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Priezjev Nikolai - One of the best experts on this subject based on the ideXlab platform.
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Shear band healing in Amorphous Materials by small-amplitude oscillatory shear deformation
2021Co-Authors: Priezjev NikolaiAbstract:The effect of small-amplitude periodic shear on annealing of a shear band in binary glasses is investigated using molecular dynamics simulations. The shear band is first introduced in stable glasses via large-amplitude periodic shear, and then Amorphous samples are subjected to repeated loading during thousands of cycles at strain amplitudes below the yield strain. It was found that with increasing strain amplitude, the glasses are relocated to deeper potential energy levels, while the energy change upon annealing is not affected by the glass initial stability. The results of mechanical tests indicate that the shear modulus and yield stress both increase towards plateau levels during the first few hundred cycles, and their magnitudes are largest when samples are loaded at strain amplitudes close to the yield strain. The analysis of nonaffine displacements reveals that the shear band breaks up into isolated clusters that gradually decay over time, leading to nearly reversible deformation within the elastic range. These results might be useful for mechanical processing of metallic glasses and additive manufacturing.Comment: 24 pages, 9 figure
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The Influence of Complex Thermal Treatment on Mechanical Properties of Amorphous Materials
SelectedWorks, 2020Co-Authors: Priezjev Nikolai, Liu Qing-longAbstract:We study the effect of periodic, spatially uniform temperature variation on mechanical properties and structural relaxation of Amorphous alloys using molecular dynamics simulations. The disordered material is modeled via a non-additive binary mixture, which is annealed from the liquid to the glassy state with various cooling rates and then either aged at constant temperature or subjected to thermal treatment. We found that in comparison to aged samples, thermal cycling with respect to a reference temperature of approximately half the glass transition temperature leads to more relaxed states with lower levels of potential energy. The largest energy decrease was observed for rapidly quenched glasses cycled with the thermal amplitude slightly smaller than the reference temperature. Following the thermal treatment, the mechanical properties were probed via uniaxial tensile strain at the reference temperature and constant pressure. The numerical results indicate an inverse correlation between the levels of potential energy and values of the elastic modulus and yield stress as a function of the thermal amplitud
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Shear band formation in Amorphous Materials under oscillatory shear deformation
SelectedWorks, 2020Co-Authors: Priezjev NikolaiAbstract:The effect of periodic shear on strain localization in disordered solids is investigated using molecular dynamics simulations. We consider a binary mixture of one million atoms annealed to a low temperature with different cooling rates and then subjected to oscillatory shear deformation with a strain amplitude slightly above the critical value. It is found that the yielding transition occurs during one cycle but the accumulation of irreversible displacements and initiation of the shear band proceed over larger number of cycles for more slowly annealed glasses. The spatial distribution and correlation function of nonaffine displacements reveal that their collective dynamics changes from homogeneously distributed small clusters to a system-spanning shear band. The analysis of spatially averaged profiles of nonaffine displacements indicates that the location of a shear band in periodically loaded glasses can be identified at least several cycles before yielding. These insights are important for development of novel processing methods and prediction of the fatigue lifetime of metallic glasses
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Heterogeneous Relaxation Dynamics in Amorphous Materials Under Cyclic Loading
SelectedWorks, 2020Co-Authors: Priezjev NikolaiAbstract:Molecular dynamics simulations are performed to investigate heterogeneous dynamics in Amorphous glassy Materials under oscillatory shear strain. We consider three-dimensional binary Lennard-Jones mixture well below the glass transition temperature. The structural relaxation and dynamical heterogeneity are quantified by means of the self-overlap order parameter and the dynamic susceptibility. We found that at sufficiently small strain amplitudes, the mean square displacement exhibits a broad subdiffusive plateau and the system undergoes nearly reversible deformation over about 104 cycles. Upon increasing strain amplitude, the transition to the diffusive regime occurs at shorter time intervals and the relaxation process involves intermittent bursts of large particle displacements. The detailed analysis of particle hopping dynamics and the dynamic susceptibility indicates that mobile particles aggregate into clusters whose sizes increase at larger strain amplitudes. Finally, the correlation between particle mobilities in consecutive time intervals demonstrates that dynamic facilitation becomes increasingly pronounced at larger strain amplitudes
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Structural relaxation in Amorphous Materials under cyclic tension-compression loading
SelectedWorks, 2020Co-Authors: Priezjev Nikolai, Jana PritamAbstract:The process of structural relaxation in disordered solids subjected to repeated tension-compression loading is studied using molecular dynamics simulations. The binary glass is prepared by rapid cooling well below the glass transition temperature and then periodically strained at constant volume. We find that the Amorphous system is relocated to progressively lower potential energy states during hundreds of cycles, and the energy levels become deeper upon approaching critical strain amplitude from below. The decrease in potential energy is associated with collective nonaffine rearrangements of atoms, and their rescaled probability distribution becomes independent of the cycle number at sufficiently large time intervals. It is also shown that yielding during startup shear deformation occurs at larger values of the stress overshoot in samples that were cyclically loaded at higher strain amplitudes. These results might be useful for mechanical processing of Amorphous alloys in order to reduce their energy and increase chemical resistivity and resistance to crystallization
J S Langer - One of the best experts on this subject based on the ideXlab platform.
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shear transformation zone theory of yielding in athermal Amorphous Materials
Physical Review E, 2015Co-Authors: J S LangerAbstract:Yielding transitions in athermal Amorphous Materials undergoing steady-state shear flow resemble critical phenomena. Historically, they have been described by the Herschel-Bulkley rheological formula, which implies singular behaviors at yield points. In this paper, I examine this class of phenomena using an elementary version of the thermodynamic shear-transformation-zone (STZ) theory, focusing on the role of the effective disorder temperature, and paying special attention to scaling and dimensional arguments. I find a wide variety of Herschel-Bulkley-like rheologies but, for fundamental reasons not specific to the STZ theory, conclude that the yielding transition is not truly critical. In particular, for realistic many-body models with short-range interactions, there is a correlation length that grows rapidly but ultimately saturates near the yield point.
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shear transformation zone theory of yielding in athermal Amorphous Materials
arXiv: Materials Science, 2015Co-Authors: J S LangerAbstract:Yielding transitions in athermal Amorphous Materials resemble critical phenomena. Historically, they have been described by the Herschel-Bulkley rheological formula, which implies singular behaviors at yield points. In this paper, I examine this class of phenomena using an elementary version of the thermodynamic shear-transformation-zone (STZ) theory, focusing on the role of the effective disorder temperature, and paying special attention to scaling and dimensional arguments. I find a wide variety of Herschel-Bulkley-like rheologies but, for fundamental reasons not specific to the STZ theory, conclude that the yielding transition is not truly critical. In particular, there is a correlation length that grows rapidly, but ultimately saturates near the yield point.
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nonequilibrium thermodynamics of driven Amorphous Materials ii effective temperature theory
Physical Review E, 2009Co-Authors: Eran Bouchbinder, J S LangerAbstract:We develop a theory of the effective disorder temperature in glass-forming Materials driven away from thermodynamic equilibrium by external forces. Our basic premise is that the slow configurational degrees of freedom of such Materials are weakly coupled to the fast kinetic-vibrational degrees of freedom and therefore that these two subsystems can be described by different temperatures during deformation. We use results from the preceding paper on the nonequilibrium thermodynamics of systems with internal degrees of freedom to derive an equation of motion for the effective temperature and to learn how this temperature couples to the dynamics of the system as a whole.
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nonequilibrium thermodynamics of driven Amorphous Materials iii shear transformation zone plasticity
Physical Review E, 2009Co-Authors: Eran Bouchbinder, J S LangerAbstract:We use the internal-variable, effective-temperature thermodynamics developed in two preceding papers to reformulate the shear-transformation-zone (STZ) theory of Amorphous plasticity. As required by the preceding analysis, we make explicit approximations for the energy and entropy of the STZ internal degrees of freedom. We then show that the second law of thermodynamics constrains the STZ transition rates to have an Eyring form as a function of the effective temperature. Finally, we derive an equation of motion for the effective temperature for the case of STZ dynamics.
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nonequilibrium thermodynamics of driven Amorphous Materials i internal degrees of freedom and volume deformation
Physical Review E, 2009Co-Authors: Eran Bouchbinder, J S LangerAbstract:This is the first of three papers devoted to the nonequilibrium thermodynamics of Amorphous Materials. Our focus here is on the role of internal degrees of freedom in determining the dynamics of such systems. For illustrative purposes, we study a solid whose internal degrees of freedom are vacancies that govern irreversible volume changes. Using this model, we compare a thermodynamic theory based on the Clausius-Duhem inequality to a statistical analysis based directly on the law of increase of entropy. The statistical theory is used first to derive the Clausius-Duhem inequality. We then use the theory to go beyond those results and obtain detailed equations of motion, including a rate factor that is enhanced by deformation-induced noisy fluctuations. The statistical analysis points to the need for understanding how both energy and entropy are shared by the vacancies and their environments.
Tsutomu Minami - One of the best experts on this subject based on the ideXlab platform.
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mechanochemical synthesis of new Amorphous Materials of 60li2s 40sis2 with high lithium ion conductivity
Journal of the American Ceramic Society, 2004Co-Authors: Hideyuki Morimoto, Masahiro Tatsumisago, Hideki Yamashita, Tsutomu MinamiAbstract:New Amorphous Materials were mechanochemically synthesized by use of crystalline starting Materials of Li2S and SiS2. The conductivity of a mechanochemically prepared sample of 60Li2S40SiS2(mol%) after a milling for 20 h was around 10-4 Scm-1 at room temperature. This conductivity was comparable to that of the corresponding glassy powders prepared by twin-roller rapid quenching of melt and then pulverizing. The transport number of lithium ions in the mechanochemically prepared sample was nearly unity. Mechanochemical synthesis is a promising way to produce new solid electrolytes for solid-state lithium secondary batteries.
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characterization of li2s sis2 lixmoy m si p ge Amorphous solid electrolytes prepared by melt quenching and mechanical milling
Solid State Ionics, 2002Co-Authors: Akitoshi Hayashi, Masahiro Tatsumisago, Hideki Yamashita, Tsutomu MinamiAbstract:Abstract The oxysulfide Amorphous Materials in the systems 95(0.6Li 2 S·0.4SiS 2 )·5Li x MO y (M=Si, P, and Ge) were prepared by melt-quenching and mechanical milling techniques. These Amorphous Materials exhibited high conductivity over 10 −4 S cm −1 at room temperature, a lithium transport number of unity, and a wide potential window of 10 V. The solid-state cells with the oxysulfide Amorphous Materials as solid electrolytes worked as lithium secondary batteries and exhibited excellent cycling performance over 100 times. The local structure of the mechanically milled Amorphous Materials containing Li 4 SiO 4 was similar to that of the corresponding melt-quenched glasses, in which the SiS 4 and SiOS 3 tetrahedral units were mainly present. The SiO n S 4− n ( n =1, 2, 3) tetrahedral units were formed in the case of the addition of Li 4 SiO 4 and Li 4 GeO 4 to the base sulfide system, while these units were not present in the addition of Li 3 PO 4 . We have concluded that the reactivity of Li x MO y derived from its basicity affected the structure and formation process of the oxysulfide Materials prepared by mechanical milling.
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solid state lithium secondary batteries using an Amorphous solid electrolyte in the system 100 x 0 6li2s 0 4sis2 xli4sio4 obtained by mechanochemical synthesis
Solid State Ionics, 2001Co-Authors: Ryoichi Komiya, Akitoshi Hayashi, Masahiro Tatsumisago, Hideyuki Morimoto, Tsutomu MinamiAbstract:Abstract Electrochemical cells were constructed using Amorphous Materials in the system (100− x )(0.6Li 2 S·0.4SiS 2 )· x Li 4 SiO 4 , obtained by mechanochemical synthesis, as an electrolyte, LiCoO 2 as a positive electrode and indium as a negative electrode. Charge and discharge behaviors of the cells at a constant current were investigated to see the possibility for utilization as secondary batteries. Charge–discharge efficiency at the 1st cycle was more than 75% in the cells using the solid electrolytes synthesized by mechanical milling (MM) for more than 5 h. Charge–discharge curves of the cells using the Amorphous Materials milled for more than 10 h, were similar to those of the cells using the corresponding melt-quenched glass samples. The charge–discharge capacity decreased gradually from 90 to 70 mA h/g till about the 10th cycle, and became stable after the 10th cycle. The Coulombic efficiency of the cell showed almost 100%, except for the 1st and 2nd cycles. The Amorphous Materials synthesized by MM were concluded to work as the electrolyte for solid state lithium secondary batteries.
Oliver Plümper - One of the best experts on this subject based on the ideXlab platform.
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Amorphous material in experimentally deformed mafic rock and its temperature dependence implications for fault rheology during aseismic creep and seismic rupture
Journal of Structural Geology, 2020Co-Authors: Sina Marti, Renée Heilbronner, Holger Stunitz, Oliver PlümperAbstract:Abstract Amorphous Materials are frequently observed in natural and experimentally produced fault rocks. Their common occurrence suggests that Amorphous Materials are of importance to fault zone dynamics. However, little is known about the physico-chemical impact of Amorphous Materials on fault rheology. Here we present deformation experiments on mafic fault rock, where Amorphous material forms due to intense mechanical wear during the experiments. The experiments are run at temperatures from 300 to 600 °C, confining pressures of 0.5 or 1.0 GPa, and at constant displacement rates of ( d ˙ ax) 2 ·10−7, 2 ·10−8 or 2 ·10−9 ms−1, resulting in bulk strain rates ( γ ˙ ) of ≈3 ·10−4, 3 ·10−5 and 3 ·10−6 s−1. At these conditions, the mafic rock material undergoes intense brittle deformation and cataclastic flow, but sample strength significantly decreases with increasing temperatures – a feature commonly attributed to viscous deformation processes. Microstructural analyses show that after an initial stage of homogeneous cataclastic flow, strain localizes into narrow (2–10 μm wide) ultra-cataclastic bands that evolve into Amorphous shear bands. With the data presented in this research paper, we argue that the temperature sensitivity recorded in the mechanical data is caused by viscous deformation of the Amorphous material. We suggest that with the formation of Amorphous Materials during brittle deformation, fault rheology becomes significantly temperature-sensitive. This has important implications for our understanding of fault strength and weakening due to the presence of Amorphous Materials. In addition, weak material along faults will lead to stress concentrations that may trigger seismic rupture.
Yasumasa Nishiura - One of the best experts on this subject based on the ideXlab platform.
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persistent homology and many body atomic structure for medium range order in the glass
Nanotechnology, 2015Co-Authors: Takenobu Nakamura, Yasuaki Hiraoka, Akihiko Hirata, Emerson G Escolar, Yasumasa NishiuraAbstract:The characterization of the medium-range (MRO) order in Amorphous Materials and its relation to the short-range order is discussed. A new topological approach to extract a hierarchical structure of Amorphous Materials is presented, which is robust against small perturbations and allows us to distinguish it from periodic or random configurations. This method is called the persistence diagram (PD) and introduces scales to many-body atomic structures to facilitate size and shape characterization. We first illustrate the representation of perfect crystalline and random structures in PDs. Then, the MRO in Amorphous silica is characterized using the appropriate PD. The PD approach compresses the size of the data set significantly, to much smaller geometrical summaries, and has considerable potential for application to a wide range of Materials, including complex molecular liquids, granular Materials, and metallic glasses.
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persistent homology and many body atomic structure for medium range order in the glass
arXiv: Soft Condensed Matter, 2015Co-Authors: Takenobu Nakamura, Yasuaki Hiraoka, Akihiko Hirata, Emerson G Escolar, Yasumasa NishiuraAbstract:Characterization of medium-range order in Amorphous Materials and its relation to short-range order is discussed. A new topological approach is presented here to extract a hierarchical structure of Amorphous Materials, which is robust against small perturbations and allows us to distinguish it from periodic or random configurations. The method is called the persistence diagram (PD) and it introduces scales into many-body atomic structures in order to characterize the size and shape. We first illustrate how perfect crystalline and random structures are represented in the PDs. Then, the medium-range order in the Amorphous silica is characterized by using the PD. The PD approach reduces the size of the data tremendously to much smaller geometrical summaries and has a huge potential to be applied to broader areas including complex molecular liquid, granular Materials, and metallic glasses.