Thick Boundary Research Articles

Insights into the reactive sintering and separated specific grain/grain boundary conductivities of Li1.3Al0.3Ti1.7(PO4)3

Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a promising candidate as solid electrolyte and Li+ conductive component in the composite electrodes of all-solid-state Li-ion batteries. For both applications, reducing the sintering temperature of LATP while preserving its electrochemical properties is highly desired. This work is dedicated to reducing the sintering temperature of LATP from conventionally around 1000 °C to a low temperature of 775 °C with adding an extra 10 wt % of Li2CO3 to the precursors by a reactive sintering process. Comparative investigations with the stoichiometric LATP prepared by the same sintering method indicate that the combination effect of reactive sintering and Li2CO3-excess promotes the liquid phase sintering within LATP yielding a high relative density of 95.3%, whereas the stoichiometric LATP can only achieve a comparable relative density at 875 °C. Furthermore, the reactive sintering assisted Li2CO3-excess LATP exhibits a significantly higher ionic conductivity of 0.65 mS cm−1 at 25 °C and lower total activation energy of 0.334 eV compared with that of the stoichiometric LATP. Correlative studies on the microstructure and the separated specific grain/grain boundary conductivities for the two samples reveal that the improvement of Li+ conductivity for Li-excess LATP is attributed to its smaller total grain boundary thickness.

Transient Analysis of Laminated composite Plate using New Higher-Order Shear Deformation Theory

This work develops transient analysis using a new higher-order displacement function for simply supported cross-ply laminated plates. Muntari’s higher-order shear deformation method for elastic composite plates is used to investigate the composite laminated thick and thin plate’s transient response. The current theory accounts for an approximately parabolic distribution of the transverse shear strains on the plate boundary surface through the thickness and tangential stress-free boundary conditions. The governing equations and boundary conditions are derived by employing the principle of virtual work. These equations are solved using closed-form solutions of a Navier’s type, plates are subjected to a different distribution of transient loadings such as step pulse, triangular pulse, and sinusoidal pulse, and many design parameters are studied, as expected minimum deflection is obtained for thick, antisymmetric, and has high orthotropy ratio laminated plate. The results obtained theoretically are compared with those available in various literature and showed a high agreement.

Effect of Stefan flow on the drag force in flow past random arrays of spheres

Stefan flow is a mass flow perpendicular to the particle surface induced by the reaction or component diffusion occurring inside particles. It significantly affects the interphase transfer process in gas–solid reacting flows. In this work, a second-order immersed boundary-lattice Boltzmann method (IB-LBM) is adopted for analyzing the influence of Stefan flow on the drag force in flows past fixed random arrays of spherical particles. The effect of Stefan flow is introduced by assigning specific fluid velocities at Lagrangian markers on the sphere surface. The simulation results show that the drag force exerting on particles decreases as the Stefan Reynolds number increases. The drag force reduction caused by Stefan flow is weakened as the solid volume fraction increases. This is because the thick boundary layer caused by Stefan flow on each particle is suppressed by Stefan flow from their neighboring particles. Based on the simulation results, a novel drag correction coefficient is developed, which considers the joint influence of the Stefan Reynolds number, particle Reynolds number and solid volume fraction.

Static and dynamic instability analysis of tapered CNTRC sandwich plates under uniform and non-uniform in-plane loadings using spline finite strip method

This paper presents the buckling analysis of rectangular sandwich plates with pure polymeric tapered cores and functionally graded carbon nanotube (FG-CNT) reinforced composite face sheets under static and harmonic dynamic loads. One uniform and four linearly-varying patterns are considered for the applied in-plane loads. The effective material properties of face sheets, in which the polymeric matrix is reinforced with aligned single-walled carbon nanotubes (SWCNT), are estimated using the extended rule of mixture. A higher-order zigzag shear deformation theory, which has the same number of dependent unknowns as the first-order theory, is employed to express the plate's displacement field. The governing equations are derived using Hamilton's principle and discretized by the spline finite strip method. The dynamic instability regions of plates with uniform and variable thickness are obtained by employing Bolotin's method. The accuracy of the present method is demonstrated by considering the problems for which solutions are available. A detailed numerical study is conducted to examine and compare the effects of different parameters, including the taper angle, type of the applied in-plane load, static and dynamic load factors, length-to-width ratios, the volume fraction of CNT, distribution pattern of CNTs along the thickness direction, temperature, and boundary conditions on the behavior of sandwich plate.

Meshfree analysis of functionally graded plates with a novel four-unknown arctangent exponential shear deformation theory

A novel refined arctangent exponential shear deformation theory (RAESDT) is presented for analysis the mechanical behavior of both isotropic and sandwich FGM plates. Material properties are set to be isotropic at each point and varied across the thickness direction obeying to a power-law distribution of the volume fraction gradation with respect to FGM core or skins of the plate. Unlike high-order shear deformation plate theories based on five or more variables, the displacement field of the novel RAESDT using arctangent exponential variations in planed displacements were approximated by only four unknowns, satisfying naturally tangential stress-free conditions at the plate surfaces and leading to reduce computational efforts. In accordance with RAESDT and enhanced moving kriging interpolation (EMKI)-based meshfree method with a new quadrature correlation function is introduced for the numerical modeling. Numerical validations with different plate configurations, geometries, length to thickness ratios and boundaries conditions are conducted. The obtained results are compared with the corresponding solutions available in the literature showing the accuracy and efficiency of the present approach.

Growth dynamics and compositional structure in periodic InAsSb nanowire arrays on Si (111) grown by selective area molecular beam epitaxy

We report a comprehensive study of the growth dynamics in highly periodic, composition tunable InAsSb nanowire (NW) arrays using catalyst-free selective area molecular beam epitaxy. Employing periodically patterned SiO2-masks on Si (111) with various mask opening sizes (20–150 nm) and pitches (0.25–2 μm), high NW yield of >90% (irrespective of the InAsSb alloy composition) is realized by the creation of an As-terminated 1 × 1-Si(111) surface prior to NW nucleation. While the NW aspect ratio decreases continually with increasing Sb content (x Sb from 0% to 30%), we find a remarkable dependence of the aspect ratio on the mask opening size yielding up to ∼8-fold increase for openings decreasing from 150 to 20 nm. The effects of the interwire separation (pitch) on the NW aspect ratio are strongest for pure InAs NWs and gradually vanish for increasing Sb content, suggesting that growth of InAsSb NW arrays is governed by an In surface diffusion limited regime even for the smallest investigated pitches. Compositional analysis using high-resolution x-ray diffraction reveals a substantial impact of the pitch on the alloy composition in homogeneous InAsSb NW arrays, leading to much larger x Sb as the pitch increases due to decreasing competition for Sb adatoms. Scanning transmission electron microscopy and associated energy-dispersive x-ray spectroscopy performed on the cross-sections of individual NWs reveal an interesting growth-axis dependent core–shell like structure with a discontinuous few-nm thick Sb-deficient coaxial boundary layer and six Sb-deficient corner bands. Further analysis evidences the presence of a nanoscale facet at the truncation of the (111)B growth front and {1-10} sidewall surfaces that is found responsible for the formation of the characteristic core–shell structure.

Neutral Vortex Necklace in a Trapped Planar Superfluid

We study quantum vortex states consisting of a ring of vortices with alternating sign, in a homogeneous superfluid confined to a circular domain. We find an exact stationary solution of the point vortex model for the neutral vortex necklace. We investigate the stability of the necklace state within both the point-vortex model and the Gross-Pitaevskii equation describing a trapped atomic Bose-Einstein condensate at low temperature. The point-vortex stationary states are found to also be stationary states of the Gross-Pitaevskii equation provided the finite thickness of the outer fluid boundary is accounted for. Under significant perturbation, the Gross-Pitaevskii evolution and point-vortex model exhibit instability as expected for metastable states. The perturbed vortex necklace exhibits sensitivity to the perturbation, suggesting a route to seeding vortex chaos or quantum turbulence.

Fluid dynamics of oscillatory flow across parallel-plates in standing-wave thermoacoustic system with two different operation frequencies

Thermoacoustic system is one of the alternative technologies that provides green working principles but the lack of understanding of the complex fluid flow and energy transfer interactions within structures inside the system is leading to difficulty in accurate analysis related to the system. This study presents fluid dynamic investigation of vortex shedding and velocity profile of an oscillatory flow across a parallel-plate structure inside a standing-wave thermoacoustic system by using a two-dimensional ANSYS FLUENT CFD (computational fluid dynamics) of SST k-ω turbulence model. The model was validated using experimental data and theoretical solution. Two different operating frequencies of 14.2 Hz and 23.6 Hz were investigated with drive ratios (defined as maximum pressure amplitude to mean pressure) from 0.3% up to 3%. The results revealed that velocity profiles and boundary layers within the area of parallel-plate stack changes with time and the changes followed the cyclic travel of vortex across the structure. Two layers of vortex formed near the surface of the solid structure. These layers, known as the main and secondary vortex layers, change with the cyclic flow, and are affecting the shape of velocity profiles within the channel. The appearance of an ‘m’ shape, a ‘slug’ shape and a ‘parabolic’ shape velocity profiles are also depending on the flow amplitude (drive ratio) and flow frequency. The ‘parabolic’ velocity profile is only found for a certain moment of flow with thick boundary layer. The results indicated that fully developed flow may not be likely for cases presented in this paper. Hence care should be exercised in the use of equations during the analysis of thermoacoustic system. As the parallel-plate structure is usually an important structure of the system, a proper understanding of the dynamics of flow within this structure is crucial. These findings are expected to give better insight for future design of thermoacoustic system.

Static and dynamic analyses of functionally graded sandwich skew shell panels

The present work is an attempt to develop a simple, accurate and widely applicable finite element formulation having a C0 continuity of transverse displacement at nodes, for static and dynamic analyses of functionally graded sandwich skew shell (FGSSS) panels. A layerwise displacement field based on first-order shear-deformation theory for each layer along with Sanders’ approximation has been adopted for the analysis. Compatibility conditions are imposed at the layer interfaces to satisfy displacement continuity. Two different configurations of FGSSS are taken up in the present investigation. In the first configuration, the top and bottom layers of the panel are made of functionally graded material (FGM) and the core is made of pure metal, whereas in the second configuration, the top and bottom layers are made of pure ceramic and pure metal, respectively and the core is considered to be made of FGM. The material properties of both configurations of FGM panels are estimated according to the rule of mixture. It is observed from the analysis that the present finite element formulation is simple, accurate and computationally efficient. Parameters like skew angle, span to thickness ratio, core to facesheet thickness ratio, volume fraction and boundary conditions have a significant effect on static and dynamic behavior of functionally graded sandwich skew shell panels.

Experimental and numerical investigation of turbulent wake flow around wall-mounted square cylinder of aspect ratio 2

The turbulent wake velocity fields around a short wall-mounted square cylinder of aspect ratio 2 fully immersing into a thick turbulent boundary layer are obtained experimentally with PIV and numerically with LES. Comparison between the two sets of data is made on the time-averaged mean velocities, turbulent fluctuating velocities, and the detailed characteristics of energetic large-scale coherent structures. It is noted that a good comparison of the low-order statistics of velocity fields does not guarantee a satisfactory reproduction of the coherent structures. These flow structures show great similarities in the spatial patterns and dynamic performance between PIV and LES, but apparent differences in turbulent kinetic energy contribution. On the horizontal plane parallel to the wall, the dominant antisymmetric spatial mode pair illustrates the evolution process of Karman vortex shedding with a clear spectral peak around the characteristic frequency while three extra frequency peaks are found in the symmetric spatial modes. Further investigation on the velocity field on the central vertical plane reveals the connection between the unsteadiness of shear layer flow at the free end and the spanwise symmetric vortex shedding activities. It is confirmed that the flapping motion and vortex convection mechanisms observed for the present cylinder could modulate the symmetric wake dynamics. The three-dimensional extreme wake patterns, available from LES results, are related to the most energetic Karman vortex shedding demonstrate upward flow in the vortex weakening side. Meanwhile, the downwash flow at the extreme time instants is found to become stronger always for this kind of short cylinder with a dipole wake pattern.

Numerical study of microstructural fatigue crack growth using damage mechanics

Abstract Generally the external load applied to engineering components is significantly below the yield strength. Yet, the materials fail without showing any visible indication. Furthermore, the fatigue crack growth behavior should be observed microscopically. Thus, the microstructural study of fatigue crack growth becomes important. The microstructural study of fatigue crack growth in metals does not only demonstrate the effect of microstructural properties (grain size, grain boundary thickness, etc.) on the mechanical response of the system but also informs about a microstructural modification to resist fatigue crack growth so that fatigue life of the component can be enhanced. In the present work, fatigue crack growth simulations are performed on compact tension (CT) specimen. The microstructure region is generated near the crack tip using the Voronoi tessellation approach. Further, an in-house MATLAB code based on the finite element method and continuum damage mechanics (CDM) is implemented to perform the numerical analysis. Damage based analysis is done on the microstructure meshing system to visualize the effect of microstructural quantities (average grain size, grain boundary thickness) and material constant on the fatigue crack growth in this work. Here, the obtained result shows good agreement with the experimental result and the effect of microstructural quantities on the crack initiation life is observed.

Improving the piezoelectric strain and anti-reduction properties of K0.5Na0.5NbO3-based ceramics sintered in a reducing atmosphere.

Lead-free 0.945K0.48Na0.52Nb0.96Ta0.04O3-0.055BaZrO3 + 6%MnO + xZrO2 piezoelectric ceramics sintered in a reducing atmosphere were prepared by conventional solid-state reaction methods. The use of the ZrO2 dopant resulted in an increase in the rhombohedral (R) phase in orthorhombic (O)/R coexisting phases. Nonstoichiometric ZrO2 dopant addition could effectively improve the anti-reduction properties of KNN-based ceramics via controlling the oxygen vacancy concentration. In particular, 2% mol nonstoichometric ZrO2 dopant addition could improve the activation energy of the grain boundary (Egb) via increasing the grain boundary thickness. The addition of the ZrO2 dopant could improve the fatigue resistance of the unipolar piezoelectric strain of 0.945K0.48Na0.52Nb0.96Ta0.04O3-0.055BaZrO3 + 6%MnO ceramics. The optimum inverse piezoelectric coefficient of ceramics at x = 0.01 reached up to ∼465 pm V-1 at a low driving electric field E of 20 kV cm-1 at room temperature, and the temperature stability of reached 155 °C. After 106 unipolar fatigue cycles, the β value of 0.945KNNT-0.055BZ + 6Mn + xZr ceramics could be preserved to more than 86%. The 0.945K0.48Na0.52Nb0.96Ta0.04O3-0.055BaZrO3 + 6%MnO + xZrO2 ceramic is a lead-free material with great potential to be applied in the fabrication of multilayer ceramic actuators with Ni inner electrodes in the future.

Determining the Interphase Boundary Parameters in Heterogeneous Binary Alloys on the Basis of the Hypothesis of Weak Nonlocality

Based on our earlier hypothesis of weak nonlocality, we developed a method for calculating the temperature dependences of the width and specific energy of the interphase boundary for binary substitutional alloys, using the concentration dependence of the internal energy or the equilibrium phase diagram of the alloy. Numerically calculated temperature dependences of the solubility limits, specific energy, and thickness of the interphase boundary are presented for three thermodynamic models: the regular solution model (Nb–Cu alloy), the quasi-regular solution model, and the general case (Fe–Cu alloy and A–B alloy that differs from Fe–Cu in the sign of excess entropy).

Dynamic responses analysis of P and S-FGM sandwich cylindrical shell panels using a new layerwise method

This research work presents a comparison of the dynamic response of the functionally graded sandwich cylindrical shell panels (FGSCS) using a new layerwise method. The layerwise method developed assumes a first-order shear deformation theory (FSDT) for top and bottom facesheets and a third-order shear deformation theory for the core. The strain-displacement relation for FGSCS panels is obtained using Sander's first approximation. Two different sandwich configurations are considered, one having a pure metallic core with top and bottom facesheets made of functionally graded material (FGM) and the other one having an FGM core with top and bottom facesheets made of pure ceramic and pure metal, respectively. Material properties of the FGM layers for the two configurations are varied along the thickness direction according to the power-law (P-FGM) and the sigmoid models (S-FGM) respectively. The newly developed layerwise finite element model in conjunction with Hamilton's principle is employed to obtain the governing differential equation. Subsequently, the Newmark-Beta time integration scheme is used to obtain the dynamic response of P and S functionally graded sandwich cylindrical shell (P and S-FGSCS) panels for two configurations. The results obtained are first compared with the exact analytical results available in the literature. Numerical results are presented to investigate the effect of volume fraction index, loading conditions, core-to-facesheet thickness ratio, curvature ratio and boundary conditions on the transient response of P and S-FGSCS panels. The analysis reveals by selecting optimum parameters and gradation model, the amplitude and frequency of dynamic response of P and S-FGSCS panels can be controlled substantially.

Simulation and experimental investigation of a ballistic compression soft recovery system

A soft recovery system is used to arrest a supersonic object over a limited distance in a controlled manner. This may be achieved through ballistic compression of gas. This work explains the motion of a supersonic object passing through a ballistic compression decelerator i.e., pressurized gas column initially sandwiched between two diaphragms. The accompanying mechanics is complex and includes diverse effects such as separation of shock from the supersonic object, travelling shocks, shock reflections, creation of a new shock, emergence and dissolution of contact discontinuities and expansion waves, and shock-shock interactions. In this work, these phenomena have been numerically and experimentally studied. While the method of characteristics was used to solve Euler’s equations in continuous regions, jump conditions derived from control volume considerations were used to obtain solutions across discontinuities. In this way, a duly validated finite difference method computer program was developed to analyze the problem. Finally, simulation predictions were validated by conducting experiments on a 7.62 mm soft recovery system tube. Our results showed that, an object having an entry velocity of 880 m/s, left the SRS with a velocity that was lower by 47% from simulation predictions. Further analysis showed that friction between the object and tube was a major contributor to this gap. Post accounting for friction, the difference between numerical analysis and experimental data got reduced to about 5% at most locations, and to 17% at the end of the SRS. We attribute this residual difference between observations and simulations to build up of pressure at a location post passage of shock by it. Our 2-D finite volume study results, which are consistent with earlier research, as well as with our experimental data, show that such a phenomenon is prominent particularly in narrow tubes due to development of significantly thick turbulent boundary layers.

Free vibration analysis of an orthotropic plate by dynamic stiffness method and Wittrick-Williams algorithm

The Wittrick–Williams algorithm is used as the solution technique in the dynamic stiffness matrix to compute the natural frequencies of the orthotropic plate for different boundary conditions, aspect ratios, thickness ratios and modulus ratios. The corresponding dynamic stiffness matrix of the orthotropic plate is developed by classical plate theory and Hamilton’s principle. Levy type boundary conditions are considered in this paper. Results obtained are compared with published results and that obtained by finite element method using commercial software Ansys.

Calculation of the three-dimensional turbulent boundary layer in the vessel’s bow and midship area by the integral method

The quality of technical solutions applied in ship design and construction is substantially determined by the validity of viscous flow parameters, especially in the vicinity of thrusters. The influence of shapes on velocity, pressure and turbulence distribution can be assessed by physical experimentation. Along with undeniable advantages, physical modelling has a number of disadvantages: high labour input and cost, limited range of parameters variation (e.g. Reynolds numbers), difficulty in separating the influence of individual factors. Therefore, the development of mathematical models and numerical calculation schemes based on them is extremely relevant. Calculation of friction resistance and calculation of the velocity field in the vicinity of a vessel comes down to the calculation of its boundary layer and trace parameters. Current mathematical models with a planar representation, i.e. working with projections rather than real curves, do not give an accurate description. This has led to the need for a mathematical model that can address all of the required characteristics of a three-dimensional turbulent boundary layer. Both differential and integral methods are used to calculate three-dimensional boundary layers. The model is capable of calculating the characteristics of the spatial boundary layer in the stern and the viscous wake, in the bow and in the middle of the vessel. The model is quite versatile: it has been successfully used both for computing the boundary layer characteristics in the bow and midship area by the integral method based on the thick boundary layer concept, and for computing the turbulent flow in the stern and viscous wake by the differential method based on the partial parabolic concept using the k-ε turbulence model. In this paper we will elaborate on the integral method calculation.

Механизмы генерации волн Лэмба доменной границей в пластине слабого ферромагнетика

The purpose of research. Study of the mechanism of Rayleigh-Lamb waves generation by the moving domain wall. Methods. The equations describing the elastic displacements generated by moving domain wall in the plate were solved by the Fourier method. Results. For yttrium orthoferrite crystal we’ve estimated the amplitudes of Lamb waves displacement for two different cases of their generation: due to bulk and surface strains arising from the movement of the domain wall. The amplitude of displacement in an unbounded crystal has the same order of magnitude as for waves excited by surface strains - 10 10 cm for the theoretical domain boundary thickness D3 = 1.1·10-6 m. The correlation between the contributions of bulk and surface mechanisms in the generation of Lamb waves by the domain wall has been determined. Conclusion. For development domain wall-based logic and memory devices it is necessary to fully investigate the factors that can affect the domain dynamics in magnetics. One of these factors is the braking of the domain wall on Rayleigh-Lamb waves. From the equations describing the elastic displacements in the orthoferrite crystal plate during the motion of the domain wall, we can conclude that there are two independent mechanisms of Rayleigh-Lamb waves generation bulk and surface. The evaluation of the contributions of these mechanisms helps to consider the effect of surfaces on the domain dynamics and can be used in the future to develop magnetic memory devices based on weak ferromagnets.

Synthesis route dependent structure, conductivity and dielectric properties of Ce0.8Gd0.2O1.9 oxygen ion conductor: A comparative approach

The main focus of this study is to investigate the effect of the synthesis route on structure, microstructure, and ionic transport properties of Ce0.8Gd0.2O1.9 ionic conductors. Three different synthesis routes, namely citrate auto–ignition, mechanical alloying, and co–precipitation method, were employed for the synthesis of Ce0.8Gd0.2O1.9 nanomaterials. The density of the composition prepared through the citrate auto–ignition method was found to be much greater than the compositions prepared by the other two methods. The dissolution of Gd3+ ions into ceria was highest for the samples prepared via this method. The crystallite and grain size of the samples was also found to depend on the synthesis route. On the other hand, the co–precipitation method produced finer nanomaterials in comparison with the other two methods. The sample prepared via the auto−ignition method exhibited the highest ionic conductivity, dielectric constant, and lowest association energy. The sample prepared using the co–precipitation method exhibited enhanced grain boundary conductivity due to the lesser value of grain boundary thickness and grain boundary blocking factor.

Tangential Displacement and Shear Stress Distribution in Non-Uniform Rotating Disk under Angular Acceleration by Semi-Exact Methods

In this paper semi-exact methods are introduced for estimating the distribution of tangential displacement and shear stress in non-uniform rotating disks. At high variable angular velocities, the effect of shear stress on Von Mises stress is important and must be considered in calculations. Therefore, He’s homotopy perturbation method (HPM) and Adomian’s decomposition method (ADM) is implemented for solving equilibrium equation of rotating disk in tangential direction under variable mechanical loading. The results obtained by these methods are then verified by the exact solution and finite difference method. The comparison among HPM and ADM results shows that although the numerical results are the same approximately but HPM is much easier, straighter and efficient than ADM. Numerical calculations for different ranges of thickness parameters, boundary conditions and angular accelerations are carried out. It is shown that with considering disk profile variable, level of displacement and stress in tangential direction are not always reduced and type of changing the thickness along the radius of disk and boundary condition are an important factor in this case. Finally, the optimum disk profile is selected based on the tangential displacement-shear stress distribution. The presented algorithm is useful for the analysis of rotating disk with any arbitrary function form of thickness and density that it is impossible to find exact solutions.