Effect Of Inhomogeneity Research Articles

Возникновение концентрационной конвекции в длинной прямоугольной области пористой среды

We solve a problem of the convective flow stability in an elongated rectangular region of a porous medium. The transport of a mixture is described using the MIM (mobile-immobile media) approach. This approach consists in dividing the concentration of the solute into mobile and immobile compo-nents. The effect of density inhomogeneity on the flow of a solution in a porous medium is taken in-to account by the filtration equation within the Darcy-Boussinesq approximation. The problem is solved numerically with the use of the finite difference method. The fields of pressure and concen-tration are obtained. The influence of the parameters of the problem on the disturbance profiles is analyzed. A modified problem of stability is solved. The modification is necessary for finding the oscillatory convective mode. To obtain the solution, the spectrum of Lyapunov exponents is calcu-lated with Gram-Schmidt orthogonalization. Neutral curves are found that make it possible to detect the threshold for the onset of convection. The ranges of parameters in which oscillatory perturba-tions are realized are obtained. The effect of sorption parameters on the occurrence of oscillations is analyzed.

Numerical Study of the Effect of Plasma Inhomogeneity with Bremsstrahlung and Photorecombination Radiation on the Absorption of an Alfven Wave

Numerical Study of the Effect of Plasma Inhomogeneity with Bremsstrahlung and Photorecombination Radiation on the Absorption of an Alfven Wave

On the combined effects of compositional inhomogeneity and ammonia addition to turbulent flames of ethylene

This paper is part of a broader program aimed at investigating the effects of co-firing clean fuels such as ammonia or hydrogen with hydrocarbons. The focus is on soot formation as well as flame stability in turbulent mixed-mode combustion, which is highly relevant in practical combustors. Ammonia substitution for nitrogen results in reduced flame stability, and this is correlated to differences in flame speed and extinction strain rate. While it is known that the addition of ammonia suppresses soot, visual inspection of compositionally inhomogeneous flames of ethylene-ammonia indicates a reduction in ammonia's ability to suppress soot formation. Measurements of soot volume fraction and laser-induced fluorescence in selected UV and visible bands are made along the centreline in selected flames to test this hypothesis. Experimental results are then compared to simulations in laminar diffusion flames, stratified counterflow flames, and partially premixed flames. All results confirm the soot-inhibiting ability of ammonia. Increasing inhomogeneity, leading to higher centreline mixture fractions, enhances soot formation, and the level of enhancement is greater for flames with ammonia than without. Moreover, it is found that partial premixing is ultimately responsible for determining the amount of soot formed as opposed to stratification of fuel mixtures near the pilot.

Магнитоэлектрические свойства феррита-граната самария

The magnetoelectricity of samarium iron garnet is theoretically investigated: the antiferroelectric structures of samarium ions are described and their connection with the configurations of the magnetic moments of the ions and their transformations during magnetic phase transitions is revealed. The possibility of the appearance at low temperatures of unusual Bloch domain walls, in which the magnetization vector rotates from the [uv0] axes to the [vu0] axes, which are not crystal symmetry axes, is established. The electric polarization of Bloch domain walls, which are realized both at low (T → 0 K) and high temperatures, is studied. It has been established that the electric polarization of Bloch boundaries, which arises because of an inhomogeneous magnetoelectric effect, depends significantly on their shape.

Lime-based nanocomposites for masonry restoration: Towards the implementation of small-scale restoration

The structural integrity of historic and traditional buildings can be affected by natural weathering and incompatible restoration interventions. Traditionally, lime binders have been used extensively for restoration applications, while the incorporation of multi walled carbon nanotubes (MWCNTs) in such a binder, enhances the restoration material with increased mechanical as well as with self-sensing properties due to its piezoresistive characteristics. The focal point of the present investigation was the examination of the electrical, mechanical, and piezoresistive properties of a composite nano-reinforced lime-based mortar paste under different geometrical sizes (scale-up tests). Firstly, prismatic specimens of two different sizes, composed of the proposed nano-reinforced lime-based mortar were subjected to testing and compared against reference prismatic prisms of traditional non-reinforced lime-based mortar with a similar composition. The results showed a 24 % increase in the compressive strength and a 37.5 % decrease in the electrical resistance. Secondly, electrical resistance measurements were carried out on a small-scaled masonry specimen built with the MWCNTs reinforced lime-based mortar, to determine potential structure inhomogeneity effects. The tests revealed approximately 50 % electrical resistance decrease in comparison to the non-reinforced reference prismatic specimens. Lastly, the composite restoration material was applied at an actual masonry restoration project at the public library “Korais” of Chios Island, Greece, with the aim to monitor the composite material’s electrical resistance under real conditions.

Effects of Compositional Inhomogeneity on the Microstructures and Mechanical Properties of a Low Carbon Steel Processed by Quenching-Partitioning-Tempering Treatment

Quenching-partitioning-tempering (Q-P-T) heat treatment is a relatively novel approach to attain excellent ductility in high-strength steels. In the present work, the microstructural evolution and the mechanical properties of a low carbon microalloyed advanced steel were systematically investigated after the Q-P-T process. The microstructural evolution was explored by employing X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results indicate that the multiphase microstructures strongly depend on both the initial microstructure and the processing parameters of the quenching and partitioning process, especially the quenching temperature. Compositional inhomogeneity during the Q-P-T process results in multiphase microstructures, in which the mechanical properties of the quenching and partitioning steels may be strongly impacted by the distribution of heterogeneous austenite phase in the steel matrix.

Synthetical effect of material inhomogeneity and welding defects on fatigue behavior of 2205 duplex stainless steel cruciform welded Joints: Experiments and Life-prediction model

This paper performed experimental and analytical investigations on the synthetical effect of material inhomogeneity and welding defects on the fatigue behavior of 2205 duplex stainless steel cruciform welded joints. A series of experiments were performed, including microstructure characterization by the electron back-scattered diffraction, fatigue mechanical tests assisted by digital image correlation technique and fracture morphology observations by scanning electron microscope. Results show that fatigue life and failure location of cruciform welded joints depended heavily on their geometric configurations for lower cyclic amplitudes. However, with the elevation of loading, material inhomogeneity played a greater roles, leading to the change of fatigue failure mode with both geometric configuration and cyclic stress amplitude. To quantize the effects of welding defects and material inhomogeneity, a modified structure strain method was proposed by considering the heterogeneous plastic properties, to accurately predict both fatigue lifetime and failure location of cruciform welded joints at both low and high cycles fatigue. Lastly, a damage tolerance-based fatigue design method was discussed to guide the highly-reliable manufacture and damage detection of duplex stainless steel cruciform welded joints in the engineering.

Analytical and numerical analysis of functionally graded (FGM) axisymmetric cylinders under thermo-mechanical loadings

This study examines the thermo-mechanical behavior of FGM hollow cylinders subjected to mechanical loading and steady thermal stresses. The distribution of temperature, displacement, and stresses on the cylinder's inside and outside surfaces is considered a function of radius. The analytic solution of the displacement and stress distributions was obtained by solving Navier's second-order differential equation using the integral and differential transform method, derived from the mechanical equilibrium and heat equations. Moreover, numerical models were built using the finite element method with USDFLD and the finite difference method to test the accuracy of the analytical solution. The analytical formulation and numerical simulation predictions have a high level of agreement, indicating that the model is accurate. The effect of inhomogeneity in the FGM thick cylinder was addressed in this study by selecting a non-dimensional parameter β=[−2,2]that may be assigned any value influencing the stresses in the cylinder. It is concluded that by altering the valueβ, the properties of FGM can be altered to achieve the lowest stress levels. It is also shown that the effect of various Boundary Conditions (B.Cs) is significant in stress fields. This present work also observed that the significance of thermal B.C. is more dominant than fixed pressure B.Cs.

Effect of anisotropy and inhomogeneity on the stability of liquid film flowing down a porous inclined plane

We examined the linear stability of a Newtonian liquid film flow past a porous inclined plane. Falling film on inclined permeable planes displays three instability modes: surface, shear, and porous mode. Most of the previous studies have examined the film flow past an isotropic and homogeneous porous medium. We could find only one study that examined the film flow past an anisotropic and inhomogeneous porous inclined plane; however, it focused on parameter regimes where the porous mode remains stable. Here, we explored the parameter regimes where all three modes become unstable and investigated the effect of the anisotropic and inhomogeneous variations in the permeability of the porous medium. The generalized Darcy model is used to describe the flow through the porous medium along with the Beavers–Joseph condition at the fluid–porous interface. We show that there is a switching of dominant instability mode from surface mode to porous mode with variation in anisotropic parameter. Our results clearly show that for a given Darcy number, the surface mode is the critical instability mode for isotropic and homogeneous porous media. However, when an anisotropic porous medium is considered with high wall-normal permeability than the wall-parallel permeability, the porous mode becomes the most unstable mode. We show a similar exchange of dominant instability mode from fluid mode (i.e., surface or shear mode) to porous mode with variations in inhomogeneity parameter. This switching of the most unstable mode from fluid mode to porous mode with variation in anisotropy and/or inhomogeneity in permeability has not been demonstrated in any of the earlier studies in the context of film flows. We also present an energy budget analysis to decipher the mechanism responsible for making the three modes unstable.

Characterization of solution grown 3D polycrystalline methylammonium lead tribromide for x-ray detection

Solution grown metal halide perovskites (MHPs) are a class of low-cost, direct conversion semiconducting materials with the potential to meet the need for large areas, high stopping power, and high sensitivity x-ray detectors. While polycrystalline MHP thin films have shown significant potential for meeting this need, their efficiencies for detecting x rays are limited by their thickness. This article presents an MHP variant, methylammonium lead tribromide (MAPB) in the form of 3D polycrystalline mosaic wafers with relatively high hole transport properties that demonstrated stable sensitivity during irradiation. An expedited and efficient detector fabrication method that did not include polishing or sintering was evaluated, and a radiograph of a brass key was produced using electron collection from the resulting wafer. However, a high dose rate was required due to very low sensitivity values. The effects of surface inhomogeneity and radiation damage were investigated as explanatory factors, and these phenomena were further characterized through IV measurements, current response as a function of electric field and x-ray dose rate, and alpha particle irradiation. The results indicated that although compromising surface quality for fabrication efficiency was the primary hindrance to the x-ray detection performance of 3D polycrystalline MAPB, stable performance could still be achieved under reasonable dose rates.

An investigation into wire arc additive manufacturing of Mg-Y-RE-Zr alloy

• Mg-Y-rE-Zr alloy without obvious defects is fabricated by WAAM . • Microstructural homogeneity occurs along the deposited direction. • The precipitates of Mg 3 (Nd, Y) and Mg 14 Nd 2 Y are found in the1 st layer. • The bottom part of the deposited wall exhibits a higher hardness. This work fabricates Mg-4Y-3RE-0.5Zr alloy by wire arc additive manufacturing (WAAM). The oxidation inclusion, as one of the main defects in the Y-containing Mg alloys prepared by laser powder bed fusion (LPBF), has not been observed. However, microstructural inhomogeneity along the building height appears due to the combined effect of the different cooling rates of different deposited layers and the subsequent multiple thermal cycles (MTCs). The effect of the microstructural inhomogeneity on the hardness distribution of the deposited wall was also revealed. It is believed that this study provides some new findings to the additive manufacturing of high-performance magnesium rare-earth (Mg-RE) alloys.

Effect of microstructure inhomogeneity on creep behavior of friction stir welding 7B50-T7451 aluminum alloy thick plate joint

Microstructure inhomogeneity and through-thickness creep properties of friction stir welding (FSW) 7B50-T7451 aluminum alloy thick plate joint were investigated. The results show that creep properties of the FSW joint deteriorate along the thickness direction from the top to the bottom. Both the grain size and fraction of the low-angle grain boundaries (LAGBs) in the weld nugget zone (WNZ) decrease from the top to bottom. A larger volume of precipitate free zone (PFZ) and coarser precipitates in the bottom slice reduce creep resistance compared with the top. The precipitates in the heat-affected zone (HAZ) exhibit continuous coarsening with the increase of creep temperature, inducing the decrease of threshold stress. The dominant creep mechanism transforms from dislocation creep in the HAZ to grain boundary sliding (GBS) in the WNZ when creep temperature increases. The fracture mode also changes from transgranular to intergranular fracture.

Effect of substructural inhomogeneity on the anisotropy of physical and mechanical properties of textured materials

Today, anisotropy of the physical and mechanical properties of textured materials is mainly calculated based on average properties of a single crystal and information about the volume percent of grains that have different orientations, which can be determined with the help of distribution function. It is a fact that, in addition to the crystallographic texture, substructural inhomogeneity develops in rolled materials, which manifests itself as a difference in the distortion of the crystalline lattice (hardening) and elastic microstrains in grains belonging to different texture components. Substructural characterization is based on the X-ray method of Generalized Direct Pole Figures, which implies that a full profile of X-ray reflections is registered for different positions of the specimen, i.e. as a direct pole figure is being built. As a result, one can obtain the FWHMs of X-ray lines and elastic microstrains distributed on the stereographic projection. It means that a textured polycrystalline material that has undergone thermo-mechanical treatme nt is characterized with a certain spectrum of structural states and the presence of residual elastic microstrains. Therefore, the degree of macroscopic anisotropy of the product properties is defined both by the predominant grain orientation in the polycrystal and by the parameters of substructural inhomogeneity of grains belonging to different texture components. In spite of the fact that the elastic properties of an individual crystallite do not change and the tensile and compressive elastic microdeformations are balanced in the studied volume of the material, the elasticity of the whole system, i.e. of a polycrystal, changes due to interacting grains and the elastic energy stored in them. The authors propose a method for calculating elastic moduli and thermal expansion coefficients while accounting for the substructural inhomogeneity of the material by minimizing the elastic energy of the textured material. The efficiency of this method is demonstrated on specimens of a semi-finished channel pipe made of Zr – 2.5% Nb alloy.This research was funded by the Ministry of Science and Higher Education of the Russian Federation; Agreement No. 075-15-2021-1352.

Impact behaviour of dry granular flow against baffle structure: coupled effect of Froude and particle characteristics

The baffle design resisting dry granular flow is still impeded by the effect of the particle size distribution coupled with the influence of Froude characteristics on baffle performance – for example, the deceleration process and run-up process. Based on discrete-element method simulation, this study investigated the baffle deceleration and granular flow run-up. Baffle deceleration is controlled by the change of particle contact behaviour behind the baffle slits and is more sensitive to the particle size than the Froude characteristics of granular flow. Although the granular flow run-up height is also affected by the debris–slit interaction, it is mainly dominated by the flow climbing along the baffle, which is more sensitive to the Froude characteristics and stress-transfer mechanism. Bidisperse granular flow has more complex interaction with the baffle compared with monodisperse flow. The effect of material inhomogeneity on baffle performance depends on the particle content. For baffle design, the first array can be considered as a reference. The estimation of the baffle deceleration potential and height with consideration to unsteady dynamics and material inhomogeneity is also presented in this paper.

Correction of the post-irradiation T1 relaxation effect for chemical exchange-sensitive MRI: A phantom study

Purpose: In many pulse sequences of chemical exchange-sensitive MRI including multi-slice chemical exchange saturation transfer (CEST) or chemical exchange sensitive spin-lock (CESL), there is a finite time delay between the irradiation preparation and the imaging acquisition, during which the T1-relaxation reduces the chemical exchange contrast and affects the accuracy for volumetric imaging. We propose a simple post-acquisition method to correct this contamination.Methods: A simple formula was derived to evaluate the cross-slice T1-relaxation contamination in multi-slice echo-planar imaging (EPI) after the irradiation preparation. CEST and CESL experiments were performed on phantoms to examine the accuracy of this approach.Results: Theoretical derivation showed that the cross-slice T1-relaxation contamination in multi-slice EPI imaging can be corrected by the signals of each slice at a parameter that suppresses the signal, e.g., at the water frequency for CEST, or with very long spin-lock pulse for CESL. This formula was confirmed by the results of phantom experiments, for both long and short irradiation durations with and without a steady-state, respectively. To minimize the effect of B0 inhomogeneity in the CEST experiment, a more accurate measurement of the signal at water frequency can be achieved with a higher pulse power and shorter duration.Conclusion: We proposed and validated a simple approach to correct the cross-slice T1-relaxation effect, which can be applied to volumetric CEST and CESL studies acquired by multi-slice EPI, or other imaging modalities with similar T1-relaxation contamination.

Microscale crack propagation in shale samples using focused ion beam scanning electron microscopy and three-dimensional numerical modeling

Reliable prediction of the shale fracturing process is a challenging problem in exploiting deep shale oil and gas resources. Complex fracture networks need to be artificially created to employ deep shale oil and gas reserves. Randomly distributed minerals and heterogeneities in shales significantly affect mechanical properties and fracturing behaviors in oil and gas exploitation. Describing the actual microstructure and associated heterogeneities in shales constitutes a significant challenge. The RFPA3D (rock failure process analysis parallel computing program)-based modeling approach is a promising numerical technique due to its unique capability to simulate the fracturing behavior of rocks. To improve traditional numerical technology and study crack propagation in shale on the microscopic scale, a combination of high-precision internal structure detection technology with the RFPA3D numerical simulation method was developed to construct a real mineral structure-based modeling method. First, an improved digital image processing technique was developed to incorporate actual shale microstructures (focused ion beam scanning electron microscopy was used to capture shale microstructure images that reflect the distributions of different minerals) into the numerical model. Second, the effect of mineral inhomogeneity was considered by integrating the mineral statistical model obtained from the mineral nanoindentation experiments into the numerical model. By simulating a shale numerical model in which pyrite particles are wrapped by organic matter, the effects of shale microstructure and applied stress state on microcrack behavior and mechanical properties were investigated and analyzed. In this study, the effect of pyrite particles on fracture propagation was systematically analyzed and summarized for the first time. The results indicate that the distribution of minerals and initial defects dominated the fracture evolution and the failure mode. Cracks are generally initiated and propagated along the boundaries of hard mineral particles such as pyrite or in soft minerals such as organic matter. Locations with collections of hard minerals are more likely to produce complex fractures. This study provides a valuable method for understanding the microfracture behavior of shales.

Effect of Material Inhomogeneity on the Crack Tip Mechanical Field and SCC Growth Rate of 52M/316L Dissimilar Metal Welded Joints

The stress–strain conditions at the crack tip in dissimilar metal welded joints (DMWJ) are a critical factor influencing stress corrosion cracking (SCC) behavior. The processing technology and working environment of DMWJ lead to a randomly inhomogeneous distribution of material mechanical properties, making the crack tip mechanical field more complex. An inhomogeneous model was obtained using a combination of physical experiments and the elastic–plastic finite element method to understand the effect of this inhomogeneous distribution of mechanical properties on the direction of SCC growth and the growth rate in DMWJ and the impact of inhomogeneity on the SCC growth behavior was compared and analyzed. The findings demonstrate that Type I (opening mode) cracks are more likely to form due to the inhomogeneity of mechanical properties and are more likely to deflect toward the Alloy 52M region at the interface between Alloy 52M and 316L stainless steel. Additionally, the strain gradient at the crack tip increases with the degree of inhomogeneity, which has a bigger impact on the accuracy of SCC growth rate predictions.

Model Development for Temperature-Dependent Degradation in Large Format Lithium-Ion Batteries

Large-format cells are achieving increasing popularity for Electric Vehicle (EV) applications to maximize volumetric and gravimetric energy densities. These large batteries are often characterized by spatial non-uniformities in temperature and resulting difficulties in maintaining uniform temperature distribution. This poor thermal management is a primary reason for the inefficient performance and safety risks associated with these large format batteries and battery packs. Further, there have been several reported degradation mechanisms which are responsible for the capacity fade within Lithium-ion (Li-ion) batteries over multiple charge/discharge cycles. In particular, the presence of thermal gradients and consequent non-uniformities greatly exacerbates degradation, and poses serious safety risks. Thus, it is imperative to identify and study the degradation mechanisms coupled with the thermal effects by incorporating detailed physics-based models to characterize the cell-level phenomena.This work aims to perform a detailed model-based study on the combined effects of battery degradation and temperature inhomogeneities within large-format Li-ion cells and battery packs. This simultaneous analysis for temperature-dependent degradation will be performed with a state-of-the-art electrochemical model like the classic pseudo-two-dimensional (p2D) model to be able to present a comprehensive analysis of the battery performance parameters. These models will be augmented to include thermal effects and various degradation mechanisms for Solid Electrolyte Interphase (SEI) formation and Lithium plating. The proposed numerical framework will be validated with experimental data for the loss in battery capacity over cycles. In addition, the model development, especially the weak form for model equations and their implementation in a finite-element solver, COMSOL Multiphysics, will be discussed in detail.This study primarily focusses on certain important aspects of temperature-dependent degradation, viz., (a) cell-to-cell temperature variation, (b) operating conditions for current, (c) topology for the cell arrangement within the battery module, and (d) choice of the degradation mechanism. The delineation of the effects of these complex factors on the cell-level signatures will be of significant utility in monitoring and identifying the performance limitations of individual cells, and thereby help maximize the performance of large format cells and battery packs.The ultimate goal is the design of a simple yet efficient numerical model with fast and robust simulations for the analysis of the temperature-dependent degradation of the Li-ion battery packs over a wide range of operating and design conditions. The proposed model will be developed to be computationally feasible for an adoption and implementation in a battery thermal management system.

Visualizing Reaction Distributions for Materials Validation and Failure Analysis in Li-Ion Batteries

The market for lithium-ion batteries (LIBs) is projected to grow from 36.7 billion to 128.3 billion in less than a decade 1. Large-scale demands for more robust LIBs are limited by battery cycle life and cost. In order to expedite the development of battery technology, current analytical techniques used to validate electrode morphology must be improved. Even excellent battery materials may result in poor electrode performance due to poor processing, such as suboptimal mixing, coating, or drying. Flawed processing leads to heterogeneities at either the particle or electrode length scale, resulting in inhomogeneous transport of lithium ions and eventually degradation and failure in LIBs 2. Limited techniques can deconvolute materials from processing effects through visualization. Methods visualizing reaction distribution in LIBs include thermal imaging, which is suitable technique for macroscale pack-level analysis, and state-of-charge electronic structure maps, which are suited for molecular analysis. These techniques are unable to characterize electrode performance at the mesoscale level and thus are inappropriate for characterizing local reactivity of electrode. Optical microscopy provides a compromise between spatial resolution and experimental accessibility. However, it is constrained to graphite and a few other battery materials that change color. In this work, we explore fluorescent microscopy as a technique to visualize battery reaction distributions. A redox-active fluorescent probe molecule illuminates electrode heterogeneities, such as hot-spots or dead-zones 3. Developing facile techniques by which researchers can evaluate electrode materials beyond cell cycling will be critical for meeting future battery technology demands. Choudhary, A. & Prasad, E. Lithium-ion Battery Market Size and Share | Industry Analysis by 2027. Allied Market Research https://www.alliedmarketresearch.com/lithium-ion-battery-market. Chung, D.-W., Shearing, P. R., Brandon, N. P., Harris, S. J. & García, R. E. Particle Size Polydispersity in Li-Ion Batteries. J. Electrochem. Soc. 161, A422–A430 (2014). Harris, S. J. & Lu, P. Effects of Inhomogeneities—Nanoscale to Mesoscale—on the Durability of Li-Ion Batteries. J. Phys. Chem. C 117, 6481–6492 (2013).

Double Sided Drift Method Reduces the Effect of Crystals' Inhomogeneity to Si(Li) Detector's ElectroPysicsal Characteristics

Double Sided Drift Method Reduces the Effect of Crystals' Inhomogeneity to Si(Li) Detector's ElectroPysicsal Characteristics