Stainless Steel Spheres Research Articles

ACOUSTIC SCATTERING BY TWO SPHERES: MULTIPLE SCATTERING AND SYMMETRY CONSIDERATIONS

Acoustic scattering by two identical spheres is theoretically, numerically and experimentally studied by highlighting the role of the symmetries of the scatterer. Incident and scattered fields are expanded over the different irreducible representations of D∞h, the continuous symmetry group of the scatterer. Then, from the boundary conditions, one obtains for each irreducible representation an infinite system of linear complex algebraic equations where the unknown scattering coefficients are uncoupled. This feature greatly simplifies the treatment of the problem and speeds up calculations. Farfield form functions are computed in the cases of Neumann boundary conditions (rigid spheres) and elastic boundary conditions (elastic spheres immersed in water). A series of experiments based on ultrasonic spectroscopy is performed in the case of two stainless-steel spheres immersed in water. The comparison between the theoretical and the experimental results provides quite a good agreement.

Aerodynamic levitation of stainless steel spheres in Argon plasma jet Part I: Hydrodynamics

Aerodynamic levitation of stainless steel spheres in Argon plasma jet Part I: Hydrodynamics

Vibro-acoustography of small spheres

Vibro-acoustography is a method for imaging the acoustic energy emitted from objects in response to an oscillatory radiation force produced by two interfering focused beams of ultrasound [M. Fatemi and J. F. Greenleaf, Science 280, 82–85 (1998)]. To facilitate quantitative study, a model is presented that describes the behavior of an elastic sphere in two plane ultrasound waves of slightly different frequencies. The vibrating velocity and the resulting acoustic emission of the sphere at the difference frequency are derived from the radiation force and the impedance of the sphere. For small steel spheres in water, the velocity and emission are predicted to have a simple relationship with the difference frequency and the size of the sphere. Experiments on small stainless steel spheres of different size are carried out for a number of difference frequencies, with a laser interferometer to measure the velocity of the sphere and a calibrated hydrophone to measure the acoustic emission from the sphere. The experimental results fit the model description well. This means that vibro-acoustography may be useful in quantitative measurement.

THE EFFECTIVE THERMAL CONDUCTIVITY OF PACKED BEDS OF SPHERES FOR A FINITE CONTACT AREA

The upper and lower bounds of the effective thermal conductivity range of packed beds of spheres is evaluated using the theoretical approach of the volume averaging method for a two-phase system. The solid mechanics and thermal problems are resolved by considering the effects of superficial roughness and pressure. The numerical solutions to the problem of thermal conduction through the periodic regular arrangement of stainless steel and aluminum spheres in the air are determined using the finite element method. As regards to the aluminum spheres, the influence of oxide stratum on the effective thermal conductivity is also considered. Finally, empirical equations are proposed for periodic regular arrangements of stainless steel and aluminum spheres.

Mechanical properties of dental investment materials.

Measurement of the elastic modulus (E) of investment materials has been difficult because of their low strength. However, these values are essential for engineering simulation and there are many methods available to assess the elasticity of materials. The present study compared two different methods with one of the methods being non-destructive in nature and can be used for specimens prepared for other tests. Two different types of investment materials were selected, gypsum-and phosphate-bonded. Method 1 is a traditional three-point bending test. Twelve rectangular bars with dimension of (70 x 9 x 3 mm) were prepared and placed on supports 56.8 mm apart. The test was conducted at a cross-head speed of 1 mm/min by use of a universal testing machine. The load applied to the test specimen and the corresponding deflection were measured until the specimen fractured. The E value was calculated from a linear part of the stress-strain plot. Method 2 is an ultra micro-indentation system to determine near surface properties of materials with nanometer resolution. The measurement procedure was programmed such that the specimens were indented with an initial contact force of 5 mN then followed by a maximum force of 500 mN. Measurement consisted of 10 indentations conducted with a spherical stainless steel indenter (R = 250 microm) that were equally spaced (500 microm). The E value rose asymptotically with depth of penetration and would approach the three-point bending test value at approximately four time's maximum contact depth for both materials. Both methods are practical ways of measuring the E of investment materials.

Environmental engineering: Stepwise pyrolysis of plastic waste

Kinetic data obtained from micro thermogravimetry and gradient free reactor experiments confirm that different molecular structures of commodity plastics bring about different reaction mechanisms of thermal decomposition, different reaction rates, and different temperature dependencies of the decomposition rates. From that, stepwise pyrolysis of mixtures of plastics seems to be reasonable where the different components of the mixture are pyrolysed at different temperatures. To perform a stepwise pyrolysis in laboratory scale a cascade of well stirred reactors has been developed where mixing of the reactor contents occurs by circulating of stainless steel spheres. Examples for the separation of single plastics by stepwise thermal decomposition of mixtures of poly(vinyl chloride), polystyrene and polyethylene are presented. In the first step hydrogen chloride from poly(vinyl chloride) is released, in the second step styrene from polysytrene is formed and in the third step aliphatic compounds from polyethylene decompositon are trapped. Differences in the thermal degradation of single polymers and mixtures of polymers, e.g. in the apparent activation energies and preexponential factors, are investigated using mixtures and blends of polyethylene and polystyrene.

Target detection by an echolocating harbor porpoise (Phocoena phocoena).

Two echolocation experiments are described. They were conducted on the same harbor porpoise housed in a sea pen, one year apart at Neeltje Jans, The Netherlands. The aims were to determine the target detection ability of an echolocating harbor porpoise, with the ultimate goal to predict the distance at which harbor porpoises can detect fishing nets. In experiment 1, the maximum distance at which the 3-year-old porpoise could detect a 7.62-cm diameter water-filled stainless-steel sphere by echolocation was determined psychophysically. The 50%-current detection threshold was reached when the sphere was at a distance of 26 m from the porpoise's rostrum. In experiment 2, conducted a year later, the maximum detection distance for a 5.08-cm water-filled stainless-steel sphere was 15.9 m. The target strengths of both targets were measured using simulated harbor porpoise echolocation signals and the results, coupled with transmission-loss calculations, indicated that the echo levels received by the porpoise with the targets at the threshold ranges in the two experiments were only 1.3 dB apart. Together with information on the target strengths of various fishing nets, the results of the present study can be used to predict the distance at which the nets can be detected by harbor porpoises.

Hypervelocity impact studies using the 2 MV Van de Graaff accelerator and two-stage light gas gun of the University of Kent at Canterbury

The hypervelocity impact facilities of the University of Kent are described. They comprise a 2 MV Van de Graaff accelerator for the electrostatic acceleration of dust particles (mass and velocities ) and a two-stage light gas gun firing millimetre-sized particles at . Results for impact ionization studies using iron dust accelerated in the Van de Graaff and hitting a variety of metal targets (gold, silver, indium, iron, rhodium and molybdenum) are presented. Over the range , the ionization yields are found to be similar to within a factor of 20 at low velocity and converge to within a factor of five at high velocity. The light gas gun is used to investigate the volumes of craters in metal targets for impacts of 1 mm diameter stainless steel spheres on aluminium at velocities in the range . For normal incidence the crater volume scales with the square of the impact velocity. For oblique impacts at a fixed velocity it is found that the crater volume scales with the cosine of the impact angle.

Sonar detection and classification of buried targets using broadband dolphin-like signals

Dolphins have been observed foraging for prey that bury themselves into a sandy bottom. The dolphins swim about 1 to 2 m above the bottom and scan in a circular motion or swim immediately off the bottom, scanning from side to side with their beams pointed approximately normal to the bottom. The dolphin has been emulated by using dolphinlike sonar signals (120-kHz peak frequency, 39-kHz bandwidth, 50-μs duration) in order to classify proud and buried targets in real time. The transducer was attached to a bottom-crawling remotely operated vehicle. Target echoes were received via a cable and digitized at 1 MHz. Short-time Fourier transform and the Morlet wavelet were used to obtain time-frequency representations of the echoes. Echoes were processed in a hierarchical neural network system to perform target classifications. Six targets (cast iron pot, stainless steel sphere, glass jar, concrete tile, and coral rock) were placed either on the ocean bottom or buried into the bottom. Echoes were separated into three target categories: (1) cast iron pot; (2) stainless steel sphere; and (3) remaining four objects. The neural network was able to correctly identify 74%, 97%, and 88% of the category 1, 2, and 3 test echoes.

Scattering from buried spheres in a shallow-water laboratory

A series of scattering measurements from buried and proud spheres in the NRL shallow-water laboratory have been conducted in order to understand the scattering of sound from targets at and below the sandy-bottom interface. The water-saturated sandy bottom was a manufactured 212-μm washed and filtered sand. The initial measurements included scattering from two spheres, a solid aluminum sphere with a 15-cm diameter, and a hollow stainless steel sphere with a 60-cm diameter and an h/a of 0.05. For baseline measurements, free-field and proud measurements of both spheres were made. Buried measurements of the spheres ensonified below the critical angle were conducted with a smoothed interface to quantify contributions from the evanescent wave field. Also investigated is the enhancement due to a roughened sand–water interface. The results of these measurements will be discussed and a preliminary analysis will be presented. [Work supported by ONR.]

Identification of the effective radiative properties of a hot, thick, porous medium

An inversion method is used to determine the spectral radiative properties (scattering albedo, extinction coefficient, and Henyey–Greenstein asymmetry factor) of a packed bed of stainless steel spheres. Spectral and directional experimental data for the intensity exiting the bed were compared to Radiative Transfer Equation (RTE) discrete ordinates method solutions in a nonlinear least-squares algorithm (modified Levenberg–Marquardt) to identify the radiative properties. The properties resulting from the inversion method showed a higher scattering albedo, more forward scattering phase function, and higher extinction coefficient than those calculated using either independent scattering theory or the correlated scattering theory of Kamiuto.

Flammability hazards of lower aliphatic aldehydes at elevated pressure and temperature

AbstractA large and potentially hazardous decrease in aldehyde autoignition temperature (AIT) occurs with increased pressure. The AIT‐pressure curve determined in a 5 L stainless steel sphere was similar for propionaldehyde and butyraldehyde in air, falling from about 185°C at atmospheric pressure to 90°C at 140 psia. Reduction of oxygen concentration had little effect on propionaldehyde AIT. At 100°C and 140 psia, autoignitions accompanied by at least a doubling of pressure were observed above 4% oxygen. In the presence of a few grams of free liquid, propionaldehyde vapor ignited in air at initial conditions significantly below the AIT. The mechanism appears to involve rapid Fe‐catalyzed exothermic liquid‐phase oxidation leading to autoignition of the adjacent heated gas layer. An acetaldehyde vapor‐air mixture in the presence of free liquid and rust exploded at room temperature when air pressure was increased to 95 psia; this result is discussed with reference to a cylinder overpressurization that occurred while making up an ostensibly sub‐LFL calibration mixture with compressed air. Propionaldehyde's limiting oxygen concentration (LOC) was investigated in the near‐autoignition region using the same 5L apparatus; the findings are discussed with reference to an overpressurization incident in an air‐liquid partial oxidation reactor. The general results are used to illustrate the application of LOC in partial oxidation processes subject to autoignition and to discuss elements of the current ASTM draft test method for LOC, which does not address test difficulties associated with condensable and/or reactive gas systems.

Stepwise pyrolysis for raw material recovery from plastic waste

High costs of pollution control for incinerators, the high energy content of plastics as well as the chemical composition of plastics are demanding for alternative treatment of plastic refuses where plastic waste is considered as a resource of energy and as chemical raw material. One possible alternative is the pyrolysis of plastics. Kinetic data obtained from micro thermogravimetry and well stirred type reactor experiments confirm, that different molecular structures of commodity plastics bring about different reaction mechanisms of thermal decomposition, different reaction rates, and different temperature dependencies of the decomposition rates. From that, stepwise pyrolysis of mixtures of plastics seems to be reasonable where the different components are pyrolysed at different temperatures. This work aims at a stepwise pyrolysis procedure where the thermal decomposition of different components of a mixture of plastics is performed consecutively at different temperatures. For a continuous process a cascade of well stirred reactors has been developed where mixing of the reactor contents occurs by circulating of stainless steel spheres. Examples for the separation of single plastics by thermal decomposition of mixtures of poly(vinyl chloride), polystyrene and polyethylene and polystyrene, polyamide 6 and polyethylene, respectively, are presented. In a first step hydrogen chloride from poly(vinyl chloride) is obtained, in the second step the monomer of polysytrene and/or polyamide 6 is formed and in the third step aliphatic compounds from polyethylene decomposition are trapped.

Steel and Titanium Hollow Sphere Foams

ABSTRACTMetal hollow sphere foams are fabricated by bonding millimeter sized metal alloy hollow spheres at points of contact. The spheres are formed as powder shells from slurries. For stainless steel spheres, the starting powder is a mixture of iron and chromium oxide. Thermal treatment in hydrogen reduces the oxides to Fe/Cr alloys with less than 2% porosity in sphere walls. The nominal composition is close to that of 405 stainless. Carburization in CO/CO2 atmosphere followed by heat treatment produces foams of either 410 or 420 type stainless steels depending on carbon content. Compressive stress-strain behavior was measured on point contact bonded stainless foams both before and after carburization. Hardness measurements on steel sphere walls were used to estimate the yield strength. Relative strengths of the foams were positioned between open and closed cell models. This was encouraging because bonding in the foams was less than optimum and the hollow sphere walls contained defects. As processing improves, strengths should increase. To produce titanium alloy spheres, the starting powder is titanium alloy hydride. Thermal treatment in an inert atmosphere decomposes the hydride and sinters the titanium powder in the sphere walls to greater than 96% relative density. Both titanium and Ti-6V-4V spheres and foams have been produced. Oxygen contents are a concern for titanium compositions and processing is being altered to reduce oxygen levels to increase ductility

Real-time sonar classification of proud and buried targets using dolphinlike echolocation signals

A broadband active sonar system using dolphinlike echolocation signals and biologically inspired signal processing algorithms was developed to classify proud and buried targets in real time. A dolphin simulator transducer was attached to a bottom-crawling remotely operated vehicle and used to transmit a dolphin click (120-kHz center frequency, 39-kHz bandwidth, 50-μs duration) through seawater. Reflected target echoes were received and transmitted via cable to a shore-based computer system where the echoes were digitized at 1 MHz and subsequently processed. Two time-frequency representations of the echoes, one based on the short-time Fourier transform and the other on the Morlet wavelet, were processed in a hierarchical neural network system to derive target classifications. Echolocation returns were collected from six objects (cast iron pot, stainless steel sphere, glass jar, concrete tile, and coral rock) that were placed either on the ocean bottom or buried by bottom sediment. Echoes were separated into three target categories: (1) cast iron pot; (2) stainless steel sphere; and (3) a miscellaneous category consisting of the remaining four objects. Following supervised neural network training, the system was able to correctly identify 74%, 97%, and 88% of the category 1, 2, and 3 test echoes.

Levan production by Zymomonas mobilis cells. Attached to plaited spheres

AbstractIn this work, an immobilization method for polymer‐levan production by a non‐flocculating Z mobilis culture was developed. The extent of cell attachment to the stainless steel wire surface, culture growth and product synthesis were described. It was established that during short‐term passive immobilization of non‐flocculation Z mobilis cells on a stainless steel wire surface, sufficient amounts of biomass for proper levan and ethano fermentation could not be obtained. Adherence of cells was improved by pressing the paste‐like biomass within stainless steel spheres knitted from wire with subsequent dehydration. Biomass fixed in metal spheres was used for repeated batch fermentation of levan. The activation period of cells within wire spheres (WS) was 48 h in duration. During this time, cell growth stabilized at production levels of ethanol and levan of Qeth = 1.238 g/l × h and qeth = 0.47 g/l × h; Qeth = 0.526 g/l × h and qeth = 0.20 g/l × h. Five stable fermentation cycles were realized using one wire sphere inoculum, and maintaining a stable ratio of 2.4 of biomass suspended in the medium to biomass fixed in the sphere. Using fixed Z mobilis biomass in the WS, the total amount of inoculum could be reduced for batch fermentation. Large plaited wire spheres with biomass may have potential in fermentation in viscous systems, including levan production.

Studies of ejecta from hypervelocity impacts on CO 2

We have studied the ejecta produced by the normal incidence impact at 5 km s −1 of 1 mm diameter stainless steel spheres on CO 2 ice. The ejecta size and angle of ejection were measured by use of thin witness foils. We reconstruct the size distribution (for angles between 20° and 80° to the ice surface) and find it is dependent on angle of ejection. Between angles of ejection of 20° and 80° we find that the measured ejected mass flow is maximum at (62.5 ± 2.5)°, and represents approximately 1.4 % of the crater mass.

高分子材料の衝撃貫通破壊について

High velocity impact tests are conducted by launching spherical stainless steel and PMMA projectiles into thin PMMA plate targets at various velocities. Ballistic phase diagrams are obtained which indicate the fracture behavior in targets and projectiles. Quasi-static perforation tests are also performed. The fracture surfaces in targets are examined microscopically.

Correlation of Measured and Computed Radiation Intensity Exiting a Packed Bed

The spectral and directional distribution of radiation intensity is measured, using a direct radiometric technique, at the exposed boundary of a packed bed of stainless steel spheres. The purpose of these measurements is to provide an experimental data base of radiation intensity with which to correlate intensity field solutions of the radiative transfer equation in participating media. The bed is considered to be one-dimensional, is optically thick, and has measured constant-temperature boundary conditions. Intensity exiting the bed is numerically simulated using a discrete ordinates solution to the radiative transfer equation, with combined mode radiation-conduction solution of the coupled energy conservation equation. Radiative properties for the bed are computed using the large size parameter correlated scattering theory derived by Kamiuto from the general theory of dependent scattering by Tien and others. The measured intensity results show good agreement with computed results in near-normal directions, though agreement in near-grazing directions is poor. This suggests that either radiative transfer near the boundaries of this medium might not be adequately represented by a continuous form of the radiative transfer equation, or that the properties derived from correlated scattering theory are insufficient. In either case, development of a more detailed radiation model for spherical packed beds appears warranted.

Scientific and Technological Progress in Binder Burnout from Metal Injection Molded Compacts

Abstract A two-component model binder system composed of the low molecular weight component stearic acid (SA) and the polymer polypropylene (PP) was chosen to study the kinetics of long-term conventional thermal debinding of SA from a metal powder compact formed from spherical stainless steel powder. The burnout temperature of the two binder components is widely different, so that the SA-weight loss could be followed in the lower temperature regime independently by thermogravimetric analysis. The experiment provides at constant temperature an exponential decrease of the SA-weight with debinding time. It is suggested that the debinding rate is controlled by diffusion of SA in the thermoplastic to inner surfaces of pores, which develop in the material during debinding. This is in correspondence with previous work on short-term debinding. The kinetics for the PP/SA-system are compared to previous results on binders with other polymer components. The second part of this paper reports about MIM-processing of c...