A proposed circle/circular arc detection method using the modified randomized hough transform

Abstract

The randomized Hough transform (RHT) is a useful tool to locate patterns in an image. In this study, we propose a modified RHT to detect circles/circular arcs efficiently. First, we segment an image into sub‐images based on edge information, then we use the proposed circular arc analysis and density check rule to modify RHT for circle/circular arc detection. In the experiments, real images are used to show the capability of the proposed method.     

Equations for helical gears with pinion circular arc teeth and gear involute teeth

Abstract

In this paper, the theory of gearing and the concept of differential geometry have been applied to derive equations for helical gears with pinion circular arc teeth and gear screw involute teeth. The paper covers: (a) generation of conjugate gear tooth surfaces with localized bearing contact; and (b) derivation of equations for gear tooth surfaces and their unit normals.     

Arc Erosion Properties of WCu Material Reinforced with Ti3SiC2 under Different Applied Voltages

Introducing reinforcements is a crucial way to modify WCu electric contacts. Herein, the arc erosion performances of WCu/Ti₃SiC₂ under various direct current voltages are investigated. The eroded microstructures are observed by a 3D laser scanning confocal microscopy and a thermal field emission scanning electron microscope. Compositions of the eroded surfaces are analyzed by a Raman spectroscopy. With the elevated voltages, values of breakdown current, arc duration, arc energy, and arc discharge distance increase, while the breakdown strength decreases. Meanwhile, the eroded regions gradually change from circular shape to irregularly curved corrugations under the elevated voltages. Copper and Ti₃SiC₂ can disperse arc during arc discharge, and the liquid and gas generated by the two phases can make differences in protecting WCu/Ti₃SiC₂.     

Barrelling of aluminium solid cylinders during cold upset forging with constraint at one end

Abstract

Experiments were carried out to generate data on the cold upset forging of solid cylinders of annealed aluminium using different lubricants, with a die at one end providing a constraint. The die had created back extrusion of metal through its hole and developed two barrels in the unrestrained portion of the cylindrical specimens. The curvatures of the barrels, top and bottom, developed in the unrestrained portion were found to conform one to one to calculated values using experimental data. The calculations were made on the assumption that the curvatures of the barrels followed circular arc geometry. It was further found that the measured radius of curvature of both barrels exhibited a straightline relationship with the new geometrical shape factor, irrespective of the aspect ratios of the cylinders. Further empirical relations were found to exist between the measured radius of curvature of both barrels and other variables, namely hydrostatic stress and stress ratio parameter.     

Interactions of interfacial arc cracks

The interaction of two interfacial arc cracks around a circular elastic inclusion embedded in an elastic matrix is examined. New results for stress intensity factors for a pair of interacting cracks are derived for a concentrated force acting in the matrix. For verifying the point load solutions, stress intensity factors under uniform loading are obtained by superposing point force results. For achieving this objective, a general method for generating desired stress fields inside a test region using point loads is described. The energetics of two interacting interfacial arc cracks is discussed in order to shed more light on the debonding of hard or soft inclusions from the matrix. The analysis based on complex variables is developed in a general way to handle the interactions of multiple interfacial arc cracks/straight cracks.     

Observations of barrelling in aluminium solid cylinders during cold upsetting using different lubricants

Abstract

This work deals with experimental derivation of friction factor values m for different lubricants and their combinations using ring compression tests and standard ring geometry 6:3:2. The values thus obtained were used to generate data on cold upsetting of annealed aluminium solid cylinders. Two aspect ratios and three strain levels were considered for the upsetting experiment. Calculations were made with the assumption that the curvature of the bulge followed a circular arc. The measured radius of curvature of the bulge was shown to agree with the value calculated using experimental data. Relationships were established between various bulge parameters such as new hoop strain, hydrostatic stress, geometrical shape factor, and stress ratio factor, and the friction factor m of different lubricants.     

Interface crack around circular inclusion: SIF, kinking, debonding energetics

The problem of an interfacial arc crack around a circular elastic inclusion embedded in an elastic matrix is examined. A general approach for generating uniform/non-uniform stress fields inside a test region through remotely applied point loads is demonstrated. The effects of stress gradient, arc crack angle, and elastic mismatch are discussed. Interfacial arc crack kinking is examined using the maximum tensile stress criterion only for such cases wherein the crack is open. Finally, the energetics of inclusion debonding is addressed for the specific case of hydrostatic loading.     

Comparative analysis of two methods for synthesis of fullerenes at different helium pressures

Abstract

The results of the effect of helium pressure in the chamber on the amount and composition of the produced fullerenes (C₆₀, C₇₀, etc.) synthesized in the arc plasma with graphite electrodes are presented. The findings obtained when the arc is powered by a direct (DC) and alternating (AC) currents of low frequency were compared in the same chamber with the electrodes located at the same angle to each other. These two methods are drastically different. The complete conversion of graphite into fullerene soot in AC occurs, but a part of the graphite is converted into a cathode deposit that does not contain fullerenes in DC, the relative amount of which increases when decreasing the helium pressure in the chamber. The highest fullerene content in fullerene soot of 10.2?wt.% is produced at a pressure of 127.5?kPa in AC arc, but in DC arc, the highest content of fullerenes in fullerene soot of 8.3?wt.% is produced at a pressure of 33.3?kPa.     

Mathematical models for the numerical study of turbulent flows

Abstract

This paper presents (1) a brief overview of the mathematical models used in the numerical study of turbulent flows; (2) a K‐? model of turbulence; and (3) extensions of the K‐? model to account for some of the effects of compressibility, low Reynolds number, streamline curvature, and preferential stress dissipation.     

Welding of austenitic stainless steel using double sided arc welding process

Abstract

This study explores an improved method of welding austenitic stainless steel. The method uses two series connected arcs to weld the workpiece simultaneously from opposite sides. Owing to this arc configuration, the welding current is forced to flow from one arc to the other through the workpiece. It is known that such current flow concentrates the arcs and thus improves the penetration capability. Also, the current flowing through the workpiece generates fluid flow within the weld pool. In addition, owing to the use of the two opposite arcs, the heating tends to be symmetric. In addition to the increased penetration, the use of this method for welding austenitic stainless steel results in improved microstructure in the resultant welds because of an increased columnar to equiaxed transition and a decreased angular distortion, which sometimes induces solidification cracking.     

Carbon Nanotubes Grown on the Surface of Cathode Deposit by Arc Discharge

Abstract

Carbon nanotubes prepared by de arc discharge of graphite electrodes in He and CH₄ gas took markedly different morphology. Thick nanotubes embellished with many carbon nanoparticles were obtained by evaporation under high CH₄ gas pressure and high arc current. Thin and long carbon nanotubes were obtained under a CH₄ gas pressure of 50Torr and an arc current of 20A for the anode with a diameter of 6mm.     

Optical Transfer Functions for Defocused Two-pupil Systems Involving Annular Geometries

Abstract

An exact solution for the cross-correlation between two different circular apertures under defocused conditions in a two-pupil system is derived. The result is directly applicable to finding the optical transfer function (OTF) for standard examples including annular apertures. Some novel examples leading to OTFs showing bandpass and band-reject properties are also investigated.     

Viscoplastic constitutive relation incorporating phase transformation – application to welding

Abstract

A viscoplastic constitutive relation of the Perznya type is used to describe structural changes for a wide range of material behaviour from solid to liquid states. Using the constitutive model, finite element simulations were carried out for two types of welding process: a circular plate welded in the centre and a butt-welded plate. The residual stress and temperature were calculated and compared with experimentally measured data.

MST/24     

Microstructural development in plasma jet forming of sheet steels

Abstract

Plasma jet forming is a newly developed flexible forming process for sheet metals using plasma arc as the energy beam and CO₂ as the cooling jet. In this paper, two different metals, low carbon mild steel and Type 304 austenitic stainless steel, were formed using the developed experimental system with series parameters. Experiments showed that the difference in forming process of these two metals depended not only upon their physical properties, but also upon their phase transformation characters. The microstructural developments in the heat affected zone of these two metals were also observed and discussed.     

Circular inhomogeneity and two concentric symmetric circular arc cracks problem in an infinite isotropic elastic plate under tension

A homogeneous infinite isotropic elastic plate contains two symmetrical circular arc cracks of equal radii and a concentric inhomogeneity. The radius of the inhomogeneity is less than that of the circular arc cracks. The plate is subjected to a traction at infinity. The stresses are found within the circular region bounded by the circular arcs, including the inhomogeneity. The problem is solved as a two-dimensional using the complex variable technique. Some numerical results are given to show the effects of the inhomogeneity.     

A combination of the finite element and singular-integral equation methods for the solution of the generally cracked body

A method which combines the finite element technique and the singular-integral equation method is presented. The association of the two methods is obtained with the help of Schwarz's alternating method (SAM). The method was applied with satisfactory results to the solution of a series of problems of a circular arc crack lying inside a finite thin plate for various lengths of the circular arc and for various dimensions of the rectangular cracked sheet.     

Broad-band superachromatic retarders and circular polarizers for the UV,visible and near infrared

Abstract

We present designs for two combinations of conventional achromatic retarders that can be used, over the wavelength range from 300 to 1100 nm, to obtain retardations of a quarter-wave and a half-wave, respectively, as well as a combination that can be used as a circular polarizer over this range of wavelengths.     

Development of EPRI P87 solid wire

Abstract

Dissimilar metal welds (DMW’s) between ferritic and austenitic materials at elevated temperatures have concerned boiler manufacturers and operators for decades because of the proven potential for premature failure. The industry has desired an improved filler metal that would minimize or eliminate DMW failures and, with the current trend toward higher boiler steam pressures and temperatures, have suitable creep strength for joining higher strength materials such as Grade 91 steels After years of research, the Electric Power Research Institute (EPRI) concluded the development and commercialization of a nickel-based filler metal, EPRI P87, for application in shielded metal arc welding (SMAW). This work describes the subsequent development of an EPRI P87 solid wire welding product for application in gas tungsten arc and gas metal arc welding (GTAW and GMAW) processes, and the initial research into the performance of DMWs produced with the new solid wire P87 product. A 135 kg heat of solid wire was produced and tested using various welding processes and evaluation methods to ensure that the material would meet required weldability and design specifications. Welding methods included GMAW-P, GTAW and hot-wire GTAW in welds up to 50mm in thickness. The weld joint tested was a dissimilar metal weld of grade 91 to 347H, which was assessed using microstructure evaluation, creep testing, hot tensile testing, circular patch, and edge build-up investigations to examine hot-cracking susceptibility. This paper summarizes the research completed to date on the EPRI 87 filler wire which supports the acceptability of this material for its intended use in high-temperature power generation applications.     

Optimal aperture configuration for a segmented and partially diluted extremely large telescope

Abstract

We analyse the feasibility of replacing hexagonal mirror segments with circular segments in very large telescopes, requiring approximately the same performance in the spatial frequency domain. The potential advantages of circular segments are that they are easier to fabricate and there is a decreased amount of stray light contribution from the edges.     

Control of Fullerene Generation Through the Macroscopic Parameters of Carbon Plasma Arc

Abstract

The erosion of graphite electrodes in the dc electric arc has been studied in fullerene synthesis process for various arc current between 50 and 120 A. The rapid expansion of carbon vapour appears to be the main factor hampering the high efficiency formation of the fullerenes.