Time filter

Source Type

Springboro, United States

Jung J.-H.,Pusan National University | Na Y.-S.,Korea Institute of Materials Science | Cho K.-M.,Pusan National University | Dimiduk D.M.,BlueQuartz Software Inc. | Choi Y.S.,Pusan National University
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2015

The microcompression behavior of single-slip oriented, single-crystal micro-pillars was simulated using a crystal plasticity finite element method, by varying a primary slip-plane inclination angle from 36.3 to 48.7 deg while keeping the same primary slip system. Simulated global deformation of the micro-pillars was separated into two types, depending upon the primary slip-plane inclination angle: the one consistent with the primary slip direction and the other diagonally opposite to the primary slip direction. © 2015 The Minerals, Metals & Materials Society and ASM International

Venkatakrishnan S.V.,Purdue University | Drummy L.F.,Air Force Research Lab | Jackson M.A.,BlueQuartz Software Inc. | Bouman C.A.,Purdue University | And 2 more authors.
Ultramicroscopy | Year: 2016

We introduce a forward model for the computation of high angle annular dark field (HAADF) images of nano-crystalline spherical particles and apply it to image simulations for assemblies of nano-spheres of Al, Cu, and Au with a range of sizes, as well as an artificial bi-sphere, consisting of solid hemispheres of Al and Cu or Al and Au. Comparison of computed intensity profiles with experimental observations on Al spheres at different microscope accelerating voltages provides confidence in the forward model. Simulated tomographic tilt series for both HAADF and bright field (BF) images are then used to illustrate that the model-based iterative reconstruction (MBIR) approach is capable of reconstructing sphere configurations of mixed atomic number, with the correct relative reconstructed intensity ratio proportional to the square of the atomic number ratio. © 2015 Elsevier B.V.

Venkatakrishnan S.,Purdue University | Drummy L.,Air Force Research Lab | Jackson M.,BlueQuartz Software Inc. | De Graef M.,Carnegie Mellon University | And 2 more authors.
2012 IEEE Statistical Signal Processing Workshop, SSP 2012 | Year: 2012

HAADF-STEM data is increasingly being used in the physical sciences to study materials in 3D because it is free from the diffraction effects seen in Bright Field STEM data and satisfies the projection requirement for tomography. Typically, reconstruction is performed using Filtered Back Projection (FBP) or the SIRT algorithm. In this paper, we develop a Bayesian reconstruction algorithm for HAADF-STEM tomography which models the image formation, the noise characteristics of the measurement, and the inherent smoothness in the object. Reconstructions of polystyrene functionalized Titanium dioxide nano particle assemblies show results that are qualitatively superior to FBP and SIRT reconstructions, significantly suppressing artifacts and enhancing contrast. © 2012 IEEE.

Chen Y.H.,University of Michigan | Park S.U.,Schlumberger | Wei D.,IBM | Newstadt G.,University of Michigan | And 4 more authors.
Microscopy and Microanalysis | Year: 2015

We propose a framework for indexing of grain and subgrain structures in electron backscatter diffraction patterns of polycrystalline materials. We discretize the domain of a dynamical forward model onto a dense grid of orientations, producing a dictionary of patterns. For each measured pattern, we identify the most similar patterns in the dictionary, and identify boundaries, detect anomalies, and index crystal orientations. The statistical distribution of these closest matches is used in an unsupervised binary decision tree (DT) classifier to identify grain boundaries and anomalous regions. The DT classifies a pattern as an anomaly if it has an abnormally low similarity to any pattern in the dictionary. It classifies a pixel as being near a grain boundary if the highly ranked patterns in the dictionary differ significantly over the pixel's neighborhood. Indexing is accomplished by computing the mean orientation of the closest matches to each pattern. The mean orientation is estimated using a maximum likelihood approach that models the orientation distribution as a mixture of Von Mises-Fisher distributions over the quaternionic three sphere. The proposed dictionary matching approach permits segmentation, anomaly detection, and indexing to be performed in a unified manner with the additional benefit of uncertainty quantification. © Microscopy Society of America 2015.

Rao S.I.,UES, Inc. | Rao S.I.,Ecole Polytechnique Federale de Lausanne | Dimiduk D.M.,BlueQuartz Software Inc. | El-Awady J.A.,Johns Hopkins University | And 3 more authors.
Acta Materialia | Year: 2015

Using atomistic simulations, the effect of jogs on the cross-slip of screw character dislocations and screw-dipole annihilation was examined for both FCC Cu and Ni. The stress-free activation energy for cross-slip at jogs is close to 0.4 eV in Cu, determined using a nudged elastic band method. This value is a factor of 4-to-5 lower than the activation energy for cross-slip of screw dislocations in the absence of a jog. Similar results were obtained for Ni. Molecular dynamics simulations were used to study the annihilation of a jog-containing screw dipole. The critical Escaig stress on the glide plane for dipole annihilation drops quickly from the 0 K value of ∼400 MPa and, dipole annihilation is nearly athermal at room temperature. At 5 K, Escaig stresses on the cross-slip plane are a factor of 1.5 less effective than Escaig stresses on the glide plane and, glide stresses on the cross-slip plane are a factor of 3 less effective for dipole annihilation by cross-slip. The activation volume for cross-slip of screw dislocations at jogs with respect to these three stress components range from 6 to 20b3. These results have been found to be useful in physics-based modeling of bulk cross-slip in higher length scale 3D dislocation dynamics simulations investigating dislocation pattern formation and fatigue structures in FCC crystals. © 2015 Acta Materialia Inc.

Discover hidden collaborations