zhuang
Physicist, Iowa State U & DOE, <>

Wang Jian-Sheng
Research Scientist, Div. Eng. & Applied Science, Har vard, <>

Williams, James C.

Wolf, Dieter
Senior Scientist, Argonne National Laboratory, <>

Wong, Channy
SMTS, Sandia National Lab, <>

Wu, Shi-Yu
Professor, Dept. of Physics, University of Louisville, <>

Zhang, Shuguang
Principal Res. Sci., Biology, MIT

Zhu, Jing
Physicist, H-Div., Livermore NL, <>


Plenary Talks:

Predicting Properties of Materials: Alchemy with Computers

Marvin Cohen
Department of Physics, University of California, Berkeley, CA 94720

Abstract: I'll discuss older pseudopotential calculations on silicon and super hard materials and newer calculations on nanotubes.

From Micrsoscopic to Semi Macroscopic Polymer Simulations

Kurt Kremer, W. Tschoef, M. Murat, O. Hahn
Max-Planck-Institute for Polymer Research, Mainz, Germany

Abstract: The talk will cover some recent attempts to map microscopic polymer models onto mesoscopic models. For the example of three different polycarbonates this is tested. Then the step back towards the microscopic conformations is performed. In addition the next scale up step to a semi macroscopic description is tested for the coarse grained models. First results on phase separation simulations on this level are presented.

Some Issues in Industrially Relevant Materials Modelling

J. Harris
MSI Inc., 9685 Scranton Rd., San Diego, CA 92121

Abstract: In the absence of knowledge of the fundamental interactions on the appropriate scales of length and time, the modeling of multiscale materials properties remains an inexact science. Progress requires two kinds of approaches. The first approach, from the academic end, seeks to build up knowledge of the elementary processes sequentially. The second approach, of more direct relevance to industry, seeks to use whatever tools are available, however imperfect, that allow some kinds of incremental improvements to be made. Successful strategies in multiscale modelling will involve a balance between the two kinds of approaches, and will offer practical value in the short term as well as the promise of long term understanding.

Systems Design of Hierarchically Structured Materials: Advanced Steels

G. B. Olson
Department of materials Science and Engineering, Northwestern University

Abstract: A systems approach integrates processing/structure/property/performance relations in the conceptual design of multilevel-structured materials. Using the example high performance alloy steels, numerical implementation of materials science principles provides a hierarchy of computational models defining subsystem design parameters which are integrated via computational thermodynamics in the comprehensive design of materials as interactive systems. Materials design class projects address application of the methods in metals, ceramics, and polymers for special applications.

Multiscale Chemicomechanical Integration and Instabilities in Alloy Design

Owen Richmond
Alcoa Technical Center, Alcoa Center, PA 15069-0001

Abstract: Materials design is one aspect of holistic material product design. It concerns the linking of atomic-scale behavior (effects of chemical composition) to coupon-scale behavior (continuum constitutive equations). It concerns the question: what alloy composition and processing history can best produce desired performance attributes at minimum cost at production scales.

Many of the constitutive equations which have been developed and used over the past 10-15 years consist primarily of sets of algebraic and quasilinear ordinary differential equations for particular alloys with time as independent variable and various dependent variables representing averaged aspects of microstructure, both physical and chemical. These constitutive equations are combined with the classical conservation laws to simulate spaciotemporal behavior of material products and processes.

In the past few years we have begun to try to link coupon-scale behavior to atomic-scale behavior through multiscale models, and to represent temporal and spaciotemporal complexity of behavior (particularly plastic flow instabilities) by refinements of the constitutive models and attention to instabilities resulting from nonlinearities. Examples will be described of the effects of plastic nonnormality and dynamic strain aging on plastic flow instabilities.

Modelling Configurational Kinetics in Driven Alloys: Dose, Dose Rate and Integrated Dose Effects

G. Martin
CEA-Saclay, DECM, Section de Recherches de Metallurgie Physique, 91191 Gif-sur-Yvette CEDEX, France

Abstract:There is some confusion between the meaning of the word "dose" in pharmacology ("do not exceed the prescribed dose!") and in metallurgy ("dose" =3D fluence or integrated flux). We show that what physicians call "the effect of dose" is what we recognize as "cascade size effects". We give example of the latter for driven alloys, as observed in computer- as well as material-experiments, for alloys both under irradiation and under ball milling.

Modeling of Dendritic Grain Structures by Means of Cellular Automata

Charles-Andre Gandin
Ecole Polytechnique Federale de Lausanne, Laboratoire de Metallurgie Physique, Lausanne, Switzerland

Abstract:The efficiency of aircraft jet engines and land-based turbines is closely related to the operating temperature that can be sustained by the materials used in such applications. In the hottest stages of these devices, Directionally Solidified (DS) and Single Crystal (SX) superalloy investment cast parts are preferentially used. The major defect encountered during the solidification processing of these parts is related to the formation of stray crystals at various locations of the castings.

In order to predict and optimize the grain structures formed in investment cast parts, a new three-dimensional (3D) Cellular Automaton -Finite Element (CAFE) model has been developed. Such a model not only takes into account the crystallographic orientation of the grains, but also the growth kinetics of the dendrites and the heterogeneous nucleation of grains at the inner surface of the mold or within the bulk of the liquid. All these microscopic phenomena calculated at the scale of the fine grid of the CA are coupled with heat flow computations based upon the coarser mesh of the model.

As will be shown, this 3D CAFE model is able to predict, for given geometries and casting conditions, the formation of stray crystals, the transitions from columnar to equiaxed grain morphologies, the grain competition and the evolution of the grain texture in the columnar zone.

Starting with the basic concepts, this presentation will also show some of the latest developments: two dimensional (2D) modeling of grain movement and its effect on the final macrostructures.

3D Elastodynamics of Cracking through Heterogeneous Solids: Crack Front Waves and Growth of Fluctuations

John W. Morrissey and James R. Rice
Division of Engineering and Applied Science and Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138

Abstract: We present simulations of 3D dynamic fracture which suggest that a persistent elastic wave is generated in response to a localized perturbation of a propagating crack front, e.g., by a local heterogeneity of critical fracture energy (Morrissey and Rice, EOS, Trans. AGU, 1996; also, submitted to J. Mech. Phys. Solids, 1997). The wave propagates along the moving crack front and spreads, relative to its origin point on the fractured surface, at a speed slightly below the Rayleigh speed. The simulations were done using the spectral elastodynamic methodology of Geubelle and Rice (J. Mech. Phys. Solids, 1995). They model failure by a displacement-weakening cohesive model, which corresponds in the singular crack limit to crack growth at a critical fracture energy. Confirmation that crack front waves with properties like in our simulation do exist has been provided by Ramanathan and Fisher (submitted to Phys. Rev. Let., 1997). Through a derivation based on the linearized perturbation analysis of dynamic singular tensile crack growth by Willis and Movchan (J. Mech. Phys. Solids, 1995), those authors found by numerical evaluation that a transfer function thereby introduced has a simple pole at a certain w/k ratio, corresponding to a non-dispersive wave.

Further, we show that as a consequence of these persistent waves, when a crack grows through a region of small random fluctuations in fracture energy, the variances of both the local propagation velocity and the deformed slope of the crack front increase, according to linearized perturbation theory, in direct proportion to distance of growth into the randomly heterogeneous region. That rate of disordering is more rapid than the growth of the variances with the logarithm of distance established by Perrin and Rice (ibid, 1994) for a model elastodynamic fracture theory based on a scalar wave equation. That scalar case, which shows slowly decaying (as t**-1/2) rather than persistent crack front waves, is analyzed here too. Simulations of cracking through heterogeneous toughness show that the wave effects can cause the effects of heterogeneities to cascade along wave paths so that, e.g., strong fluctuations of crack velocity, and possibly instantaneous arrest of propagation, are induced at heterogeneities which would normally be too weak to strongly affect the crack motion.

It has been found experimentally that smooth tensile fracture surfaces in glass (Wallner, Z. Physik, 1939) and tungsten (Hull and Beardmore, Int. J. Fracture Mech., 1965) can exhibit long-lived pulse markings, now called Wallner lines, produced by disturbances at the intersection of the main crack front and the specimen surface, or at internal heterogeneities. The crack front waves discussed, at least if some generalization of them exists that includes small out-of-plane perturbations of the crack front, may provide an explanation of such lines.

Instability Dynamics in Rapid Fracture: Studying Materials Failure Using Millions of Atoms

Farid Abraham
IBM, Research Division, Almaden Research Center, San Jose, CA 95120

Abstract: Continuum fracture theory typically assumes that cracks are smooth and predicts that they accelerate to a limiting velocity equal to the Rayleigh speed, or surface sound speed, of the material. In contrast, experiment tells us that, in a common fracture sequence, an initially smooth and mirror-like fracture surface begins to appear misty and then evolves into a rough, hackled region with a limiting velocity of about six-tenths the Rayleigh speed. Recent experiments have clearly shown that violent crack velocity oscillations occur beyond a speed of about one-third the Rayleigh speed and are correlated with the roughness of the crack surface. All of these features are unexplained using conventional continuum theory.

With the advent of scaleable parallel computers, computational approaches are being extended for providing immediate insights into the nature of fracture dynamics. We have studied the rapid brittle fracture of solids using molecular dynamics for 10-millions of atoms and finite-element continuum mechanics. We have been able to follow the crack propagation over sufficient time and distance intervals so that a comparison with experiments is feasible. Most important, we can "see" what is happening on the atomic scale.

A detailed comparison between laboratory and computer experiments demonstrates that many of the recent laboratory findings occur in our simulation experiments, one of the most intriguing being a dynamic instability of the crack tip and its associated properties. Microscopic processes have been identified, and an explanation for the limiting is discovered. The origin of the instability dynamics at the atomic level is best seen in a video of the fracture simulations. In a 100-million atom simulation, we have discovered a dynamic brittle-to-brittle transition in the rapid cleavage of fcc solids, immediately leading to the initiation of plastic failure, crack arrest and the spontaneous proliferation of dislocations. We will discuss how this problem scales to the future teraflop regime in scientific computing.

Multimedia versions of our 2D and 3D atomistic simulation studies of fracture are available via the World Wide Web:
2D fracture: http://www/
3D fracture:

Mesoscopic Simulations of Dislocations and Plasticity

Ladislas Kubin
LEM, CNRS-ONERA, Leclerc, Chatillon, France

Abstract: The connection between atomistic and continuum mechanical approaches of plasticity can be achieved by means of numerical modeling at the scale of the microstructure. Such mesoscopic simulations are discussed and various examples of application are shown.

Simulation of Interfaces between Coexisting Phases in Materials

K. Binder, M. M|ller, F. Schmid, A. Werner
Institut fur Physik, Johannes Gutenberg-Universitat Mainz, Staudingerweg 7, D - 55099 Mainz, Germany

Abstract: Simulation of coexisting phases (e.g. liquid coexisting with saturated vapor, or A-rich phase coexisting with B-rich phase in a binary AB polymer mixture, etc.) is of interest as a tool both for the study of bulk phase properties and of interfacial properties (interfacial width, interfacial tension, etc.). Likewise, analogous experimental techniques are useful in thin film geometries.

This talk reviews recent work on interfaces in polymer blends, including adsorbed block copolymers as surfactants. It is emphasized that the interfacial profile and width depends sensitively on both the lateral (L) and perpendicular (D) linear dimension of the simulation box. It is shown that simulations help to understand analogous fluctuation broadening of interfacial widths in experiment. Evidence is presented that analogous phenomena occur also for antiphase domain walls in solid ordered binary alloys.

Interfacially Controlled Atomic Structure and High-temperature Behavior of Polycrystalline Microstructures by Molecular Dynamics Simulation

Dieter Wolf
Materials Science Division, Argonne National Laboratory

Abstract: Molecular-dynamics simulations of the synthesis, characterization and high-temperature plastic deformation of idealized, fully dense, three-dimensional polycrystalline microstructures with a 5-10 nanometer grain size will be reviewed, with particular emphasis on silicon. The role of the atomic structures and dynamical properties of the grain boundaries and grain junctions in these microstructures in their high-temperature behavior will be elucidated. An attempt will be made to formulate a conceptual framework for understanding microstructural evolution and mechanical deformation of polycrystalline microstructures at high temperatures. The basis for such a framework comes from a comparison with the dynamical properties of geometrically well-defined, microstructurally unconstrained grain boundaries in bicrystal geometries. Such a framework will enable mesoscale-type simulations of grain-boundary-controlled properties of polycrystalline microstructures based on an atomic-level understanding of bicrystalline boundaries and on insights gained on the effects of the microstructural constraints.

Electrical and Mechanical Properties of Metallic Nano-contacts

Adrian Sutton
Department of Materials, Oxford University

Abstract: Metallic contacts at the nanometre scale have been made experimentally by a variety of techniques ranging from using STM tips to make contacts, to the mechanically controllable break junction technique developed at Leiden. In a typical experiment, one makes a metallic contact and stretches it to fracture while measuring the electronic conductance. It is found that the conductance decreases in jumps, and that in the final stages, where the contact is just one or two atoms across, the conductance is quantized in units of 2e**2/h. The origin of the jumps has been the subject of considerable dispute, and computer simulations have shed a great deal of light on this matter.

I will describe the work Tchavdar Todorov and I have done at Oxford to model the mechanical evolution of these contacts during fracture, and our simultaneous calculations of the conductance. We explain the origin of the vast majority of the jumps in the conductance in terms of mechanical instabilities within the contact. I will also describe the very close interactions between experiment and simulation that has led to the present consensus that mechanical instabilities are indeed the principal cause of the jumps.

Finally, if time permits, I will describe our recent thinking about electromigration. This is where one asks what effect the current flow has on the mechanical evolution of the contact, rather than the effect the mechanical evolution of the contact has on the current flowing through the contact.

Ferroelectric Instabilities in Perovskites

David Vanderbilt
Department of Physics & Astronomy, Rutgers University

Abstract: I will discuss aspects of our recent work on the theory of ferroelectric instabilities in cubic perovskites, focusing on BaTiO3. I will show that the correct sequence of phase transitions can be obtained from an approach in which Monte Carlo simulations are applied to an effective Hamiltonian that is extracted from ab initio calculations. This approach can then be used to study such higher-order problems as the structure and energetics of ferroelectric domain boundaries, the influence of surfaces on ferroelectric order, and the finite-temperature bulk peizoelectric response.

Microstructure and Mechanical Performance of Polymeric Materials: Toughening Semi-Crystalline Polymers

Mary C. Boyce
Department of Mechanical Engineering, MIT

Abstract: It is widely recognized by polymeric material producers that the key to polymer penetration into new and wider product markets is not the development of a novel monomer, but is, instead, the optimization of the numerous existing polymers on the market today. The major advantage that thermoplastics offer are cost, weight, manufacturability and recyclability. The limitations primarily lie in the mechanical properties; particularly low stiffness and low toughness. Recent research in the polymer community has demonstrated the ability to provide remarkable increases in the toughness of semi-crystalline polymers through blending of rubber particles; however, this is at the large expense of reducing the stiffness to the point of all but ruling out the competitive use of the polymer in practical applications.

In this presentation, a new interdisciplinary research program at MIT on microstructure and mechanical performance of polymeric materials is discussed. A current focus of the program is the problem of toughening semi-crystalline polymers. The commercial market for semi-crystalline polymers has been expanding; but these materials exhibit both notch and temperature embrittlement. Recently, we have demonstrated the ability to tailor polymer microstructure in order to produce a super-tough semi-crystalline polymer which also exhibits an enhanced stiffness. Furthermore, this toughness is maintained at low temperatures. The microstructure tailoring was accomplished by exploiting our fundamental understanding of the underlying deformation mechanisms and the operative material length scales which govern mechanical performance. Both experimental and modelling efforts of this program will be presented. The experimental effort focuses on probing the mechanical properties (stiffness, strength, toughness) and the microstructure. The modelling effort focuses on simulating the deformation of the heterogeneous material system by incorporation of continuum material models which account for the material behavior at the crystallographic level. The experiments and the simulations show the importance of the role of the local material microstructure in producing macroscopic toughening in these heterogenous material system.

Coupled Mechanical-Nonmechanical Interactions in Integrated Systems

S. Suresh
Deparatment of Materials Science and Engineering, MIT

Abstract:This presentation will deal with experimental, analytical and computational studies of the mechanical and non-mechanical coupling in integrated systems of major technological significance. The applications to be considered include: microelectronic devices, flat-panel displays and ferroelectric "smart" materials for sensors and actuators. Firstly, the thermal and mechanical coupling will be examined to derive guidelines for processing and geometry in the fabrication of 300-mm diameter Si wafers. The combined effects of thermal-mechanical-body force coupling will then be addressed for the stress and deformation analysis of flat-panel displays. The presentation will conclude with a discussion of the mechanical-dielectric coupling where the particular issue of normal contact between a piezoelectric material and a conducting or insulating body. A new method involving indentation will be proposed for the estimation of mechanical or dielectric constants for the piezoelectric material. Strategies for controlling cracking propensity under contact by recourse to purely mechanical means will also be addressed.

Microphotonic Materials and Structures

John Joannopoulos
Department of Physics, MIT

Abstract: An introduction and survey of the field of photonic crystals is presented. These materials provide capabilities along a new dimension for the control and manipulation of light. the results of theoretical calculations which predict exciting novel applications of photonic crystals are discussed.

Simulations of Silicon Device Processng Using Atomistic Models

G. H. Gilmer
Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974

Abstract: The fabrication of complex silicon devices requires accurate models to predict the result of the many processing steps involved in current manufacturing methods. The sizes of features such as vias, gates, and interconnect lines on silicon devices are being reduced to a point where atomistic effects will soon become important. Fluctuations in the number of dopant atoms, variations in film thickness, and other effects will need to be controlled to a high level in order to have reproducible device properties. For this reason, atomistic models of device processing are being developed. We will discuss the hierarchy of simulation methods which can be used to improve the accuracy of the predictions; with emphasis on Monte Carlo and molecular dynamics models of implantation and doping. We discuss the damage produced by the implanted ions, and the enhanced diffusion caused by this damage during subsequent processing steps. Finally, the use of Monte Carlo models to treat the deposition of interconnect metal will be mentioned.

Multiscale Simulations of Thin Film Growth - Linking Quantum Chemistry, Monte Carlo and Finite Element Predictions of Semiconductor Growth Processes

Klavs F. Jensen, Harsono Simka, Raj Venkataramani, Istvan Lengyel, Seth Rodgers
Departments of Chemical Engineering and Materials Science and Engineering, MIT

Abstract: Chemical vapor deposition (CVD) of thin films is an important reactive processing step in the fabrication of thin film composites for electronic and optical applications. The process involves reactive gas flow combined with surface processes including adsorption, diffusion, nucleation, and growth. The complex coupling of transport phenomena with gas-phase and surface chemical kinetics on different length scales means that more than one type of modeling approach is needed to understand the entire CVD process. Macroscopic predictions (growth rate, film uniformity, and film composition), "mesoscopic" predictions (surface morphology), and microscopic predictions (adatom diffusion and reaction) are all necessary to realize particular thin film performance characteristics. A methodology is presented for linking different length scale models for the process. Two- and three-dimensional finite element (FEM) simulations are used to solve the governing macroscopic conservation equations describing fluid flow, heat and mass transfer with chemical kinetics in CVD reactor enclosures so as to predict the type and concentration of growth and impurity precursors arriving at the growth front. Three-dimensional Monte Carlo (MC) simulations of growth front evolution provide additional understanding of surface morphology evolution and impurity incorporation mechanisms. Ab initio molecular orbital and density functional theory quantum chemistry computations, combined with transition state calculations, are used to determine thermochemical and kinetic data for reaction pathways needed in the different levels of physical models. Each of the length scale-specific simulations is validated through comparison with experimental results. The "linked" models are shown to provide new insight into macroscopic and microscopic experimental observations that cannot be accurately represented by a single length scale simulation approach.


  1. The design of cathode oxides for rechargeable Li batteries using the first-principles pseudo potential method
    G. Ceder, M.K. Aydinol, A. Van der Ven
    Department of Materials Science and Engineering, Massachusetts Institute of Technology

    Abstract: In principle, the properties of a material of a given composition and structure can be determined solely from the basic laws of physics. Such "first-principles" calculations are the dream of any materials developer, as they allow one to obtain information on materials without synthesizing them. In our research on rechargeable lithium batteries, we have used computational modeling to direct the search for cathode-active materials, leading to the first realization of a "quantum engineered" high-performance material.

    By combining the first-principles pseudopotential method with basic thermodynamics we establish a clear relation between the structure, chemistry and intercalation voltage for Li in metal oxides. Contrary to conventional wisdom, which dictates that cathode oxides should contain a transition metal to charge-compensate for variation in Li+ ion concentration, first-principles computations suggest that even better properties can be achieved with p-block metals. These results have led to a set of design criteria for new, higher energy density materials. Experiments on these novel materials will also be shown.

  2. Predicting effects of alloying on ductility of MoSi2 from first principles
    U. V. Waghmare and E. Kaxiras*, V. Bulatov**, M. S. Duesbery***
    *Department of Physics, Harvard University, **Department of Mechanical Engineering, MIT, ***Fairfax Materials Research, Inc.

    Abstract: We investigate the possibility of enhancing the ductility of MoSi2 by sustitutional alloying, through the changes that this introduces to the relevant surface and unstable stacking fault energies. We obtain these energies using the ab-initio pseudopotential total energy method based on a conjugate gradient algorithm. Effects of V, Nb, Tc substitution for Mo, and Mg, Al, Ge, P substitution for Si are investigated. Incorporating these results in a fracture mechanics model for dislocation nucleation and the Griffith criterion for brittle failure, we predict the effects of substitutional alloying on ductility of MoSi2 for all the substitutional elements considered.

  3. Thermoelastic modeling of complex ceramics: A non-empirical DFT approach
    A. V. G. Chizmeshya, G. H. Wolf, W. T. Petuskey
    Materials Research Science and Engineering Center, Arizona State University, Tempe, AZ 85287

    Abstract: Among the most difficult properties to extract reliably from simulations of complex ceramics is the elastic/stiffness tensor, and in particular, its pressure and temperature dependence. Large unit cells containing rare-earth and transition metal atoms often vitiate the application of ab initio methods to this problem, while simplified schemes based on empirical interaction potententials usually reproduce one physical property at the expense of betraying another. We describe an efficient but quantitative simulation approach to the calculation of thermoelastic properties that has been used extensively within our group as a counterpart to experimental investigations. The variational principle is used to determine the minimum Gibbs free energy of a crystal composed of compressible Kohn-Sham atoms/ions. Many-body effects emerge naturally from a coupling between the ionic and electronic degrees of freedom, and all salient properties, including a thermodynamically consistent finite-T phonon spectrum can be readily obtained. Elastic properties are computed from a long wavelength analysis of the finite temperature and pressure quasi-harmonic phonon spectrum. We demonstrate the methods' performance by calculating a wide range of thermal and mechanical properties of some technologically important ionic compounds including oxide perovskites, corundum, aluminum nitride and the layered perovskites KCa(2)Nb(3)O(10), K(2)Ca(3)Nb(4)O(13).

  4. First-principles study of a nanoscale friction using local orbitals in adaptive real-space coordinates
    Greg S. Smith, Normand A. Modine, Umesh Waghmare, Efthimios Kaxiras
    Department of Physics, Harvard University

    Abstract: We introduce a computational method for the efficient treatment of systems with complex structure and highly inhomogeneous electronic density distributions, in the context density functional theory. The method uses a local orbital basis represented on an adaptive real-space grid. We apply this approach to study the properties of an atomically flat interface between a nanoscale MoO3 crystal and a MoS2 substrate, a system found experimentally to exhibit a large friction anisotropy [1]. This is an ideal example for the study the effects of microscopic structure on macroscopic phenomena such as friction. Based on our calculations, we obtain estimates of the critical force which must be applied through an atomic force microscope in order to move the MoO_3 crystal, for different shapes of the crystal and different relative orientations with respect to the substrate.
    [1] P.E. Sheehan and C.M. Lieber, Science 272, 1158 (1996).

  5. Test of Herring's scaling laws at the nanoscale
    P. Zeng, P. C. Clapp, J. A. Rifkin
    Center for Materials Simulation, Institute of Materials Science, University of Connecticut, Storrs, CT 06269-3136

    Abstract: Molecular Dynamics techniques with Embedded Atom Method potentials has been used to study sintering in arrays of pure Cu nanofibers. The sintering studies on multi-particle arrays several hundred degrees below the melting point of pure Cu show unexpectedly large contributions from plastic deformation processes, mechanical rotations, amorphization and highly driven surface and grain boundary diffusion effects. These results strongly indicate that the standard sintering theories developed for micron scale powders do not apply at the nanoscale. A detailed test of Herring's scaling law has also been performed and it is found to fail over the entire range of sintering sizes at the nanoscale. Reasons for this failure will be offered. Computer movies will be displayed to illustrate the dynamics of the competing sintering processes.

  6. Can micron-scale sintering and grain growth theories be applied at the nanoscale?
    P. C. Clapp, P. Zeng, S. Zajac J. A. Rifkin
    Center for Materials Simulation, Institute of Materials Science, University of Connecticut, Storrs, CT 06269-3136

    Abstract: We are using Molecular Dynamics techniques with Embedded Atom Method potentials to study sintering, surface diffusion and grain boundary mobility in nanoparticle arrays. Preliminary results of the sintering studies on multi-particle arrays several hundred degrees below the melting point of pure Cu and Au show unexpectedly large contributions from plastic deformation processes, mechanical rotations and highly driven surface and grain boundary diffusion effects. These results strongly indicate that the standard sintering theory developed for micron scale powders (e. g. Ashby sintering diagrams) will have to be heavily revised, if not abandoned, before accurate predictions of nanoscale sintering kinetics will be possible. Computer movies will be displayed to illustrate the dynamics of the competing sintering processes.

  7. Nanoporous semiconductors
    A. Demkov*, and O. Sankey**

    *Predictive Engineering Laboratory, Motorola, Inc., Mesa, AZ
    **Department of Physics, Arizona State University

    Abstract: We investigate theoretically a new class of nanoporous semiconductor phases. First we describe novel phases of Si which we call silisils. Silisils may be thought of as zeolites without oxygen; their structures are derived by reducing the (4;2)-connected nets of zeolites to simple 4-connected nets. Two of these structures have bandgaps almost twice that of the diamond phase. These materials have unusual electronic properties, and we will discuss the latest experimental results. By reducing the (4;2)-connected nets of AlPO molecular sieves, a novel class of binary semiconductors such as GaAS is introduced. We use an ab-initio local-orbital quantum molecular-dynamics method to investigate these GaAs materials and their properties. The most important result is that the total energies of the nanoporous Si and GaAs structures are in the range of 0.1-0.2 eV/atom above the corresponding ground state structure (diamond or zinc-blende). These energy differences are significantly less than any of those for the high pressure phases.

  8. Initial stages of oxidation of silicon (001) surfaces: A case study in managing multiple scales within the DFT
    N. A. Modine, G. Zumbach, G. Smith, Efthimios Kaxiras
    Department of Physics, Harvard University

    Abstract: The oxidation of Si surfaces is a problem of central importance to electronic device applications. First-principles calculations for the oxidation of Si surfaces are challenging due to the presence of 3 length scales: short wavelengths are required to represent accurately the 2p orbitals of O, moderate length scales are associated with the Si atoms, and a comparatively low resolution is needed for efficient simulation of the interlayer vacuum region. Our recently developed Adaptive Coordinate Real-space Electronic Structure (ACRES) method [1] treats this range of length scales efficiently by using a regular mesh in curvilinear space, which is mapped by a change of coordinates to an adaptive mesh in real space. Use of parallel computing makes this approach particularly efficient from a computational point of view.

    Using the ACRES method, we study several mechanisms of incorporating a sub-monolayer coverage of oxygen into the characteristic (2X1) dimer reconstruction of the Si(001) surface. Based on our results, we propose a physically motivated two step pathway for the initial incorporation of an oxygen atom into the dimerized surface, and we explain what formerly appeared to be puzzling Ultraviolet Photoelectron Spectroscopy measurements which indicated that each initial oxygen atom saturates two dangling surface bonds.

    We also discuss how the Linear Combination of Atomic Orbitals (LCAO) approximation can be integrated easily into the ACRES framework, and we note that the freedom in boundary conditions allowed by a real-space method make ACRES an ideal starting point for linking the DFT to effective methods for the treatment of longer length scales.
    [1] N.A. Modine, G. Zumbach and E. Kaxiras, Phys. Rev. B 55, 10289 (1997).

  9. Modeling quantum effects in the Raman spectra of carbon nanotubes
    R. Saito*, T. Takeya*, T. Kimura*, G. Dresselhaus** M. S. Dresselhaus**
    *University of Electro-Communications, Tokyo, Japan, **MIT

    Abstract: Using non-resonant bond polarization theory, the Raman intensity of a single-wall carbon nanotube is calculated as a function of the polarization of light and the chirality of the carbon nanotube. The force constant tensor for calculating phonon dispersion relations in the nanotubes is scaled from those for two-dimensional graphite. The calculated Raman spectra do not depend much on the chirality while their frequencies clearly depend on the diameter. The polarization and sample orientation dependence of the Raman intensity shows that the symmetry of Raman modes can be obtained by varying the direction of the nanotube axis with fixed polarization vectors of light.

  10. Models for low dimensional thermoelectricity
    M. S. Dresselhaus (MIT), T. Koga (Harvard University), X. Sun (MIT), S. B. Cronin, (MIT), K.L. Wang, UCLA, G. Chen, UCLA

    Abstract: Enhanced ZT has been predicted theoretically for low dimensional electronic systems under appropriate experimental conditions. Enhanced ZT has been observed experimentally within 2D quantum wells of PbTe, and good agreement between theory and experiment has been obtained. The advantages of low dimensional systems for thermoelectric applications are described, and prospects for further enhancement of ZT are discussed.

  11. Intrinsic Crossover Mechanism for Thermal Conduction in Rare-Gas Crystals
    Hideo Kaburaki and Sidney Yip
    Abstract The thermal conductivity of solid Argon crystals has been calculated by the equilibrium Green-Kubo method. We derived the temperature dependence of thermal conductivity in the high temperature region by the molecular dynamics method and compared the results with experiment. We have found that the heat-flux correlation function consists of two stages and the long-time stafe disappears as the temperature approaches the melting point.

  12. Tight-binding simulation of the amorphous-crystal interface in silicon
    Noam Bernstein, Efthimios Kaxiras Michael Aziz
    Division of Engineering and Applied Sciences, Harvard University

    Abstract: We study the structural features of the interface between crystalline and amorphous Si in the (001) plane using a non-orthogonal tight-binding model. This tight-binding Hamiltonian was optimized for the types of structures and local bonding distortions expected in defective crystalline and amorphous structures as well as the transition states between metastable configurations [1]. An analysis of the energetics of the resulting interface models indicates the presence of a number of atoms near the interface that can be moved with little energetic cost. Structural features include defects such as dimerized atom pairs in the <110> chains in the predominantly crystalline regions, as well as <110> chains in the predominantly amorphous regions that lose their coherence over the distance of a few atoms. Pathways for processes leading to the repair of the defects and extension of the crystal are calculated, and found to have energy barriers in the range 1.2 -- 2.2 eV.

    [1] N. Bernstein and E. Kaxiras, MRS Symposium Proceedings, Vol. 408, p. 55, edited by E. Kaxiras, J. Joannopoulos, P. Vashishta and R.K. Kalia (Materials Research Society, Pittsburgh, 1996).

  13. Tight-binding simulation of the amorphous-crystal interface in silicon
    N. Bernstein, E. Kaxiras, M. Aziz
    Division of Engineering and Applied Science, Harvard Univ.

  14. Environment-dependent interatomic potential for bulk silicon
    Martin Z. Bazant and Efthimios Kaxiras*, Joao Justo, Vasily Bulatov, Sidney Yip**
    *Harvard University, **MIT

    Abstract: Empirical interatomic potentials are essential for the prediction of material properties because they extrapolate the results of ab initio electronic structure calculations to the larger systems needed for atomistic simulations of crystalline defects and disordered phases. Many advances in computation have been made, but the theoretical validation of this linking of scales is unsatisfactory for covalently bonded solids (such as Si, Ge and C). Although more than thirty fitted potentials have been proposed in the prototypical case of Si, realistic simulations of plastic deformation, diffusion, crystallization, melting and other important bulk phenomena are still problematic. In order to guide the the fitting process, we use analytic techniques to extract features of potentials directly from ab initio energy calculations. Elastic constant relations test models of sp2 and sp3 hybrid covalent bonding, and inversion of cohesive energy curves sheds light on the covalent to metallic transition and the nature of angular forces. These results are captured by a functional form with only a few fitting parameters which we call the Environment-Dependent Interatomic Potential (EDIP). The parameters were fitted to a large data base of ab initio results for bulk structures and point and planar defects. The fitting of EDIP for Si has already led to unprecedented transferability for bulk defects and condensed phases, and extensions to other elements and alloys may be possible.

  15. Transformation toughening of ceramic composites by transformation weakening of interphases
    W. M. Kriven, S. J. Lee, C. M. Huang, D. Zhu, Y. Xu, S. M. Mirek
    Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign Urbana, IL 61801

    Abstract: A new concept for debonding of interphases between fibers and matrix or between laminates in oxide ceramic composites is introduced. It is based on a thermal or shear stress induced phase transformation which is accompanied by a volume contraction or significant shape change, leading to microcracks. Thermally induced transformation above the critical particle particle size was demonstrated in enstatite (MgO*SiO2) due to an orthorhombic protoenstatite (PE) to monoclinic clinoenstatite (CE) transformation which is accompanied by a 5.5% volume contraction during cooling at 865 =B0C, forming intragranular microcracks. Thermal or shear stress induced transformation was also observed in (Ca, Al)-doped cristobalite (SiO2) where the cubic (b) to tetragonal (a) transformation occurs on cooling at 265 =B0C, with a ~3.2 % volume contraction. Laminates of mullite/cordierite separated by cristobalite interphases were fabricated to optimize thermal expansion mismatch. Crack propagation was observed within the transformed interphases and graceful failure was observed in 4-point flexure testing.

  16. On the role of length-scale in the prediction of failure of composite structures: Assessment and Needs
    S. Mark Spearing, Paul A. Lagace Hugh L. N. McManus
    Technology Laboratory for Advanced Composites, Department of Aeronautics and Astronautics, MIT

    Abstract: The role of modeling in the design of structural composite components against failure is discussed. Composite materials fail due to damage processes operating at several length-scales. The interactions between these processes, and between the scales at which they act, offer the principal challenges to applying mechanism-based models at structural scales beyond the ply level. A methodology is proposed to increase theefficiency of the design process, analogous to the "building block" approach, which provides a framework for integrating mechanism-based models with the current experimentally-based design process. The available models are reviewed, and their key elements identified. General concepts are illustrated via a discussion of the particular issues pertaining to notched components. Key steps needed to allow the evolution of the design process to the envisioned process are identified.

  17. Multiscale Atomistic Continuum Modelling of Crack Propagation in 2-D Metallic Plates
    H. Rafii-Tabar. Lu, Hua & M. Cross
    Abstract: A novel multiscale modelling of brittle fracture in an Ag plate with macroscopic dimensions is proposed in which the crack propagation is identified with the stochastic movement of the crack tip atom through the material. The model couples the atomistic dynamics of the crack growth at the nanoscopic scale with the continuum-based theories of fracture mechanics. The linkage is established via Ito stochastic calculus. The atomistic aspect of the modelling is based on molecular dynamics simulation method using a many-body interatomic potential. The continuum-based computations employ the finite-element. Well-known crack characteristics at the nano-scale, such as the mirror-to-mist-to-hackle transitions, are obtained as well as the stochastic trajectory of the crack propagation on the macroscopic scale.

  18. Study of the Plasticity of Silicon at a mesoscopic scale by numberical 3D simulation
    Antoine Moulin
    Abstract: Featuring an exhaustive study of the Frank-Read source emission and a study of the yield pint phenomenon.

  19. Application of the fast multipole method to Microdynamics
    Gregory Rodin
    Abstract:I will explain how the fast multipole method can be applied to large-scale three-dimensional micromechanics problems that involve a large number of interacting defects like second-phase particles or dislocations.

  20. A Mesoscopic Approach to Dislocation Mobili Mechanical Response in bcc Single Crystals

    Tang, Meijie, L P. Kubin and C R.
    Abstract: This work will present a method that links single dislocation properties (activation energy and mobility) to the macroscopic mechanical response in b cc single crystals. It will show that realistic dislocation behavior as well as stress vs. s train curves can be obtained, and address the credibility of extracting single dislocation pro perties from low temperature mechanical testings.

  21. Why L12 intermetallics are brittle and how to make it ductile
    Wang, Jian-Sheng
    Abstract: The origin of the intrinsic and extrinsic brittleness of L12 intermetallics are discussed and the alloying principles to improve the ductility are suggested.

  22. The size and shape of self-assembled micelles
    P.H. Nelson, T.A. Hatton, G.C. Rutledge
    Department of Chemical Engineering, MIT

    Abstract: Equilibrium size and shape distributions of self-assembled micelles are investigated using a course grained Monte Carlo simulation technique. The micellar size distributions are shown to include a Gaussian peak of spherical micelles, in combination with an exponential tail of cylindrical micelles.

  23. Time and strain dependence of the mechanical behavior of elastomers
    J. S. Bergstrom, M. C. Boyce
    Department of Mechanical Engineering, MIT

    Abstract: The mechanical behavior of elastomeric materials is known to be rate dependent and to exhibit hysteresis upon cyclic loading. Although these features of the rubbery constitutive response are well-recognized and important to its function, few models attempt to quantify these aspects of response perhaps due to the complex nature of the behavior and its apparent inconsistency with regard to current reasonably successful static models of rubber elasticity.

    By performing a careful experimental investigation, it has been possible to probe the material response to different strain histories and to find the influence of different microstructural parameters such as concentration of filler particles and number density of crosslinking sites. From the experimental data a constitutive model based on reptational relaxational motion of chain molecules has been developed. In the model, the macroscopic mechanical behavior is determined by the dynamic interaction between two networks acting in parallel: a perfect network giving the equilibrium response and an elastically `inactive' network that deforms with the perfect network during fast macroscopic deformations but, when given sufficient time, relaxes towards a lower energy state.

    By comparing the predictions from proposed model both with the experimental data and with molecular dynamics simulations we conclude that the constitutive model predicts the rate-dependence and relaxation behavior well.

  24. Molecular dynamics simulation of boundary lubricated interfaces
    S. Yim, N. Saka, N. Sonwalkar
    Department of Mechanical Engineering, MIT

    Abstract: A molecular dynamics simulation study of friction in boundary lubrication was conducted in order to investigate the atomic-scale behavior of the lubricant molecules during the sliding motion. The simulated system consisted of two silicon (001) semi-infinite substrates lubricated by a thin, three layer film of dodecane. Silicon was modeled using the Stillinger-Weber potential, and the dodecane with the Consistent Force Field potential function; a novel scheme was used to generate the silicon-dodecane interaction potentials. The simulations show that the dodecane molecules strongly prefer to adsorb into ledges on the silicon surface. The orientation of the adsorbed molecules depends heavily on the concentration of the lubricant at the Si surface, showing a tendency to stand up at high lubricant concentrations. In sliding, the dodecane layers adsorbed on the silicon surfaces behave as a solid, whereas the middle layer exhibits more liquid-like characteristics. The friction coefficient of this well-lubricated case was calculated to be 0.07, well within the range for boundary lubricated systems.

  25. Materials Processing Center (MPC) and Industry Collegium: The industry and government link to materials research at MIT
    L. C. Kimerling, G. B. Kenney, C. Reif
    Materials Processing Center, MIT

    Abstract: The Materials Processing Center (MPC) is a focal point for the 150+ member, multi-disciplinary materials community around MIT, and a bridge to domestic and international industry. MPC's purpose is to provide an environment where students and professionals from industry, government and academia can collaborate to identify and address pivotal issues in materials processing and manufacturing. Sectors of research include biomaterials, transportation, structural materials, energy, primary materials, and electronics. A proactive forum for the exchange of knowledge exists through the MPC Industry Collegium. The Collegium serves as a direct link between on-going materials research and industry needs, providing a one-on-one conduit between industry personnel and MIT faculty, staff and students. Industry partners receive special publications andaccess to focused workshops and symposia, and have the opportunity to create and promote cooperative or sponsored research programs with knowledgeable experts and students who are committed to working with industry. Collegium members may also send Visiting Scientists to participate in cooperative research at MIT.

  26. Lattice Monte Carlo simulations as link between ab-initio calculations and macroscopic behavior of dopants and defects in silicon
    Marius M. Bunea* and Scott T. Dunham**
    *Physics Department and Department of Electrical and Computer Engineering**, Boston University

    Abstract: We use recent ab-initio dopant/vacancy binding energies (Pankratov et al., Nelson et al., Ramamoorthy and Pantelides) to calculate hopping rates of vacancies for use in lattice Monte Carlo (LMC) simulations of diffusion and aggregation in silicon. The lattice Monte Carlo simulations consider the biased nature of hop frequencies in the neighborhood of dopants, with interactions up to ninth nearest neighbor distances included. We use these LMC simulations to investigate the expected macroscopic diffusion behavior, as well as the process by which dopant/defect aggregation occurs. Specific phenomena investigated include dopant fluxes in the presence of a vacancy gradient, collective phenomena leading to greatly enhanced diffusivity at high doping levels, and the time dependence of effective diffusivity due to the formation of dopant/vacancy clusters.


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