Microscale Effects Research Articles

Synergetic strengthening effects on copper matrix induced by Al2O3 particle revealed from micro-scale mechanical deformation and microstructure evolutions

Abstract The micro-scale effect of Al 2 O 3 particle on the deformation behaviors of the copper matrix was investigated using nanoindentation. Moderate strengthening effects were produced by the Al 2 O 3 as indicated from the mechanical deformation evolutions. Specifically, the displacement recovery ratio and elastic work ratio is 6% and 9% higher for the Cu-5 wt% Al 2 O 3 (C5A) composite material compared with that of the pure copper (PC) material, respectively. While for the indentation hardness and indentation modulus, the increment is 36% and 75%, respectively. Notably, the moderate strengthening effects were quantitatively illuminated from the power law index m for the C5A indent (1.2) and PC indent (1.1–1.3). In addition, synergetic strengthening effects were proposed from the microstructure evolutions in the C5A composite material. Specifically, the increment in yield strength deduced from the grain refinement is 120 MPa, which is 67% higher than that of the Al 2 O 3 particle dispersion strengthening. The synergetic strengthening effects revealed from the microstructure evolutions are expected to provide new strengthening approaches for the ceramic particle reinforced metal matrix composite materials.

Thermal Comfort and Longwave Radiation over Time in Urban Residential Complexes

Large cities with a high concentration of high-rise buildings are shaded by urban canyon. This brings a cooling effect compared to the space exposed to the sun, but is not always cool due to the longwave radiation emitted from buildings and the built environment. We tested the micro-scale effects of major external spatial factors, trees, and buildings, under shade on longwave radiation shifts to understand the effects of large shaded areas in megacities. Incoming and outgoing longwave radiations (ILR and OLR, respectively) were found to decrease the overall observation by time zone. Longwave radiation on a micro-scale was also inversely proportional to the tree volume. From mean radiant temperature (MRT) analysis, we found that about a 10% decrease in MRT could be achieved by increasing tree volume by around 50%. Larger tree volumes corresponded to greater blocking effects on longwave radiation. Considering the tree volume, a multilayer urban tree canopy composition can more favorably improve the thermal environment and energy sustainability of a city compared to a single-layer canopy. Larger trees planted with harmonious shrubs are the most effective in reducing longwave radiation.

Microscale effects of Bingham-plastic liquid behavior considering electroviscous effects in nano- or microsized circular tubes

Although microscale phenomena are ubiquitous in fluid flow through nano- or microsized channels and pores, the mechanisms remain unclear. To clarify these mechanisms, we investigate herein Bingham-plastic liquids with electroviscous effects (EVEs) in nano- and microsized circular tubes. The constitutive equation and electroviscous forces are introduced into the governing equations, and approximate analytical solutions are obtained. Velocity reduction results from the combined effects of the Bingham characteristics and EVEs. The Bingham behavior reduces the strength of the EVE electric field, and EVEs increase the width of the flow core. The dimensionless average velocity decreases as the tube radius decreases and goes to zero upon approaching the lower limit of the movable fluid radius (Rm). As the pressure gradient decreases, the average velocity first decreases linearly, then decreases nonlinearly in a concave shape, and finally approaches zero as the pressure reaches the threshold pressure gradient (TPG). The Bingham plastic behavior causes both the Rm and the nonlinear flow with TPG, and Rm is still caused by the van der Waals forces under liquid compressibility more obviously. The EVE parameters only affect the degree of nonlinearity when the liquid exhibits Bingham-plastic behavior. These results are consistent with experimentally observed de-ionized water flowing in microscale silica tubes. We infer that the Newtonian fluid displays the Bingham-plastic behavior in nano- or microsized channels in what we call “microscale effects.” These results elucidate the mechanism that leads to nonlinear or low-speed non-Darcy flow in nano- or microsized channels and pores from the liquid characteristic and liquid-solid interaction.

Fatigue of fibre-reinforced plastics due to cryogenic thermal cycling

Due to the different thermal expansion of the constituent materials, cyclic thermal loading of fibre reinforced plastics induces alternating stresses in the material at two scales: (1) at the microscale (level of fibre–matrix-interaction) and (2) at the macroscale (level of the multidirectional laminate). Especially the effect of the thermal-induced stresses at the microscale is not comprehensively investigated yet. In the present paper, the effects of both scales are analysed. For the investigation of the microscale effect, unidirectional laminates are thermally cycled between 293 K and 90 K up to 1000 times. Afterwards, by mechanical tests at room temperature, the elasticity and strength properties in the different material directions are determined as function of the number of thermal cycles. Additionally, thermally cycled specimens are microscopically investigated in order to observe the matrix crack forming process at thermal fatigue loading. Contrary to the expectations, no significant matrix cracking and therefore no significant reduction of the elasticity and strength properties due to the thermal cycling are observed. In order to analyse the effect of the superposition of the thermal-induced stresses on micro- and macroscale, cross-ply laminates are investigated in the same manner. In these laminates matrix cracks are detected after 1000 cycles, which, however, do not reduce the stiffness and strength of the cross-ply laminates.

Analysis of Bifurcation and Chaos of the Size-dependent Micro–plate Considering Damage

Abstract In this research, nonlinear dynamics and characteristics of a micro–plate system under electrostatic forces on both sides are studied. A novel model, which takes micro-scale effect and damage effect into account, is established on the basis of the Talreja’s tensor valued internal state damage model and modified couple stress theory. According to Hamilton principle, the dynamic governing equations of the size-dependent micro–plate are derived by variational method and solved via Galerkin method and the fourth order Runge-Kutta method. The effects of damage variable and material length scale parameter on bifurcation and chaos of the micro–plate system are presented with numerical simulations using the bifurcation diagram, Poincare map. Results provide a theoretical basis for the design of dynamic stability of electrically actuated micro- structures.

Microscale effects of oxygen and light on bacterial sulfate reduction in organic-rich lacustrine sediments

Biogeochemical cycling involves the exchange of electrons between chemical species through redox reactions. Microorganisms can utilize energy released by redox reactions for their metabolism following a thermodynamic sequence. Among these reactions, the dissimilatory reduction of sulfate (SO42−) to produce hydrogen sulfide (H2S) is one of the most important microbially-mediated pathways. The use of microelectrodes at the water-sediment interface provided a better understanding of sulfate reduction processes in the suboxic and anoxic zones. The goal of this study was to assess the microzonation of H2S and O2 under different conditions of light and oxygen in the water column. For this purpose, organic-rich lacustrine sediments from Pétrola Lake (SE Spain) were used. Sediment incubations were performed in mesocosm devices. The highest production of H2S (up to 0.36 nmol/cm-3s-1) was observed under anoxic and dark conditions. Production under those conditions was several orders of magnitude higher than those measured when oxygen was present in the water column. Furthermore, the absence of O2 in the water column significantly altered the microzonation of H2S in depth. The absence of light seems not to affect the dynamics of O2 and H2S in depth. The study contributes to our understanding of microzonation in organic-rich sediments.

Meso and micro-scale effects of loading and air scouring on nitrifying bio-cord biofilm

The municipal wastewater treatment industry is currently facing the challenges of increased loading, restricted land availability and stringent discharge regulations.

Experimental investigation and probabilistic models for residual mechanical properties of GFRP pultruded profiles exposed to elevated temperatures

Here, we investigate the influence of elevated temperatures with negligible ambient oxygen on mechanical properties of various embedded glass fiber reinforced polymer (GFRP) profiles, as well as the application of a predictive Bayesian model for predicting these properties. Both the flexural and compressive properties of FRP profiles were investigated through the tests of I-shaped and box-shaped profiles. To determine the impact of low and high elevated temperature, the profiles were exposed to a wide range of temperatures (i.e., 25–550 °C); effects of the exposure time were also investigated. Experiments showed that specimens exposed to higher elevated temperatures for longer time periods lose more of their mechanical properties. We used profiles in a simulated embedded environment to prevent combustion and charring, thus reducing fire vulnerability of the GFRP material at high elevated temperatures. We found that elevated temperature for 15 min produces slight strength deterioration in the embedded FRP profiles. Also, exposure to a high elevated temperature for 45 min reduced the maximum loads by up to 30%. Next, we performed a filled emission scanning electronic microscopy (FE-SEM) study before and after the mechanical tests to examine both the control specimens and conditioned specimens that were exposed to elevated temperatures. This approach allowed us to investigate the microscale effect of the elevated temperatures as well as the failure mode mechanisms of FRP profiles under flexure and compression. The micrographs revealed that a glut of small cracks formed in FRP profiles exposed to high elevated temperatures, leading to sole resin failure in the mechanical tests. Finally, Bayesian linear regression was applied to the laboratory test results, which led to a predictive model for mechanical properties of FRP profiles exposed to elevated temperatures.

Finite Element Simulation Analysis of Diamond Bi-directional Coining Neck Hole Forming Process

A new method of Necking Hole Forming (NHF) is proposed in this paper, which coining metal sheet in two directions by micro-scale effects of the blunt circle at the edge of the diamond. It has an important application value in the industry. For the complexity of NHF forming process, start with technological parameters of the diamond indenter and coining model, deform-3d is used to analyze the plastic flow law inside the material and the pore formation. NHF process is studied from three aspects which are material flow, stress distribution, and load curve. The results show that uses of a small cone angle indenter are beneficial to the formation of NHF and good surface quality could be obtained; The upper and lower indenter cone angle is different, there is a sudden change in the axial force of the copper sheet when the hole is formed, which is used as a basis for monitoring micro-pore formed.

Pore-scale investigations on the effects of ice formation/melting on methane hydrate dissociation using depressurization

Ice phase affects the methane hydrate dissociation in the porous medium channels. Thus, the investigations on the roles of ice formation and melting in hydrate dissociation around the freezing point are necessary. A model that considers the interphase heat transfer and microscale effects was developed in our previous work. In this study, we extended the work to investigate the effects of ice formation/melting on methane hydrate dissociation in micro porous media channels. Our investigations showed that water temperature, distribution of water and methane, pressure, cumulative methane generation and residual methane hydrate and heat changes in the system are affected seriously by the ice phase. The formation of ice favors the hydrate dissociation for a while, and then inhibits the dissociation of methane hydrate due to the thickening ice. The pressure variations are indications of the possible reformation of methane hydrate and deformation of porous medium channels. The change in heat as one of the key factors for hydrate decomposition shows a more complex changing peculiarity as a result of the ice formation/melting.

Pore-scale lattice Boltzmann simulation of two-component shale gas flow

Shale gas is usually a multi-component gas mixture dominated by CH4. Moreover, CO2 sequestration in shale reservoirs and CO2-enhanced shale-gas recovery also result in multi-component gas flow in shale reservoirs. Therefore, compared with single-component gas flow, multi-component gas flow is more often encountered in practice. Furthermore, shale rock contains a lot of nano-pores in which the micro-scale effect makes the multi-component gas flow become more complex. In this paper, the lattice Boltzmann method is employed to simulate the two-component shale gas flow in a two-dimensional micropore under different conditions. The pore-scale transport mechanism of the two-component shale gas is investigated and the gas separation phenomenon for the shale gas flow is discussed in detail. It is found that the molar fraction of each species in shale gas does not distribute uniformly along the micropore and the gas separation phenomenon exists in the two-component pressure-driven shale gas flow. The molar fraction distribution of each species along the micropore is affected by the Knudsen number, pressure ratio, shale gas composition and molar fraction of each species for the pressure-driven gas flows. In particular, we find that the molar fraction distribution and pressure distribution for two-component shale gas along the micropore are related to the pressure ratio and are unrelated to the pressure gradient. With increasing the molar fraction of CH4 in shale gas, both the gas-mixture velocity at the outlet and the slip velocity along the micropore become larger. Both the Knudsen number and pressure ratio affect the molar fraction distribution of CO2 for the CH4CO2 mixture in the micropore during CO2 injection, while the influence of them works oppositely. Furthermore, the concentration diffusion without the external force is affected by the micropore width and the concentration difference between the gas mixtures.

On the dynamics of imperfect shear deformable microplates

This paper investigates the nonlinear forced dynamical behaviour of a geometrically imperfect viscoelastic shear-deformable microplate. The third-order shear deformation plate theory and the Kelvin–Voigt viscoelastic model are utilised in the framework of the modified version of the couple-stress theory to develop a model for the microsystem. The developed model is in the form of partial differential equations (PDEs) and accounts for geometric nonlinearities, damping nonlinearities, micro-scale size effects, and initial imperfection. Five coupled PDEs are derived for the five independent displacements and rotations. These PDEs are truncated to a set of nonlinearly coupled ordinary differential equations via application of a two-dimensional modal decomposition based on the Galerkin technique. The final set of equations consists of quadratic and cubic nonlinear terms for both damping and stiffness. An efficient numerical algorithm based on a continuation scheme is utilised to analyse the nonlinear forced vibration characteristics of such complicated system. The effects imperfection amplitude, damping nonlinearities, and micro-scale size on forced resonant vibration response are highlighted.

Research on Numerical Simulation of Gas Flow in Shale Matrix Micro Pore

In view of Longmaxi shale core in Sichuan basin, two-dimensional images of shale core were given by using scanning electron microscopy (SEM), and processed by ImageJ software to reconstruct the 3D shale matrix digital core, the digital core can reflect the nano pore structure more accurately. LBM model of gas flow in shale porous medium is established based on lattice Boltzmann method. The corresponding boundary conditions were established based on slip phenomenon for shale gas in porous medium micro flow, which can simulate gas flow in the micro pore in shale more realistic. The numerical results show that the microscale effect becomes obvious with the increase of Knudsen number, and the more obvious the non-Darcy phenomenon of gas flow in the shale matrix. The research results of this paper provide a theoretical basis for shale matrix permeability calculation, shale gas well productivity evaluation and development scheme design.

Experimental Study on Propane/Air Flame Propagation Characteristics in a Disc-Like Gap Chamber

ABSTRACTA disc-like gap chamber was developed to investigate the microscale effects on flame propagation characteristics in closed chamber, which is very important to understand the combustion process in micro internal combustion engines. Under initially normal pressure and temperature, the morphology and evolution of outwardly propagating flame, the flammable limit, flame speed and flame instability of propane-air flames influenced by gap width and equivalence ratio were experimentally studied. The results show that, as the gap width nearly equals to the quenching distance, the sustained propagation was possible only with rich flames. The smooth flames and wrinkled flames were observed. It clearly shows that the flame wrinkles developed gradually instead of instantaneously. The flame speed was slower in the 2.0 mm gap chamber than in a conventional combustion bomb, and the flame speed decreased with the increase of flame radius. As a result, the flame acceleration was not observed in present experiments. With the smaller gap width, the wrinkled flame occurred early, and the flame speed was slower. Due to the geometry of disc-like gap chamber, simple theoretical analysis indicates that the heat loss and elevated pressure play important roles in reducing flame speed.

Demystifying the Flow: Biocatalytic Reaction Intensification in Microstructured Enzyme Reactors.

Continuous (flow) reactors have drawn a wave of renewed interest in biocatalysis. Many studies find that the flow reactor offers enhanced conversion efficiency. What the reported reaction intensification actually consists in, however, often remains obscure. Here, a canonical microreactor design for heterogeneously catalyzed continuous biotransformations, featuring flow microchannels that contain the enzyme immobilized on their wall surface are examined. Glycosylations by sucrose phosphorylase are used to assess the potential for reaction intensification due to microscale effects. Key variables are identified, and their corresponding relationship equations, to describe, and optimize, the interplay between reaction characteristics, microchannel geometry and reactor operation. The maximum space-time-yield (STY_max) scales directly with the enzyme activity immobilized on the available wall surface. Timescale analysis, comparing the characteristic times of reaction (τreac ) and diffusion (τdiff ) to the mean residence time (τres ), reveals operational conditions for optimum reactor output. Theoretical insight into determinants of microreactor performance is applied to biocatalytic syntheses of α-d-glucose 1-phosphate and α-glucosyl glycerol. Process boundaries for enzyme showing, respectively, high (80 U mg-1 ) and low (4 U mg-1 ) specific activities are thus established and options for process design revealed. Opportunities, and limitations, of the application of principles of microscale flow chemistry to biocatalytic transformations are made evident.

Free and forced vibration analysis of rectangular/circular/annular plates made of carbon fiber-carbon nanotube-polymer hybrid composites

Abstract A multiscale finite element method is adopted in this paper to study the vibrational characteristics of polymer matrix composite plates reinforced with the combination of carbon fibers (CFs) and carbon nanotubes (CNTs). The effects of nanoscale and microscale are coupled through a two-step procedure. In the first step, random dispersion of CNTs into the polymer matrix is modelled using a three-phase representative volume element (RVE). In the selected RVE, the influence of the interphase formed because of non-bonded interactions between the polymer matrix and CNTs is taken into account. In the second step, the distribution of CFs into the composite is modelled, and the elastic properties of CF-CNT-polymer matrix hybrid composite are calculated for various values of volume fractions of reinforcement phases. Then, the free and forced vibration behaviors of composite plates are analyzed. It is considered that the plates have rectangular, circular, and annular shapes and are under clamped/simply supported edge conditions. The effects of CNT/CF reinforcement on the elastic modulus and density of composite and on the free/forced vibration response of the considered structures are investigated. It is shown that the vibrational behavior of plates is significantly affected by the hybrid reinforcement with CNT and CF.

Simulation tool for prediction of cutting forces and surface quality of micro-milling processes

The improvement of micro-milling processes implies the application of advanced analysis and modeling techniques to derive a deeper process understanding. Because of micro-scale effects, monitoring, and measurement systems applied in conventional milling are in most cases not suitable for identifying optimal cutting conditions. Therefore, analytical and mechanical models have been developed in recent years to account for impact factors dominating the micro-milling errors. Within the research presented in this publication, geometric, kinematic, and dynamic models have been adjusted and dimensioned according to the dominating impact factors in micro-milling and have been consolidated to enable for a time-domain simulation. The effect of element size of discretized workpiece and tool as well as the time step size on cutting forces has been evaluated. The accuracy of predicting cutting forces has been investigated and a good agreement of measured and simulated cutting forces has been found. Finally, a mold for a micro-fluidic device has been machined virtually and experimentally to evaluate the accuracy of the integrated models in predicting the final quality of a micro-milled part in terms of surface quality parameters.

Effect of Mesoscale Land Use Change on Characteristics of Convective Boundary Layer: Semi-Idealized Large Eddy Simulations over Northwest China

Although large-scale topography and land use have been properly considered in weather and climate models, the effect of mesoscale and microscale heterogeneous land use on convective boundary layer (CBL) has not been fully understood yet. In this study, the influence of semi-idealized strip-like patches of oases and deserts, which resemble irrigated land use in Northwest China, on the CBL characteristics, is investigated based on the Weather Research and Forecasting (WRF)-large eddy simulation (LES) driven by observed land surface data. The influences of soil water content in oases on aloft CBL flow structure, stability, turbulent kinetic energy (TKE), and vertical fluxes are carefully examined through a group of sensitivity experiments. The results show that secondary circulation (SC)/turbulent organized structures (TOS) is the strongest/weakest when soil water content in oases is close to saturation (e.g., when the oases are irrigated). With the decrease of soil water content in oases (i.e., after irrigation), SC (TOS) becomes weak (strong) in the lower and middle CBL, the flux induced by SC and TOS becomes small (large), which has a dramatic impact on point measurement of eddy covariance (EC) fluxes. The flux induced by SC and TOS has little influence on EC sensible heat flux, but great influence on EC latent heat flux. Under this circumstance, the area averaged heat flux cannot be represented by point measurement of flux by the EC method, especially just after irrigation in oases. Comparison of imbalance ratio (i.e., contribution of SC and TOS to the total flux) reveals that increased soil moisture in oases leads to a larger imbalance ratio as well as enhanced surface heterogeneity. Moreover, we found that the soil layer configuration at different depths has a negligible impact on the CBL flux properties.

Considering Realistic Microstructure Heterogeneity: Variational Multiscale Modeling of Li-Ion Batteries

The simulation of battery systems needs to consider structural heterogeneity in battery electrodes as the electrodes are highly irregular in shape and size while containing pores or even cracks at different length scales, which may result in non-uniform transport and kinetics throughout the electrodes. A more realistic battery model necessitates considering realistic microstructure heterogeneity as well as incorporating ongoing microscale phenomena (e.g., the predictability of diffusion, interfacial side reactions, and stress evolution) into numerical problems governing macroscale behaviors. However, developing such model with detailed 3D microstructure can be very computationally expensive for direct simulations, as shown in Figure 1. Here, we propose to reduce the computational cost by developing a more realistic battery model via the variational multiscale method (VMM). The VMM couples micro- and macro- scales by decomposing the problem into micro- and macro- scale problem. In detail, we apply the VMM to decompose the response (e.g., ) into coarse-scale (e.g., 1D macro-scale) and fine-scale (e.g., 3D micro-scale), as shown in Figure 1. The associated governing PDEs will accordingly be decomposed into coarse-scale components and fine-scale components. Without introducing the assumption of scale separation, one of the key features of VMM lies in that the relevant governing PDEs will be decomposed into coarse-scale and fine-scale components. Therefore, two sets of solution will be obtained on different domains, i.e., is the macro solution at, and is the micro solution at. The developed model aims at obtaining accurate micro-solution at micro-scale in a subdomain where it is known a priori that important physicochemical phenomena are likely to occur. The effect of micro-scale is then considered in the solution of the problem. Due to consideration of integrals or the weak formulation as distribution (i.e., average of functions over certain areas of the computational domain), we can perform integration operation on the function that represents the solution to the problem, regardless of existence of discontinuity points in the domain. Thus, one of the main advantageous of developed model is that it resolves the heterogeneities of micro-scale without considering the minor details (such as discontinuity points) but rather our focus in invested in the distribution of the function in the a priori areas of the subdomain, which reduces the computational costs of the numerical analysis. This is of significant importance, especially for cases that the effect of ongoing micro-scale phenomena is more significant than the minor details of the micro-scale. Figure 1

Microscale effects on methane hydrate dissociation at low temperature in the micro porous media channels by depressurization

As for the dissociation of methane hydrate accompanied by multiphase multicomponent flow through micro porous media channels, it is necessary to investigate the microscale effects on the multiphase flow behavior as well as the mass and heat transfer between phases. Meanwhile, the interaction between hydrate dissociation or reformation and ice formation or melting is one of the most important factors. In this paper, with the consideration of ice formation/melting and heat transfer between phases, the momentum and energy equations for all phases and a comprehensive Users’ Defined Subroutine (UDS) are solved in a proposed numerical model to investigate methane hydrate dissociation. The reliability of current model has been proved by comparing with the experiment data and previous simulation results in a good agreement, and then the model was used to study the methane hydrate dissociation at low temperature in the micro porous media channels. The microscale effects on methane hydrate dissociation was studied in two cases (with/without microscale effects), and our results showed that water temperature, volume fraction of phases, ice distribution, hydrate dissociation rate, methane velocity, mass transfer rate between water and ice and saturation of phases are affected seriously by the microscale effects. Especially the water temperature, which is one of the critical factors for hydrate dissociation, shows an unstable change when the microscale effects is ignored.