Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J24: Focus Session: Multiscale Modeling: Structural Materials |
Hide Abstracts |
Sponsoring Units: DCOMP DMP Chair: Zhiqiang Wang, University of North Texas Room: D167 |
Tuesday, March 22, 2011 11:15AM - 11:51AM |
J24.00001: Origin of Plasticity Length-Scale Effects in Fracture and Deformation Invited Speaker: Engineering design of essentially all metallic components used in structural applications relies heavily on the framework of continuum plasticity. However, many experiments now show that the plastic flow stress in metals increases in micron-scale material volumes, i.e. ``smaller is stronger". The failure of conventional plasticity is particularly manifest at a crack tip, where infinite toughness can be predicted. Phenomenological strain-gradient plasticity models and discrete-dislocation models have emerged to handle size effects but there is no clear physical identification of material length scales controlling size-dependence, in spite of wide speculation. Here, we use a new discrete-dislocation/cohesive-zone model to unambiguously demonstrate that the spacing between obstacles to dislocation motion is one dominant material length scale controlling the fracture toughness of plastically deforming metals. With this insight, we propose a new ``stress gradient plasticity" concept based on the behavior of dislocations in a ``pile-up" at an obstacle under a stress gradient, which (i) rationalizes our fracture results and (ii) predicts size-effects under other loading conditions (bending, torsion, indentation). Quantitative agreement between theory and experiments is then demonstrated in several cases. [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:27PM |
J24.00002: Chemistry and Deformation: First Principles Studies of Local Plasticity Invited Speaker: In order to understand the how chemistry influences deformation, an adequate description of the strain field near the center of dislocations (i.e. the core) is required. Continuum level descriptions of deformation ignore this short-range coupling between dislocations and the local atomic lattice. Interactions at this scale are non-linear and can strongly influence plastic deformation in fcc and bcc metals. Here, density functional theory is used in conjunction with a flexible boundary condition method to calculate the equilibrium dislocation core structure in a variety of bcc and fcc metals. The problem is divided into two parts: a solution for the nonlinear dislocation-core region and a solution for the long-range elastic response. Solving these individual problems is straightforward and by iteratively coupling the two solutions we can efficiently solve for the strain field in all space. Chemical effects, in the form of local solute-dislocation interactions, can also be calculated using this method. Derived solute-dislocation interactions are used to inform new models of solution hardening (and softening) in bcc Mo-X (X=Re, Pt) and fcc Al-X (X=Mg, Cr, Si, Cu) alloys. Currently, solute dislocation interactions are being assessed in bcc Fe-H alloys using this first principles technique. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 12:39PM |
J24.00003: Ab-initio Concurrent Multiscale Method to Address Defects in Metals Georg Schusteritsch, Thomas K\"uhne, Efthimios Kaxiras We present a concurrent multiscale method for metallic systems based on coupling a region calculated using Kohn-Sham Density-Functional-Theory (KS-DFT) to a macroscopic region employing the Embedded Atom Method (EAM). By construction, our method is particularly well suited for treating defects such as grain boundaries (GBs), dislocations and chemical impurities, where quantum mechanical interactions in a small region near the defect may affect the mechanical properties at the macroscopic scale. Results for two metals, Nickel and Copper, are presented in the context of chemical embrittlement. We study the effects of impurities near GBs and investigate the surrounding strain field. This gives us insights into the role defects play in the underlying physical mechanism of chemical embrittlement. [Preview Abstract] |
Tuesday, March 22, 2011 12:39PM - 12:51PM |
J24.00004: Multiscale Modeling of Irradiation Induced Hardening in Ferritic-Martensitic Steels Hussein Zbib, Ioannis Mastorakos, Mohammad Khaleel, Xin Sun The development of structural materials for use in new generation nuclear reactors depends critically on predicting and understanding the underlying physical mechanisms responsible for microstructural evolution along with corresponding dimensional instabilities and mechanical property changes. As the phenomena involved are very complex and span in several length scales, a multiscale approach is necessary in order to fully understand the degradation of materials in irradiated environments. The purpose of this work is to study the mechanical behaviour of Fe systems (namely a-Fe, Fe-Cr and Fe-Ni) under irradiation using both Molecular Dynamics (MD) and Dislocation Dynamics (DD) simulations. Critical information is passed from the atomistic (MD) to the microscopic scale (DD) in order to study the degradation of the material under examination. In particular, information pertaining to the dislocation-defects (particularly voids, helium bubbles and prismatic loops) interaction is obtained from MD simulations. This information is used in large scale DD simulations to analyze systems with high dislocation and defect densities, predicting the dependence of strength and ductility on defect density. [Preview Abstract] |
Tuesday, March 22, 2011 12:51PM - 1:03PM |
J24.00005: A QCDFT Study of Hydrogen embrittlement at Crack Tip Qing Peng Study of hydrogen embrittlement is of great importance due to widespread availability of hydrogen in all environmentally influenced cracking phenomena. We used QCDFT: Density functional theory based Quasi-continuum method to study the system where hydrogen atoms are presented on crack tip surface in single aluminum crystal under mode-I loading. We found that the presence of 0.1{\%} hydrogen atoms increases the energy for nucleation of dislocations and enhance the brittlement of aluminum by 5{\%}. The presence of hydrogen atoms also makes the geometry of crack tip to be sharp. The bonding and electronic charge transfer between hydrogen atoms and aluminum atoms were studied and the mechanism of hydride-induced embrittlement will be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 1:03PM - 1:15PM |
J24.00006: Models of defects at bi-material interfaces Kipton Barros, Turab Lookman Multi-phase composite materials with a high density of bi-material interfaces can exhibit striking strength and robustness in extreme conditions such as shock and radiation damage. Laminar composites of Ag-Cu, Cu-Nb, and Ag-Fe with submicron to nano-scale layer thicknesses have recently been fabricated, but theoretical models of such systems are lacking. The plastic deformation behavior of nano-scale composites is dominated by defects, such as dislocations and twins, that are controlled by the interfaces. We investigate the phenomenology of defect dynamics at bi-material interfaces using Landau theory based models that span atomic and mesoscales. [Preview Abstract] |
Tuesday, March 22, 2011 1:15PM - 1:27PM |
J24.00007: First Principles Simulations of Beta to Omega Transformation in the Titanium-Molybdenum System Arun Devaraj, Niraj Gupta, Soumyu Nag, Hamesh Fraser, Raj Banerjee, Srinivasan Srivilliputhur The omega phase precipitation in beta titanium (Ti) alloys influence the beta to alpha phase transformation, and ultimately the mechanical properties of these alloys. Molybdenum (Mo) and other alloying additions affect both the relative phase stability and the energy barrier of the transformation. In this work we perform first principle calculations using Nudeged Elastic Band Method(NEB) implemented in Vienna Ab initio Simulation Package (VASP) to determine the minimum energy path, and thereby the energy barrier in beta Ti-Mo alloys with up to 20wt.{\%} Mo. We report the energetics of beta to omega transformation path, proposed by De. Fontaine et al (Acta Metallurgica, vol. 19, p 1153 (1971)). The atomic configurations along the minimum energy transformational path will be compared with our 3D atom probe tomography and probe corrected high-resolution scanning transmission electron microscopy results. [Preview Abstract] |
Tuesday, March 22, 2011 1:27PM - 1:39PM |
J24.00008: Shock-induced Spallation Phenomena in Copper-Niobium Nanolayered Composites Niraj Gupta, Alexander Stukowski, Michael Baskes, Srinivasan Srivilliputhur Shock-induced spallation phenomena in Copper-Niobium nanolayered composites conforming to a Kurdjumov-Sach's orientation relation were simulated using molecular dynamics to determine both spallation strength and the nature of void formation. The target structures consisted of varying numbers of alternating copper and niobium layers with thicknesses varying from 1 nm to 22 nm. Flyer velocities ranged from 3.5 to 11.5 A/ps, corresponding to an approximate strain rate of 10$^{9}$ s$^{-1}$. Spallation occurs in the vicinity of the Cu-Nb interface, and always in the copper layer. The proposed factors contributing to spallation will be discussed, as well as what effect the layer morphology has on the strength of the target. [Preview Abstract] |
Tuesday, March 22, 2011 1:39PM - 1:51PM |
J24.00009: A First-Principles Study of Structure and Stability of Nickel Carbides Josh Gibson, Jamal Uddin, Nelli Bodiford, Thomas Cundari, Angela Wilson Computational studies of nickel carbides, particularly Ni2C, are scarce. A systematic density functional theory study is reported for Ni2C, along with NiC and Ni3C, to understand the stability and electronic structure of nickel carbides of varying stoichiometry. A comprehensive study was executed that involved 28 trial structures of varying space group symmetry for Ni2C. An analysis of the electronic structure, geometry and thermodynamics of Ni2C is performed, and compared with that for Ni3C and NiC as well as several defect structures of varying composition. It is found that the most stable ground state arrangement of Ni2C exists within a simple orthorhombic lattice and that it has metallic character. The calculated formation energies (kcal/mol) of NiC, Ni2C, and Ni3C are 48.6, 7.9 and 6.4, respectively. [Preview Abstract] |
Tuesday, March 22, 2011 1:51PM - 2:03PM |
J24.00010: Atomistic Simulations of Deformation of Nanoscale FCC Materials Shivraj Karewar, Niraj Gupta, Alex Stukowski, Michael Baskes, Srinivasan Srivilliputhur We compare the deformation behavior of gold single crystal nanospheres with $\sim$6-30 nm diameters with gold spherical shells of varying inner to outer diameter ratios. Gold nanospheres are modeled with an EAM potential and the indenter is described by a repulsive potential. Yield strength dependence on sample size, geometry and temperature was studied in these nanospheres. The deformation mechanism is aided by the continuous displacement burst accompanying dislocation escape from the nanospheres. Based on this, a dislocation starvation mechanism has been discussed. Extended dislocations are found to be the prominent defect type in both solid and hollow nanospheres. Flow stresses are lower in hollow nanoshells. Low flow stresses are accounted for the presence of additional surface area for dislocation nucleation and emergence at the inner surface of the hollow shell. [Preview Abstract] |
Tuesday, March 22, 2011 2:03PM - 2:15PM |
J24.00011: First-principles investigation of migration barriers in bulk (Cr,Co)-doped Ni$_{3}$Al ($\gamma )$ and Ni$_{3}$Al/Ni ($\gamma $'/$\gamma )$ interface Priya Gopal, Srinivasan Srivilliputhur Ni-based super-alloys possess desirable high-temperature properties including ductility, fracture toughness as well as resistance to creep and oxidation mainly due to the precipitation of ordered Ni$_{3}$Al $\gamma $' precipitates within a $\gamma $ (Ni,Al) matrix. Various studies have shown that the mechanical properties can be improved by adding substitutional elements. It is thus very important to understand the electronic structure and diffusion kinetics of the substitutional elements and the role each one has on the overall microstructure. $\backslash $pardthis work we present our results on the systematic study of the energetics and migration barriers of Cr and Co in bulk Ni$_{3}$Al and Ni$_{3}$Al/Ni ($\gamma $'/$\gamma )$ interface. We did simulations of migration of vacancy and substitutional element in a complete set of migration paths and evaluated the barrier energies in both bulk Ni$_{3}$Al and Ni$_{3}$Al/Ni ($\gamma $'/$\gamma )$ interface using density functional theory methods. We will briefly discuss our results on the effect of migration barriers on the partitioning behavior of Cr and Co between the and ' phases in Ni-based super-alloy. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700