Stephen Thomas

Profile Information
Name
Dr. Stephen Thomas
Institution
Boise State University
Position
Graduate Assistant
h-Index
ORCID
0000-0002-8562-2217
Publications:
"TEM in situ cube-corner indentation analysis using ViBe motion detection algorithm" Matthew Swenson, Janelle Wharry, Kayla Yano, Stephen Thomas, Yang Lu, Journal of Nuclear Materials Vol. 502 2018 201-212 Link
Transmission electron microscopic (TEM) in situ mechanical testing is a promising method for understanding plasticity in shallow ion irradiated layers and other volume-limited materials. One of the simplest TEM in situ experiments is cube-corner indentation of a lamella, but the subsequent analysis and interpretation of the experiment is challenging, especially in engineering materials with complex microstructures. In this work, we: (a) develop MicroViBE, a motion detection and background subtraction-based post-processing approach, and (b) demonstrate the ability of MicroViBe, in combination with post-mortem TEM imaging, to carry out an unbiased qualitative interpretation of TEM indentation videos. We focus this work around a Fe-9%Cr oxide dispersion strengthened (ODS) alloy, irradiated with Fe2+ ions to 3 dpa at 500?°C. MicroViBe identifies changes in Laue contrast that are induced by the indentation; these changes accumulate throughout the mechanical loading to generate a “heatmap” of features in the original TEM video that change the most during the loading. Dislocation loops with b?=?½ <111> identified by post-mortem scanning TEM (STEM) imaging correspond to hotspots on the heatmap, whereas positions of dislocation loops with b?=?<100> do not correspond to hotspots. Further, MicroViBe enables consistent, objective quantitative approximation of the b?=?½ <111> dislocation loop number density.
Additional Publications:
"Morphological distribution mapping: Utilisation of modelling to integrate particle size and shape distributions" Ilgaz Akseli, Ana P. Ferreira, Michael Leane, Stephen Thomas, Mike Tobyn, Robert C. Wadams, John F. Gamble, [2023] International Journal of Pharmaceutics · DOI: 10.1016/j.ijpharm.2023.122743 · ISSN: 0378-5173
"Particle Property Characterization and Data Curation for Effective Powder Property Modeling in the Pharmaceutical Industry" Ilgaz Akseli, Jacob Albrecht, Ana P. Ferreira, John F. Gamble, Michael Leane, Stephen Thomas, Yue Schuman, Lauren Taylor, Mike Tobyn, Robert C. Wadams, [2022] AAPS PharmSciTech · DOI: 10.1208/s12249-022-02434-2 · ISSN: 1530-9932
"Data-smart machine learning methods for predicting composition-dependent Young’s modulus of pharmaceutical compacts" Hannah Palahnuk, Hossein Amini, Ilgaz Akseli, Stephen Thomas, [2021] International Journal of Pharmaceutics · DOI: 10.1016/j.ijpharm.2020.120049 · ISSN: 0378-5173
"General-Purpose Coarse-Grained Toughened Thermoset Model for 44DDS/DGEBA/PES" Stephen Thomas, Mone’t Alberts, Carla E. Estridge, Brittan Farmer, Olivia McNair, Eric Jankowski, Michael M. Henry, [2020] Polymers · DOI: 10.3390/polym12112547 · ISSN: 2073-4360

The objective of this work is to predict the morphology and material properties of crosslinking polymers used in aerospace applications. We extend the open-source dybond plugin for HOOMD-Blue to implement a new coarse-grained model of reacting epoxy thermosets and use the 44DDS/DGEBA/PES system as a case study for calibration and validation. We parameterize the coarse-grained model from atomistic solubility data, calibrate reaction dynamics against experiments, and check for size-dependent artifacts. We validate model predictions by comparing glass transition temperatures measurements at arbitrary degree of cure, gel-points, and morphology predictions against experiments. We demonstrate for the first time in molecular simulations the cure-path dependence of toughened thermoset morphologies.

"Three-dimensional mortar models using real-shaped sand particles and uniform thickness interfacial transition zones: Artifacts seen in 2D slices" Md Aminul Islam, Stephen Thomas, Edward J. Garboczi, Yang Lu, [2020] Construction and Building Materials · DOI: 10.1016/j.conbuildmat.2019.117590 · ISSN: 0950-0618
"Perspective on coarse-graining, cognitive load, and materials simulation" Neale Ellyson, Jenny W. Fothergill, Michael M. Henry, Mitchell H. Leibowitz, Evan D. Miller, Mone’t Alberts, Samantha Chesser, Jaime D. Guevara, Chris D. Jones, Mia Klopfenstein, Kendra K. Noneman, Rachel Singleton, Ramon A. Uriarte-Mendoza, Stephen Thomas, Carla E. Estridge, Matthew L. Jones, Eric Jankowski, [2020] Computational Materials Science · DOI: 10.1016/j.commatsci.2019.109129 · ISSN: 0927-0256
"Characterizing In Situ and In Transit Analytics of Molecular Dynamics Simulations for Next-Generation Supercomputers" Stephen Thomas, Michael Wyatt, Tu Mai Anh Do, Loic Pottier, Rafael Ferreira da Silva, Harel Weinstein, Michel A. Cuendet, Trilce Estrada, Ewa Deelman, Michela Taufer, [2019] 2019 15th International Conference on eScience (eScience) · DOI: 10.1109/escience.2019.00027
"Routine million-particle simulations of epoxy curing with dissipative particle dynamics" Monet Alberts, Michael M Henry, Carla E Estridge, Eric Jankowski, Stephen Thomas, [2018] Journal of Theoretical and Computational Chemistry · DOI: 10.1142/s0219633618400059 · ISSN: 0219-6336

Mesoscale simulation techniques have helped to bridge the length scales and time scales needed to predict the microstructures of cured epoxies, but gaps in computational cost and experimental relevance have limited their impact. In this work, we develop an open-source plugin epoxpy for HOOMD-Blue that enables epoxy crosslinking simulations of millions of particles to be routinely performed on a single modern graphics card. We demonstrate the first implementation of custom temperature-time curing profiles with dissipative particle dynamics and show that reaction kinetics depend sensitively on the stochastic bonding rates. We provide guidelines for modeling first-order reaction dynamics in a classic epoxy/hardener/toughener system and show structural sensitivity to the temperature-time profile during cure. We conclude with a discussion of how these efficient large-scale simulations can be used to evaluate ensembles of epoxy processing protocols to quantify the sensitivity of microstructure on processing.

"TEM in situ cube-corner indentation analysis using ViBe motion detection algorithm" S. Thomas, M.J. Swenson, Y. Lu, J.P. Wharry, K.H. Yano, [2018] Journal of Nuclear Materials · DOI: 10.1016/j.jnucmat.2018.02.003 · EID: 2-s2.0-85042090940
"Improved Model for Three-Dimensional Virtual Concrete: Anm Model" Yang Lu, E. J. Garboczi, Stephen Thomas, [2016] Journal of Computing in Civil Engineering · DOI: 10.1061/(asce)cp.1943-5487.0000494 · EID: 2-s2.0-84959036637
"Anm Model Approach for Lunar Soil Simulant Properties Study" Stephen Thomas, Yang Lu, [2015] Earth and Space 2014 · DOI: 10.1061/9780784479179.010
Source: ORCID/CrossRef using DOI