Anisotropic Aspect Research Articles

Heat transfer mechanism and thermal conductivity prediction in short carbon fiber reinforced polymer composites

Carbon fiber is commonly used as a heat dissipation filler for composite materials in aerospace and electrical systems. Based on representative volume element (RVE) finite element simulation and mathematical analysis, the anisotropic thermal conductivity of short carbon fiber/polymer (SCF/polymer) composites under non-uniform factors was predicted and analyzed. A joint analysis method was proposed for uniform unit cell (UUC) model considering uniform factors and correction unit cell (CUC) model considering non-uniform factors. This article establishes a UUC model for SCF/polymer composites and investigates the effects of factors such as the thermal conductivity of the polymer matrix, the anisotropic thermal conductivity, aspect ratio, and deflection angle of SCF, and interfacial thermal resistance on the anisotropic thermal conductivity of the composite material. In order to study the influence of non-uniform factors, a CUC model of SCF/polymer composite materials was established, and the effects of position offset, angle deviation, and distribution ratio of SCF in different directions on the anisotropic thermal conductivity of composite materials were discussed. The results of the above non-uniform factors were analyzed, and the range of correction factors for three non-uniform factors was obtained. The accuracy of the joint analysis method of UUC and CUC in predicting the anisotropic thermal conductivity of SCF/polymer composites was verified by comparing experimental results.

Modeling of Plasma Nitriding of Austenitic Stainless Steel through a Mask

In this work, 2D simulations of stainless steel nitriding through a mask were performed with two configurations: with and without lateral adsorption under the mask, depending on the strength of the mask adhesion. The stress-induced diffusion and trapping–detrapping process are included as the main mechanisms of nitrogen mass transport. The main focus is on the analysis of the swelling process, which affects the expansion of the material. The surface concentration profiles and topographical profiles along the surface are calculated and compared with experimentally registered ones taken from the literature, and they show a good agreement. This allows for estimation of the values of model parameters. Because nitriding processes takes place in vertical and horizontal directions, the anisotropic aspect of nitriding are analyzed. It is shown that the adherence of the mask significantly influences the topographical profile and the anisotropy of nitriding, because in the case of a weakly adhered mask, a lateral adsorption process takes place under the mask. The influence of swelling and anisotropy in the case of pattern nitriding in small dimensions is discussed.

The Combined Effect of Coriolis Force and Double Diffusive for the Convention in a Rectangular Isotropic and Anisotropic Porous Channel

The combined effects of Coriolis force, heat, and mass diffusion for the convection in a horizontal rectangular channel filled with fluid in both isotropic and anisotropic porous channels is studied in the three-dimensional case for which the governing equations with the boundary conditions are derived with the help of the following assumptions: the fluid is incompressible; the flow is axisymmetric about the y-axis; the fluid is steady; thermal diffusion is larger than the viscous diffusion. With the help of the stream function, the resultant equations are made dimensionless, and non-dimension parameters like Rac, Rs along with anisotropic aspect ratio of permeabilities and thermal diffusivities are introduced. Later, the resulting linear partial differential equations are solved by the method of Fourier series analysis. The effect of the non-dimensional numbers plays a vital role in controlling parameters like velocity, temperature, and concentration for both isotropic and anisotropic cases. The expression for critical Rayleigh number has been established for both isotropic and anisotropic cases. Various computations are carried out in order to study the effects of velocity, temperature, concentration, and Critical Rayleigh number for different values of non-dimensional parameters. The obtained results are in good agreement with previous literary works and also have a wide application in the real world which can be seen in different industries.

Analysis of optical emission spectroscopy data during silicon etching in SF6/O2/Ar plasma

Silicon etching is an essential process in various applications, and a major challenge for etching process is anisotropic high aspect ratio etching characteristics. The etch profile is determined by the plasma parameters and process parameters. In this study, the plasma state with each process parameters were analyzed through the optical emission spectroscopy (OES) plasma diagnostic sensor by both chemical and physical approaches. Electron temperature and electron density were additionally acquired using the corona model with OES data that provides chemical species information, and the etch profile was evaluated through scanning electron microscope measurement data. The results include changes in profile with gas ratio, bias power, and pressure. We figure out that factors like ion energy and ion angular distribution as well as chemical reaction affect the anisotropic profile.

Copper molybdate synthesized by sonochemistry route at room temperature as an efficient solid catalyst for esterification of oleic acid

Copper molybdate nanoplates were synthesized by a sonochemical process at room temperature, which we report as a simple and cost-effective route. Structural analysis of the material by the Rietveld method of X-ray diffraction (XRD) data revealed lindgrenite Cu3(MoO4)2(OH)2 in a single-phase structure. All the vibrational modes characteristic of the space group were identified by Raman vibrational and near-infrared (NIR) spectroscopies. The profile obtained for N2 adsorption/desorption was type III hysteresis, characteristic of mesoporous materials, with a surface area of 70.77(1) m2 g−1. The micrographs of the material obtained by scanning electron microscopy showed nanoplates with nanometric sizes and an anisotropic growth aspect. The catalytic activity of lindgrenite was evaluated by esterifying oleic acid with methanol, showing high conversion rate to methyl oleate and good catalyst stability after seven recycling cycles. Above all, the best catalytic performance was reached when we optimized parameters such as oleic acid:methanol molar ratio of 1:5, 5% of catalyst dosage, and reaction time of 5 h, resulting in 98.38% of conversion at 413 K. Therefore, sonochemically synthesized lindgrenite proved to be a high potential material for biofuel production by oleic acid esterification.

A non-local damage model for the fatigue behaviour of metallic polycrystals

ABSTRACT The development of fatigue damage in metallic materials is a complex process influenced by both intrinsic (e.g. texture, defects) and extrinsic (e.g. loading mode, frequency) factors. To better understand this process, some efforts have been made to develop microstructure-sensitive models that consider the impact of microstructural heterogeneities on the formation of fatigue cracks. An important limitation of such models is their inability to describe the transition between the nucleation and growth stages in a consistent thermodynamic framework. To circumvent this limitation, a constitutive model, which is appropriate for the description of both nucleation and early growth, is proposed. For this purpose, non-local damage mechanics is used to construct a set of constitutive relations that explicitly considers the progressive stiffness reduction due to the formation of fatigue cracks. Specifically, a damage variable is attached to each slip system, which allows considering both the anisotropic aspect of fatigue damage and closure effects. The spatial gradients of the damage variables are treated as additional state variables to account for the increase of surface energy associated with the formation of fatigue cracks. For the evolution equations to be compatible with the second law of thermodynamics, a modified form of the entropy production inequality is adopted. For illustration purposes, the non-local damage model is implemented in a spectral solver. Some numerical examples are then presented. These examples allow discussing the ability of the proposed model to describe the impact of loading conditions and pre-existing defects on the fatigue behaviour of metallic polycrystals.

An indentation-based approach to determine the elastic constants of soft anisotropic tissues

Characterization of the mechanical properties of tissue can help to understand tissue mechanobiology, including disease diagnosis and progression. Indentation is increasingly used to measure the local mechanical properties of tissue, but it has not been fully adapted to capture anisotropic properties. This paper presents an indentation-based method to measure elastic constants of soft anisotropic tissues without additional mechanical tests. The approach uses measurement of the indentation modulus and the aspect ratio of the elliptical contact introduced by anisotropic mechanical properties of tissue to determine the elastic constants from finite element analysis. The imprinted area imparted by a fluorescent bead-coated spherical indenter showed the aspect ratio of the contact area, giving a generalized sense of the level of anisotropy, and instrumented indentation determined the indentation modulus. A parametric study using finite element simulation of the indentation tests established the relationship between the aspect ratio of contact and the non-dimensional ratios, Ex/Ey and Gxy/Ey; here, Ex and Ey are the Young's moduli (Ex > Ey) and Gxy is the shear modulus in the xy plane. For strongly anisotropic materials (Ex/Ey > 150), aspect ratio and indentation modulus are sufficient to determine Gxy and Ey. For weakly anisotropic materials, indentation modulus in the transverse direction, Ey, and the aspect ratio of contact in the anisotropic plane can be used to determine the elastic constants. The proposed approach improves the elastic characterization of soft, anisotropic biological materials from indentation and helps to elucidate the complex mechanical behavior of soft anisotropic tissues.

A continuum damage mechanics-based approach for the high cycle fatigue behavior of metallic polycrystals

Polycrystalline elasto-plasticity models provide a general framework for investigating the effect of microstructural heterogeneities (e.g. grains, inclusions, pores) on the high cycle fatigue behavior of metallic materials. In this work, continuum damage mechanics is used to construct a set of constitutive relations to describe the progressive degradation of certain mechanical properties at the grain scale. The damage is considered to be coupled with the elastic behavior of the material. Special care is taken to include the anisotropic aspect of fatigue damage and the effect of intragranular internal stresses. The constitutive relations are then implemented within a self-consistent model to evaluate intergranular interactions. Finally, the model is used to investigate the high cycle fatigue behavior of polycrystalline copper. It is shown that the influence of certain loading conditions on the high cycle behavior is correctly reproduced. Specifically, the application of a mean shear stress does not result in an increase in damage; however, a mean normal stress is damaging. That is, a decrease in the fatigue resistance is predicted when the mean normal stress is increased.

Nonlinear dependence of X-ray diffraction peak broadening in InxGa1−xSb epitaxial layers on GaAs substrates

The configuration of the interfacial misfit array at InxGa1−xSb/GaAs interfaces with different indium compositions and thicknesses grown by metalorganic chemical vapor deposition was systematically analyzed using X-ray diffraction (XRD) reciprocal space maps (RSMs). These analyses confirmed that the epilayer relaxation was mainly contributed to by the high degree of spatial correlation of the 90° misfit array (correlation factors <0.01). The anisotropic peak-broadening aspect ratio was found to have a non-linear composition dependence as well as be thickness-dependent, related to the strain relaxation of the epilayer. However, the peak-broadening behavior in each RSM scan direction had different composition and thickness dependences.

Numerical analysis of anisotropic elasto-plastic deformation of porous materials with arbitrarily shaped pores

The objective of this work is to numerically investigate the anisotropic compressive behavior of porous materials with randomly distributed, arbitrarily shaped pores in various directions. The relative pore volume fraction, the anisotropic aspect ratio and the pore arrangement are taken into account. The direction and anisotropic aspect ratio dependences of Young׳s modulus and the initial yield stress are examined. Our results indicate that the anisotropic aspect ratio has a significant effect on the elasto-plastic behaviors of porous materials. Independent of pores distribution, Young׳s modulus and the yield stress are found to be symmetric with the transverse direction. However, with increasing the aspect ratio Young׳s modulus and the initial yield stress are greatly enlarged in the longitudinal direction of pores than those of other directions while the minimum variations are observed in transverse direction. Moreover, equations for arbitrary porous materials are developed by relating Young׳s modulus and the initial yield stress in various directions to those in the transverse direction, which provides a simple and effective method for predicting the deformation of porous materials in arbitrary directions based on that in the transverse direction.

Non-linear imaging and characterization of atherosclerotic arterial tissue using combined SHG and FLIM microscopy.

Atherosclerosis is one of the leading causes of death in the Western World and its characterization is extremely interesting from the diagnostic point of view. Here, we employed combined SHG-FLIM microscopy to characterize arterial tissue with atherosclerosis. The shorter mean fluorescence lifetime measured within plaque depositions (1260 ± 80 ps) with respect to normal arterial wall (1480 ±100ps) allowed discriminating collagen from lipids. SHG measurements and image analysis demonstrated that the normal arterial wall has a more anisotropic Aspect Ratio (0.37 ± 0.02) with respect to plaque depositions (0.61 ± 0.02) and that the correlation length can be used for discriminating collagen fibre bundles (2.0± 0.6µm) from cholesterol depositions (4.1 ± 0.6µm). The presented method has the potential to find place in a clinical setting as well as to be applied in vivo in the near future. Graphic composition of SHG and FLIM images representing normal arterial wall and plaque depositions.

Thermal conductivity of epoxy resins filled with MWCNT and hydrotalcite clay: Experimental data and theoretical predictive modeling

In this work, the effect of hydrotalcite clay on the thermal conductivity of epoxy resin filled with carbon nanotubes (CNTs) has been studied. Thermal and morphological experiments show that the presence of hydrotalcite clay in a mesh of carbon nanotubes gives rise to aggregates and twisted bundles, resulting in a lower thermal conductivity of epoxy nanocomposites. Simple model for evaluation of the thermal conductivity of the composites is presented as analytical function of volume fraction, anisotropic thermal conductivities, aspect ratio, non‐straightness, and interfacial thermal resistance of the CNTs. The model predictions agree very well with the measured thermal conductivities of epoxy nanocomposites and confirm the hypothesis that the presence of a clay in a mesh of nanotubes results in a lower elongation of CNT. POLYM. COMPOS., 36:1118–1123, 2015. © 2014 Society of Plastics Engineers

Electrochemical Impedance of a Battery Electrode with Anisotropic Active Particles

Electrochemical impedance spectra for battery electrodes are usually interpreted using models that assume isotropic active particles, having uniform current density and symmetric diffusivities. While this can be reasonable for amorphous or polycrystalline materials with randomly oriented grains, modern electrode materials increasingly consist of highly anisotropic, single-crystalline, nanoparticles, with different impedance characteristics. In this paper, analytical expressions are derived for the impedance of anisotropic particles with tensorial diffusivities and orientation-dependent surface reaction rates and capacitances. The resulting impedance spectrum contains clear signatures of the anisotropic material properties and aspect ratio, as well as statistical variations in any of these parameters.

A micromechanics-based model for estimating localized failure with effects of fabric anisotropy

This paper presents a micromechanics-based approach to investigate the effects of fabric anisotropy on the behavior of localized failure in granular materials. Based on a micromechanical analysis, the origin of deviatoric stress is decomposed into two components: contact force anisotropy and fabric anisotropy. Using a micro–macro approach, the back stress is interpreted as an contribution to the change of the fabric’s principal direction. The evolution of the back stress is deduced from the stress–fabric relationship and determined with reference to the deviation of the principal directions between the rate of the reduced stress tensor and the actual reduced stress tensor. With this micro–macro framework, a mixed (isotropic–kinematic) hardening model is developed based on the classical isotropic hardening theory. A laboratory simple shear test is first analyzed to validate the proposed model and illustrate the kinematic-hardening mechanism which is usually displayed under non-proportional loading. The analysis further focuses on the anisotropic aspect of localized failure. It has been discovered that the fabric anisotropy can play an important role in the occurrence of shear banding. An increasing degree of fabric anisotropy tends to delay the initiation of the strain localization and result in higher failure strength. The effects of fabric anisotropy have also been illustrated by comparing the theoretical predictions and measured results on the shear band inclination angle, shear strain level and dilatancy at bifurcation.

A fast algorithm for computation of discrete Euclidean distance transform in three or more dimensions on vector processing architectures

In this note, we introduce a function for calculating Euclidean distance transform in large binary images of dimension three or higher in Matlab. This function uses transparent and fast line-scan algorithm that can be efficiently implemented on vector processing architectures such as Matlab and significantly outperforms the Matlab’s standard distance transform function “bwdist” both in terms of the computation time and the possible data sizes. The described function also can be used to calculate the distance transform of the data with anisotropic voxel aspect ratios. These advantages make this function especially useful for high-performance scientific and engineering applications that require distance transform calculations for large multidimensional and/or anisotropic datasets in Matlab. The described function is publicly available from the Matlab Central website under the name “bwdistsc”, “Euclidean Distance Transform for Variable Data Aspect Ratio”.

Super-selective cryogenic etching for sub-10 nm features

Plasma etching is a powerful technique for transferring high-resolution lithographic masks into functional materials. Significant challenges arise with shrinking feature sizes, such as etching with thin masks. Traditionally this has been addressed with hard masks and consequently additional costly steps. Here we present a pathway to high selectivity soft mask pattern transfer using cryogenic plasma etching towards low-cost high throughput sub-10 nm nanofabrication. Cryogenic SF6/O2 gas chemistry is studied for high fidelity, high selectivity inductively coupled plasma etching of silicon. Selectivity was maximized on large features (400 nm–1.5 μm) with a focus on minimizing photoresist etch rates. An overall anisotropic profile with selectivity around 140:1 with a photoresist mask for feature size 1.5 μm was realized with this clean, low damage process. At the deep nanoscale, selectivity is reduced by an order of magnitude. Despite these limits, high selectivity is achieved for anisotropic high aspect ratio 10 nm scale etching with thin polymeric masks. Gentler ion bombardment resulted in planar-dependent etching and produced faceted sub-100 nm features.

Numerical simulation of damage–Permeability relationship in brittle geomaterials

Finding a coupling model between a hydraulic parameter such as permeability and a mechanical parameter such as damage is the key element for several recent engineering problems. A review of the technical literature reveals that several mechanical constitutive laws exist which allow determining a damage tensor for a damageable porous material under loading. But the present work develops a method to deduce the permeability change due to the damage propagation. From a phenomenological point of view, a microscopic approach is often used for analyzing the permeability evolution by the fluid flow through cracks. However, a macroscopic approach is appropriate for studying the mechanical characteristics of material such as stress–strain relationship after damage. So, this article illustrates both microscopic and macroscopic damage tensors and establishes a relation between them, then find the permeability change by this relation. Cracks are modeled by a disc-shaped distribution in a three-dimensional space. Geometrical characteristics of each disc (radius, direction and opening) follow the statistical distribution laws, depending on the type of loading (compression or extension). A double porosity method is also employed to simulate the flow through the network of cracks/porosity and to evaluate the equivalent permeability by a homogenization method. The discussed double porosity aspect demonstrates the application of the model for fractured porous materials. The observation of a percolation threshold shows the ability of the model to make a connection between the cracks. The model pays a special attention to the anisotropic aspect of the relation between damage and permeability tensors. Characteristics parameters used in the model, giving the intensity of this coupling must be determined experimentally for each specific material.

Buckling of anisotropic films on cylindrical substrates: insights for self-assembly fabrication of 3D helical gears

We propose an effective way of fabricating true three-dimensional helical gear-like structures (with inclined gear teeth) by using self-assembled stress-driven buckling of anisotropic films on compliant cylindrical substrates. Key parameters characterizing the helical undulation profile, in particular the gear teeth number and the inclined teeth angle, are investigated numerically using finite element simulations. Based on the insights from numerical calculations, a simplified theoretical model is established to effectively predict the teeth number. The results show that the anisotropic modulus ratio has a larger effect on the teeth number than the anisotropy angle. The orientation of gear teeth is related to the coupled effects of the anisotropic modulus ratio, anisotropy angle, substrate curvature and substrate aspect ratio. In general, the undulation orientation tends to be perpendicular to the direction of minimum bending stiffness in the film. The findings in this paper provide useful guidance for the self-assembly fabrication of helical gears and other 3D structures at various length scales.

Anisotropic rheology of a cubic medium and implications for geological materials

Dislocation creep, which is the dominant deformation mechanism in the upper mantle, results in a non-Newtonian anisotropic rheology. The implication of non-Newtonian rheology has been quite extensively studied in geodynamic models but the anisotropic aspect remains poorly investigated. In this paper, we propose to fill this gap by (1) introducing a simple mathematical description of anisotropic viscosity and (2) illustrating the link between plastic crystal deformation and bulk material rheology. The study relies on the highest symmetry of the anisotropic tensor, a cubic symmetry, for which anisotropy is characterized by one parameter only, δ. First-order implications of anisotropy are quantitatively explored as a function of δ. The effective rheology of the material is described as a function of the orientation of the crystals and of the imposed stress and the validity of the isotropic approximation is discussed. The model, applied to ringwoodite, a cubic crystal with spinel-type structure, predicts that the dynamics of the transition zone in the Earth's mantle is going to be strongly affected by mechanical anisotropy.

Beam effect on electromagnetic ion-cyclotron waves with general loss – cone distribution function in an anisotropic plasma-particle aspect analysis

Abstract. The effect of upgoing ion beam and temperature anisotropy on the dispersion relation, growth rate, parallel and perpendicular resonant energies, and marginal instability of the electromagnetic ion cyclotron (EMIC) waves, with general loss-cone distribution function, in a low β homogeneous plasma, is discussed by investigating the trajectories of the charged particles. The whole plasma is considered to consist of resonant and non-resonant particles. The resonant particles participate in an energy exchange with the waves, whereas the non-resonant particles support the oscillatory motion of the waves. The effects of the steepness of the loss-cone distribution, ion beam velocity, with thermal anisotropy on resonant energy transferred, and the growth rate of the EMIC waves are discussed. It is found that the effect of the upgoing ion beam is to reduce the energy of transversely heated ions, whereas the thermal anisotropy acts as a source of free energy for the EMIC waves and enhances the growth rate. It is found that the EMIC wave emissions occur by extracting energy of perpendicularly heated ions in the presence of an upflowing ion beam and a steep loss-cone distribution function in the anisotropic magnetoplasma. The effect of the steepness of the loss-cone is also to enhance the growth rate of the EMIC waves. The results are interpreted for EMIC emissions in the auroral acceleration region.