Average Element Size Research Articles

Systematic in-silico evaluation of fibrosis effects on re-entrant wave dynamics in atrial tissue.

Despite the key role of fibrosis in atrial fibrillation (AF), the effects of different spatial distributions and textures of fibrosis on wave propagation mechanisms in AF are not fully understood. To clarify these aspects, we performed a systematic computational study to assess fibrosis effects on the characteristics and stability of re-entrant waves in electrically-remodelled atrial tissues. A stochastic algorithm, which generated fibrotic distributions with controlled overall amount, average size, and orientation of fibrosis elements, was implemented on a monolayer spheric atrial model. 245 simulations were run at changing fibrosis parameters. The emerging propagation patterns were quantified in terms of rate, regularity, and coupling by frequency-domain analysis of correspondent synthetic bipolar electrograms. At the increase of fibrosis amount, the rate of reentrant waves significantly decreased and higher levels of regularity and coupling were observed (p < 0.0001). Higher spatial variability and pattern stochasticity over repetitions was observed for larger amount of fibrosis, especially in the presence of patchy and compact fibrosis. Overall, propagation slowing and organization led to higher stability of re-entrant waves. These results strengthen the evidence that the amount and spatial distribution of fibrosis concur in dictating re-entry dynamics in remodeled tissue and represent key factors in AF maintenance.

Microstructure and Mechanical Properties of β-Titanium Ti-15Mo Alloy Produced by Combined Processing including ECAP-Conform and Drawing

At present, researchers pay great attention to the development of metastable β-titanium alloys. A task of current importance is the enhancement of their strength and fatigue properties. An efficient method for increasing the strength of such alloys could be severe plastic deformation. The object of this study was a medical metastable β-titanium alloy Ti-15Mo (ASTM F2066). The alloy in the (α + β) state was for the first time deformed by combined processing, including equal channel angular pressing-conform and drawing. Such processing enabled the production of long-length rods with a length of 1500 mm. The aim of the work was to study the effect of the combined processing on the alloy's microstructure and mechanical properties. An ultrafine-grained structure with an average size of structural elements less than 100 nm was obtained. At the same time, high strength and ductility (σuts = 1590 MPa, δ = 10%) were achieved, which led to a record increase in the endurance limit (σ-1 = 710 MPa) under tension-compression terms.

Development of Ultrafine–Grained and Nanostructured Bioinert Alloys Based on Titanium, Zirconium and Niobium and Their Microstructure, Mechanical and Biological Properties

For this paper, studies of the microstructure as well as the mechanical and biological properties of bioinert titanium, zirconium, and niobium alloys in their nanostructured (NS) and ultrafine-grained (UFG) states have been completed. The NS and UFG states were formed by a combined two-step method of severe plastic deformation (SPD), first with multidirectional forging (MDF) or pressing into a symmetrical channel (PSC) at a given temperature regime, and then subsequent multi-pass groove rolling (MPGR) at room temperature, with pre-recrystallization annealing. Annealing increased the plasticity of the alloys in the NS and UFG states without changing the grain size. The UFG structure, with an average size of structural elements of no more than 0.3 μm, was formed as a result of applying two-step SPD and annealing. This structure presented significant improvement in the mechanical characteristics of the alloys, in comparison with the alloys in the coarse-grained (CG) or small-grained (SG) states. At the same time, although the formation of the UFG structure leads to a significant increase in the yield strength and tensile strength of the alloys, their elastic modulus did not change. In terms of biocompatibility, the cultivation of MG-63 osteosarcoma cells on the polished and sandblasted substrates demonstrated high cell viability after 10 days and good cell adhesion to the surface.

ON THE INFLUENCE OF THE PARAMETERS OF GLOBULAR GRAPHITE INCLUSIONS ON THE ACOUSTIC CHARACTERISTICS OF CAST IRON AND ULTRASONIC LONGITUDINAL WAVE SIGNALS

Based on analytical models, the dependence of the velocity and attenuation coefficient of the longitudinal ultrasonic wave in cast iron with globular graphite on the average size of graphite elements and its volume content is shown. Computer modeling of acoustic paths for a medium – cast iron with globular graphite for standard normal probes was carried out to assess the influence of such a medium on the characteristics of the transmitted and recorded signals during ultrasonic testing. Calculations of directivity characteristic of probes with normalization of each directivity characteristic to its maximum for steel and cast iron with globular graphite, a slight change in the width of the directivity characteristics due to the lower velocity of longitudinal waves in cast iron compared to steel. It is established that the amplitude of the bottom signal in cast iron with globular graphite can exceed its values for structural steel. Evaluation of the nonlinearity of attenuation for cast iron with globular graphite showed that it is very small. The features of DGS-diagrams for cast iron with globular graphite are noted, associated with higher attenuation of longitudinal waves than in steel, as well as with lower velocities of their propagation.

Structural strength evaluation of a 3000 dwt river-barge, under oblique quasi-static design waves

The present study consists of the 3D-FEM global structural analysis of a typical open-top, double-hull, 3000 DWT inland navigation barge, having 90 m in length. The 3D-FEM model developed to perform the evaluation idealizes the barge structure with high accuracy, average element size being in the range of 50-75 mm. Two loading cases were analyzed, consisting of the ballast and full loading conditions. For the equilibrium floating condition in calm water and oblique design waves, an eigen iterative scheme has been used to generate the input parameters for the 3D-FEM analyzed cases. The push-barge finite element model has been subjected to oblique quasi-static design waves, headings ranging from 0 to 75 degrees. Wave heights considered in the analysis range from 0 to 1.2 m, step 0.3 m, corresponding to the Danube navigation conditions and freeboard limit imposed by the classification societies for inland navigation vessels. Numerical results following the FE analysis have been assessed by the yielding stress ratio, von Mises criterion, and the maximum deformation, thus indicating the structural areas that need to be improved in the design process.

ON THE INFLUENCE OF THE SIZE OF FLAKE GRAPHITE INCLUSIONS AND ITS VOLUME CONTENT ON THE ACOUSTIC PARAMETERS OF CAST IRON AND THE CHARACTERISTICS OF ULTRASONIC LONGITUDINAL WAVE SIGNALS

Algorithms have been presented for calculating the velocity (in the approximation of a fine-layered model) and the attenuation coefficient of a longitudinal ultrasonic wave in cast iron, depending on the average size of graphite elements and its volume content, the calculation results for which are qualitatively confirmed experimentally. The calculation was performed using a fine-layered model of the structure, the graphite inclusions were described in the form of plane-parallel layers placed in an isotropic elastic medium (metal base). Computer simulation of acoustic paths for a mediumcast iron with flake graphite for standard direct converters is carried out in order to study the influence of such a medium on the characteristics of transmitted and received signals during ultrasonic testing. In the course of the research, a previously developed model was used to calculate the attenuation coefficient of longitudinal waves in cast iron with flake graphite due to their Rayleigh and phase scattering on graphite inclusions. Computer simulation of the acoustic characteristics of the signals of a direct linear probe with a phased array in cast iron with flake graphite was carried out, during which the shape of the acoustic pulses of the longitudinal wave was calculated, depending on the distance traveled by the wave and the value of the attenuation coefficient for various models of cast iron. The main modeled characteristics of the transducer include the directivity characteristic and the change in the signal amplitude along the acoustic axis. It is shown that for cast iron with flake graphite, there are cases when the directivity of the probe with a phased array transmitted into the cast iron is practically absent.

Kinetics of dynamic recrystallization in low - and medium carbon steels during warm ECA pressing

In this study, electron microscopy was employed to examine the microstructure evolution mechanisms and dynamic recrystallization kinetics in low and medium carbon steels with a lamellar structure of perlite during equal channel angular pressing (ECAP) at 400 °C. Mechanisms of the subgrain structure formation and its transformation into a grain-subgrain structure with average element size of 200–500 nm were revealed. It was found that new ultrafine grains with high-angle boundaries are formed in the ferrite phase as a result of dynamic recrystallization beginning after the second ECAP pass. It was shown that the growth rate of the recrystallized fraction increases drastically after 3 ECAP passes. Fragmentation of ferrite lamellas within perlite colonies and strain induced split of cementite plates was detected suppressing the recrystallization in AISI 1045 steel. Enhanced mobility of dislocations in ferrite phase of AISI 1020 steel assisted in severe strain hardening and subsequent dynamic recrystallization.

Effect of rotary swaging and subsequent aging on the implant-relevant properties of magnesium alloy WE43

The magnesium alloy WE43 were pre-strained by rotary swaging (RS) with a final temperature of 350°C. RS led to a significant grain refinement with the formation of a predominantly subgrain structure. The average size of the structural elements decreased up to 450±50 nm after RS. In addition, the RS-induced precipitation of intermetallic Mg41Nd5 particles with an average size of 210±13 nm was observed. Subsequent heat treatment caused the average size of structural elements and intermetallic particles to grow to 781±88 nm and 494±51 nm, respectively. After RS, the ultimate tensile strength (UTS) of the alloy rose to 363±2 MPa with tensile elongation of 11.4±0.6%. After heat treatment, the UTS of the alloy increased to 376±9 MPa, with some drop of tensile elongation to 7.6±0.4%. Interestingly, the biocorrosion resistance of the alloy was not compromised by RS, while subsequent heat treatment of the swaged alloy reduced its biodegradation rate. No significant differences in the biocompatibility of the alloy WE43 between different microstructural states were observed. It was found that RS with subsequent aging of the alloy WE43 reduces the adhesion of yeast to its surface, which in the long term may reduce the risk of infectious complications after orthopedic surgery.

Effect of Hydrogen on the Deformation Behavior and Localization of Plastic Deformation of the Ultrafine-Grained Zr–1Nb Alloy

In this paper, comparison studies of the hydrogen effect on the structural and phase state, deformation behavior, and mechanical properties of the fine- (average grain size 4 µm) and ultrafine-grained (average element size 0.3 and 0.4 µm) Zr–1wt.%Nb (hereinafter Zr–1Nb) alloy under tension at temperatures in the range of 293–873 K were conducted. The formation of an ultrafine-grained structure is established to increase the strength characteristics of the Zr–1Nb alloy by a factor of 1.5–2 with a simultaneous reduction of its resistance to the localization of plastic deformation at the macro level and the value of deformation to failure. The presence of hydrogen in the Zr–1Nb alloy in the form of a solid solution and hydride precipitates increases its resistance to the localization of plastic deformation at the macro level if the alloy has an ultrafine-grained structure and decreases if the structure of the alloy is fine-grained. In the studied temperature range, the Zr–1Nb alloy in the ultrafine-grained state has a higher resistance to hydrogen embrittlement than the alloy in the fine-grained state.

Thermal Stability of the Structure and Microhardness of the Al–0.05 vol % Al2O3 Nanocomposite Fabricated by Accumulative Roll Bonding

The evolution of the microstructure and microhardness of the Al–0.05 vol % nAl2O3 nanocomposite (where nAl2O3 are aluminum nanoparticles) and aluminum without nanoparticles fabricated by accumulative roll bonding with annealing in a temperature range of 373–573 K is investigated. Ball-shaped Al2O3 nanoparticles with an average diameter of 50 nm are introduced between rolled plates of technically pure aluminum from the first to fourth rolling cycles, while the fifth to the tenth rolling cycles are performed without nanoparticles. The average grain size and aspect ratio of elements of the material grain–subgrain structure in the initial state and after annealing at 473 K are measured using transmission electron microscopy. It is shown that the nanocomposite microhardness is 5–13% higher than the corresponding value of HV for aluminum over the entire studied annealing temperature range. The main factor of the higher nanocomposite microhardness is precipitation hardening due to Al2O3 nanoparticles. The contribution of the substructural and grain-boundary hardening is identical in both materials. The thermal stability of the nanocomposite microhardness is only ~25 K higher than that of aluminum, which is caused by the nonuniform distribution of nanoparticles in the matrix and their low volume fraction. The high thermal stability of the fine-grain structure itself, formed by accumulative roll bonding, when compared with other methods of intense plastic deformation, also plays a role. It is established that most Al2O3 nanoparticles remain at the grain boundaries of nanocomposite after annealing at 473 K; therefore, the ability to fasten the boundary by Al2O3 nanoparticles under the conditions under study is retained at least to 473 K.

Geotechnical localization analysis based on Cosserat continuum theory and second-order cone programming optimized finite element method

Based on the Hellinger-Reissner mixed variational principle, a second-order cone programming optimized finite element method for elastic and elastoplastic analyses of Cosserat continuum (named CosFEM-SOCP) is proposed. To examine the correctness and effectiveness of CosFEM-SOCP, three well-known numerical examples are revisited. In the plane-strain elastic problem of stress concentration around a circular hole, the stress concentration factors calculated by CosFEM-SOCP are in good agreement with the existing solutions, and the correctness of CosFEM-SOCP can be verified. In the analysis of load-displacement response of a flexible strip footing resting on the soil ground, it is found that load-displacement response may be affected by the internal characteristic length lc, and generally a larger lc may result in a wider and deeper slip surface as well as more elements being included in the shear bands. From the plane-strain soil strip with the Drucker-Prager (DP) failure criterion subjected to the prescribed incremental displacement, it can also be observed that the pathologically mesh-dependent problem can be partially or even completely removed by employing CosFEM-SOCP, as long as the mesh is fine enough so that the average element size in the mesh discretization is smaller than lc.

Value associations bias ensemble perception

Ensemble perception refers to awareness of average properties, e.g. size, of “noisy” elements that often comprise visual arrays in natural scenes. Here, we asked how ensemble perception might be influenced when some but not all array elements are associated with monetary reward. Previous studies show that reward associations can speed object processing, facilitate selection, and enhance working-memory maintenance, suggesting they may bias ensemble judgments. To investigate, participants reported the average element size of brief arrays of different-sized circles. In the learning phase, all circles had the same color, but different colors produced high or low performance-contingent rewards. Then, in an unrewarded test phase, arrays comprised three spatially inter-mixed subsets, each with a different color, including the high-reward color. In different trials, the mean size of the subset with the high-reward color was smaller, larger, or the same as the ensemble mean. Ensemble size estimates were significantly biased by the high-reward-associated subset, showing that value associations modulate ensemble perception. In the test phase of a second experiment, a pattern mask appeared immediately after array presentation to limit top-down processing. Not only was value-biasing eliminated, ensemble accuracy improved, suggesting that value associations distort consciously available ensemble representation via late high-level processing.

Electroosmotic pressure in the process of a biocompatible coating applying on the inner surfaces of nanostructured ceramics

The role of the effect of electroosmosis in the process of electrochemical deposition of a biocompatible coating on the inner surfaces of porous nanostructured ceramics, a material used to make endoprostheses and implants in medicine, is discussed. The biocompatibility of endoprostheses and implants with the human body is ensured by applying a special coating on the internal and external surfaces of the base material. The commonly acepted chemical compound used to form this coating is hydroxyapatite Ca10(PO4)6(OH)2. Multicomponent ceramic materials, from which the basis of endoprostheses and implants are made, are usually obtained by the traditional method of powder metallurgy - sintering, i.e., exposure of a mixture of powders at an elevated temperature under pressure. The material obtained in this way is a polycrystal. In addition, the structure of such a material contains a certain amount of voids in the form of individual pores or their associations (capillaries). The paper shows that the use of nano-structured ceramic materials with a characteristic average size of structural elements (grains, pores and their aggregations) of the order ≈(10–9–10–7)м as a material for the manufacture of implants may determine the greater efficiency of the process of electrochemical application of a biocompatible coating on them, since the resulting large electroosmotic pressure in the capillaries leads to a greater degree of filling of the porous system with electrolyte. The magnitude of the electroosmotic pressure can be increased by increasing the strength of the acting electric field or by decreasing the dielectric constant of the electrolyte ε when additional chemical additives are introduced into the electrolyte. The maximum degree of hollow channels (capillaries) filling with electrolyte, and, consequently, the efficiency of applying a biocompatible coating to the internal surfaces of ceramics using the electrochemical method, is achieved with the capillary system of the material being completely open.

Strengthening of Magnesium Alloy WE43 by Rotary Swaging

The article presents the results of an investigation of microstructure, mechanical properties and corrosion resistance of magnesium alloy WE43 processed by rotary swaging. The resulting microstructure is characterized by an average size of structural elements of 0.5 – 0.8 μm. The grain refinement leads to an increase in the strength of the alloy to 393 – 416 MPa while the tensile elongation stays at a level of 7 – 12.5%. The microstructure produced by rotary swaging does not lead to deterioration of the resistance of the alloy to electrochemical and chemical corrosion.

Phase composition of macroporous Ni-Al alloys obtained by combustion synthesis

This paper discusses the phase composition of macroporous Ni-Al alloys obtained by self-propagating high-temperature synthesis. The alloys have been synthesized in a nonstationary combustion mode. The combustion wave consists of super adiabatic foci, and macroporous structure is realized under the action of capillary hydrodynamic effects. The influence of reaction mixture composition of aluminium in the range of 13.5-31.5 wt.% is also discussed. The specific requirements to obtain the single phase B2 NiAl and LI2 Ni3Al as well as biphase gas permeable alloys with the average size of structure elements in the range of 1.2-3.15 mm are described in the paper.

Evolution of the structure and properties of pure aluminum under severe plastic deformation

The influence of severe plastic deformation (SPD) by equal-channel angular pressing (ECAP) on the formation of the structure and the mechanical properties of pure aluminum is studied. It is established that an ultrafine-grained structure is formed with an average size of structural elements of ∼ 1.5 µm. X-ray diffraction studies have shown that SPD results in a broadening of interference lines with a decrease in their intensity, which indicates an increase in the imperfection of the structure and its high dispersion. SPD also results in a significant enhancement of microhardness, yield stress and ultimate tensile strength in aluminum.

Effect of ECAP on structural, mechanical and functional characteristics of the austenitic Cr-Ni-Ti steels

In this study, equal-channel angular pressing (ECAP) of austenitic Cr-Ni-Ti stainless steel was carried out. Effect of ECAP on the evolution of the microstructure and mechanical and service properties of the Cr-Ni-Ti steel was investigated. The microstructure in the completely austenitic state processed by 6 passes of ECAP at 200 °C was obtained and examined by optical and transmission electron microscopy. Mechanical properties were determined by the Vickers micro-hardness measurements and tensile testing. Fracture toughness was evaluated and tribological properties of Cr-Ni-Ti stainless steel processed by ECAP were studied. It was revealed that submicrocrystalline structure with an average size of structural elements of 100 nm produced by ECAP significantly increased the strength properties of Cr-Ni-Ti stainless steel than that in the quenched state. After ECAP the ultimate tensile strength increased by 1.7 times, the fatigue limit by 1,5 times than that in the initial state. It was revealed that Cr-Ni-Ti steel after ECAP demonstrates 2.9 times higher fracture toughness than that in the quenched state. It is established that ECAP does not significantly affect the coefficient of friction and mass wear.

Mesh Convergence Behavior and the Effect of Element Integration of a HumanHead Injury Model.

Numerous head injury models exist that vary in mesh density by orders of magnitude. A careful study of the mesh convergence behavior is necessary, especially in terms of strain most relevant to brain injury. To this end, as well as to investigate the effect of element integration scheme on simulated strains, we re-meshed the Worcester Head Injury Model at five mesh densities (~ 7.2-1000k high-quality hexahedral elements of the brain). Results from explicit dynamic simulations of three cadaveric impacts and an in vivo head rotation were compared. First, scalar metrics of the whole brain only considering magnitude were used, including peak maximum principal strain and population-based median strain. They were further extended to deep white matter regions and the entire brain elements, respectively, to form two "response vectors" to account for both magnitude and distribution. Using benchmark enhanced full-integration elements (C3D8I), a minimum of 202.8k brain elements werenecessary to converge for response vectors of the deep white matterregions. This model was further used to simulate with reduced integration (C3D8R). We found that hourglass energy higher than the commonrule of thumb (e.g., up to 44.38% vs. < 10% of internal energy) was necessary to maintain comparable strain relative to C3D8I. Based on these results, it is recommended that a humanhead injury model should have a minimum number of 202.8 k elements, oran average element size of no larger than 1.8mm, for the brain. C3D8R formulation with relax stiffness hourglass control using a high scaling factor is also recommended to achieve sufficient accuracy without substantial computational cost.

The Effect of Microarc Oxidation on the Structure and Hardness of Aluminum-Oxide Coatings Formed by Plasma Spraying on Titanium

Coatings formed by plasma spraying of electrocorundum on VT6 titanium alloy and subsequent microarc oxidation at different current densities were examined. The parameters of structure and hardness of metal-oxide layers were studied. The effect of current density on them was also found. During microarc oxidation, the open porosity (from 50.3 ± 4.5 to 10.3 ± 1.5%), the thickness (from 47.4 ± 3.3 to 30.2 ± 5.3 μm), and the average size of structural elements of presprayed coating were decreased, while its hardness was increased from 760 ± 486 to 875 ± 238 HV2. The magnitude of changes in the structure of the plasma coatings depended on the current density during modification. Microarc oxidation makes it possible to form structural elements in the form of pores and crystals with a size from 15 to 150 μm on the surface of sprayed aluminumoxide coatings.

Methodical uncertainty in the two-point measurement of parts prismatic elements linear dimensions

The article is devoted to the topical problem of the reliability of measurements of geometrical specifications of technical products. The purpose of this article is to improve the quality control of the linear dimensions of the parts by the two-point measurement method. The goal of the article is the study of advanced methodical uncertainties of measurement of linear dimensions of plane-parallel prismatic elements. The method of research is geometric modeling of deviations of the element surfaces form and position in the rectangular coordinate system. The research was carried out for various executive elements with regard to their information content corresponding to the classes of kinematic pairs in the theory of mechanics and the number of constrained degrees of freedom in function of the basic elements. Prismatic elements with informative content 3, 2, 1 and θ (zero) were studied. Uncertainty assessment of two-point measurements were made by comparing the measurements results of linear dimensions and functional dimensions of the element maximum and minimum material constrained by the limits of maximum and minimum. As a result of studies of the two-point measurements accuracy, it is found that the methodical uncertainty is formed when measuring the average size of elements for all types of form deviations. The two-point measurement method cannot account for deviations of the location dimension of the element and therefore its use for items with less than the maximum informativeness creates unacceptably large methodical uncertainties of measurement the maximum, minimum and medium linear sizes. The same methodical uncertainties occur under the arbitration control of the parts linear dimensions by the limit two-point gauges.