Inclusions Of Different Shapes Research Articles

Backscattering of Ultrasonic Waves as the Basis of the Method of Control of Structure and Physicо-Mechanical Properties of Cast Irons

Increasing the reliability of control of cast iron structure and its physical and mechanical characteristics is an important scientific and technical task of the machine-building industry. The paper studies the possibilities of controlling the structure of cast irons using structural noise created by ultrasonic scattering on graphite inclusions of different shapes. The subject of the present studies was such characteristics of structural noise as amplitude-temporal A(t) and as root mean square value of the amplitude of the ultrasonic waves backscattering field AN, compared with the data on ultrasonic velocity and strength or tensile strength of cast iron samples. As a result of the studies, a significant difference between the amplitude parameters of the AN structural noise obtained for samples with different shapes of graphite inclusions at 5 MHz was revealed for the first time. So, for example, for samples of gray cast iron (Russian: СЧ10, СЧ15, СЧ20, СЧ25), having predominantly plate-like form of graphite inclusions, the value of AN on 14–15 dB exceeds that measured in high-strength specimens of the cast iron with the prevailing form of spherical graphite inclusions ВЧ50 (Russian), etc. At the same time growth of longitudinal ultrasonic velocity amounted to 20–25 %. The method of rejection of gray cast iron from high-strength cast iron according to the data of amplitude parameters of structural noise AN at unilateral and local sounding of the object without using an additional reference signal reflected from its oppositional wall is suggested.

Research on bending vibration characteristics of phononic crystal plates based on Mindlin’s piezoelectric plate theory

Based on Mindlin’s theory and the plane wave expansion method, the formulas are proposed for the governing equations and dispersion relations of bending waves in piezoelectric phononic crystal plates. The shear correction factors can be obtained through transcendental equations based on forced vibrations of the plate. The plates are made of inclusions of different shapes and lattice types, finding that the inclusion shape dramatically affects the mid-to-high frequency band gaps. Piezoelectric materials exhibit distinct eigenfrequencies at the high-symmetry point Γ at low frequencies. Thickness affects the band gap width differently than in two-dimensional models, and cuts influence band gap width significantly.

Effect of voids shape on deformation of 3D-printed closed-cell porous structures

The aim of this work is to investigate the influence of the shape of voids in porous 3D printed closed-cell porous structures on their elastic properties and mechanical behavior using the results of morphological analysis of microstructure based on multipoint statistical characterization, finite element modelling and experimental data. The geometrical models of representative volume elements (RVEs) for structures with non-overlapping inclusions of different shapes and parameters were created and produced using FDM/FFF 3D printing technology. Evaluation of various morphological parameters has been performed based on the analysis of multipoint statistical characteristics. The elastic behavior and properties of the studied RVEs were modelled using finite element analysis. The relationship between mechanical properties and statistical characteristics has been analyzed.

A micromechanical model for heterogeneous nanograined metals with shape effect of inclusions and geometrically necessary dislocation pileups at the domain boundary

Heterogeneous nanostructured materials, including metals, alloys, and composites, have attracted significant scientific interest because of their outstanding performance in overcoming the strength-ductility trade-off, enhancing fatigue strength, and reducing friction and wear damage. In this study, we developed a new micromechanical model to predict the overall mechanical response of heterogeneous nanograined metals that consist of plastically deformable soft and hard domains. This dual-domain heterogeneous structure was modeled as a matrix-inclusion system, and the problem was solved through a secant-moduli approach that considered the existence of geometrically necessary dislocation (GND) pileups at the domain boundaries. We assumed that the inclusions are aligned along one direction according to experimental observations. A significant improvement in this development from previous micro-mechanical models was that the hetero-deformation induced extra strengthening inside the plastically deformable inclusions of different shapes due to the GND pileups was taken into account. In this process, the stress-strain responses of the constituent phases of various grain sizes that spanned over four orders of magnitude are also established by the dislocation density-based model. In accordance with Eshelby's equivalent-inclusion principle, the inclusions are taken to be of spheroidal shape, with an aspect ratio (i.e., length-to-diameter ratio, denoted by β) that could be much larger or smaller than unity. We considered in details the condition that the overall uniaxial tension is applied along the direction of the aligned inclusions, and examined the consequences if the extra strengthening is not considered and if it is considered. It is found that, if extra strengthening was not considered, the inclusion shape had a significant influence on the strain-hardening capability of the heterogeneous metals. The strain-hardening rate increased with increasing β if β≥1, whereas it decreased with increasing β if β<1, which resulted in a maximum strain-hardening rate at β=100 and a minimum one at β=0.5 among all the aspect ratios considered. Interestingly, the strength-ductility trade-off could be overcome by modulating only the shape of the inclusions. In contrast, if extra strengthening was incorporated, the variation of the strain-hardening rate was reversed because larger β (as β≥1) provided less strain partitioning, lower GND density, and reduced back stress, whereas bigger β (as β<1) yielded higher ones. When the overall uniaxial stress was applied normal to the direction of the aligned inclusions, the β dependence of the strain-hardening rate was different. Our findings showed that the tuning of inclusions shape, extra strengthening, grain sizes, and volume fractions of the inclusions circumvented the strength-ductility trade-off and achieved outstanding strength-ductility synergy as demonstrated by the strength-ductility map.

Investigation of Bending of Anisotropic Plates with Inclusions with the Help of Singular Integral Equations

We consider the problem of bending of an anisotropic plate of constant thickness with rigid inclusions. The algorithm of its solution is constructed on the basis of reduction of the problem of bending of a multiply connected anisotropic plate with inclusions to the evaluation of the Lekhnitskii potentials for an auxiliary plane problem of the theory of elasticity with properly chosen elastic constants. To solve this auxiliary problem, we use the method of singular integral equations in the complex form. We consider the problems of bending for plates with inclusions subjected either to the action of moments at infinity (for infinitely large plates) or to transverse loading (for finite plates). We also present some examples of evaluation of stresses acting in the plates containing rigid inclusions of different shapes or systems of inclusions of this kind.

An efficient method for the elastic field in a transversely isotropic full space due to arbitrary inclusions

The present study is on the analytical solution for the elastic field due to a cuboidal inclusion of uniform eigenstrain within a transversely isotropic full-space material, and a numerical method to model inclusions of any arbitrary shapes and with any eigenstrain distributions as the integration of a set of such cuboidal inclusions. The fast Fourier transform (FFT) is applied for efficient computation. The developed method and results are implemented to analyze the elastic field in a transversely isotropic full-space material containing inclusions of different shapes, different eigenstrain distributions, and multiple cuboids of different densities. Furthermore, the effect of material anisotropy on the stress field subjected to a spherical inclusion with pure dilatant eigenstrains is explored by comparing the behavior of a transversely isotropic material with that of a corresponding isotropic one. The numerical results show that the induced stresses are drastically influenced by the Young’s moduli of transversely isotropic materials, and that material constant C33 has a large influence on normal stress σ33.

Enhancing Sharp Features by Locally Relaxing Regularization for Reconstructed Images in Electrical Impedance Tomography.

Image reconstruction in EIT is an inverse problem, which is ill posed and hence needs regularization. Regularization brings stability to reconstructed EIT image with respect to noise in the measured data. But this is at the cost of smoothening of sharp edges and high curvature details of shapes in the image, affecting the quality. We propose a novel iterative regularization method based on detection of probable location of the inclusion, for locally relaxing the regularization by appropriate amount, to overcome this problem. Local relaxation around inclusion allows reconstruction of its high curvature shape details or sharp features at the same time giving benefits of higher regularization in remaining areas of the image. The proposed method called DeTER is implemented using a small plug-in to EIDORS (Electrical Impedance and Diffused Optical Reconstruction Software) in a MATLAB environment. Parameters like CNR, correlation coefficients of shape descriptor functions and relative size of reconstructed targets have been computed to evaluate the effectiveness of the technique. The performance of DeTER is tested and verified on simulated data added with Gaussian noise for inclusions of different shapes. Both conducting and nonconducting inclusions are considered. The method is validated using open EIT data shared by ‘Finnish inverse problem society’ and also by reconstructing image of internal void of a papaya fruit from the data acquired by an EIT system developed in our laboratory. The reconstructed images corresponding to the open EIT data clearly show the shapes similar to original objects, with sharp edges and curvature details. The shapes obtained in the papaya image are shown to correspond to the actual void using shape descriptor function. The results demonstrate that the proposed method enhances the sharp features in the reconstructed image with few iterations without causing geometric distortions like smoothening or rounding of the edges.

Dyakonov surface waves at the interface of nanocomposites with spherical and ellipsoidal inclusions

The dispersion properties of different types of surface electromagnetic waves which are supported by the interface of two nanocomposite materials with inclusions of different shape are studied theoretically and numerically. Both nanocomposites are made of doped n-type semiconductor inclusions which are evenly distributed in a transparent dielectric matrix. First nanocomposite contains semiconductor inclusions of spherical shape and can be represented as isotropic material with scalar effective dielectric permittivity. Second nanocomposite contains semiconductor inclusions of ellipsoidal shape and can be modeled as a uniaxial anisotropic crystal with two different principal effective permittivity components. Influence of physical and geometrical parameters of the nanocomposites on dispersion properties of surface waves is studied. It is shown that when dissipations in the semiconductor inclusions are taken into account the angular spectrum of Dyakonov surface wave existence becomes wider, and several dispersion curves of surface modes can simultaneously exist.

Polystyrene-Based Composites with Aluminosilicate Inclusions of Different Shapes

Samples of composites based on polystyrene with addition of halloysite nanotubes, mica, and montmorillonite aluminosilicates are obtained and the influence of these fillers on viscoelastic, mechanical, and structural properties of composites is studied. It is shown that an addition of up to 5% of mica can increase the rigidity of composites along with maintaining their strength at the level of pure polystyrene and without considerable embrittlement of samples. The addition of halloysite nanotubes and montmorillonite also increases the material stiffness but reduces its strength and elasticity. A significant (up to 50%) increase in the bending elasticity modulus of the composite was achieved by addition of 15% of halloysite nanotubes or 5% of mica.

Internal damage evaluation of composite structures using phased array ultrasonic technique: Impact damage assessment in CFRP and 3D printed reinforced composites

The application of non-destructive techniques for the evaluation of internal damage in composite materials is a challenge due to their complexity. The aim of this study is to analyse the ability of ultrasonic technique to identify and evaluate manufacturing defects and internal damage in composite laminates. Artificial object inclusions of different shapes, sizes and materials were embedded in carbon fibre reinforced epoxy (CFRP) laminates. Comprehensive investigation of non-destructive evaluation using phased array ultrasonic testing to trace and characterize the embedded defects is presented. Phased array ultrasonic technique was able to precisely locate most of the artificial inclusion in the composite laminates. Nerveless, the shape and size of the inclusions were not accurately determined due to the high signal attenuation and distortion characteristics of the carbon fibre epoxy composite.Furthermore, a major concern affecting the efficient use of composite laminates is their vulnerability to low velocity impact damage. The dynamic behaviour of composite laminates is very complex as there are many concurrent phenomena during composite laminate failure under impact loading. Thus, the practicality of the previous results is demonstrated by the evaluation of impacted carbon fibre reinforced epoxy laminates using ultrasonic testing. The influence of laminate thickness and impact energy on impact damage is also investigated. The performance of phased array ultrasonic testing for the inspection of composite laminates with barely visible impact damage is evaluated. In addition, fibre-reinforced thermoplastic composites are becoming more significant in industrial applications due to their excellent mechanical performance and potential recycling. In this study, impact damage in 3D printed continuous glass fibre reinforced thermoplastic laminates is also analysed. Phased array ultrasonic testing is performed and the amount of damage is quantified in terms of delaminated area.

Wavelet transform applied to lock-in thermographic data for detection of inclusions in composite structures: Simulation and experimental studies

In this work, we focused on lock-in infrared thermography as a non-destructive testing method for detection of inclusions in glass fiber reinforced plastic composite structures. The sample consisted of artificial inserts made of copper sheets to simulate inclusions of different shapes and sizes at varying depth levels. In an experimental study, the sample was excited at several modulation frequencies by a sinusoidal heat flux, and a thermal infrared camera was utilised for monitoring of surface temperature of a thermal wave that propagated into the sample. In simulation, ThermoCalc™-3D software based on finite difference method was used for the replication of the physical phenomena that were present in the experiment. The effect of the applied heat flux and time for different sizes and depths of inclusions was analysed to investigate the thermal response. Wavelet transform was applied to compute phase angle data from the temperature-time history of each pixel for the assessment of the inclusions. The investigation into the effects of wavelet parameters; scale and shift, modulation frequencies, inclusion sizes, and depths on the phase contrast was conducted and discussed. The simulation results were found to have a good correlation with the experimental results, thus demonstrating potential in detecting inclusions.

Topological optimization of thermoelastic composites with maximized stiffness and heat transfer

The topological optimization of composite structures is widely used while tailoring materials to achieve the required engineering physical properties. In this paper, the problem of topological optimization of the microstructure of a composite aimed at the construction of a material with most effective values of the bulk modulus of elasticity and thermal conductivity taking into account competing mechanical and thermal properties of the materials included in the composite is defined and solved. A two-phase composite consists of two base materials, one of which has a higher Young modulus but lower thermal conductivity, while the other has a lower Young modulus but higher thermal conductivity. A new class of problems for composites containing material pores or technological inclusions of different shapes is considered. Effective thermoelastic properties are obtained using the asymptotic homogenization method. A modified solid isotropic material with penalization (SIMP) model is used to regularize the problem. The problem of the isoperimetric constraints is solved by the method of moving asymptotes (MMA). The influence on optimal topology of the composite in the presence of two competing materials, and optimality criteria using linear weight functions are investigated. Pareto spaces that provide deep understanding of how these goals compete in achieving optimal topology are constructed.

Breakup of heterogeneous water drop immersed in high-temperature air

The enhancement of the evaporation rate of a heterogeneous water drop is experimentally investigated. A water drop encapsulating a solid graphite inclusion is instantaneously placed in the very hot air. Under action of the high ambient temperature and due to different thermal properties between water and solid inclusion, the initial drop explodes and creates numerous very small droplets. The vaporization rate of the water drop is strongly increased leading to a short time life of the drop. High speed video recording is used to detail the explosive breakup mechanism of a drop immersed in hot air when its temperature varies in the range between 1073K and 1373K. The target of the study is to determine the possible conditions for the increase of the water/air surface of the drop after breakup, i.e., the ratio of the final to initial surface, Sout/Sin, and to verify that this enlargement is responsible of the evaporation rate enhancement. For this purpose, we investigate drops of different initial volumes (5–15µl) with graphite solid inclusions of different shapes and volumes: 2×2×1mm, 2×2×2mm, or 2×2×3mm. The water surface ratio Sout/Sin is given as function of Vw/Vinc, which is the ratio of initial volume of water drop Vw to the volume of solid graphite inclusion Vinc. The study has shown that the maximum value of the ratio Sout/Sin≈15 can be reached when Vw∼Vinc. When, the ratio of Sout/Sin varies in the range 1 to 15. The increase of the evaporating surface is of the highest interest to improve the heat transport and to be used and developed in heat technologies.

Study of the interaction of matrix crack with inclusions of different shapes using the method of caustic

In this study, the interactions of matrix crack with inclusions of different shapes were investigated using the method of caustic. First, the specimens with inclusions of different shapes were prepared, where glass was used as inclusion and epoxy was used as matrix. Then, caustic experiments were conducted, and the typical caustic spots at the crack tip with varied distances from three different shapes of inclusions were obtained. Ultimately, the stress intensity factors of the cracks shielded by different shapes of inclusions were extracted from the caustic spots, and finite element simulations were conducted to verify the experimental results using the ABAQUS software. The results show that the stress intensity factors measured by the caustic method are in good agreement with the finite element simulation results.

Effects of the hydraulic conductivity microstructure on macrodispersivity

AbstractHeterogeneity of the hydraulic properties is one of the main causes of the seemingly random distribution of solute concentration observed in contaminated aquifers, with macrodispersivity providing a global measure of spreading. Earlier studies on transport of solutes in heterogeneous formations, either theoretical or numerical, expressed dispersivity as a function of the geostatistical properties of the hydraulic conductivity K. In most cases, K follows a second‐order statistical characterization, which may not be adequate when heterogeneity is high. In this work, we adopt the Multi‐Indicator Model–Self Consistent Approach (MIMSCA) to compute the longitudinal and transverse macrodispersivity. This methodology enables to model the K field by using geological inclusions of different shapes and orientation (defined here as the microstructure), while replicating the heterogeneous macrostructure obtained by the second‐order statistics. The above scheme attempts to reproduce the effect on macrodispersion of different distribution and orientation of local facies, and for instance it may represent the orientation and spatial features of the layers that are often observed in aquifers. The relevant impact of the microstructure on effective conductivity, longitudinal and transverse macrodispersivities is analyzed and discussed, for both binary and lognormally distributed K fields.

Evaporation, boiling and explosive breakup of heterogeneous droplet in a high-temperature gas

Experimental investigation of evaporation and boiling was carried out on fixed water droplet containing a single nontransparent solid inclusion and placed in gaseous environment at high-temperature (500–1100K). We carried out experiments with water droplets (diameters 3–5mm) containing graphite inclusions of different shapes (sphere, disk, cone, parallelepiped and polyhedron) with sizes between 2 and 4mm. These droplets were in the hot flux on top of combustion of industrial ethanol. The behavior of the droplets was recorded by high-speed (up to 105 frames per second) video cameras “Phantom” and “TEMA Automotive” software. Conditions for intensive vaporization at solid/liquid interface inside droplets were determined. A phenomenon of explosive disintegration occurred when heating some of the heterogeneous droplets. Time of heating until an explosive disintegration and complete evaporation was recorded. Influence of gas temperature and inclusion sizes were measured.

Development of oil inclusions under the action of chemical reagents on the reservoir

Various conditions of formation of motionless closed hydrocarbon inclusions are considered: viscous instability of fluid displacement and inhomogeneous rock structure. Conditions of dynamic equilibrium of the inclusion in a water flow are given for one-dimensional and two-dimensional motion. Distributions of the oil content in inclusions of different shapes are numerically calculated. It is found that the amount of unrecovered oil depends on the ratio of the pressure gradients in the filtration flow of water pumped into the reservoir and the characteristic capillary pressure on the boundary of immiscible phases. It is demonstrated that the use of chemical reagents can substantially reduce the effect of capillary forces and promotes oil entrainment by the overall flow.

Nanoparticle Electromagnetic Properties for Sensing Applications

Nanoparticles play a crucial role in biomedical and sensing applications. In this paper the design of non-spherical gold nanoparticles, operating in the near infrared and visible regime, is proposed. The structures consist of metallic resonating inclusions of different shapes embedded in a dielectric environment. Different geometries, such as cube, elliptical cylinder and rod are considered. The main purpose of this study is to develop new analytical formulas useful in the nanoparticle design for specific biomedical and sensing applications. These analytical models are developed in order to describe the electromagnetic behavior of the nanoparticles in terms of resonant wavelength position, magnitude and amplitude width for absorption and scattering cross section. The obtained results are compared to the numerical ones, performed by full-wave simulations, and to the experimental values existing in literature. A good agreement among analytical, experimental and numerical results was obtained. Then, the structure is analyzed in terms of sensitivity properties. Exploiting the proposed analytical models, it is possible to design the nanostructures with the desired electromagnetic properties. The results show that these structures can be successfully applied for sensing applications.

The dielectric permittivity of carbonate formations from the unified microstructure model

Abstract In this paper we study the influence of pore microstructure and saturation of pore systems on the dielectric permittivity of double-porosity formations. The dielectric permittivity calculations were fulfilled using the unified model approach. This approach is based on the calculation of different physical properties from the single microstructure model applying the symmetric variant of the effective medium approximation (EMA). Porous rock is considered as a composed material that consists of solid grains and fluid filled pores of a small scale (primary porosity) that form a homogeneous isotropic matrix. Secondary pores of a large scale are represented by inclusions of different shapes placed in this matrix. Each component of rock (grains, primary and secondary pores) is approximated by a three-axial ellipsoid. The aspect ratios of grain and primary-pore ellipsoids are introduced as a function of porosity. The shapes of secondary pores such as a crack, vug, and channel are modeled by varying ellipsoidal aspect ratios. The distribution of saturating immiscible fluids in pore space is described by two models: (1) water (the wetting component) is concentrated in a film attached to the pore walls while oil or gas (the non-wetting component) occupies the central part of a pore; in this model a pore is considered as a layered ellipsoid with the wetting component in the outer layer; (2) the saturating fluid contains spherical drops of oil placed in the water. The dielectric permittivity obtained by using the unified microstructure model with variable aspect ratios of matrix grains and pores demonstrates a good agreement with the experimental data. The influence of secondary pores on the dielectric permittivity depends on pore shape and decreases with oil saturation.

Effect of “melt-crystal” interphase surface energy in iron on its structure in castings

Problems of the influence of “melt-graphite” interphase energy in iron on formation of graphite inclusions of different shapes are considered. The effect of the content of elements surface-active with respect to graphite in the melt on the shape of graphite inclusions is considered. The direction of their action on the variation of the “melt-graphite” interphase energy, which is the main factor of shaping of graphite inclusions in cast iron, is shown and the intensity of this action is evaluated.