Control over electric field in traveling wave applicators

A method of optimal material design is applied to the problem of controlling the distribution of the electric field within a material heated by microwaves in closed cavities. Analytical and computational procedures are presented for a layer in a single-mode rectangular waveguide applicator. These determine the optimal placing and micro-geometry of composite controlling materials. The particular case of a lossless layer is illustrated numerically: it is shown that the controlling material becomes uniform with a dielectric constant which always exceeds the layer to be heated.     

Finite layer analysis of layered elastic materials using a flexibility approach. Part 2—Circular and rectangular loadings

The finite layer techniques introduced in Part 1 of this paper are extended to allow the analysis of circular or general loadings applied to horizontally layered anisotropic materials. The analysis is considerably simplified through the use of Hankel transforms (circular loadings) and double Fourier transformations (general loadings). Once again an exact flexibility matrix is found for each finite layer, and it is shown that this flexibility matrix has precisely the same form whether the loading is a strip, circular or general loading. The flexibility matrix has the advantage of not becoming singular for incompressible materials as is the case for the stiffness matrices used in a conventional finite strip analysis. Examples are given of the behaviour of circular and general (rectangular) loadings applied to multilayered anisotropic materials. It is also shown by means of an example, that the method is extremely useful for analysis of problems involving incompressible materials.     

Nonstationary frictional heat production in the course of sliding of a composite layer over the surface of a half space

We obtain the analytic solution of a nonstationary thermal problem of friction for a system formed by a composite plane-parallel layer and a homogeneous semiinfinite base. The layer slides over the surface of the base with a constant velocity. Due to the action of friction forces, the bodies are heated. In the course of interaction, convective heat transfer with the environment takes place on the outer surface of the layer. For the rectangular shape of the cross section of composite fibers, we study the influence of the thermal properties of the materials of the fiber and the matrix on the distribution of temperature in the tribosystem.     

Ceramic composite components with gradient porosity by powder injection moulding

Various components used in the industries may benefit from having layered structures with gradient porosity in each layer. In this paper, bi-layer composite components with gradient porosity made by Powder Injection Moulding (PIM) have been investigated. The ceramic spinel materials of AR7845 having coarse particle size and AR7820 having fine particle size were used. It shows that AR7820 and AR7845 powders have different sintering behaviour with the fine powder having faster shrinkage as compared to coarse powder. Curling or bending is found in the bi-layer rectangular composite component fabricated from these two powders. This is due to induced stress caused mainly by strain rate mismatch of the two materials during sintering. The degree of curling is also related to thickness ratio of two materials in each layer. Composite components can be designed into cylindrical shape so as to avoid curling as observed in rectangular composite components. No interfacial debonding and part cracking are observed in both rectangular and cylindrical composite components. The microstructure shows that continuously straight joining lines along the interfaces are formed in these composite components.     

Evaluation of R-curve behavior of ceramic-metal functionally graded materials by stable crack growth

This paper deals with the fracture toughness and R-curve behavior of ceramic-metal functionally graded materials (FGMs). A possibility of stable crack growth in a three-point-bending specimen is examined based on the driving force and resistance for crack growth in FGMs, and the distribution of fracture toughness or R-curve behavior is evaluated on FGMs fabricated by powder metallurgy using partially stabilized zirconia (PSZ) and stainless steel (SUS 304). The materials have a functionally graded surface layer (FGM layer) with a thickness of 1 mm or 2 mm on a SUS 304 substrate. Three-point-bending tests are carried out on a rectangular specimen with a very short crack in the ceramics surface. On the three-point-bending test, a crack is initiated from a short pre-crack in unstable manner, and then it propagates in stable manner through the FGM layer with an increase in the applied load. From the relationship between applied load and crack length during the stable crack growth in the FGM layer, the fracture toughness is evaluated. The fracture toughness increases with an increase in a volume fraction of SUS 304 phase.     

Transient dynamic stress intensity factors around two rectangular cracks in a nonhomogeneous interfacial layer between two dissimilar elastic half-spaces under impact load

Summary Transient dynamic stresses around two rectangular cracks in a nonhomogeneous interfacial layer sandwiched between two dissimilar elastic half-spaces are examined. The material properties vary continuously in the layer within a range from those of the upper half-space to those of the lower half-space. An incoming shock stress wave impinges perpendicular on the crack surfaces. In order to solve the problem, the interfacial layer is divided into several homogeneous layers that have different material properties. Application of Laplace and Fourier transforms reduces the problem to the solution of a pair of dual integral equations. To solve the equations, the differences in the crack surface displacements are expanded into a series of functions that vanish outside the crack. The unknown coefficients in the series are solved using the Schmidt method. The stress intensity factors are defined in the Laplace transform domain and these are inverted numerically in physical space. Numerical calculations are carried out for composite materials made of a ceramic half-space and a steel half-space.     

Effective elastic properties of solids with irregularly shaped inclusions

A unit rectangular cell is usually cut out from a medium for investigating fracture mechanism and elastic properties of the medium containing an array of irregularly shaped inclusions. It is desirable to clarify the geometrical parameters controlling the elastic properties of heterogeneous materials because they are usually embedded with randomly distributed particulate. The stress and strain relationship of the rectangular cell is obtained by an ad hoc hybrid-stress finite element method. By matching the boundary condition requirements, the effective elastic properties of composite materials are then calculated, and the effect of shape and arrangement of inclusions on the effective elastic properties is subsequently considered by the application of the ad hoc hybrid-stress finite element method through examining three types of rectangular cell models assuming rectangular arrays of rectangular or diamond inclusions. It is found that the area fraction (the ratio of the inclusion area over the rectangular cell area) is one dominant parameter controlling the effective elastic properties.     

Effects of a liquid layer on thickness-shear vibrations of rectangular AT-cut quartz plates

Thickness-shear vibrations of rectangular AT-cut quartz with one face in contact with a layer of Newtonian (linearly viscous and compressible) fluid are studied. The two-dimensional (2D) governing equations for vibrations of piezoelectric crystal plates given previously are used in the present study. The solutions for 1D shear wave and compressional wave in a liquid layer are obtained, and the stresses at the bottom of the liquid layer are used as approximations to the stresses exerted on the crystal surface in the plate equations. Closed form solutions are obtained for both free and piezoelectrically forced thickness-shear vibrations of a finite, rectangular AT-cut quartz plate in contact with a liquid layer of finite thickness. From the present solutions, a simple and explicit formula is deduced for the resonance frequency of the fundamental thickness-shear mode, which includes the effects of both shear and compressional waves in the liquid layer and the effect of the thickness-to-length ratio of the crystal plate. The formula reduces to the widely used frequency equation obtained by many previous investigators for infinite plates. The resonance frequency of a rectangular AT-cut quartz, computed as a function of the thickness of the adjacent liquid layer, agrees closely with the experimental data measured by Schneider and Martin (Anal. Chem., vol. 67, pp. 3324-3335, 1995)     

Local Buckling Delamination of a Rectangular Sandwich Plate Containing Interface Embedded Rectangular Cracks and Made From Elastic and Viscoelastic Materials

A three-dimensional buckling delamination problem for a rectangular sandwich plate made from elastic and viscoelastic materials is studied. It is supposed that the plate contains interface embedded rectangular cracks and that the edge-surfaces of these cracks have initial infinitesimal imperfections. The evolution of these initial imperfections with an external bi-axial compressed force (for the case where the materials of the layers of the plate are elastic) or with duration of time (for the case where the materials of the layers of the plate are viscoelastic) is investigated. The corresponding boundary value problem is formulated within the framework of the piecewise homogeneous body model with the use of three-dimensional geometrically nonlinear field equations of the theory of viscoelastic bodies. This problem is solved by employing boundary form perturbation techniques, Laplace transform and FEM. According to the initial imperfection criterion, the values of the critical parameters are determined. Numerical results on the critical force and critical time are presented and discussed. In particular, it is established that the values of the critical forces obtained for the buckling delamination around the rectangular embedded interface cracks are significantly greater than those obtained for the corresponding edge and band cracks.     

Mechanism of high energy absorption by foamed materials-foamed rigid polyurethane and foamed glass

Energy absorbability of foamed rigid materials, polyurethane and glass, was studied under a compressive load. The brittle materials were proved to absorb much energy in a manner similar to ductile materials. A mechanism for such high energy absorption was proposed, based on a fracture model in which crushing of cells initiates at the weakest cell followed by propagation to cells lying in the layer containing the weakest one and lying in a direction perpendicular to the compressive force; then the crushing propagates to another layer under the compressive force after the completion of the first layer crushing. In the period of one layer crushing, the strain energy stored in the period of compression prior to the crushing is temporarily released, and it is stored again in the period of compression after the crushing. The store and release of strain energy is assumed to be repeated until all cell layers are crushed. This mechanism of layer-by-layer crushing allows the cells to absorb strain energy repeatedly, and causes high energy absorption in the brittle foamed material. The calculated energy based on the mechanism agrees well with the observed one.     

Marangoni Convection Instabilities Induced by Evaporation of Liquid Layer in an Open Rectangular Pool

In order to investigate the Marangoni convection instability of 0.65cSt silicone oil induced by evaporation in liquid layer, a series of experiments are carried out in an open rectangular pool. The effects of side wall temperature as well as ambient temperature on competitions between BM convection and thermocapillary convection are analyzed thoroughly. Increasing of the side wall temperature would inevitably enhance thermocapillary convection and suppress the formation of BM cells by transferring hot fluid from border to surface. As long as the side wall temperature is high enough, BM cells would disappear completely and multicellular rolls as well as hydrothermal waves would occur in the whole layer. Increasing ambient temperature would enhance both BM convection and thermocapillary convection, but the later one benefits more from it because hydrothermal waves can occur at a lower Ma number. Critical Marangoni numbers for the incipience of hydrothermal waves and that disappearance of BM convection cells are obtained under different ambient temperatures.     

Recent Progress in Interconnection Layer for Hybrid Photovoltaic Tandems

Hybrid tandem solar cells offer the benefits of low cost and full solar spectrum utilization. Among the hybrid tandem structures explored to date, the most popular ones have four (simple stacking design) or two (terminal/tunneling layer addition design) terminal electrodes. Although the latter design is more cost-effective than the former, its widespread application is hindered by the difficulty of preparing an interface between two solar cell materials. The oldest approach to the in-series bonding of two or more bandgap solar cells relies on the introduction of a tunneling layer in multijunction III–V solar cells, but it has some limitations, e.g., the related materials/technologies are applicable only to III–V and certain other solar cells. Thus, alternative methods of realizing junction contacts based on the use of novel materials are highly sought after. Here, the strategies used to realize high-performance tandem cells are described, focusing on interface control in terms of bonding two or more solar cells for tandem approaches. The presented information is expected to aid the establishment of ideal methods of connecting two or more solar cells to obtain the highest performance for different solar cell choices with minimized energy loss through the interface.     

Some experiments on the elastic stability of some highly elastic bodies

Uniaxial compression experiments on solid circular bars, rectangular bars, and thick-walled circular tubes made of rubber materials are described, and the data are compared with known theoretical results derived for neo-Hookean materials. It is found in all cases that the general nature of certain global analytical estimates are in good qualitative agreement with existence of a transition slenderness ratio that separates buckling characteristic of long bars from axisymmetrie bulging characteristic of short bars. The data agrees qualitatively also with other more precise analytical results for circular and rectangular bars, but only as regards Euler type buckling. Specific analytical results for axisymmetrie deformation of circular tubes are found to be without experimental foundation.     

Microwave detection and depth determination of disbonds in low-permittivity and low-loss thick sandwich composites

Nondestructive evaluation (NDE) of disbonded low-permittivity and low-loss dielectric multilayered composite media is of considerable interest in many applications. The ability of microwaves to penetrate inside dielectric materials makes microwave NDE techniques very suitable for interrogating structures made of multilayered dielectric composites. Additionally, the sensitivity of microwaves to the presence of dissimilar layers in such materials allows for accurate detection of a disbonded layer. In a multilayered composite, a disbond may occur between any two (or more) layers. The potential of utilizing microwave NDE techniques for the detection and depth estimation of disbonds in a thick sandwich composite is investigated. This study utilizes a theoretical model developed for investigating the interaction of microwave radiation from an open-ended rectangular waveguide sensor with ann-layer dielectric composite medium. The influence of the standoff distance between the sensor and the medium and the operating frequency on the sensitivity of disbond detection and depth estimation is studied to obtain an optimum set of parameters for enhanced detection sensitivity. Results of the theoretical study are presented with a discussion on the optimization process for a thick sandwich composite composed of 13 dielectric layers.     

The Sound Radiation Characteristic from Un-baffled Rectangular Plates

The sound radiation characteristic from un-baffled rectangular plates is studied in this paper. Both the pressure jump and the transverse displacement of vibrating rectangular plates are also presented. The sound power level radiated from un-baffled plates is numerically calculated by using a double layer integral representation of the sound radiation pressure and the modal coupling coefficients. Rectangular plates with clamped support and elastically support encountered frequently are calculated as numerical experiments. The sound power level radiated from baffled rectangular plates with the same boundary conditions are also calculated in numerical experiments for comparison. From the viewpoint of energy, average velocity square of un-baffled and baffled rectangular plates with␣different boundary conditions is also calculated respectively. The relationship of sound radiation efficiency between un-baffled and baffled rectangular plates is also deduced.This Works is supported by the National Natural Science Foundation of China (Grant No. 50075029)     

Joining Fragmented Epistyles Using Threaded Titanium Bars: A Numerical Analysis

Abstract:  The mechanical behaviour of marble architraves, restored with titanium bars and suitable cementitious material, is studied with the aid of the finite-element method. The study was motivated by the needs of the conservation project in progress on the Parthenon Temple of the Acropolis of Athens. A realistic numerical model was created taking into account the exact geometry of the threaded bars as well as the exact mechanical properties of the materials involved. The architrave was considered as a prismatic beam of rectangular cross section, centrally fractured and restored with one threaded titanium bar. The bar was inserted in a hole of slightly greater diameter drilled in the member and filled with suitable cementitious material. In this way, a sequence of three materials appears (marble–cement–titanium) giving birth to two interfaces (marble–cement and cement–titanium). Emphasis was given to the influence of the cement layer on the stress and strain fields. The cement was modelled as either linear or bilinear material and the analysis indicated the crucial role of this layer for the drastic reduction in the strain discontinuities.     

Geometrically nonlinear free vibrations of the symmetric rectangular honeycomb sandwich panels with simply supported boundaries

Geometrically nonlinear free vibrations of symmetric rectangular honeycomb sandwich panels with simply supported boundaries at the four edges are investigated using the homotopy analysis method (HAM). The honeycomb core of hexagonal cells is modeled as a thick layer of orthotropic material whose parameters of physical and mechanical properties are calculated by the corrected Gibson’s formula. The basic formulation of nonlinear free vibrations has been developed based on the third-order shear deformation plate theory and the nonlinear strain–displacement relation. The equilibrium equations have been obtained using Hamilton’s principle. Effects of axial half-waves, height and height ratio on the nonlinear free vibration response have been investigated for honeycomb sandwich panels.     

Quasi three-dimensional, n-bit optical memory based on the ellipsometric principle: model calculations

Model calculations on the ellipsometric memory are presented. The ellipsometric memory is an n-bit optical memory whose information is extracted by use of the ellipsometric principle. The memory cells of the device consist of thin-film multilayer structures, and the information of each memory cell is contained in the optical properties of the thin films. Several thin-film multilayer structures were examined in order to find out how different choices of layer materials and other system parameters such as layer thicknesses and wavelength affect resolutions and limitations of the ellipsometric memory. Such calculations are also useful for optimizing the readout resolution. It was found that it is possible to use memory cells having up to at least eight layers, which would permit 8-bit words to be stored at each location. It was also found that, in principle, several types of materials can be used as layer materials, and various aspects of different choices of materials are discussed.     

Progress in Materials Development for the Rapid Efficiency Advancement of Perovskite Solar Cells

The efficiency of perovskite solar cells (PSCs) has undergone rapid advancement due to great progress in materials development over the past decade and is under extensive study. Despite the significant challenges (e.g., recombination and hysteresis), both the single‐junction and tandem cells have gradually approached the theoretical efficiency limit. Herein, an overview is given of how passivation and crystallization reduce recombination and thus improve the device performance; how the materials of dominant layers (hole transporting layer (HTL), electron transporting layer (ETL), and absorber layer) affect the quality and optoelectronic properties of single‐junction PSCs; and how the materials development contributes to rapid efficiency enhancement of perovskite/Si tandem devices with monolithic and mechanically stacked configurations. The interface optimization, novel materials development, mixture strategy, and bandgap tuning are reviewed and analyzed. This is a review of the major factors determining efficiency, and how further improvements can be made on the performance of PSCs.     

Dependence of the tracking performance of an optical disk on the direction of the incident-light polarization

In optical-disk data-storage systems, the signal that provides tracking information is dependent on the groove shape, the optical constants of the materials involved, and the polarization state of the incident light. In this paper, we show that the tracking signal can be described by two measurable quantities, both of which are largely independent of aberrations in the optical system. Using these two quantities, we match the tracking performance of a given disk to an equivalent disk having rectangular grooves-the adjustable parameters being the rectangular groove depth and the duty cycle. By assumption, these rectangular grooves modulate only the phase of the incident beam and disregard its state of polarization. The effective groove depth and the duty cycle thus become dependent on the polarization state of the incident beam. We examine these dependences for various disks having different groove geometries and different combinations of materials.