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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.


PubMed | University of Michigan, IBM, BlueQuartz Software Inc., U.S. Air force and 2 more.
Type: Journal Article | Journal: Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada | 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 pixels 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.


PubMed | Carnegie Mellon University, EDAX and BlueQuartz Software Inc.
Type: | Journal: Ultramicroscopy | Year: 2015

Electron Backscatter Diffraction (EBSD) provides a useful means for characterizing microstructure. However, it can be difficult to obtain index-able diffraction patterns from some samples. This can lead to noisy maps reconstructed from the scan data. Various post-processing methodologies have been developed to improve the scan data generally based on correlating non-indexed or mis-indexed points with the orientations obtained at neighboring points in the scan grid. Two new approaches are introduced (1) a re-scanning approach using local pattern averaging and (2) using the multiple solutions obtained by the triplet indexing method. These methodologies are applied to samples with noise introduced into the patterns artificially and by the operational settings of the EBSD camera. They are also applied to a heavily deformed and a fine-grained sample. In all cases, both techniques provide an improvement in the resulting scan data, the local pattern averaging providing the most improvement of the two. However, the local pattern averaging is most helpful when the noise in the patterns is due to the camera operating conditions as opposed to inherent challenges in the sample itself. A byproduct of this study was insight into the validity of various indexing success rate metrics. A metric based given by the fraction of points with CI values greater than some tolerance value (0.1 in this case) was confirmed to provide an accurate assessment of the indexing success rate.


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.


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.


PubMed | Carnegie Mellon University, BlueQuartz Software Inc., Purdue University and Air Force Research Lab
Type: | Journal: Ultramicroscopy | Year: 2015

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.


Jackson M.,BlueQuartz Software Inc. | Simmons J.P.,U.S. Air force | De Graef M.,Carnegie Mellon University
Modelling and Simulation in Materials Science and Engineering | Year: 2010

A new digital file format is proposed for the long-term archival storage of experimental data sets generated by serial sectioning instruments. The format is known as the multi-dimensional eXtensible Archive (MXA) format and is based on the public domain Hierarchical Data Format (HDF5). The MXA data model, its description by means of an eXtensible Markup Language (XML) file with associated Document Type Definition (DTD) are described in detail. The public domain MXA package is available through a dedicated web site (mxa.web.cmu.edu), along with implementation details and example data files. © 2010 IOP Publishing Ltd.


Lewis A.C.,U.S. Navy | Qidwai S.M.,U.S. Navy | Jackson M.,BlueQuartz Software Inc. | Geltmacher A.B.,U.S. Navy
JOM | Year: 2011

For the most comprehensive modeling and prediction of materials behavior at the microscale, experimentally measured three-dimensional (3-D) microstructural datasets must be incorporated as initial input into computational models. Although the capability to collect and store large amounts of 3-D microstructural data is advancing continuously, computational resources for the processing and simulation can limit the amount of data that can be analyzed. Depending on the features and properties of interest, several approaches can be applied to optimize processing, reduce the amount of data that needs to be simulated, and increase the effi ciency of simulations to maximize the statistical signifi cance of microstructure analyses. This paper presents examples of four such approaches to efficient integration of large 3-D datasets into modeling and simulations of mechanical behavior in an efficient yet statistically significant manner.


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


Donegan S.P.,BlueQuartz Software Inc. | Rollett A.D.,Carnegie Mellon University
Acta Materialia | Year: 2015

A numerical method for solving the thermoelastic problem in heterogeneous polycrystals based on fast Fourier transforms is applied to thermal barrier coating systems. Several high resolution microstructures are generated synthetically to approximate thermal barrier coatings, with control over the grain size, grain morphology, and texture. Interfaces between coating layer materials are further modified by applying a localized Potts model to introduce interface rumpling. The global results of residual stress and elastic energy density are compared across the various microstructure instantiations. The local variations in elastic energy density are correlated to the amount of interface rumpling. The simulation result are also compared to an analytical result for an idealized interface morphology. The implications of the behavior of the local variations in elastic energy density are discussed in the context of thermal barrier coating failure. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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