Showing papers by "Adrian P. Sutton published in 2017"
TL;DR: In this article, a coarse-grained representation of the monomers has been developed to facilitate these simulations, which captures essential features of the stereochemistry of the polyamide monomers and of amide bonding between them.
69 citations
TL;DR: It is suggested 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.
Abstract: 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.
48 citations
TL;DR: The motivation to hold the discussion meeting is introduced, the contents of the issue are given and a brief overview of the contents are given.
Abstract: 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’.
38 citations
TL;DR: In this paper, closed form expressions for the energy of elastic interaction between dislocation loops and between dislocations loops and vacancy clusters are derived to enable simulations of elastically biased microstructural evolution of irradiated materials.
28 citations
TL;DR: In this article, an extension of the Green's function formulation of Gu et al. for the climb of curved dislocations, including evaporation and growth of cavities and the effects of free surfaces is presented.
Abstract: 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 (Paris and Canas, 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).
20 citations
TL;DR: Molecular simulation is used to compute the solubility of small gases in nitrile butadiene rubber with a Widom particle-insertion technique biased by local free volume, and a strong bias is found for CO2 and H2O in particular to be situated near nitrogen sites in the elastomer.
Abstract: Molecular simulation is used to compute the solubility of small gases in nitrile butadiene rubber (NBR) with a Widom particle-insertion technique biased by local free volume. The convergence of the method is examined as a function of the number of snapshots upon which the insertions are performed and the number of insertions per snapshot and is compared to the convergence of the unbiased Widom insertion technique. The effect of varying the definition of local free volume is also investigated. The acrylonitrile content of the polymer is altered to examine its influence on the solubility of helium, CO2, and H2O, and the solubilities of polar gases are found to be enhanced relative to those of nonpolar gases, in qualitative agreement with experiment. To probe this phenomenon further, the solubilities are decomposed into contributions from the neighborhoods of different atoms, using a Voronoi cell construction, and a strong bias is found for CO2 and H2O in particular to be situated near nitrogen sites in the ...
18 citations
TL;DR: It is proposed that the reduction of the susceptibility to CDF of Ti-6242 at temperatures above about 200°C is due to the activation of 〈c+a〉 slip in ‘hard’ grains, which reduces the loading of grain boundaries.
Abstract: We test a hypothesis to explain why Ti-6242 is susceptible to cold dwell fatigue (CDF), whereas Ti-6246 is not. The hypothesis is that, in Ti-6246, substitutional Mo-atoms in α-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 (Qiu et al. 2014 Metall. Mater. Trans. A45, 6075-6087. (doi:10.1007/s11661-014-2541-5)) that Ti-6246 has a much smaller susceptibility to CDF because it has a smaller grain size and a more homogeneous distribution of grain orientations. We propose that the reduction of the susceptibility to CDF of Ti-6242 at temperatures above about 200°C is due to the activation of 〈c+a〉 slip in 'hard' grains, which reduces the loading of grain boundaries.
14 citations
TL;DR: In this article, an elastodynamic analysis of the shielding of a stationary crack tip by dislocations was performed using Dynamic Discrete Dislocation Plasticity (D3P), and the resulting attenuation of K I (t ) was found to be directly proportional to the applied load and to t.
Abstract: Employing Dynamic Discrete Dislocation Plasticity (D3P), an elastodynamic analysis of the shielding of a stationary crack tip by dislocations is studied. Dislocations are generated via Frank–Read sources, and make a negligible contribution to the shielding of the crack tip, whereas dislocations generated at the crack tip via homogeneous nucleation dominate the shielding. Their effect is found to be highly localised around the crack, leading to a magnification of the shielding when compared to time-independent, elastostatic predictions. The resulting attenuation of K I ( t ) is computed, and is found to be directly proportional to the applied load and to t .
14 citations
TL;DR: In this article, a method for injecting quiescentrum screw dislocations into a crystal of tungsten is simulated using non-equilibrium molecular dynamics and the resulting stress fields are compared to those of elastodynamic solutions for the injection of a straight screw dislocation.
Abstract: The injection (creation) process of a straight screw dislocation is compared atomistically with elastodynamic continuum theory. A method 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 create the dislocation, affecting the displacement field along the dislocation line (z), and introducing displacement field components perpendicular to the line (along x and y). It is argued that, in part, this emission is the result of the finite time required to inject the dislocation, whereby the atoms in the cut surface must temporarily be displaced to unstable positions in order to produce the required slip. By modelling this process in the continuum it is shown that the displacements components normal to the dislocation line arise from transient displacements of atoms in the cut surface parallel to x and y. It is shown that once these displacements are included in the elastodynamic continuum formulation the plane wave emission in uz is correctly captured. A detailed comparison between the atomistic and continuum models is then offered, showing that the main atomistic features can also be captured in the continuum.
11 citations
TL;DR: In this paper, the authors calculated the surface of the first-order pyramidal planes in -titanium polycrystals and found one low energy and one high energy stacking fault with energies of 163 and 681, respectively.
Abstract: Using first principles methods, we calculated the entire -surface of the first-order pyramidal planes in -titanium. Slip on these planes involving dislocations with -type Burgers vectors is one means by which -titanium polycrystals may supplement slip on prism planes with -type Burgers vectors to maintain ductility. We find one low energy and one high energy stacking fault with energies of 163 and 681 , respectively. Contrary to previous suggestions, we do not find a stable stable stacking fault at .
8 citations
TL;DR: In this article, a simple discrete dislocation plasticity model is proposed to study the evolution of the dislocation content that arises as a micro-hydride repeatedly precipitates and dissolves over a series of thermal cycles.
Abstract: 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.
TL;DR: In this article, Mendelev, Underwood, and Ackland developed interatomic potentials (IPs) for hexagonal close-packed Ti to model atomistically defects, plasticity, and phase changes in Ti.
Abstract: Recently Mendelev, Underwood, and Ackland1 (MUA) published three interatomic potentials (IPs) Ti1, Ti2, and Ti3 for pure Ti. These IPs were developed to model atomistically defects, plasticity, and phase changes in Ti. In this comment we compare quantitatively the γsurfaces predicted by these IPs on the basal and {11̄01} first order pyramidal or pyramidal I planes of hexagonal close-packed Ti with those we computed recently by density functional theory (DFT)2. We also compare with the γ-surfaces computed with the IP developed by Ackland3, which we call Ti0. Local minima in the γ-surface4 correspond to stable stacking faults, which indicate the possibility, depending on the energy of the local minimum, of dissociation of lattice dislocations into partial dislocations separated by the stacking fault. In addition, the slope of the γ-surface determines the force per unit area tending to constrict the core of dislocations in the slip plane5. The accuracy of a γ-surface is therefore of some importance for modelling plasticity on that slip plane.