bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular Dynamics Simulations of the Mechanical Response of Metallic glass/BCC Nanocomposite Materials
Authors: Shi Yunfeng , Falk Michael L 
Published: June 2019

AbstractBulk metallic glass (BMG) has been of intense interest recently because of its unique combination of excellent mechanical properties including high strength. One of the major drawbacks of monolithic BMG materials is the limited ductility due to strain localization. Except a few recent reports on monolithic ductile BMG, the most popular method to enhance the ductility of the BMG samples is to introduce a crystalline or quasicrystalline phase by precipitation or mixing. The composite material usually exhibits some degree of strain hardening along with significantly higher impact resistance and fracture toughness. However, the mechanism of this strain hardening is not well understood. We present simulated uniaxial compression tests on a monatomic model amorphous system embedded with body-center cubic (BCC) nanocrystals. The advantage of this model system is that intimate amorphous-crystal interfaces can be obtained. We observe that when comparing to monolithic glassy samples where a single shear band normally dominates, multiple shear bands appear in the BCC-amorphous composite samples. The plastic deformation initiates at the interfaces between nanocrystals and the glassy phase due to stress concentration. Furthermore, we demonstrate that shear along the bands results in growth of the nanocrystals.
Effect of Crystallinity on the Friction Behavior of Ultra-high-molecular-weight-polyethylene
Authors: Kanaga Subramanian Kanaga Karuppiah , Bruck Angela L , Sundararajan Sriram , Lin Zhiqun 
Published: June 2019

AbstractIn this study we evaluate the interfacial shear strength and scratch resistance of medical grade ultra-high molecular weight polyethylene (UHMWPE) (GUR 1050 resin) as a function of polymer crystallinity. Crystallinity was controlled by heating UHMWPE samples to a temperature above its melting point and varying the hold time and cooling rates. Degree of crystallinity of the samples was evaluated using differential scanning calorimetry (DSC). Quantitative nanoscale friction experiments were conducted using an atomic force microscope with commercially available Si3N4 probes under dry conditions. A higher crystallinity resulted in lower friction force and lower interfacial shear strength as well as increased scratch resistance. The trend in friction response was observed in microscale friction measurements.
X-ray Diffraction Study of the Mechanical Elastic Properties of Nanometric W/Cu Multilayers
Authors: Villain Pascale , Girault Baptiste , Renault Pierre-Olivier , Le Bourhis Eric , Goudeau Philippe , Badawi Frederic 
Published: June 2019

AbstractThe mechanical behavior of W/Cu multilayers with a period of 24 nm and a 1/3 W/Cu thickness ratio prepared by magnetron sputtering was analyzed using a method combining X-ray diffraction and tensile testing. Tests were performed both with a conventional and a synchrotron light source to analyze the elastic response of the system. Comparison between the strain-load curves obtained in both experimental conditions and estimated curves clearly shows that high quality synchrotron measurements are a preliminary condition for size-effect studies. Moreover, cyclic tests were used to determine the elastic domain of each material and compare their mechanical responses. Plastic strain was observed in copper while tungsten layers were still elastically strained until cracks appeared.
Strength of Coherently Strained Nanolayers Under High Temperature Nanoindentation
Authors: P'ng Mok Yew , Hou X. D. , Dunstan D. J. , Bushby A. J. 
Published: June 2019

AbstractSemiconductor strained layer superlattices are an ideal model material to study the effects of coherency strain in plasticity, due to the fine control of nanolayer thickness and internal strain afforded by MBE deposition. Previously, nanoindentation of bulk InGaAs at 300K gave a yield pressure of 6GPa (Jayawera et al Proc. Roy Soc, A459, 2049, 2003) while bending at 500 centigrade gave a yield value of 30MPa (Pp’ ng et al Phil. Mag. 85, 4429, 2005). In contrast, coherently strained InGaAs superlattices gave nanoindentation values of 3GPa at room temperature and bending at 500oC gave a yield value also around 3GPa. It appears that the coherency strain can impart an athermal strengthening to the superlattice. It is clearly necessary to do mechanical testing over the range 300-800K that will be able to link the room temperature nanoindentation with the results from the high temperature bending experiment and to determine the relationship between strength, coherency strain and temperature. Preliminary experiments on these samples at elevated temperatures using a hot stage and the UMIS nanoindentation system is difficult but feasible with the help of AFM to verify the contact area.
Glass Transition Temperature in Confined Polymers
Authors: Ozisik Rahmi , Liu Tong , Siegel Richard W. 
Published: June 2019

AbstractGlass transition temperature of polyetherimide (PEI) thin films and nanoporous PEI samples was investigated using differential scanning calorimetry. In both of these systems, the glass transition temperature decreased with respect to the bulk value. In the nanoporous system, scanning electron microscope images were used to characterize pore size distribution, and Monte Carlo simulations were performed to calculate the nearest neighbor pore-to-pore distances. Pore-to-pore distances and thin film thickness values were used to establish a quantitative analogy between thin films and nanoporous system.
High Temperature Clay Filled Epoxy Composites
Authors: Raghavan Dharmaraj , Langat Joseph Ktoo , Zammarano Mauro , Gilman Jeffrey 
Published: June 2019

AbstractThe primary objective of this study is to improve the thermal stability of clay and clay filled composite. An epoxy-clay composite has been prepared by dispersing 1-hexadecyl-3-(6-hydroxyhexyl)-2-methylimidazolium modified clay in an epoxy resin and cured with metaphenylene diamine (m-PDA) at 110.0 °C for 7 h and post cured at 140°C for 4 h. The thermal stability of the modified clay and clay filled epoxy composite was characterized via thermogravimetric analysis (TGA). The onset decomposition temperature of the imidazolium functionalized clay was 360°C. Transmission Electron Microscopy (TEM) of the composite showed mixed morphology with predominant fraction of intercalated clay platelets in the epoxy matrix. The onset decomposition temperature of the modified clay filled epoxy composite was found to be higher than that of pristine epoxy.
Using Elasticity to Correct for Boundary Effects in Calculations of Stress-Diffusion Coupling Parameters
Authors: Puchala Brian , Falk Michael , Garikipati Krishna 
Published: June 2019

AbstractThe effect of stress on diffusion during semiconductor processing becomes important as device dimensions shrink from microns to nanometers. Simulating these effects requires accurate parameterization of the formation and migration volume tensors of the defects that mediate diffusion on the atomistic scale. We investigate the effect of boundary conditions on the accuracy of atomistic calculations of defect formation energies and formation volume tensors. Linear elasticity provides a correction to the effect of the boundaries on the resulting relaxation volume tensor. By a formal proof we show that the correction term is zero for free boundaries and for periodic boundary conditions with zero mean boundary stress. This is demonstrated in the far field for periodic and free boundary conditions for an isotropic (vacancy) and an anisotropic (<110> intersitial) defect in Stillinger-Weber silicon. For periodic boundary conditions, formation volume tensor components converge to within 5% in a 216 atom simulation cell. For free boundary conditions, slow convergence of elastic constants results in slow convergence of formation volumes. Most significantly, this provides a new method to calculate the formation volume from constant volume calculations. This removes the need for relaxing boundaries, allowing for simpler and more efficient algorithms. We apply this method to both the vacancy and the <110> interstitial in Stillinger-Weber silicon.
A method for analyzing nanomechanical deformation of nanocrystalline Ni at higher timesteps than is possible in classical molecular dynamics
Authors: Tomar Vikas 
Published: June 2019

AbstractA majority of computational mechanical analyses of nanocrystalline materials have been carried out using classical molecular dynamics (MD). Due to the fundamental reason that the MD simulations must resolve atomic level vibrations, they cannot be carried out at the timescale of the order of microseconds. Additionally, MD simulations have to be carried out at very high loading rates (∼108 s−1) rarely observed in experiments. In this investigation a modified Hybrid Monte Carlo (HMC) method that can be used to analyze time-dependent (strain rate dependent) atomistic mechanical deformation of nanocrystalline structures at higher timescales than currently possible using MD is established. In this method there is no restriction on the size of MD timestep except that it must be such that to ensure a reasonable acceptance rate between consecutive Monte-Carlo (MC) time-steps. For the purpose of comparison HMC analyses of a nanocrystalline Ni sample at a strain rate of 109 s−1 with three different timesteps, viz. 2 fs, 4fs, and 8 fs, are compared with the analyses based on MD simulations at the same strain rate and a MD timestep of 2 fs. MD simulations of nanocrystalline Ni reproduce the defect nucleation and propagation results as well as strength values reported in the literature. In addition, HMC with timestep of 8 fs correctly reproduces defect formation and stress-strain response observed in the case of MD simulations with permissible timestep of 2 fs (for the interatomic potential used 2 fs is the highest MD timestep). Simulation time analyses show that by using HMC a saving of the order of 4 can be achieved bringing the atomistic analyses closer to the continuum timescales.
Multiscale Modelling of bcc-Fe Based Alloys for Nuclear Applications [PowerPoint Submission]
Authors: Malerba Lorenzo 
Published: June 2019

AbstractUnderstanding the basic mechanisms that determine microstructure changes in neutron irradiated steels is vital for a safe lifetime management of existing nuclear reactors and a safe design of future nuclear options. Low-alloyed ferritic steels containing Cu, Ni, Mn and Si as principal solute atoms are used as structural materials for current reactor vessels. The microstructural evolution under irradiation in alloys is decided by the interplay between defect formation and thermodynamic driving forces, together determining the appearance of phase transformations (precipitation, segregation, …) and favouring or delaying the nucleation and growth of point-defect clusters, their diffusion and their mutual recombination or removal at sinks. A reliable description of the production, evolution and accumulation of radiation damage must therefore start from the atomic level and requires being able to describe multicomponent systems for timescales ranging from few picoseconds to years. This goal demands firstly the fabrication of interatomic potentials for alloys that must be both consistent with the thermodynamic properties of the system and capable of reproducing correctly the characteristic solute-point defect interactions, versus ab initio or experimental data. Secondly the performance of extensive molecular dynamics (MD) simulations, to grasp the main mechanisms of defect production, diffusion, mutual interaction, and interaction with solute atoms and impurities. Thirdly, the development of simulation tools capable of describing the microstructure evolution beyond the timeframe and lengthscale of MD, while reproducing as much as possible the atomic-level origin of the mechanisms governing the evolution of the system, including phase changes.In this presentation the results of recent efforts made in this direction in the case of Fe-Cu, Fe-Cr and Fe-Ni alloys, as basic model alloys for the description of steels of technological relevance, are highlighted. In particular, advanced techniques to fit interatomic potentials consistent with thermodynamics are proposed and the results of their application to the mentioned alloys are presented. Next, the development of advanced methods, based on the use of artificial intelligence, to improve both the physical reliability and the computational efficiency of kinetic Monte Carlo codes for the study of point-defect clustering and phase changes beyond the scale of MD, is reported. These recent progresses bear the promise of being able, in the near future, of producing reliable tools for the description of the microstructure evolution of realistic model alloys under irradiation.
Ab Initio and Kinetic Rate Theory Modeling of 316SS with Oversized Solute Additions on Radiation-Induced Segregation [PowerPoint Submission]
Authors: Hackett Micah J 
Published: June 2019

AbstractDeleterious effects of radiation in nuclear reactor systems cause material degradation and the potential for component failure. Radiation damage is fundamentally due to freely migrating point defects produced in collision cascades. A reduction in the freely migrating point defect population should, then, reduce radiation damage and increase component lifetime. The addition of oversized solute atoms such as Zr or Hf to 316SS, a common structural material in reactors, is expected to reduce point defect population through a trapping mechanism that enhances recombination. The mechanism, however, requires a strong binding energy between the oversized solute atom and vacancies in order for the mechanism to significantly reduce the defect population. Experimental measurements of this binding energy are unavailable, but can be determined with atomistic calculations. Ab initio methods are used here to determine binding energies and atomic volumes of either Hf or Zr oversized solutes with vacancies in a face-centered cubic Fe matrix. The binding energies are then used to parameterize a kinetic rate-theory model, which is used here to calculate radiation-induced segregation (RIS). The calculated values of RIS are then compared to experimental measurements to benchmark the calculations and offer insight into the proposed point defect trapping mechanism.
Three-Dimensional Boundary Element-Dislocation Dynamics Modeling of Plastic Flow in Small Volumes [PowerPoint Submission]
Authors: El-Awady Jaffar A. , Takahashi Akiyuki , Ghoniem Nasr M 
Published: June 2019

AbstractWe present a self-consistent formulation of 3-D Parametric Dislocation Dynamics (PDD) with the Boundary Element method (BEM) to describe dislocation motion, and hence microscopic plastic flow in finite volumes. We develop quantitative measures of the accuracy and convergence of the method by considering a comparison with known analytical solutions. It is shown that the method displays absolute convergence with increasing the number of quadrature points on the dislocation loop and the surface mesh density. For example, at a distance of one lattice parameter from the surface, the relative error is less than 5% for a surface mesh with an element size of 1000 × 2000 lattice parameters, and 64 quadrature points. The Eshelby twist in a finite length cylinder containing a coaxial screw dislocation is also used to benchmark the method. Simulation results of single slip behavior in cylindrical microcrystals is presented, and the general features are compared to single-crystal compression experiments. The method is utilized to study size scaling aspects of plastic flow in small volumes and assess the role of the dislocation starvation mechanism.
Cooling Mechanism and Structural Change of Local Regions With a Different Cooling Rate of Excimer Laser Annealed Si
Authors: Lee Byoung-Min , Seong Baek Seok , Kim Hak Rho , Munetoh Shinji , Motooka Teruaki 
Published: June 2019

AbstractTo investigate the cooling mechanism and the local structural changes of excimer laser-annealed silicon (Si), molecular dynamics (MD) simulations were performed. Heat flow of molten Si showed a strong dependency of the local region during a natural cooling. An amorphous-to-liquid transition near an interface in the temperature range of 1600 K ∼ 1800 K was expected with the results of the local diffusion coefficients calculated by integrating the velocity autocorrelation functions. It was confirmed that the structure of the interface region affected the cooling rate of the overall system. The structural properties at the various local regions after a cooling were assessed in terms of the configurational properties including the coordination and bond-angle distributions. A spontaneous nucleation of Si near a interface was observed during a natural cooling.
Growth study of nanocrystalline Ni and Ni3Al using molecular dynamics
Authors: Zhang Z. Y. , Meng X. K. , Wang J. , Huang Hanchen , Liu X.-Y. 
Published: June 2019

AbstractThe growth of nanocrystalline materials has received much attention recently due to its importance in nanocrystalline thin film properties and fabrications. Research studies of this subject have so far focused on the face-centered-cubic metals. Two mechanisms, grain-rotation induced grain coalescence and curvature-driven grain-boundary migration are considered as the dominant mechanisms in the nanograin growth. In this work, we use molecular dynamics method to simulate the growth of Ni and Ni3Al alloy. We find the above mechanisms can describe the growth behavior well. A detailed comparison of the nanograin growth between the two systems is discussed in terms of grain rotation and grain sliding. We also study the temperature effect and the size effect in the nanograin growth. The tendency of twinning in the nanograin growth is discussed.
Simulations of Multi-atom Vacancies in Diamond
Authors: Laszlo Istvan , Kertesz Miklos , Gogotsi Yury 
Published: June 2019

AbstractMulti-atom vacancies and pores in diamond-structured carbon phases play an important role in carbon sieves and carbon based storage. The size and shape of pores have a profound effect on the energetics of adsorptive storage. We are modeling large numbers of vacancy configurations with a combination of ab initio density functional theory (DFT), tight binding DFT and simpler methods based on Brenner-potentials and modified Brenner potentials. The more accurate calculations serve as the basis of the parametrization which is then used in lattice Monte Carlo simulations on more complex vacancies. The results will be put in the context of SiC-derived porous carbon materials with the purpose to explore basic questions of energetics in porous carbons.
Multiscale Modeling of Growth and Structure of Silicon Nanoparticles in an Oxide Matrix
Authors: Yu Decai , Lee Sangheon , Hwang Gyeong S 
Published: June 2019

AbstractA first principles-based multiscale model is developed to examine mechanisms underlying Si nanocrystal formation in Si-rich SiO2. Using the multiscale approach, we have found that the embedded nanocrystal formation is mainly driven by suboxide penalty arising from incomplete O coordination, with a minor contribution of strain, and it is primarily controlled by O diffusion rather than excess Si diffusion and agglomeration. The overall behavior of Si cluster growth from our Monte Carlo simulations based on these fundamental findings agrees well with experiments.
New Ferromagnetic Nitrides, CaN and SrN, and their “Recipe”
Authors: Geshi Masaaki , Kusakabe Koichi , Nagara Hitose , Suzuki Naoshi 
Published: June 2019

AbstractWe have designed new materials, CaN and SrN in a rock-salt structure (RS). They are ferromagnetic nitrides. Their ferromagnetic states are quite stable. Our calculations for the formation energy and first-principles MD simulations suggested that RS-CaN is at least metastable and stable in normal condition. Based on our results we have proposed the synthesis process of RS-CaN. Our proposed process is (1) heat up α-Ca3N2 until it is transformed into β-Ca3N2, (2) compress it above 50 GPa until 2Ca3N2 →2CaN+Ca reaction occurs, (3) cool down them to room temperature and (4) decompress them into an ambient pressure. We consider that this high pressure and high temperature synthesis is one of the hopeful method to synthesize new materials.
Phase Separation and Solidification of Fluid Phosphorus
Authors: Katayama Yoshinori , Inamura Yasuhiro , Saitoh Hiroyuki , Utsumi Wataru 
Published: June 2019

AbstractFluid phosphorus exhibits a macroscopic phase separation during a pressure-induced first-order phase transition between low-density fluid and high-density fluid. Solidification process of the phase-separated fluid sample was monitored by x-ray radiography and the obtained solid sample was investigated by optical and scanning electron microscopy. A solid mixture of black parts and red parts was obtained from the phase-separated sample. Three different morphologies were observed in the red part of the sample.
High Pressure Structural Phase Transition and Elastic Properties of MgX (X = S, Se, Te) Semiconducting Compounds
Authors: Varshney Dinesh , Kaurav Netram , Choudhary Kamal Kumar , Kinge R. , Singh R. K. 
Published: June 2019

AbstractPressure-induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structure in MgX [X = S, Se, Te] semiconductors are presented. An effective interionic interaction potential (EIOP) with long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach is developed. Particular attention is devoted to evaluate the vdW coefficients following the variational method, as both the cation and the anion are polarizable. Our result on vast volume discontinuity in pressure volume phase diagram identifies the structural phase transition from B1 to B2 structure. The estimated value of the phase transition pressure (Pt) is consistent with results previously published. The variations of elastic constants with pressure follow a systematic trend identical to that observed in others compounds of NaCl type structure family.
Synchrotron Moessbauer Spectroscopy and Resistivity Studies of Iron Oxide Under High Pressure
Authors: Struzhkin Viktor V. , Eremets Mikhail I. , Eremets Ivan M. , Lin Jung-Fu , Sturhahn Wolfgang , Zhao Jiyong , Hu Michael Y 
Published: June 2019

AbstractThe strong electron correlations play a crucial role in the formation of a variety of electronic and magnetic properties of the transition metal oxides. In strongly correlated electronic materials many theoretical predictions exist on pressure-induced insulator-metal transitions, which are followed by a collapse of localized magnetic moments and by structural phase transitions [1]. The high-pressure studies provide additional degree of freedom to control the structural, electronic, optical, and magnetic properties of transition metal oxides. With the development of the high-pressure diamond-anvil-cell technique the experimental studies of such transitions are now possible with the advanced synchrotron techniques. In our studies, the iron monooxide Fe0.94O was studied under high pressures up to 200 GPa in diamond anvil cells. The single crystals enriched with Fe57 isotopes have been prepared for nuclear resonance measurements. The results of synchrotron Mössbauer spectroscopy (nuclear forward scattering -NFS), and electro-resistivity measurements suggest a complicated scenario of magnetic interactions governed by band-broadening effects.