Cavities Of Various Shapes Research Articles

The effect of cavity shape on critical high-temperature regions formation pattern and structural evolution difference in explosive particle bed

The occurrence of critical high-temperature regions within explosives is a crucial factor in initiating combustion and explosion. The primary causes of hot regions in cavity-containing explosives are dissipative processes occurring inside the explosive or at its interface, such as shear, friction, viscosity, plasticity, and heat transfer. Currently, there is limited research on the generation and dissipation mechanisms of critical high-temperature regions in cavity-containing explosives during impacts, based on the mesoscale analysis that describes particle motion. In this study, a model based on the discrete element method is employed allowing for an accurate analysis of the dynamic and thermodynamic processes among particles, which systematically considers the shear history between particles, elastoplastic collisions, and heat transfer between particles. The temporal evolution of particle temperature and dissipated work contours during the impact process of explosives with different cavity shapes is analyzed. Explosives with cavities undergo three stages during the impact process: the formation of the trapezoidal high-temperature region, cavity collapse, and dispersion of the particle bed, ultimately leading to the formation of two main critical high-temperature regions: near the cavity and near the wall. The temperature rise of hot particles near the wall can be roughly divided into two stages, and the temperature rise mechanisms are different. Initially, the temperature rise is primarily attributed to plastic dissipation of hot particles, and the same initial impact velocity results in the same temperature rise. During the cavity collapsing, continuous momentum transfer occurs between the hot particles near the wall and the particles in the high-temperature shear bands, deeply influencing the development of the high-temperature shear bands through the movement of the hot particles near the cavity. Therefore, the different collapse modes of hot particles near cavities of different shapes lead to differences in the later temperature evolution of the hot particles near the wall. The unique aggregation processes of hot particles near cavities of various shapes result in distinct high-temperature region morphologies: circular cavity exhibits approximate “——” shape, triangular cavity displays arch shape, and inverted triangular cavity presents “M” shape. Significantly, a new mechanism resulting from the interaction of two opposing “jet “flows for the formation of higher-temperature hot regions near the circular cavity has been discovered.

Cavity nucleation in single-component homogeneous amorphous solids under negative pressure

Understanding the cavity formation and cavity growth mechanisms in solids has fundamental and applied importance for the correct determination of their exploitation capabilities and mechanical characteristics. In this work, we present the molecular dynamics simulation results for the process of homogeneous formation of nanosized cavities in a single-component amorphous metallic alloy. To identify cavities of various shapes and sizes, an original method has been developed, which is based on filling cavities by virtual particles (balls) of the same diameter. By means of the mean first-passage time analysis, it was shown that the cavity formation in an amorphous metallic melt is the activation-type process. This process can be described in terms of the classical nucleation theory, which is usually applied to the case of first order phase transitions. Activation energy, critical size and nucleation rate of cavities are calculated, the values of which are comparable with those for the case of crystal nucleation in amorphous systems.

Wear mechanism and quantification of polycrystalline diamond milling cutter in high speed trimming of carbon fiber reinforced epoxy

The use of polycrystalline diamond cutters (PCD) in machining of composite material is increasing. Understanding their wear mechanism and clarity on wear measurement methodology will lead to their productive usage and cost justification. This study focuses on understanding wear in PCD milling cutters at the micro, macro level, and its physical characterization when employed for fibrous composite machining. This leads to the development of a proposal for a clear methodology on consistent wear measurement, which includes a suitable selection of techniques and identification of wear parameters. Continuous diamond skeleton structure made during binder infiltration is captured in worn out PCD edge with the help of scanning electron microscopy. Overall wear process appears to be a complex mixture of losing binder, smaller grains, and pieces of continuous diamond skeleton. This results in cavities of various shapes and forms on the cutting edge making substantial variations in edge recession and edge width. After analyzing, different tool parameters, it was found out that the distance from apex to edge roundness of clearance or rake face is a reliable and repeatable wear parameter. These are shown to be comparable between different wear locations, flutes, and tools suggesting higher wear predictive capabilities. Among different techniques, three-dimensional high-resolution profile scanning of the cutter has been identified as the most efficient tool for tracking wear at regular intervals in tool life prediction studies.

Numerical simulation of seismic wave field in graded geological media containing multiple cavities

In this study, we develop an efficient boundary integral equation method for estimation of seismic motion in a graded medium with multiple cavities under antiplane strain conditions. This inhomogeneous and heterogeneous medium is subjected to either time-harmonic incident shear seismic waves or to body waves radiating from a point seismic source. Three different types of soil material gradient are considered: (i) density and shear modulus vary proportionally as quadratic functions of depth, but the wave velocity remains constant; (ii) the soil material is viscoelastic, with a shear modulus and density that vary with respect to the spatial coordinates in an arbitrary fashion, so that the wave velocity is both frequency and position-dependent and (iii) the soil material has position-dependent shear modulus and constant density, yielding a linear profile for the wave velocity. Three different, frequency-dependent boundary integral equation schemes are respectively developed for the aforementioned three types of graded soil materials based on: (i) Green's function for the quadratically graded elastic half-plane; (ii) a fundamental solution for the viscoelastic full-plane with position-dependent wave speed profiles and (iii) a fundamental solution for an elastic full-plane with a linearly varying wave speed profile. Next, a number of cases involving geological media with position-dependent material properties and any number of cavities of various shapes and geometry are solved in the frequency domain. The numerical results reveal the dependency of the wave fields and zones of stress concentration on the following key factors: (i) type and properties of the soil material gradient; (ii) type and characteristics of the applied seismic load; (iii) shape, position and number of cavities and (iv) interaction phenomena between the cavities and the free surface.

Effect of Enclosed Space Configuration and Freezing Medium Volume on Refreezing Pressure

In building underground structures (bases and foundations of residential and industrial buildings, boreholes for hydrocarbon extraction, etc.) in cryolithic zones, cavities of various shapes and sizes saturated with liquid media often develop. When they refreeze, the refreezing pressure occurs; this may result in failure of the structural member continuity, and further failure of the structure as it is. The paper describes the calculation techniques for the refreezing pressure depending on cavity shapes and sizes.

Torsion of elliptical composite bars containing neutral coated cavities

Using complex variable methods and conformal mapping techniques, we establish the existence of coated cavities of various shapes that do not disturb the warping function in a host elliptical bar. These cavities are known as ?partly neutral cavities?. Our results show that the two axes corresponding to the neutral elliptical coating are parallel to those of the host elliptical bar and that the centre of the elliptical coating can be located arbitrarily on the major axis of the host bar. Examples of neutral coated non-elliptical cavities are provided.

Skeletal evidence of tuberculosis in a modern identified human skeletal collection (Certosa cemetery, Bologna, Italy).

The diagnosis of tuberculosis (TB) in osteoarcheological series relies on the identification of osseous lesions caused by the disease. The study of identified skeletal collections provides the opportunity to investigate the distribution of skeletal lesions in relation to this disease. The aim of this study was to examine the skeletal evidence for TB in late adolescent and adult individuals from the identified human collection of the Certosa cemetery of Bologna (Italy, 19th-20th c.). The sample group consists of 244 individuals (138 males, 106 females) ranging from 17 to 88 years of age. The sample was divided into three groups on the basis of the recorded cause of death: TB (N = 64), pulmonary non-TB (N = 29), and other diseases (N = 151). Skeletal lesions reported to be related to TB were analyzed. The vertebral lesions were classified into three types: enlarged foramina (EnF, vascular foramina with diameter of 3-5 mm), erosions (ER), and other foramina (OtF, cavities of various shapes > 3 mm). A CT scan analysis was also performed on vertebral bodies. Some lesions were seldom present in our sample (e.g., tuberculous arthritis). OtF (23.7%) and subperiosteal new bone formation on ribs (54.2%) are significantly more frequent in the TB group with respect to the other groups. The CT scan analysis showed that the vertebrae of individuals who have died of TB may have internal cavities in the absence of external lesions. These traits represent useful elements in the paleopathological diagnosis of TB.

Optimal design for the fluid cavity shape in hydromechanical fine blanking

Hydromechanical fine blanking with fluid cavities of various shapes is investigated in this work. In this paper, seven shapes (V, angled, U, and four elliptical shapes) are studied. It is shown that the U-shape produces the greatest burnished length among the seven flow cavity shapes. Furthermore, the hybrid experimental optimization technique is used to optimize the parameters of the U-shaped cavity. It is found that the burnished surface obtained from this approach can nearly reach the full thickness of the blank in one operation, which means that the fracture zone can be almost entirely eliminated. In addition, the surface roughness of the burnished surface ranges between 0.5 and 0.098 μm, and the tolerance band for the diameter is between IT5 and IT7. These results represent an improvement over the values obtained with conventional fine blanking.

Electrowetting Assisted Air Detrapping in Transfer Micromolding for Difficult-to-Mold Microstructures

As a widely applicable process for fabricating micro- or nanostructures, micromolding in atmosphere would require the removal or minimization of air-trapping in mold cavities so as to fill the liquid prepolymer fully into the mold for generating an exact polymer duplicate. This has been difficult, if not impossible, especially for a mold with high aspect ratio, varying size/shape, or isolated cavities because the air can be trapped inside such mold cavities in most variants of the molding process. This paper presents an electrowetting assisted transfer micromolding process to solve this problem. A feeding blade continuously supplies a UV-curable prepolymer over a dielectric-coated conductive mold placed on a progressively advancing stage. A voltage applied to the electrode pair composed of the feeding blade and mold generates an electrowetting of the prepolymer to the mold. The electrowetting allows for the three-phase contact line to pass progressively along the sidewalls and bottoms of the cavities, completely pushing out the air initially occupying the cavities, or generates an electrocapillary force large enough to pull the prepolymer deeply into the mold by compressing the air already trapped inside the cavities to a minimized volume. An experiment has been performed for micromolding with deep cavities of various shapes and sizes, demonstrating an essential improvement in the structural integrity of the polymer duplicates.

APPLICATIONS AND FUTURE PROSPECTS FOR MICROSTRIP ANTENNAS USING HETEROGENEOUS AND COMPLEX 3-D GEOMETRY SUBSTRATES

This paper critically reviews the electromagnetic advantages of altering the dielectric substrate section of the antenna as opposed to the conducting elements. Changing the dielectric has been used to improve the bandwidth, e-ciency and gain of antennas. Heterogeneous substrates have also been employed to lower the efiective permittivity, suppress surface waves for high indexed substrate materials and reduce mutual coupling. In the second half of this paper, 3-D printing has been used to create substrates with reduced material consumption for a lightweight ∞exible wearable antenna. Consumer demand for small devices with wireless connectivity has put increasing pressure on antenna engineers to improve electromagnetic performance in smaller packages. These design constraints are further exacerbated by increasing demand for improved bandwidth, e-ciency and frequency coverage. Including an additional degree of design freedom by manipulating the substrate shape and properties can help address these challenges. These synthetic substrates are very di-cult to manufacture using conventional technologies. Complex 3-D printed geometries can easily be manufactured from computer aided design models that can be exported directly from electromagnetic simulation software. 3-D printing allows the geometry to be varied in all three dimensions, therefore printed cavities of various shapes and sizes can lead to a smooth or discrete change in the efiective permittivity. With the latest advances in additive manufacturing and 3-D printing, the antenna and radiofrequency designer will be able to control the local efiective permittivity and the substrate shape to gain electromagnetic advantages. Section 1 of this paper reviews the advantages of using heterogeneous substrates. Section 2 investigates the minimisation of the substrate volume. Section 3 details how these samples can be manufactured using 3-D printing. Conclusions are drawn in Section 4. 1.1. Control of Surface Waves and Current Modes Microstrip antennas are light, low proflle, conformal, compact structures which are normally fabricated on a homogeneous substrate. They can be regarded as a dielectric fllled parallel plate waveguide radiating at discontinuities (1,2). The size of an antenna can be easily reduced by using a dielectric with a high-valued permittivity but this also increases the energy in the surface wave modes (3). These surface waves decrease the e-ciency of the antenna and also cause interference with the radiation pattern by getting difiracted from the edges of the flnite sized ground plane (4). These detrimental efiects can therefore be reduced by suppression of surface wave modes. Heterogeneous substrates have been utilised, for a circular microstrip antenna, to completely suppress the surface waves caused by TM0 mode, which is the main cause of surface wave radiation for thin substrate microstrip antennas (4). The

Torsion of an elastic space containing an axially symmetric narrow cavity

By the method of singular integral equations, we solve the axially symmetric problem of torsion for an elastic space containing a smooth cavity. We obtain the stress distributions and their maximum values at the edges of cavities of various shapes. We also compute the stress concentration factors on the surfaces of axially symmetric cavities in the entire range of values of the radii of rounding of their tips under the conditions of torsion of the elastic body. The numerical results are obtained for cavities of different configurations.

The formation of organic (propolis films)/inorganic (layered crystals) interfaces for optoelectronic applications

Propolis (honeybee glue) organic films were prepared from an alcoholic solution on the surfaces of inorganic layered semiconductors (indium, gallium and bismuth selenides). Atomic force microscopy (AFM) and X-ray diffraction (XRD) are used to characterize structural properties of an organic/inorganic interfaces. It is shown that nanodimensional linear defects and nanodimensional cavities of various shapes are formed on the van der Waals (VDW) surfaces of layered crystals as a result of chemical interaction between the components of propolis (flavonoids, aminoacids and phenolic acids) and the VDW surfaces as well as deformation interaction between the VDW surfaces and propolis films during their polymerization. The nanocavities are formed as a result of the rupture of strong covalent bonds in the upper layers of layered crystals and have the shape of hexagons or triangles in the (0001) plane. The shape, lateral size and distribution of nanodimensional defects on the VDW surfaces depends on the type of crystals, the magnitude and distribution of surface stresses. We have obtained self-organized nanofold structures of propolis/InSe interface. It is established that such heterostructures have photosensitivity in the infrared range h ν < 1.2 eV (the values of energy gap are 1.2 eV for InSe and 3.07 eV for propolis films at room temperature).

Fabrication of silicon and oxide membranes over cavities using ion-cut layer transfer

Silicon and oxide membranes were fabricated using an ion-cut layer transfer process, which is suitable for sub-micron-thick membrane fabrication with good thickness uniformity and surface micro-roughness. After hydrogen ions were implanted into a silicon wafer, the implanted wafer was bonded to another wafer that has patterned cavities of various shapes and sizes. The bonded pair was then heated until hydrogen-induced silicon layer cleavage occurred along the implanted hydrogen peak concentration, resulting in the transfer of the silicon layer from one wafer to the other. Using this technique, we have been able to form sealed cavities and channels of various shapes and sizes up to 50-/spl mu/m wide, with a 1.6-/spl mu/m-thick silicon membrane. As a process variation, we have also fabricated silicon dioxide membranes for optically transparent applications.

Compliance tensors of ellipsoidal inclusions

Fourth rank H-tensors that determine the contribution of an inclusion into the overall strain under given loads were calculated earlier for a number of two- and three-dimensional "empty" cavities of various shapes by Kachanov et al. (1994). Shafiro and Kachanov (1997) found H-tensors for cavities containing compressible fluid. Here, we extend these results to the ellipsoidal inclusion having arbitrary elastic constants.

Some Scaling Rules for the Overall Thermal Conductivity in Porous Materials

The overall thermal conductivity in an isotropic porous medium containing cavities of various shapes is studied in this work. The cavity shapes under consideration include spherical and cylindrical pores, prelate and oblate spheroids, and cylindrical cavities with rectangular cross sections. The unique feature lies in the derivation of the scaling rules governing the overall thermal conductivity in porous media containing various shapes of internal cavities. The temperature distribution around the representative cavity surface, the central quantity in the present differential formulation, is obtained by the boundary element method employing the exterior formulation.

Nephrotic tunnels in glomerular basement membrane as revealed by a new electron microscopic method.

To clarify the ultrastructure in situ of the normal human glomerular basement membrane and ultrastructural changes of the glomerular basement membrane in patients with nephrotic syndrome, specimens of normal renal tissue and specimens from patients with membranous nephropathy, lupus nephritis, minimal change nephrotic syndrome, diabetic nephropathy, and Alport's syndrome were obtained. Specimens were examined by transmission electron microscopy by the newly devised "tissue negative staining method." Normal glomerular basement membrane showed a three-dimensional lattice-like meshwork of fibrils measuring 1.9 +/- 0.4 nm in diameter that formed numerous uniform, round, oval, or polygonal pores 2.5 +/- 0.4 nm in short diameter and 2.8 +/- 0.5 nm in long dimension. The nephrotic glomerular basement membrane revealed varying degrees of ultrastructural defects, the most prominent being tunnels and cavities. Tortuous tunnels measuring approximately 15 to 50 nm in diameter penetrated the entire glomerular basement membrane. Cavities of various shapes measuring 15 to 200 nm in diameter were diffusely scattered in the glomerular basement membrane and occasionally aggregated to form a honeycomb structure that occupied the whole thickness of the glomerular basement membrane. These defects appeared to be the pathway for protein leakage.

Effective Moduli of Solids With Cavities of Various Shapes

Effective elastic properties of solids with cavities of various shapes are derived in two approximations: the approximation of non-interacting cavities and the approximation of the average stress field (Mori-Tanaka’s scheme); the latter appears to be appropriate when mutual positions of defects are random. We construct the elastic potential of a solid with cavities. Such an approach covers, in a unified way, cavities of various shapes and any mixture of them. No degeneracies (or a need in a special limiting procedure) arise when cavities shrink to cracks. It also provides a unified description of both isotropic and anisotropic effective properties and recovers results available in the literature for special cases. Elastic potentials dictate the choice of proper parameters of cavity density. These parameters depend on defect shapes. Even in the case of random orientations, the isotropic overall properties cannot be characterized in terms of porosity alone; for elliptical holes, for example, a second parameter - “eccentricity” - is needed.

Some measurements of the penetration of turbulence into small cavities

Within a cavity, bordering a fluid in turbulent flow, mass and heat transport, along with phenomena which depend on them (such as corrosion), are likely to be affected by penetration of turbulence from without. Experimental measurements of velocities within cavities have been carried out by hot film velocimetry. Measurements were carried out in a wind tunnel with cavities of various shapes, of width 2–10 mm. Turbulence was generated by a grid upstream of the cavity and velocity fluctuations were observed in the cavity for all but the smallest cavities. It is suggested that an eddy will penetrate a cavity if the cavity is larger than the Prandtl eddy length.

Compressibility of Two-Dimensional Cavities of Various Shapes

Muskhelishvili-Kolosov complex stress functions are used to find the stresses and displacements around two-dimensional cavities under plane strain or plane stress. The boundary conditions considered are either uniform pressure at the cavity surface with vanishing stresses at infinity, or a traction-free cavity surface with uniform biaxial compression at infinity. A closed-form solution is obtained for the case where the mapping function from the interior of the unit circle to the region outside of the cavity has a finite number of terms. The area change of the cavity due to hydrostatic compression at infinity is examined for a variety of shapes, and is found to correlate closely with the square of the perimeter of the hole.

Dynamic Stresses and Displacements Around Cylindrical Cavities of Arbitrary Shape

Dynamic stresses and displacements around cylindrical cavities of various shapes, namely, circular, triangular, and square cavities are presented in this paper. Also presented are results for a pair of circular cavities of equal radii and a pair of circular and square cavities. These results are of interest in estimating the effects of corners and multiple scattering on the distribution of dynamic displacements and stresses around cylindrical holes or openings. Since exact analytical solutios are not available in these cases (except for a single circular hole) a numerical technique combining the finite element method (FEM) and the method of eigenfunction expansions is used here.