Publications
247 results found
Sutton AP, Todorov TN, 2021, Theory of electroplasticity based on electromagnetic induction, PHYSICAL REVIEW MATERIALS, Vol: 5, ISSN: 2475-9953
Reali L, Balint DS, Sutton A, et al., 2021, Plastic relaxation and solute segregation to β-Nb second phase particles in Zr-Nb alloys: a discrete dislocation plasticity study, Journal of the Mechanics and Physics of Solids, Vol: 156, ISSN: 0022-5096
There is clear evidence in the literature that iron segregates to the interface of second phase particles (SPPs) in unirradiated Zr-Nb alloys, and that it does not do so in the presence of radiation damage. In this work, a discrete dislocation plasticity model is developed that takes into account the long-range stress field of the SPP interface. A simple analytical model is also outlined, providing an upper bound for estimating the amount of interstitial segregation. The model provides a possible mechanism to explain both the iron segregation to coherent SPPs and its subsequent loss after irradiation. Qualitatively, the model proved to be insensitive to variations of all geometrical and computational parameters, allowing for general conclusions to be drawn. The model suggests that the segregation originates from a tensile field of order 1 GPa induced by the dislocations generated during the plastic relaxation around the SPP. This leads to the six-fold increase in the iron concentration observed in experiments. In the model, the loss of SPP/matrix coherency after irradiation causes the dislocations to drift away from the interface, and the iron concentration is homogenised accordingly. The hydrogen concentration was also predicted and found to be about 50% higher than in the bulk zirconium matrix at room temperature. The computational framework is built to be fast, making possible a statistical analysis on over five hundred simulations for improved reliability of the predictions.Keywords: Discrete dislocation plasticity; Zr-Nb alloys; second phase particles; interfacial segregation.
Gurrutxaga Lerma B, Verschueren J, Sutton A, et al., 2021, The mechanics and physics of high-speed dislocations: a critical review, International Materials Reviews, Vol: 66, Pages: 215-255, ISSN: 0950-6608
High speed dislocations have long been identified as the dominant feature governing the plastic response of crystalline materials subjected to high strain rates, controlling deformation and failure in industrial processes such as machining, laser shock peening, punching, drilling, crashworthiness, foreign object damage, etc. Despite decades of study, the role high speed dislocations have on the materials response remains elusive. This article reviews both experimental and theoretical efforts made to address this issue in a systematic way. The lack of experimental evidence and direct observation of high speed dislocations means that most work on the matter is rooted on theory and simulations. This article offers a critical review of the competing theoretical accounts of high speed mechanisms, their underlying hypothesis, insights, and shortcomings, with particular focus on elastic continuum and atomistic levels. The article closes with an overview of the current state of the art and suggestions for key developments in future research.
Patel M, Reali L, Sutton AP, et al., 2021, A fast efficient multi-scale approach to modelling the development of hydride microstructures in zirconium alloys, COMPUTATIONAL MATERIALS SCIENCE, Vol: 190, ISSN: 0927-0256
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Reali L, Wenman MR, Sutton AP, et al., 2021, Plasticity of zirconium hydrides: a coupled edge and screw discrete dislocation model, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, Vol: 147, ISSN: 0022-5096
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- Citations: 4
Sutton AP, 2020, Physics of Elasticity and Crystal Defects, Publisher: Oxford University Press, USA, ISBN: 9780198860785
This novel approach will be new to most engineers and it will appeal to physicists. There are exercises for the student to work through, with complete solutions free to course instructors from the OUP website.
Ebrahimi M, Balint D, Sutton A, et al., 2019, A discrete crack dynamics model of toughening in brittle polycrystalline material by crack deflection, Engineering Fracture Mechanics, Vol: 214, Pages: 95-111, ISSN: 0013-7944
This paper focuses on the study of the effect of the interfacial strength of grain boundaries and elliptical inclusions on crack path deflection. The method is developed to channel a crack into a toughening configuration (arrays of elliptical holes and inclusions are considered) in order to obtain the optimised microstructure required to enhance fracture toughness through different mechanisms. The proposed technique is shown to reproduce experimental crack propagation paths in various configurations and is capable of capturing the effect of that variation of the GB and the inclusion interfacial strength; it provides a powerful tool to understand the interplay between microstructural features and improve materials performance.
Cimbaro L, Sutton A, Balint D, et al., 2019, Embrittlement of an elasto-plastic medium by an inclusion, International Journal of Fracture, Vol: 216, Pages: 87-100, ISSN: 0376-9429
A mathematical model for the embrittlement of a long elastic-plastic crack by a relatively small, misfitting inclusion is presented. The model makes direct contact with the Dugdale–Bilby–Cottrell–Swinden model as a limiting case. The particular case of an oxide inclusion with a triangular cross-section at the tip of an intergranular crack in the Ni-based superalloy RR1000 at 650∘C is considered. The positive misfit of the intrusion provides an additional tensile load on the crack tip and on the plastic zone, raising the local stress intensity factor kI and the crack tip opening displacement Δu above those when the inclusion is replaced by a dislocation-free zone of the same length. It is shown that for a given misfit strain and inclusion shape, the enhancement of kI and Δu is controlled by a dimensionless parameter ω=(σ/σ1)c/(2l)−−−−−√ where σ is the applied stress, σ1 is the yield stress, c is the crack length and l is the length of the inclusion. The anti-shielding effect of the intrusion is significant only when ω≲6. As a result of the anti-shielding effect of the intrusion, the stress singularity at the crack tip always exceeds the compressive normal stress that exists within the thickest part of the intrusion when it is isolated. It is also shown that the gradient of the hydrostatic stress within the intrusion subjected to different applied stresses drives the oxygen diffusion and, hence, assists the oxidation at the grain boundary. The fracture toughness is considerably greater than that of a bulk sample of the oxide particle, which we attribute to the plastic zone.
Sutton A, Drautz R, Vitek V, 2019, David Godfrey Pettifor. 9 March 1945—16 October 2017, Biographical Memoirs of the Fellows of the Royal Society, Vol: 66, ISSN: 0080-4606
David Pettifor was a theoretical physicist who changed the nature of materials science by raising the status of materials modelling to that of materials characterization and processing. He believed that the subject advanced through the development of simple models that withstood rigorous testing against experiments and the most accurate numerical computations. Having been a pioneer of total energy density functional theory calculations, he went on to derive analytic interatomic potentials for transition metals and nearly-free-electron metals and alloys from quantum mechanical principles. He is probably best known for the development of highly successful structure maps for binary and pseudo-binary alloys that were used by alloy developers in industry to create intermetallic alloys with improved properties. At Oxford he established the first materials modelling laboratory, bringing together physicists, chemists, materials scientists and engineers to model materials across length and time scales, which became a flagship laboratory for materials scientists world-wide.
Tajabadi-Ebrahimi M, Dini D, Balint DS, et al., 2018, Discrete crack dynamics: a planar model of crack propagation and crack-inclusion interactions in brittle materials, International Journal of Solids and Structures, Vol: 152-153, Pages: 12-27, ISSN: 0020-7683
The Multipole Method (MPM) is used to simulate the many-body self-consistentproblem of interacting elliptical micro-cracks and inclusions in single crystals. Acriterion is employed to determine the crack propagation path based on the stressdistribution; the evolution of individual micro-cracks and their interactions withexisting cracks and inclusions is then predicted using what we coin the DiscreteCrack Dynamics (DCD) method. DCD is fast (semi-analytical) and particularlysuitable for the simulation of evolving low-speed crack networks in brittle orquasi-brittle materials. The method is validated against finite element analysispredictions and previously published experimental data.
Verschueren J, Gurrutxaga-Lerma B, Balint D, et al., 2018, Instabilities of high speed dislocations, Physical Review Letters, Vol: 121, ISSN: 0031-9007
Despite numerous theoretical models and simulation results, a clear physical picture of dislocations traveling at velocities comparable to the speed of sound in the medium remains elusive. Using two complementary atomistic methods to model uniformly moving screw dislocations, lattice dynamics and molecular dynamics, the existence of mechanical instabilities in the system is shown. These instabilities are found at material-dependent velocities far below the speed of sound. We show that these are the onset of an atomistic kinematic generation mechanism, which ultimately results in an avalanche of further dislocations. This homogeneous nucleation mechanism, observed but never fully explained before, is relevant in moderate and high strain rate phenomena including adiabatic shear banding, dynamic fracture, and shock loading. In principle, these mechanical instabilities do not prevent supersonic motion of dislocations.
Rovelli I, Dudarev SL, Sutton AP, 2018, Statistical model for diffusion-mediated recovery of dislocation and point-defect microstructure, Physical Review E, Vol: 98, ISSN: 1539-3755
The evolution of the defect microstructure in materials at high temperature is dominated by diffusion-mediated interactions between dislocations, cavities, and surfaces. This gives rise to complex nonlinear couplings between interstitial and vacancy-type dislocation loops, cavities, and the field of diffusing vacancies that adiabatically follows the evolution of microstructure. In our previous work, we developed a nonlocal model for the climb of curved dislocations and the morphological evolution of cavities during postirradiation annealing of structural components in nuclear reactors. We now expand the formalism to include the treatment of population of very small defects and dislocation loops that are below the experimental detection limit. These are taken into account through a mean field approach coupled with an explicit real-space treatment of larger-scale discrete defect clusters. We find that randomly distributed small defects screen diffusive interactions between larger discrete clusters, renormalizing the free diffusion Green's functions and transforming them into Yukawa-type propagators. The evolution of the coupled system is modelled self-consistently, showing how the defect microstructure evolves through a nonmonotonic variation of the distribution of sizes of dislocation loops and cavities, treated as discrete real-space objects.
Molinari N, Sutton A, Mostofi AA, 2018, Mechanisms of reinforcement in polymer nanocomposites, Physical Chemistry Chemical Physics, Vol: 20, Pages: 23085-23094, ISSN: 1463-9076
Coarse-grained molecular dynamics simulations are used to elucidate molecular mechanisms responsible for different mechanical behaviours of elastomers containing spherical particles with different volume fractions. We observe that different filler volume fractions result in qualitatively different responses of the polymer nanocomposite to tensile strain. At relatively low filler volume fraction a yield drop appears in the stress–strain curve. As the filler volume fraction increases there is a reduction in the rate of plastic hardening, becoming plastic softening at sufficiently high filler volume fraction. We demonstrate that these behaviours are a result of the network formed by the polymer chains and filler particles. We identify three distinct molecular structural motifs between polymer and filler particles whose relative prevalence varies with the filler volume fraction and as the system is dynamically strained. We show how this evolution in molecular structure is directly linked to the observed mechanical response.
Zhang X, Han J, Plombon JJ, et al., 2017, Nanocrystalline copper films are never flat, Science, Vol: 357, Pages: 397-400, ISSN: 1095-9203
We used scanning tunneling microscopy to study low-angle grain boundaries at the surface of nearly planar copper nanocrystalline (111) films. The presence of grain boundaries and their emergence at the film surface create valleys composed of dissociated edge dislocations and ridges where partial dislocations have recombined. Geometric analysis and simulations indicated that valleys and ridges were created by an out-of-plane grain rotation driven by reduction of grain boundary energy. These results suggest that in general, it is impossible to form flat two-dimensional nanocrystalline films of copper and other metals exhibiting small stacking fault energies and/or large elastic anisotropy, which induce a large anisotropy in the dislocation-line energy.
Ready A, Haynes PD, Sutton AP, 2017, Comment on ``Development of an interatomic potential for the simulation of defects, plasticity, and phase transformations in titanium'' [J. Chem. Phys. 145, 154102 (2016)], Journal of Chemical Physics, Vol: 147, ISSN: 1089-7690
Ready AJ, Haynes PD, Grabowski B, et al., 2017, The role of molybdenum in suppressing cold dwell fatigue in titanium alloys, Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 473, ISSN: 1364-5021
We test a hypothesis to explain why Ti-6242 is susceptible to cold dwell fatigue, whereas Ti-6246 is not. The hypothesis is that in Ti-6246 substitutional Mo-atoms in $\alpha$-Ti grains trap vacancies thereby limiting creep relaxation. In Ti-6242 this creep relaxation enhances the loading of grains unfavourably oriented for slip and they subsequently fracture. Using density functional theory to calculate formation and binding energies between Mo-atoms and vacancies we find no support for the hypothesis. In the light of this result, and experimental observations of the microstructures in these alloys, we agree with the recent suggestion [J. Qiu, {\it et al.}, Metall. Mater. Trans. A {\bf 45}, 6075 (2014)] that Ti-6246 has a much smaller susceptibility to cold dwell fatigue because it has a smaller grain size and a more homogeneous distribution of grain orientations. We propose that the reduction of the susceptibility to cold dwell fatigue of Ti-6242 at temperatures above about 200~$^\circ$C is due to the activation of $\langle \mathbf{c} + \mathbf{a} \rangle$ slip in `hard' grains, which reduces the loading of grain boundaries.
Patel M, Waheed S, Wenman MR, et al., 2017, Discrete dislocation plasticity modeling of hydrides in zirconium under thermal cycling, MRS Advances, Vol: 2, Pages: 3353-3358, ISSN: 2059-8521
Understanding the ratcheting effect of hydrogen and hydride accumulation in response to thermal cycling is important in establishing a failure criterion for zirconium alloy nuclear fuel cladding. We propose a simple discrete dislocation plasticity model to study the evolution of the dislocation content that arises as a micro-hydride repeatedly precipitates and dissolves over a series of thermal cycles. With each progressive thermal cycle, we find a steady growth in the residual dislocation density in the vicinity of the hydride nucleation site; this corresponds to a gradual increase in the hydrogen concentration and, consequently, the hydride population. The simulated ratcheting in the dislocation density is consistent with experimental observations concerning the hysteresis in the terminal solid solubility of hydrogen in zirconium, which can be correlated to the plastic relaxation of hydrides.
Paxton AT, Sutton AP, Finnis MW, 2017, The challenges of hydrogen and metals, Journal: Philosophical Transactions A: Mathematical, Physical and Engineering Sciences, Vol: 375, ISSN: 1471-2962
The Royal Society Scientific Discussion Meeting ‘The challenges of hydrogen and metals’ was held in Carlton House Terrace, London, UK, on 16–18 January 2017. This is the introductory article to the discussion meeting issue which includes contributed papers and seven discussion papers. Here, we introduce the motivation to hold the Meeting and give a brief overview of the contents. We conclude with acknowledgements.This article is part of the themed issue ‘The challenges of hydrogen and metals’.
Paxton AT, Sutton AP, Finnis MW, 2017, The challenges of hydrogen and metals, The Challenges of Hydrogen and Metals, Publisher: Royal Society, The, ISSN: 1471-2962
Rovelli I, Dudarev SL, Sutton AP, 2017, Non-local model for diffusion-mediated dislocation climb and cavitygrowth, Journal of the Mechanics and Physics of Solids, Vol: 103, Pages: 121-141, ISSN: 1873-4782
To design efficient thermal recovery procedures for structural materials in fusion energy applications it is important to characterise quantitatively the annealing timescales of radiation-induced defect clusters. With this goal in mind, we present an extension of the Green’s function formulation of Gu et al. (2015). for the climb of curved dislocations, to include in the same framework the evaporation and growth of cavities and the effects of free surfaces. This paper focuses on the mathematical foundations of the model, which makes use of boundary integral equations (París and Cañas, 1997) to solve the steady-state vacancy diffusion problem. Numerical results are also presented in the simplified case of a dilute configuration of prismatic dislocation loops and spherical cavities in a finite-size medium, which show good agreement with experimental data on high temperature annealing in ion-irradiated tungsten (Ferroni et al., 2015).
Ready AJ, Haynes PD, Rugg D, et al., 2017, Stacking faults and the gamma-surface on first-order pyramidal planes in alpha-titanium, Philosophical Magazine, Vol: 97, Pages: 1129-1143, ISSN: 1478-6435
Using first principles methods we calculated the entire gamma-surface of the first-order pyramidal planes in alpha-titanium. Slip on these planes involving dislocations with c+a-type Burgers vectors is one means by which alpha-titanium polycrystals may supplement slip on prism planes with a-type Burgers vectors to maintain ductility. We find one low energy and one high energy stacking fault with energies of 163~mJ/m2 and 681~mJ/m2 respectively. Contrary to previous suggestions we do not find a stable stable stacking fault at (c+a})/2.
Sutton AP, Nazarov R, Majevadia JS, et al., 2016, First-principles calculation of the elastic dipole tensor of a point defect: Application to hydrogen in α-zirconium, Physical Review B, Vol: 94, ISSN: 1550-235X
The elastic dipole tensor is a fundamental quantity relating the elastic field and atomic structure of a point defect. We review three methods in the literature to calculate the dipole tensor and apply them to hydrogen in α-zirconium using density functional theory (DFT). The results are compared with the dipole tensor deduced from earlier experimental measurements of the λ tensor for hydrogen in α-zirconium. There are significant errors with all three methods. We show that calculation of the λtensor, in combination with experimentally measured elastic constants and lattice parameters, yields dipole tensor components that differ from experimental values by only 10%–20%. There is evidence to suggest that current state-of-the-art DFT calculations underestimate bonding between hydrogen and α-zirconium.
Duarev SL, Sutton AP, 2016, Elastic interactions between nano-scale defects in irradiated materials, Acta Materialia, Vol: 125, Pages: 425-430, ISSN: 1359-6454
Closed form expressions are derived for the energy of elastic interaction between dislocation loops, and between dislocation loops and vacancy clusters, to enable simulations of elastically biased microstructural evolution of irradiated materials. The derivations assume the defects are separated by distances greater than their size. The resulting expressions are well suited for real-space simulations of microstructural evolution involving thousands of elastically interacting defects in 3D. They play a similar role to interatomic potentials in molecular dynamics simulations.
Khawaja M, Sutton AP, Mostofi AA, 2016, Molecular simulation of gas solubility in nitrile butadiene rubber, Journal of Physical Chemistry B, Vol: 121, Pages: 287-297, ISSN: 1520-6106
Molecular simulation is used to compute the solubility of small gases in nitrile bu-tadiene rubber (NBR) with a Widom particle-insertion technique biased by local freevolume. The convergence of the method is examined as a function of the numberof snapshots upon which the insertions are performed and the number of insertionsper snapshot, and is compared to the convergence of the unbiased Widom insertiontechnique. The effect of varying the definition of the local free volume is also investi-gated. The acrylonitrile content of the polymer is altered to examine its influence onthe solubility of helium, CO2and H2O, and the solubilities of polar gases are found tobe enhanced relative to nonpolar gases, in qualitative agreement with experiment. Toprobe this phenomenon further, the solubilities are decomposed into contributions fromneighbourhoods of different atoms, using a Voronoi cell construction, and a strong biasis found for CO2and H2O in particular to be situated near nitrogen sites in the elas-tomer. Temperature is shown to suppress the solubility of CO2and H2O, but increasethat of helium. Increasing pressure is found to suppress the solubility of all gases, butat different rates according to a balance between their molecular size and electrostaticinteraction with the polymer. These results are relevant to the use of NBR seals atelevated temperatures and pressures, such as in oil and gas wells.
Muscatello J, Muller EA, Mostofi AA, et al., 2016, Multiscale molecular simulations of the formation and structure of polyamide membranes created by interfacial polymerization, Journal of Membrane Science, Vol: 527, Pages: 180-190, ISSN: 0376-7388
Large scale molecular simulations to model the formation of polyamide membranes have been carried out using a procedure that mimics experimental interfacial polymerization of trimesoyl chloride (TMC) and metaphenylene diamine (MPD) monomers. A coarse-grained representation of the monomers has been developed to facilitate these simulations, which captures essential features of the stereochemistry of the monomers and of amide bonding between them. Atomic models of the membranes are recreated from the final coarse-grained representations. Consistent with earlier treatments, membranes are formed through the growth and aggregation of oligomer clusters. The membranes are inhomogeneous, displaying opposing gradients of trapped carboxyl and amine side groups, local density variations, and regions where the density of amide bonding is reduced as a result of the aggregation process. We observe the interfacial polymerization reaction is self-limiting and the simulated membranes display a thickness of 5–10 nm. They also display a surface roughness of 1–4 nm. Comparisons are made with recently published experimental results on the structure and chemistry of these membranes and some interesting similarities and differences are found.
khawaja, molinari, sutton AP, et al., 2016, A molecular model for HNBR with tunable cross-link density, Journal of Physical Chemistry B, Vol: 120, Pages: 12700-12707, ISSN: 1520-6106
We introduce a chemically-inspired, all-atom model of HNBR and assess its perfor-mance by computing the mass density and glass transition temperature as a functionof cross-link density in the structure. Our HNBR structures are created by a procedurethat mimics the real process used to produce HNBR, i.e., saturation of the carbon-carbon double bonds in NBR, either by hydrogenation or by cross-linking. The atomicinteractions are described by the all-atom “Optimized Potentials for Liquid Simula-tions" (OPLS-AA). In this paper we: first assess the use of OPLS-AA in our models,especially using NBR bulk properties, and second evaluate the validity of the proposedmodel for HNBR by investigating mass density and glass transition as a function ofthe tunable cross-link density. Experimental densities are reproduced within 3% forboth elastomers, and qualitatively correct trends in the glass transition temperature asa function of the monomer composition and cross-link density are obtained.
Jonas Verschueren, Gurrutxaga Lerma B, Balint DS, et al., 2016, The injection of a screw dislocation into a crystal: atomistics vs. continuum elastodynamics, Journal of the Mechanics and Physics of Solids, Vol: 98, Pages: 366-389, ISSN: 1873-4782
The injection (creation) process of a straight screw dislocation is compared atomistically with elastodynamic continuum theory. Amethod for injecting quiescent screw dislocations into a crystal of tungsten is simulated using non-equilibrium molecular dynamics.The resulting stress fields are compared to the those of elastodynamic solutions for the injection of a quiescent screw dislocation.A number of differences are found: a plane wave emission is observed to emanate from the whole surface of the cut used to createthe dislocation, affecting the displacement field along the dislocation line (z), and introducing displacement field componentsperpendicular to the line (along x and y). It is argued that, in part, this emission is the result of the finite time required to injectthe dislocation, whereby the atoms in the cut surface must temporarily be displaced to unstable positions in order to produce therequired slip. By modelling this process in the continuum it is shown that the displacements components normal to the dislocationline arise from transient displacements of atoms in the cut surface parallel to x and y. It is shown that once these displacements areincluded in the elastodynamic continuum formulation the plane wave emission in uzis correctly captured. A detailed comparisonbetween the atomistic and continuum models is then offered, showing that the main atomistic features can also be captured in thecontinuum.
Gurrutxaga Lerma B, Balint DS, Dini D, et al., 2016, A dynamic discrete dislocation plasticity study of elastodynamic shielding of stationary cracks, Journal of the Mechanics and Physics of Solids, Vol: 98, Pages: 1-11, ISSN: 0022-5096
Employing Dynamic Discrete Dislocation Plasticity (D3P), an elastodynamic analysis of theshielding of a stationary crack tip by dislocations is studied. Dislocations are generated via FrankReadsources, and make a negligible contribution to the shielding of the crack tip, whereas dislocationsgenerated at the crack tip via homogeneous nucleation dominate the shielding. Theireffect is found to be highly localised around the crack, leading to a magnification of the shieldingwhen compared to time-independent, elastostatic predictions. The resulting attenuation of KI (t)is computed, and is found to be directly proportional to the applied load and to √t.
Swinburne TD, Glavicic MG, Rahman KM, et al., 2016, Picosecond dynamics of a shock-driven displacive phase transformation in Zr, Physical Review B, Condensed Matter, Vol: 93, ISSN: 0163-1829
High pressure solid state transformations at high strain rates are usually observed after the fact,either during static holding or after unloading, or inferred from interferometry measurements of thesample surface. The emergence of femtosecond X-ray diffraction techniques provides insight intothe dynamics of short-timescale events such as shocks. We report laser pump-probe experiments ofthe response of Zr to laser driven shocks over the first few nanoseconds of the shock event, enablingthe α → ω transition and orientation relationship to be observed in real time with picosecondresolution. A clear orientation relationship of (10¯10)α||(10¯11)ω is found, in conflict with ω → αannealing experiments in zirconium and the two α → ω pathways proposed for titanium.
Sutton AP, 2016, Response to commentary by Morawiec, Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 472, ISSN: 1471-2946
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