Michael R TonksUniversity of Florida | UF · Department of Materials Science and Engineering
Michael R Tonks
Ph.D. Mechanical Engineering
About
165
Publications
35,885
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
4,447
Citations
Introduction
I am a computational materials scientist specializing in predicting the coevolution of microstructure and physical properties within materials in harsh environments. At the University of Florida, I lead a research group in this area. I am the creator of the NEAMS-sponsored MARMOT mesoscale fuel performance code. I am also a major user of the MOOSE framework and contributor to the MOOSE phase field and tensor mechanics modules. My current Research Interests include: evaluation of accident tolerant fuel concepts; simulation of sintering and densification; mesoscale modeling of fracture; nuclear thermal propulsion; ablative thermal protection systems.
Additional affiliations
August 2017 - present
August 2015 - August 2017
July 2013 - August 2015
Education
August 2002 - October 2008
August 2001 - August 2002
August 1995 - August 2001
Publications
Publications (165)
This study focuses on the precipitation of nanoscale hydrides in polycrystalline zirconium as a first step to predicting the hydride morphology observed experimentally and investigating the mechanisms responsible for hydride reorientation at the mesoscale. A quantitative phase-field model, which includes the elastic anisotropy of the nanoscale zirc...
The role of anisotropic grain boundary energy in grain growth is investigated using textured microstructures that contain a high proportion of special grain boundaries. Textured and untextured Ca‐doped alumina was prepared by slip casting inside and outside a high magnetic field, respectively. At 1600°C, the textured microstructure exhibits faster...
An electrochemical micro-scale phase-field model is developed to simulate the stripping and plating kinetics of a Na-metal anode in all-solid-state Na-ion batteries. In this model, in addition to the metallic anode and ceramic separator regions, a highly conductive but Na-poor region representing the free space is assumed to simulate the shrinking...
Crystallographic texture is an important descriptor of material properties but requires time-intensive electron backscatter diffraction (EBSD) for identifying grain orientations. While some metrics such as grain size or grain aspect ratio can distinguish textured microstructures from untextured microstructures after significant grain growth, such m...
High-energy x-ray diffraction microscopy (HEDM) nondestructively maps microstructures in 3D, allowing for the same grains and boundaries to be tracked over time during annealing experiments. Here, HEDM was applied to observe grain growth in strontium titanate. These results are compared to a 3D isotropic grain growth simulation that starts from the...
Understanding the impact of microstructure on corrosion rates can aid the development of corrosion-resistant alloys for molten salt reactors. In this work, we develop an electrochemical phase-field model for capturing the microstructure-dependent corrosion of structural alloys by molten salts. As a demonstration problem, we apply this model to capt...
UO2 fuel fragmentation and pulverization during loss-of-coolant accidents (LOCAs) is an ongoing safety concern that has gained importance due to recent interest in increasing burnup limits for light water reactor fuel. In this work, we investigate the importance of bubble pressure on fragmentation using 2D phase field fracture simulations of UO2 po...
Experimental grain growth observations often deviate from grain growth simulations, revealing that the governing rules for grain boundary motion are not fully understood. A novel deep learning model was developed to capture grain growth behavior from training data without making assumptions about the underlying physics. The Physics-Regularized Inte...
Experimental grain growth observations often deviate from grain growth simulations, revealing that the governing rules for grain boundary motion are not fully understood. A novel deep learning model was developed to capture grain growth behavior from training data without making assumptions about the underlying physics. The Physics-Regularized Inte...
Current grain growth models have evolved to account for the relationship between grain boundary energy/mobility anisotropy and the five degrees of grain boundary character. However, the role of grain boundary networks on overall growth kinetics remains poorly understood. To experimentally investigate this problem, a highly textured Al2O3 was fabric...
We have developed a flexible method for calculating the grain boundary (GB) inclinations of voxelated grain structure data using smoothing algorithms. We compared the performance of four algorithms: the linear interpolation, Allen–Cahn, level-set, and vertex algorithms. We assessed their accuracy using 2D and 3D cases with known inclinations. The v...
This paper presents the state-of-the-art knowledge about the micro-mechanical modelling of the fuel behavior under irradiation with normal and off normal operating conditions. Modelling of fundamental processes can provide key insights in the behavior of the material. Such models target specific phenomena due to the limits of computational resource...
A phase-field model is parameterized to study the effect of elastic stresses on the migration of He gas bubbles in Fe under a temperature gradient. Stresses caused by the gas bubble pressure and residual stress in the Fe matrix are considered. The dependence of He bubble migration velocity on the magnitude of the residual stress, average temperatur...
To efficiently capture the energy of the nuclear bond, advanced nuclear reactor concepts seek solid fuels that must withstand unprecedented temperature and radiation extremes. In these advanced fuels, thermal energy transport under irradiation is directly related to reactor performance as well as reactor safety. The science of thermal transport in...
In this paper, we developed a multiphysics mesoscale model of carbon fiber oxidation in the upper most layer of a phenolic impregnated carbon ablator thermal protection system. The presented model uses the phase-field method to capture the reduction of carbon fibers due to an oxidation reaction between carbon and oxygen to form carbon monoxide. The...
Fission gas release within uranium dioxide nuclear fuel occurs as gas atoms diffuse through grains and arrive at grain boundary (GB) bubbles; these GB bubbles grow and interconnect with grain edge bubbles; and grain edge tunnels grow and connect to free surfaces. In this study, a hybrid multi-scale/multi-physics simulation approach is presented to...
Strain energy decomposition methods in phase field fracture models separate strain energy that contributes to fracture from that which does not. However, various decomposition methods have been proposed in the literature, and it can be difficult to determine an appropriate method for a given problem. The goal of this work is to facilitate the choic...
To efficiently capture the energy of the nuclear bond, advanced nuclear reactor concepts seek solid fuels that must withstand unprecedented temperature and radiation extremes. In these advanced fuels, thermal energy transport under irradiation is directly related to reactor performance as well as reactor safety. The science of thermal transport in...
Oxidation kinetics and scale formation were examined in 21-2 N Stainless Steel alloys in a CO2 environment at 700 °C. Several characterization techniques were used to identify the morphology, crystallographic structure, and chemical composition of the oxide scale formation during exposures up to 1925 hours. High manganese content played an importan...
A ceramic–metal composite (cermet) of uranium nitride (UN) particles embedded in a tungsten-molybdenum (W/Mo) alloy matrix is being considered as reactor fuel for nuclear thermal propulsion (NTP). One possible issue is the loss of fissile uranium atoms during reactor operation. We begin by reviewing historical data that suggest that a likely mechan...
In light water nuclear reactors, waterside corrosion of the cladding material leads to the production of hydrogen, a fraction of which is picked up by the zirconium cladding and precipitates into brittle hydride particles. These nanoscale hydride particles aggregate into mesoscale hydride clusters. The principal stacking direction of the nanoscale...
Reactive molecular dynamics (MD) simulations are performed to study the initial stage of the oxidation of carbon fiber and amorphous carbon char with atomic oxygen at temperatures ranging from 1000 K to 4500 K. The carbon fiber and amorphous char models are generated by kinetic Monte-Carlo and liquid quench methods, respectively. The species formed...
In this work, a phase field fracture model is proposed that includes single crystal anisotropy in both the elastic constants and the fracture energy. The strain energy is decomposed into tensile and compressive parts, and only the tensile part contributes to crack propagation. Anisotropic fracture energy is included to capture the impact of crystal...
This work investigated brittle fracture of polycrystalline materials due to thermal stresses arising from anisotropic thermal expansion. We used phase-field fracture simulations with the properties of α-uranium (α-U) and assumed a linear elastic mechanical response. Three-dimensional simulations were used to predict fracture for various conditions...
The contribution of the author Pierre-Clément A. Simon has been added to the CRediT authorship contribution statement:
Pierre-Clément A. Simon: Conceptualization, Methodology, Software, Validation, Visualization, Writing - original draft, Writing - review
& editing.
Nuclear thermal propulsion (NTP) provides a consistent source of thrust for long space missions. However, fuel development for NTP reactors is a major technological hurdle. Existing modeling and simulation tools developed by the U.S. Nuclear Engineering Advanced Modeling and Simulation (NEAMS) program for power reactors can be leveraged to help acc...
The ability to identify features within finite element simulations and track them over time is necessary for understanding and quantifying complex behaviors as disparate as turbulent vortices in a flow field to microstructure evolution. We extend our previous research on feature identification in parallel unstructured meshes with the novel ability...
Amphiphilic gels consisting of acrylamide (AAM)/2-hydroxyethyl methacrylate (HEMA), hexafluorobutyl methacrylate (HFBMA) and non-isocyanate urethane dimethacrylate (NIUDMA) of varying molecular weights were compared. A three-level Taguchi analysis was performed using the amount of AAM/HEMA, HFBMA, NIUDMA and reaction time as dependent variables to...
A high-fidelity model is necessary for understanding the properties of carbon fibers (CFs) and developing the next generation of CFs and related composites. Using kinetic Monte Carlo combined with large-scale Molecular Dynamics (kMC-MD), we generate two types of CF models at a wide range of initial densities (from 1.2 g/cm³ to 2.0 g/cm³). These fib...
Irradiation-enhanced densification (IED) is a form of sintering that occurs within ceramic nuclear fuels during reactor operation. It affects the fuel microstructure and density, which in turn affect the temperature profile and fission gas behavior. In this work, we modify the grand potential sintering model to describe IED. This new model is verif...
Because hydride microstructure can significantly influence Zr alloy nuclear fuel cladding’s ductility, a new metric has been developed to quantify hydride microstructure in 2D micrographs and relate it to crack propagation. As cladding failure usually results from a hoop stress, this new metric, called the Radial Hydride Continuous Path (RHCP), is...
High thermal conductivity additives are being considered to create composite nuclear fuels with a higher effective thermal conductivity (ETC) to reduce the peak fuel temperatures during reactor operation. However, the benefits of the additive may be reduced, or possibly eliminated, when placed into a reactor environment. In this work, we investigat...
A CALPHAD-informed (Computer Coupling of Phase Diagrams and Thermochemistry) constituent redistribution model was developed for Zr-based metallic fuels and incorporated into the BISON fuel performance code. Three uncertain model parameters associated with β and γ phase kinetics were calibrated using integral test data from U-Zr fuel elements irradi...
The purpose of this work is to develop a mechanistic model of grain growth in UO2 fuel during reactor operation. The model development builds on published experimental data on UO2 grain growth, as well as atomistic and mesoscale simulation results. We begin by developing new fits with temperature T (in K) for the average grain boundary (GB) energy...
Introducing elastic energy in the phase field method has been shown to influence interfacial energy, depending on the elastic interpolation scheme. This study investigates the impact of the elastic energy when using a grand potential-based phase field method, comparing the result of Khachaturyan’s strain interpolation scheme (KHS) and Voight-Taylor...
U3Si2 is a potential accident-tolerant fuel that shows promise due to its high thermal conductivity and higher uranium density relative to UO2. However, its swelling and fission gas release behavior in light water reactor (LWR) conditions is relatively unknown. To provide mechanistic insight and determine parameters for engineering-scale fuel perfo...
High thermal conductivity additives are being explored to make next generation accident tolerant fuels for light water reactors (LWRs). The goal is to create composite fuels that will more effectively dissipate heat, thus lowering the high centerline temperatures that develop in current LWR fuel. These fuels can employ various additives and the fue...
Turing (or double-diffusive) instabilities describe pattern formation in reaction-diffusion systems, and were proposed in 1952 as a potential mechanism behind pattern formation in nature, such as leopard spots and zebra stripes. Because the mechanism requires the reacting species to have significantly different diffusion rates, only a few liquid ph...
Multi-metallic layered composite (MMLC) fuel cladding is designed to survive a longer period of time during accident scenarios for light water reactor (LWR) fuel. One proposed MMLC cladding concept joining Zircaloy to steel via interaction barrier layers will increase corrosion resistance, but result in a neutron absorption penalty. This cladding c...
Microstructure is a controlling factor in the behavior of sintered materials. This work presents a quantitative phase field model of thermal sintering that predicts the evolution of the microstructure by capturing the sintering stress, GB/vacancy interactions, non-uniform diffusion, and grain coarsening without introducing a separate rigid body mot...
Bajpai, ParikshitPoschmann, MaxAndrš, DavidBhave, ChaitanyaTonks, MichaelPiro, Markus materials are highly complex Multiscale, multiphysics systems, and an effective prediction of nuclear reactor performance and safety requires Simulation capabilities that tightly couple different physical phenomena. The Idaho National Laboratory’s Multiphysics Obj...
Chromium-doped UO is a widely-studied near-term deployable accident-tolerant fuel concept because it results in a dense, large-grain structure that increases the fuel resistance to densification, swelling, and fission gas release. A new charged-interstitial mechanism was recently proposed to describe the behavior of dopants like chromium in sintere...
The purpose of this work is to develop a model for normal grain growth in U3Si2. The average grain boundary energy was determined from previously published molecular dynamics simulations. The grain growth kinetics were quantified at various temperatures by annealing nanocrystalline samples. The mobility was determined by comparing phase field grain...
In this manuscript, a new phase field model of brittle fracture is proposed that accounts for any elastic anisotropy using spectral decomposition of the stress. To verify the model, both Mode I and Mode II fracture simulations were performed to ensure that the correct crack paths were predicted. Next, the fracture of face-centered cubic (FCC) and h...
In this chapter, we provide three case studies for carrying out sensitivity analysis and uncertainty quantification (UQ) on mesoscale simulations. These three examples are focused on understanding the behavior of porous UO2, looking at grain growth and fracture simulations (using the phase field method) and effective thermal conductivity (using hea...
Interest in U-Zr metallic nuclear fuels has been on the rise, but sparsity in the available diffusion data continues to hinder efforts to model irradiation behaviors like constituent redistribution. In the current work, we develop a quantitative phase-field model for the influential β and γ phases of U-Zr and use it to reexamine data from a publish...
We have investigated the grain boundary scattering effect on the thermal transport behavior of uranium dioxide (UO$_2$). The polycrystalline samples having different grain-sizes (0.125, 1.8, and 7.2 $\mu$m) have been prepared by spark plasma sintering technique and characterized by x-ray powder diffraction (XRD), scanning electron microscope (SEM),...
The existing Pu–Zr binary phase diagrams report the stability of the compound θ-(Pu,Zr) in the low temperature region between 300 and 0 °C. Furthermore, the current understanding is that θ-(Pu–Zr) is thermodynamically favored over the metastable δ-(Pu,Zr) phase. In an effort to shed light on the phases formed in Pu–Zr binary alloys and reduce uncer...
We have investigated the grain-boundary scattering effect on the thermal transport behavior of uranium dioxide (UO2). The polycrystalline samples having different grain-sizes (0.125, 1.8, and 7.2μm) have been prepared by a spark plasma sintering technique and characterized by x-ray powder diffraction, scanning electron microscope, and Raman spectro...
Scientific communities struggle with the challenge of effectively and efficiently sharing content and data. An online portal provides a valuable space for scientific communities to discuss challenges and collate scientific results. Examples of such portals include the Micromagnetic Modeling Group (μMAG) [1], the Interatomic Potentials Repository (I...
Mesoscale modeling and simulation approaches provide a bridge from atomic-scale methods to the macroscale. The phase field (PF) method has emerged as a powerful and popular tool for mesoscale simulation of microstructure evolution, and its use is growing at an ever-increasing rate. While initial research using the PF method focused on model develop...
Constituent redistribution in U–Zr fuels produces radially-distributed phase fields, each with different material properties and behaviors. The location and composition of the phase fields evolve dynamically due to the influence of swelling, fission gas release, and sodium infiltration on the thermal conductivity of the fuel. Gaps in the understand...
Phase diagrams constructed for the Pu-Zr binary system report the existence of θ-(Pu,Zr), δ-(Pu,Zr), γ-Pu, α-Pu, β-Pu, and ζ-Pu28Zr phases in Pu-enriched region, when Pu concentrations exceed 75 at.% (equivalent to 89 wt% Pu). The compound θ-(Pu,Zr) has been said to occur at about 20 at.% Zr, but the regions for θ-(Pu,Zr) on the Pu-rich side have n...
A phase-field model of fission gas bubble evolution was developed and applied to gain an improved understanding of the microstructure-level processes leading to fission gas release from nuclear fuel, and to inform engineering-scale fission gas release models. The phase-field model accounts for multiple fuel grains and fission gas bubbles and tracks...
Dense nanocrystalline and microcrystalline UO2 samples with controlled grain structure and stoichiometry were prepared by high energy ball milling and spark plasma sintering (SPS). Nano-indentation and micro-indentation testing were performed at different temperatures of 25 °C, 300 °C, and 600 °C in order to study the mechanical properties of the s...
Turing (or double-diffusive) instabilities describe pattern formation in reaction-diffusion systems, and were proposed in 1952 as a potential mechanism behind pattern formation in nature, such as leopard spots and zebra stripes. Because the mechanism requires the reacting species to have significantly different diffusion rates, only a few liquid ph...
A report of the work done on the uncertainty quantification and validation of the phase field fracture model implemented in MARMOT.
Hydrogen absorbed into zirconium alloy nuclear fuel cladding as a result of the waterside corrosion reaction can affect the properties of nuclear fuel, principally through the precipitation of brittle hydride particles. Multiple phenomena are involved in this overall process: after hydrogen pickup degradation of mechanical properties is controlled...
Minor actinide transmutation fuels, of which U-Pu-Zr is one of the most promising, have been the subject of renewed interest for fast reactor applications. Unfortunately, we lack the understanding necessary to make quantitative, mechanistic predictions about the complex phase behaviors exhibited by U-Pu-Zr. This prevents the efficient development a...
U-Pu-Zr is a promising metallic fuel candidate. However, fuel selection and qualification will require the ability to accurately predict its behavior. Unfortunately, the system's complex phase behaviors promote formation of heterogeneities that cannot be adequately described using bulk properties. This work presents an equilibrium phase-field model...
U3Si2 and U3Si5 are two important uranium silicide phases currently under extensive investigation as potential fuel forms or components for light water reactors (LWRs) to enhance accident tolerance. In this paper, their irradiation behaviors are studied by ion beam irradiations with various ion mass and energies, and their microstructure evolution...
This work is a review of two density changes common in UO2 nuclear fuel: sintering and irradiation-enhanced densification. These density changes must be understood in order to predict fuel behavior, increase fuel lifetime, and design safer and more economical reactor fuels. The physical causes of each dimensional change are summarized. Then a summa...
The phase field (PF) method provides a valuable means of predicting radiation induced microstructure evolution of domains ranging roughly from 100 nm to 100 microns in size and for lengths of time ranging from microseconds to years, depending on the rate of diffusion. In this work we summarize how to apply the PF method to modeling radiation damage...