Microscale Domain Research Articles

Inhomogeneous domain switching near an electrode edge in orthorhombic K0.5Na0.5NbO3 piezoceramic

To characterize the inhomogeneous field distributions and their effect on ferroelectric/ferroelastic domain switching in potassium sodium niobate-based piezoceramics, a partially electroded orthorhombic phase K0.5Na0.5NbO3 ceramic sample containing a distinct edge was investigated using micro-beam, high-energy XRD with applied fields. Under the field application, the partial-electrode sample exhibits orientation-dependent and position-sensitive domain switching. The experimental measurements of micro-scale domain texture correlate reasonably with simulated electric fields calculated from a finite element analysis. Both experimental and simulated results reveal that the domain switching is induced inhomogeneously up to the millimeter-scale across the sample and that the electric field is significantly concentrated near the electrode edge. Integrating the experimental results with the model demonstrates that the local electric field directions and amplitudes drive the local orientation dependence of domain switching and, conversely, the direction of the local electric field can be inferred from the direction in which the maximum domain switching is measured.

Multiscale analysis for characterization of tensile properties in extrusion-based 3D printed carbon nanocomposites

In this study, we proposed a multiscale modeling methodology to predict tensile properties of carbon-based nanocomposites produced through extrusion-based 3D printing. This stepwise method integrates results across scales, from the nanoscale to the macroscale. The stochastic continuum model, informed by molecular dynamics, captures the direction-dependent stiffness of nanocomposites at the atomic level, integrating the transverse isotropic properties and morphological variations, along with process-induced uncertainties in a microscale domain. Considering the variable periodic layered filament shape determined by the printing conditions, we defined the geometry of the representative volume element and derived its homogenized equivalent effective properties. We validated the results of our model by comparing them with experimental stress-strain curves. Using this approach, we simulated the nonlinear response and analyzed the off-axis tensile characteristics of the specimens under various printing conditions. The alignment and orientation of the graphene flakes played pivotal roles in determining the mechanical properties of the nanocomposites. The proposed approach effectively assessed the overall behavior of nanocomposites produced using an extrusion-based 3D printing process, helping to accurately predict the mechanical properties and investigate the effects of the parameters on the macroscopic nonlinear response in applications using 3D printed nanocomposites.

Multiscale simulation scheme by using a finite-difference derivative framework for lubrication surface

To exactly describe lubrication problems modelling micro-scale influence in rough lubricated contact is unavoidable. In this study a novel computational scheme for lubricated problem is presented based on two-scale homogenization method, which facilitates solving the two-scale problem. Homogenization model of mass fluxes is implemented at the micro-scale domain, and represents the influence of surface topography. A linearization method is developed to derive finite derivatives of mass fluxes at the micro-scale domain defined by scale separation. The key strength of the proposed procedure is the finite difference derivative coupling which represents the lubricated problem inclusive of the effect of surface topography. The effectiveness of the proposed multiscale scheme is validated by comparing with the deterministic method. The numerical results show that increasing topography amplitude can improve the performance of journal bearing in terms of load carrying capacity and friction coefficient.

Microscale domain permeability prediction of fiber reinforcement structures based on the lattice Boltzmann method and machine learning

Microscale domain permeability prediction of fiber reinforcement structures based on the lattice Boltzmann method and machine learning

Observation of Micro-Scale Domain Structure Evolution under Electric Bias in Relaxor-Based PIN-PMN-PT Single Crystals

Relaxor ferroelectrics play a vital role as functional components in electromechanical devices. The observation of micro-scale domain structure evolution under electric bias in relaxor ferroelectrics has posed challenges due to their complex domain morphology characterized by small-sized domains. The present study aims to investigate the dielectric diffusion–relaxation characteristics, domain structure, and domain switching evolution under electric bias in high-performance single crystals of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-33PbTiO3. The findings reveal the presence of strip-like domain patterns that interlock irregular small-sized nanodomains in PIN-PMN-33PT single crystals. Furthermore, the sample undergoes three distinct stages under electric bias, including the nucleation of new domains, the gradual forward expansion of domains, and the lateral expansion of domains. These observations provide valuable insights for understanding and exploring domain engineering techniques in relaxor ferroelectrics.

Sensitivity analysis of WRF-CFD-based downscaling methods for evaluation of urban pedestrian-level wind

Computational fluid dynamics (CFD) techniques are widely adopted for predicting pedestrian-level wind (PLW). However, the lack of on-site measurement data is the primary impediment to establishing a reliable inflow wind profile. We propose a downscaling method that enables accurate modeling of PLW without the need for on-site measurements. The downscaling method involves three stages of Weather Research and Forecasting (WRF)-CFD simulations conducted in Meteodyn software. The WRF model is utilized to generate a time series of mesoscale data of mesoscale cells covering the microscale domain. The microscale CFD model consists of two nested CFD models, a parametric model and a full-information model, to ensure a smooth transition of the downscaled information. The physical-statistics method is employed to couple the mesoscale and microscale wind flow information. The sensitivity of the 6 downscaled schemes with different configurations is evaluated. To eliminate the effects of high-rise buildings, 3 potential mesoscale data heights are examined as inputs for the CFD simulations. The accuracy of the proposed downscaling method is validated using long-term on-site measurement data. We recommend utilizing mesoscale data at a height of 200 m as an input to the CFD model for PLW modeling in complex urban environments.

Effects of cell orientation on drug delivery into biological tissues: A computational study

The development of multiscale method in the heterogeneous multiscale method (HMM) framework requires microscale models to extract the macroscopic information. The microscale models are constrained by a reconstruction operator based on the macroscopic state variables. In this study, two novel reconstruction operators are proposed to overcome the shortcoming of operators used in the literature. An improved multiscale method is proposed in the HMM framework incorporating the new reconstruction operator. The effects of cell orientation on the penetration and distribution of drug in the biological tissues are investigated for the first time. The simulation results reveal that cell orientation is an important factor that can affect drug penetration and distribution in tissues. Furthermore, the local sensitivity analysis is performed, and it shows that the model is most sensitive to the microscale domain size whereas least sensitive to the cell membrane permeability and intracellular diffusivity.

DeepBND: A machine learning approach to enhance multiscale solid mechanics

Effective properties of materials with random heterogeneous structures are typically determined by homogenising the mechanical quantity of interest in a window of observation. The entire problem setting encompasses the solution of a local PDE and some averaging formula for the quantity of interest in such domain. There are relatively standard methods in the literature to completely determine the formulation except for two choices: i) the local domain itself and the ii) boundary conditions. Hence, the modelling errors are governed by the quality of these two choices. The choice i) relates to the degree of representativeness of a microscale sample, i.e., it is essentially a statistical characteristic. Naturally, its reliability is higher as the size of the observation window becomes larger and/or the number of samples increases. On the other hand, excepting few special cases there is no automatic guideline to handle ii). Although it is known that the overall effect of boundary condition becomes less important with the size of the microscale domain, the computational cost to simulate such large problem several times might be prohibitive even for relatively small accuracy requirements. Here we introduce a machine learning procedure to select most suitable boundary conditions for multiscale problems, particularly those arising in solid mechanics. We propose the combination Reduced-Order Models and Deep Neural Networks in an offline phase, whilst the online phase consists in the very same homogenisation procedure plus one (cheap) evaluation of the trained model for boundary conditions. Hence, the method allows an implementation with minimal changes in existing codes and the use of relatively small domains without losing accuracy, which reduces the computational cost by several orders of magnitude. A few test cases accounting for random circular and elliptical inclusions are reported aiming at proving the potentials of the DeepBND method.

Computational homogenization of fully coupled hydro-mechanical analysis of micro-fractured porous media

In this paper, a computational homogenization technique is developed for fluid flow through the deformable micro-fractured porous media. The coupled hydro-mechanical analysis is performed using an efficient multiscale procedure. Micro-fractures are defined within the microscopic domain, which is associated with each macro-scale quadrature point. According to the first-order homogenization approach, proper form of virtual power relations is defined by applying the Hill-Mandel principle of macro-homogeneity to achieve a consistent multiscale formulation. Moreover, the transient behavior of micro-structures is taken into account by employing transient governing equations for the micro-scale problem. In order to transfer the transient effects of micro-structures, an additional domain integral constraint is augmented to the conventional periodic boundary conditions in the micro-scale analysis. The fractures in micro-scale domain are modeled using the X-FEM technique with appropriate enrichment functions for the displacement and pressure fields. In order to study the accuracy of the proposed computational approach, several numerical examples with different boundary conditions and crack configurations, such as mechanical and hydro-mechanical analyzes are solved and the results are compared with those obtained from the direct numerical simulation. It has been shown that the proposed computational multiscale algorithm on the basis of domain integral constraint, which is augmented to periodic boundary conditions can be used efficiently to achieve accurate results in comparison with the direct numerical simulations, while the linear boundary conditions fails to produce acceptable results in some complex cases.

A multiscale study on the effect of compression on lithium-ion battery separators

Separators play a vital role within Li-ion batteries. Separators allow rapid Li-ion transport while isolating the cathode and anode to prevent electrical short circuits. Herein, the effects of compression on the mechanical and transport properties of the separator were investigated using a multiscale approach. The microscale domain of the separator was stochastically reconstructed based on the scanning electron microscopy images of a Celgard 2400 membrane. The reconstructed model was then imported to perform explicit dynamic simulations to investigate the mechanical behavior of the separator at different compression ratios. A pore-scale model was employed to calculate the effective transport properties of the deformed models. This was then used in a 3D macroscopic multiphysics model to evaluate the impact of compression on the battery performance. The simulation results revealed the effect of compression on the separator's mechanical properties and battery performance from the microscale to macroscale level. The compression of the separator was found to adversely influence the charging performance of the Li-ion battery. When the compression ratio reaches 40 %, the charging performance of the battery decreased significantly. The present study demonstrates a multiscale approach for investigating the effect of compression on Li-ion battery separators. This is a powerful method for optimizing separators in the future.

A Thermo-Electrochemical Model for Simulating Internal Short Circuits in a Li-Ion Battery Depending on Lithium Dendrites

An internal short circuit (ISC) is known to be the main cause of fatal accidents in Li-ion batteries (LIBs). If two electrodes come into contact with each other because of any event, the inner temperature of LIBs increases rapidly within the very short time. If the temperature can increase over the threshold temperature, fire or explosion accidents can occur in the LIB, which is called thermal runaway (TR). Because the fire in the LIBs is not easily extinguished and can cause significant damage of life and property, we should understand the fundamental electrochemical and thermal behavior of ISC-TR in order to prevent or delay these severe accidents. For this purpose, there have been tremendous attempts to analyze different ISC cases with a variety of LIB cells experimentally through penetrating nails, pucks, shape memory alloys, etc. However, experimental methods have limitations in measuring internal temperatures and estimating current density and lithium-ion concentration within LIB cells. Also it is still challenging to control the types and locations of ISCs practically. To compensate these experimental limitations, many simulation studies have also been conducted. However, many simulation research have been considering a two-dimensional-based microscale domain, which may have relatively inaccurate simulation results or cannot consider three-dimensional placement, or a three-dimensional-based large domain, which calculates ISC only in mm units or more. In this work, we developed an advanced thermo-electrical model to simulate the responses of LIB cells depending on the sizes, numbers, and locations of lithium dendrites or impurities. This model can calculate the current density, which causes joule heat flux, and simulate heat transfer. Thus, this model can provide us with information on what kinds or how many of lithium dendrites will lead to thermal runaway. Also, it is possible to analyze the thermal behavior of LIBs according to the various physical and temperature conditions of the lithium dendrites.

Determination of detonation characteristics by laser-induced plasma spectra and micro-explosion dynamics.

Determination of macroscale detonation parameters of energetic materials (EMs) in a safe and rapid way is highly desirable. However, traditional experimental methods suffer from tedious operation, safety hazards and high cost. Herein, we present a micro-scale approach for high-precision diagnosis of explosion parameters based on radiation spectra and dynamic analysis during the interaction between laser and EMs. The intrinsic natures of micro-explosion dynamics covering nanosecond to millisecond and chemical reactions in laser-induced plasma are revealed, which reveal a tight correlation between micro-detonation and macroscopic detonation based on laser-induced plasma spectra and dynamics combined with statistic ways. As hundreds to thousands of laser pulses ablate on seven typical tetrazole-based high-nitrogen compounds and ten single-compound explosives, macroscale detonation performance can be well estimated with a high-speed and high-accuracy way. Thereby, the detonation pressure and enthalpies of formation can be quantitatively determined by the laser ablation processes for the first time to our knowledge. These results enable us to diagnose the performance of EMs in macroscale domain from microscale domain with small-dose, low-cost and multiple parameters.

Evaluating Terrain as a Turbulence Generation Method

When driving microscale large-eddy simulations with mesoscale model solutions, turbulence will take space to develop, known as fetch, on the microscale domain. To reduce fetch, it is common to add perturbations near the boundaries to speed up turbulence development. However, when simulating domains over complex terrain, it is possible that the terrain itself can quickly generate turbulence within the boundary layer. It is shown here that rugged terrain is able to generate turbulence without the assistance of a perturbation strategy; however, the levels of turbulence generated are improved when adding perturbations at the inlet. Flow over smoothed, but not flat, terrain fails to generate adequate turbulence throughout the boundary layer in all tests conducted herein. Sensitivities to the strength of the mean wind speed and boundary layer height are investigated and show that higher wind speeds produce turbulence over terrain features that slower wind speeds do not. Further, by increasing the height of the capping inversion, the effectiveness of topography alone to generate turbulence throughout the depth of the boundary is diminished. In all cases, the inclusion of a perturbation strategy improved simulation performance with respect to turbulence development.

Local Shock Properties Measurement Using Time-Resolved Raman Spectroscopy

In this article, the dynamic response of a heterogeneous microstructure of polymer bonded composite was analyzed to a short duration shock pulse. The composite microstructure studied is a polymerbonded sugar (PBS) with single-crystal sucrose embedded inside the polydimethylsiloxane binder. The shock pulse was created by the impact of the aluminum disk at high speeds using a laser-based projectile launch system. The mechanical response on the microscale domain was measured using ultrafast time-resolved Raman spectroscopy. The in-situ analysis of the change in Raman spectra from PBS during shock compression was captured in the time domain using a streak camera. The results show a steeply rising shock front after the impact where the shock pressure rise time was estimated from the time-resolved Raman spectra. The viscoplastic behavior in the local microscale domain was characterized by quantifying effective shock viscosity measured in the vicinity of the crystal-binder interface.

Flow simulation considering adsorption boundary layer based on digital rock and finite element method

Due to the low permeability of tight reservoirs, throats play a significant role in controlling fluid flow. Although many studies have been conducted to investigate fluid flow in throats in the microscale domain, comparatively fewer works have been devoted to study the effect of adsorption boundary layer (ABL) in throats based on the digital rock method. By considering an ABL, we investigate its effects on fluid flow. We build digital rock model based on computed tomography technology. Then, microscopic pore structures are extracted with watershed segmentation and pore geometries are meshed through Delaunay triangulation approach. Finally, using the meshed digital simulation model and finite element method, we investigate the effects of viscosity and thickness of ABL on microscale flow. Our results demonstrate that viscosity and thickness of ABL are major factors that significantly hinder fluid flow in throats.

Effect of nanoparticle size, magnetic intensity, and tumor distance on the distribution of the magnetic nanoparticles in a heterogeneous tumor microenvironment

Tumor microenvironment involves physical parameters that impede the transport of therapeutic agents and create an abnormal extracellular matrix (ECM) at the region with an elevated interstitial fluid pressure (IFP). This is the main reason that the chemotherapy drug agents could not fully penetrate the solid tumors. To overcome this resistance, drug-coated magnetic nanoparticle (MNP) had been proposed as a therapeutic agent affected by an external magnetic force. Three variables as the MNP’s size, magnetic field intensity, and the tumor-magnet distance are proposed to see their effects on the distribution of the drugs to the tumor tissue. A micro-scale computational domain is assumed as the normal and tumor tissues with the discrete microvessels. The results determine a moderate effect on the drug penetration to the tumor tissue by the magnetic field and size variations. This moderate effect is due to the consequent of the high density of ECM and high amount of IFP leading only a 36% increase in the drug penetration to the tumor tissue with a 10 nm MNP and under the 2.5 T magnetic field intensity. While, a slight percent increase about 11% is obtained from 0.6 T to 2.5 T. We conclude that the dense ECM, high IFP, and the existence of microvessels have negative effects on the systemic delivery of the MNP distribution leading to a low impact of Magnetic field on the MNPs’ penetration. Therefore, The systemic drug delivery of MNP under the magnetic field has a lower effect in comparison to local drug delivery of MNPs to the homogenous solid tumors. However, the convection rate in the tumor tissue shows a percent increase in the rate of drug distribution to the tumor tissue. The size and the magnetic field are the two most promised parameters for improving the convection term in the tumor region. the finding of this study can help to better understanding the magnetic effects on the distribution rate of MNP to the solid tumor and to overcome the tumor microenvironmet barriers for better drug efficacy.

Homogenization approach for liquid flow within shale system considering slip effect

In the last years, the huge success of shale gas and oil exploitation in North America and enhanced oil recovery by injecting carbon dioxide have attracted more attentions in petroleum industry. The reasonable scheme for shale oil production is a key step for sustainable and high-efficiency products of shale resources, which is dependent on the basic law of liquid flow.In this paper, a multiscale model is established based on homogenization theory to investigate the law of liquid flow within shale system. Considering the results of molecular dynamics simulation, the Navier-Stokes equation coupled with slip boundary is used to describe the liquid flow within microscale domain and the slip-corrected Darcy-like transport model in which clear physical meaning can be shown for every parameter can be derived for macroscale domain. In order to validate derived model, three cases including water and oil flow within simple nanopores are implemented and the results show that homogenization models match well with the results of molecular dynamics simulation for water flow with different contact angle and oil flow within inorganic pore. However, high-order slip-corrected model will deviate from the molecular dynamics simulation for oil flow within simple organic pore when pore size is smaller than 5.24 nm. Then the fractal porous medias are reconstructed based on Monte Carlo simulation and the several critical parameters are discussed. Finally, the results of homogenization model are applied in reservoir scale model to investigate shale oil production performance for economic evaluation and production optimization.

Evaluation of the Impact of Horizontal Grid Spacing in Terra Incognita on Coupled Mesoscale–Microscale Simulations Using the WRF Framework

Abstract Coupled mesoscale–microscale simulations are required to provide time-varying weather-dependent inflow and forcing for large-eddy simulations under general flow conditions. Such coupling necessarily spans a wide range of spatial scales (i.e., ~10 m to ~10 km). Herein, we use simulations that involve multiple nested domains with horizontal grid spacings in the terra incognita (i.e., km) that may affect simulated conditions in both the outer and inner domains. We examine the impact on simulated wind speed and turbulence associated with forcing provided by a terrain with grid spacing in the terra incognita. We perform a suite of simulations that use combinations of varying horizontal grid spacings and turbulence parameterization/modeling using the Weather Research and Forecasting (WRF) Model using a combination of planetary boundary layer (PBL) and large-eddy simulation subgrid-scale (LES-SGS) models. The results are analyzed in terms of spectral energy, turbulence kinetic energy, and proper orthogonal decomposition (POD) energy. The results show that the output from the microscale domain depends on the type of turbulence model (e.g., PBL or LES-SGS model) used for a given horizontal grid spacing but is independent of the horizontal grid spacing and turbulence modeling of the parent domain. Simulation using a single domain produced less POD energy in the first few modes compared to a coupled simulation (one-way nesting) for similar horizontal grid spacing, which highlights that coupled simulations are required to accurately pass the mesoscale features into the microscale domain.

Transparent Bendable Secondary Zinc-Air Batteries by Controlled Void Ionic Separators

First ever transparent bendable secondary zinc-air batteries were fabricated. Transparent stainless-steel mesh was utilized as the current collector for the electrodes due to its reliable mechanical stability and electrical conductivity. After which separate methods were used to apply the active redox species. For the preparation of the anode, zinc was loaded by an electroplating process to the mesh. For the cathode, catalyst ink solution was spray coated with an airbrush for desired dimensions. An alkaline gel electrolyte layer was used for the electrolyte. Microscale domain control of the materials becomes a crucial factor for fabricating transparent batteries. As for the presented cell, anionic exchange polymer layer has been uniquely incorporated on to the cathode mesh as the separator which becomes a key procedure in the fabrication process for obtaining the desired optical properties of the battery. The ionic resin is applied in a fashion where controlled voids exist between the openings of the grid which facilitates light passage while guaranteeing electrical insulation between the electrodes. Further analysis correlates the electrode dimensions to the transparency of the system. Recorded average light transmittance is 48.8% in the visible light region and exhibited a maximum power density of 9.77 mW/cm2. The produced battery shows both transparent and flexible properties while maintaining a stable discharge/charge operation.

Combining radial point interpolation meshless method with a new homogenization technique for trabecular bone multiscale structural analyses.

Bone tissue is a dynamic tissue, possessing different functional requirements at different scales. This layered organization indicates the existence of a hierarchical structure, which can be characterized to distinguish macro-scale from micro-scale levels. Structurally, both scales can be linked by the use of classic multiscale homogenization techniques. Since in bone tissue each micro-scale domain is distinct form its neighbour, applying a classic multiscale homogenization technique to a complete bone structure could represent an inadmissible computational cost. Thus, this work proposes a homogenization methodology that is computationally efficient, presenting a reduced computational cost, and is capable to define the homogenized microscale mechanical properties of the trabecular bone highly heterogeneous medium. The methodology uses the fabric tensor concept in order to define the material principal directions. Then, using an anisotropic phenomenological law for bone tissue correlating the local apparent density with directional elasticity moduli, the anisotropic homogenized material properties of the micro-scale patch are fully defined. To validate the developed methodology, several numerical tests were performed, measuring the sensitivity of the technique to changes in the micro-patch size and preferential orientation. The results show that the developed technique is robust and capable to provide a consistent material homogenization. Additionally, the technique was combined with two discrete numerical techniques: the finite element method and radial point interpolation meshless method. Structural analyses were performed using real trabecular patches, showing that the proposed methodology is capable to accurately predict the micro-scale patch mechanical behavior in a fraction of the time required by classic homogenization techniques.