Dynamic Non-equilibrium Processes Research Articles

Cryogenic Investigations into the Effect of Impact-Oscillatory Loading on Changes in the Mechanical Properties and Structural Condition of VT23M Two-Phase Titanium Alloy.

Impact-oscillatory loading of variable intensity was applied to the VT23M high-strength sheet two-phase titanium alloy in liquid nitrogen. This was carried out to investigate the effect of this loading type on changes in the mechanical properties and structural condition of the alloy upon subsequent static tensioning at normal temperature. Dynamic non-equilibrium process (DNP) realized at a temperature of liquid nitrogen proved to be unable to impair the strength properties of the VT23M titanium alloy compared to room temperature; however, they caused a significant decrease in ductility (down to 16%). The impaired plastic properties of the alloy were shown to entail additional defects in the structural components of the alloy. The authors have found patterns of damage accumulation in the structural components of the alloy depending on the DNP parameters. They are in good agreement with the findings of the fractographic research.

An appropriate statistical approach for non-equilibrium particle production

The incapability of thermal models to accurately reproduce the horn-like structure of the Kaon-to-pion ratio measured at AGS, SPS, and low RHIC energies, as well as confirmed in the beam energy scan program, has long been a persistent problem. This issue is believed to have arisen due to the inappropriate application of statistics, particularly the extensive additive Boltzmann–Gibbs (BG) statistics. The assumption that the analysis of particle production, a dynamic non-equilibrium process, should be primarily conducted using extensive BG or non-extensive Tsallis statistics, has proven to be an unsuccessful approach that has been followed for several decades. By employing generic (non)extensive statistics, two equivalence classes [Formula: see text] emerge, thereby undermining the validity of any ad hoc assumption. Consequently, the degree of (non)extensivity exhibited by the statistical ensemble is determined by its own characteristics. This encompasses both extensive BG statistics, characterized by [Formula: see text], and non-extensive Tsallis statistics, characterized by [Formula: see text]. The energy dependence of light-, [Formula: see text], and strange-quark occupation factor, [Formula: see text], suggests that the produced particles are most appropriately described as a non-equilibrium ensemble. This is evidenced by a remarkable non-monotonic behavior observed in the [Formula: see text] horn, for instance. On the other hand, the resulting equivalence classes [Formula: see text] are associated with a generic non-extensivity related to extended exponential and Lambert-[Formula: see text] exponentially generating distribution function, which evidently arise from free, short- and long-range correlations. The incorporation of generic non-extensive statistics into the hadron resonance gas model yields an impressive ability to rightfully reproduce the non-monotonic [Formula: see text] ratio.

An Operando Study of the Thermal Reduction of BaTiO3 Crystals: The Nature of the Insulator–Metal Transition of the Surface Layer

The insulator-to-metal transition upon the thermal reduction of perovskites is a well-known yet not completely understood phenomenon. By combining different surface-sensitive analysis techniques, we analyze the electronic transport properties, electronic structure, and chemical composition during the annealing and cooling of high-quality BaTiO3 single crystals under ultra-high-vacuum conditions. Our results reveal that dislocations in the surface layer of the crystal play a decisive role as they serve as easy reduction sites. In this way, conducting filaments evolve and allow for turning a macroscopic crystal into a state of metallic conductivity upon reduction, although only an extremely small amount of oxygen is released. After annealing at high temperatures, a valence change of the Ti ions in the surface layer occurs, which becomes pronounced upon the quenching of the crystal. This shows that the reduction-induced insulator-to-metal transition is a highly dynamic non-equilibrium process in which resegregation effects in the surface layer take place. Upon cooling to the ferroelectric phase, the metallicity can be preserved, creating a “ferroelectric metal.” Through a nanoscale analysis of the local conductivity and piezoelectricity, we submit that this phenomenon is not a bulk effect but originates from the simultaneous existence of dislocation-based metallic filaments and piezoelectrically active areas, which are spatially separated.

Impact of the Initial Phase Composition of Alloys on the Effects Manifested by Yield Sites That Occur on Sheet Aluminum Alloys Subjected to Impact-Oscillatory Loading

The impact of the initial phase composition of alloys was evaluated, in particular, the content of Cu, Mn, and Mg in aluminum alloys D16ChATW, 2024-T351 and aluminum alloy T, which in its physical and mechanical characteristics is close to alloy 6013. The impact was evaluated on the effects manifested by yield sites that occur on aluminum alloys that were subject to the dynamic non-equilibrium processes (DNPs) at the expense of impact-oscillatory loading of different intensities under conditions of static tensioning, The one-time DNP, to which the investigated aluminum alloys were subjected at the pre-set levels of elastic strain followed by static tensioning, was found to cause yield sites formation. This is due to self-organization of the alloy structure, which contributes to alloy plasticization. The initial phase alloys composition impact on the yield sites, which occurs when impulse energy of a different intensity is applied to the alloys, was analyzed. The specimens from the aluminum alloys undergoing DNPs of the same level were compared. This made it possible to conclude that alloys D16ChATW and 2024-T351, which have a higher content of Cu, Mn, and Mg, have longer yield sites upon subsequent static tensioning. On the basis of the experimental results, in particular, physical studies, the authors derived a physical and mathematical model of the yield sites that appear after DNPs.

Plastic Anisotropy Effect on Variation of Mechanical and Structural Properties of VT23 Titanium Alloy Subjected to Impact-Oscillatory Loading.

The main regularities in the impact of varying intensity impact-oscillatory loading on the variation of the mechanical and structural properties of the VT23 high-strength two-phase transverse-rolled sheet titanium alloy have been found. The intensity of the impulse introduction of energy into the alloy under the dynamic non-equilibrium process (DNP) was estimated by εimp (the increment of dynamic strain). The pulse intensity was found to change the shape of the static strain diagram with further tensioning, as compared to the initial state. This indicates the effect from the structure self-organization inherent in the VT23 titanium alloy upon the DNP. After the DNP (εimp = 1.44%), with further static deformation, the tensile diagram revealed yield sites up to 6.5% long. In most cases, the DNP was found to have a negative effect on the variation of the mechanical properties of the VT23 titanium alloy, especially if the latter was rolled in the transverse direction. The optimal DNP intensity is εimp~1.5%. In this case, the DNP can be used as an effective plasticization technology for the VT23 titanium alloy (regardless of the rolling direction) in the stamping of high-strength titanium alloys. Changes in the mechanical and structural condition of the VT23 titanium alloy subjected to the DNP were confirmed by the fractographic investigation of specimen fractures.

Dynamic Elucidation of Lithium Insertion Reaction into MgMn2O4 Spinel

Since the expansion of Li-ion battery applications from portable electronic devices to electric vehicles and renewable energy storage, high-power capability is becoming increasingly important as a battery performance metric. Elucidation of the reaction mechanism of Li insertion materials is a major task in the battery research field, because it offers crucial insights into both the kinetics of the Li insertion reaction and the development of high-power Li-ion batteries. In this study, the mechanism for Li insertion into MgMn2O4 spinel, across the entire reaction range, was elucidated by fitting the current response during constant-potential discharge reaction using solid-state kinetic reaction (nucleation-growth, diffusion, and contraction) models. The fitting results revealed that the Li insertion reaction in the dynamic (non-equilibrium) process proceeds via nucleation-growth followed by solid-state Li-ion diffusion (single-phase), while Li insertion into MgMn2O4 proceeds through a two-phase coexistence reaction in the equilibrium state, as observed by ex situ XRD analysis. The finding that the reaction mechanisms in the dynamic and equilibrium processes are different indicates that the kinetics of the Li insertion reaction should be considered through a dynamic rather than an equilibrium process viewpoint.

Phenomenological Models and Peculiarities of Evaluating Fatigue Life of Aluminum Alloys Subjected to Dynamic Non-Equilibrium Processes

Physical-mechanical models for predicting the fatigue life of aluminum alloys D16ChATW and 2024-T351 are proposed and tested. Damage accumulation patterns are established for these alloys in the initial state and after dynamic non-equilibrium processes (DNP) of different intensity that occur at maximum cycle stresses σmax from 340 to 440 MPa, cycle asymmetry coefficients R = 0.1 and load frequency f = 110 Hz. The main model parameters are the initial alloy hardness HV and the limiting parameters of scatter of hardness values m. These parameters are evaluated in the process of cyclic loading with fixed maximum stresses of the cycles. Relative values me are also considered. For the alloys in the initial state, the proposed models are shown to be in good agreement with the experimental results. Conversely, structural changes taking place in alloys after DNP complicate the prediction of their fatigue life.

Understanding the structural diversity of chitins as a versatile biomaterial.

Chitin is one of the most abundant biopolymers, and it has adopted many different structural conformations using a combination of different natural processes like biopolymerization, crystallization and non-equilibrium self-assembly. This leads to a number of striking physical effects like complex light scattering and polarization as well as unique mechanical properties. In doing so, chitin uses a fine balance between the highly ordered chain conformations in the nanofibrils and random disordered structures. In this opinion piece, we discuss the structural hierarchy of chitin, its crystalline states and the natural biosynthesis processes to create such specific structures and diversity. Among the examples we explored, the unified question arises from the generation of completely different bioarchitectures like the Christmas tree-like nanostructures, gyroids or helicoidal geometries using similar dynamic non-equilibrium growth processes. Understanding the in vivo development of such structures from gene expressions, enzymatic activities as well as the chemical matrix employed in different stages of the biosynthesis will allow us to shift the material design paradigms. Certainly, the complexity of the biology requires a collaborative and multi-disciplinary research effort. For the future's advanced technologies, using chitin will ultimately drive many innovations and alternatives using biomimicry in materials science.This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Three Essays on the Theory of Money and Financial Institutions Essay 2: The Exchange Economy, Money, and Markets

This essay is the second of three. The first is nontechnical and in part autobiographical describing the evolution of my approach to developing a micro economic theory of money and financial institutions. This essay is devoted to a mathematical sketch of a closed economic exchange system with general equilibrium GE and rational expectations RE viewed game theoretically. It squeezes the last drop out of statics and an illusory dynamics in the form of the RE extension of GE with no other externalities beyond money and markets. The third essay builds on process models adding uncertainty, innovation, an active government, nonsymmetric information and other externaties that all lead away from a static equilibrium model to an evolving entity where competition involving fi nance and innovation is part of a dynamic non-equilibrium process.

Molten pool structure, temperature and velocity flow in selective laser melting AlCu5MnCdVA alloy

Selective Laser Melting (SLM) has become one of the most promising technologies in Metal Additive Manufacturing (MAM), which is a complex dynamic non-equilibrium process involving heat transfer, melting, phase transition, vaporization and mass transfer. The characteristics of the molten pool (structure, temperature flow and velocity flow) have a decisive influence on the final forming quality of SLM. In this study, both numerical simulation and experiments were employed to study molten pool structure, temperature flow and velocity field in Selective Laser Melting AlCu5MnCdVA alloy. The results showed the structure of molten pool showed different forms (deep-concave structure, double-concave structure, plane structure, protruding structure and ideal planar structure), and the size of the molten pool was approximately 132 μm × 107 μm × 50 μm: in the early stage, molten pool was in a state of deep-concave shape with a depth of 15 μm due to multiple driving forces, while a protruding shape with a height of 10 μm duo to tension gradient in the later stages of forming. The metal flow inside the molten pool was mainly driven by laser impact force, metal liquid gravity, surface tension and recoil pressure. For AlCu5MnCdVA alloy, metal liquid solidification speed was extremely fast (3.5 × 10−4 S), the heating rate and cooling rate reached 6.5 × 107 K S−1 and 1.6 × 106 K S−1, respectively. Choosing surface roughness as a visual standard, low-laser energy AlCu5MnCdVA alloy optimum process parameters window was obtained by numerical simulation: laser power 250 W, hatching space 0.11 mm, layer thickness 0.03 mm, laser scanning velocity 1.5 m s−1. In addition, compared with experimental printing and numerical simulation, the width of the molten pool was about 205 um and about 210 um, respectively, and overlapping between two adjacent molten tracks was all about 65 um. The results showed that the numerical simulation results were basically consistent with the experimental print results, which proved the correctness of the numerical simulation model.

Variation of Relief Topography and Hardness of Surface Layers of Materials Due to Impact-Oscillatory Loading

It was shown previously that cyclic loading can be used to extend the fatigue life of sheet plastic materials subjected to the preliminary impact-oscillatory loading. This type of loading causes dynamic non-equilibrium processes (DNP) in materials, which lead to the formation of dissipative structures in materials and on their surface. The density of these dissipative structures is less than that of the base metal. In this paper, the results of investigations into the relief and hardness of surface layers modified by impact-oscillatory loading are analyzed on the example of five structural materials. The signs of a regular, orderly system of microextrusions formed on flat surfaces of all materials due to DNP are considered along with the alignment of roughness parameters Rz and Ra of relief profiles. The effect of impact-oscillatory loading is one of the main causes that lead to the extension of the fatigue life of materials.

Modification of Mechanical Properties of High-Strength Titanium Alloys VT23 and VT23M Due to Impact-Oscillatory Loading

A simple technological method is proposed and tested experimentally, which allows for the improvement of mechanical properties in sheet two-phase high-strength titanium alloys VT23 and VT23M on the finished product (rolled metal), due to impact-oscillatory loading. Under impact-oscillatory loading and dynamic non-equilibrium processes (DNP) are realized in titanium alloys, leading to the self-organization of the structure. As a result, the mechanical properties of titanium alloys vary significantly with subsequent loading after the realization of DNP. In this study, the test modes are found, which can be used in the production conditions.

Kinetic Simulation of Nonequilibrium Kelvin-Helmholtz Instability**Supported by the Natural Science Foundation of China under Grant Nos. 91441120, 51806116, 11875001, and 11602162, the China Postdoctoral Science Foundation under Grant No. 2017M620757, the Center for Combustion Energy at Tsinghua University, and the Natural Science Foundation of Hebei Province under Grant Nos. A2017409014, ZD2017001, and A201500111, and the UK Engineering and Physical Sciences

The recently developed discrete Boltzmann method (DBM), which is based on a set of uniform linear evolution equations and has high parallel efficiency, is employed to investigate the dynamic nonequilibrium process of Kelvin-Helmholtz instability (KHI). It is found that, the relaxation time always strengthens the global nonequilibrium (GNE), entropy of mixing, and free enthalpy of mixing. Specifically, as a combined effect of physical gradients and nonequilibrium area, the GNE intensity first increases but decreases during the whole life-cycle of KHI. The growth rate of entropy of mixing shows firstly reducing, then increasing, and finally decreasing trends during the KHI process. The trend of the free enthalpy of mixing is opposite to that of the entropy of mixing. Detailed explanations are: (i) Initially, binary diffusion smooths quickly the sharp gradient in the mole fraction, which results in a steeply decreasing mixing rate. (ii) Afterwards, the mixing process is significantly promoted by the increasing length of material interface in the evolution of the KHI. (iii) As physical gradients are smoothed due to the binary diffusion and dissipation, the mixing rate reduces and approaches zero in the final stage. Moreover, with the increasing Atwood number, the global strength of viscous stresses on the heavy (light) medium reduces (increases), because the heavy (light) medium has a relatively small (large) velocity change. Furthermore, for a smaller Atwood number, the peaks of nonequilibrium manifestations emerge earlier, the entropy of mixing and free enthalpy of mixing change faster, because the KHI initiates a higher growth rate.

Impact of Dynamic Non-Equilibrium Processes on Fracture Mechanisms of High-Strength Titanium Alloy VT23

The complex analysis of fractures of high-strength titanium alloy VT23 was performed at the macro- and microlevels, and the basic patterns of fracture under static stretching and after the realization of dynamic non-equilibrium processes caused by impact-oscillatory loading and subsequent static stretching were revealed. The morphological regularities in the formation of dimples of tearing and alloy stratification at the macro level were established with the help of 3-D profilometry. The micromechanisms of fracture were numerically characterized by the methods of optical-digital analysis, in particular, by highlighting the bound areas, which are the objects of interest—the dimples of tearing. The analysis of the surface of ductile tearing under different loading conditions at the microlevel was performed by analyzing the parameter distribution patterns of the dimples found on it.

Influence of Dynamic Nonequilibrium Processes on the Mechanical Properties and Corrosion Resistance of Titanium Alloy

We compare the mechanical properties and corrosion resistance of specimens made of sheet two-phase VT22 high-strength titanium alloy in the intact state, after static tension, and after realization of dynamic nonequilibrium processes with subsequent static tension. It is shown that one-time dynamic nonequilibrium processes realized under impact vibration loading significantly increase the initial plastic deformation in this alloy and almost do not affect its corrosion resistance.

Influence of dynamic non-equilibrium processes on strength and plasticity of materials of transportation systems

New experimental results on the effect of additional force impulse loading on the variation of the initial structure of the aircraft material (alloys D16, 2024-T3, VT22) at various stages of deformation are presented and a significant enhancement of its initial plasticity is achieved. Complex investigations into the material properties after a dynamic non-equilibrium process made it possible to describe the main regularities in the nature of deformation and fracture of materials, which allowed proposing general recommendations on using the revealed physical and mechanical regularities in the evaluation of strength of aircraft structures.

Modification of the Mechanical Properties of the Sheet Two-Phase High-Strength Titanium Alloy VT 23 Due to Impulse Introduction of Energy

This study shows the effect of the specific impact-oscillatory loading (dynamic non-equilibrium processes) on the variation of the mechanical properties of the sheet two-phase high-strength titanium alloy VT 23. The results of fractographic research are used for interpreting the results of mechanical tests.

Enhancing plasticity of high-strength titanium alloys VT 22 under impact-oscillatory loading

The purpose of this paper is to provide new experimental data for high-strength VT 22 titanium α + β-type alloy under impact-oscillatory loading and dynamic non-equilibrium process. Based on the performed experimental studies, it was found that overall plastic deformation of this alloy can be increased by a factor 2.75 compared with its initial state without significant loss of strength. To achieve this goal, a new methodology to study the impact behaviour of materials under non-equilibrium process has been used. Physical research revealed that significant microstructural refinement of the alloy is observed after such type of loading, as the result of which the fine grains are formed with subgrain refinement which takes place within the basis of alloy.

Prediction of Phase Formation in Nanoscale Sn-Ag-Cu Solder Alloy

In a dynamic nonequilibrium process, the effective heat of formation allows the heat of formation to be calculated as a function of concentrations of the reacting atoms. In this work, we used the effective heat of formation rule to predict the formation and size of compound phases in a nanoscale Sn-Ag-Cu lead-free solder. We calculated the formation enthalpy and effective formation enthalpy of compounds in the Sn-Ag, Sn-Cu, and Ag-Cu systems by using the Miedema model and effective heat of formation. Our results show that, considering the surface effect of the nanoparticle, the effective heat of formation rule successfully predicts the phase formation and sizes of Ag3Sn and Cu6Sn5 compounds, which agrees well with experimental data.

Self-Organisation of the Heat Resistant Steel Structure Following Dynamic Non-Equilibrium Processes

Using an original experimental methodology and software for contactless investigation into strains applying the method of digital image correlation, conditions for DNP realization in the test setup with pre-set rigidity have been found. Strain velocities have been determined to be equal to 2...10 s–1 in the processes of forming and developing a dissipative structure of heat resistant steel under the DNP (dynamic non-equilibrium process).