Large Number Of Holes Research Articles

Forming limit diagram of perforated sheet

The proper design and manufacture of tube sheets in heat exchangers and shadow masks in color picture tubes require the characterization of the deformation behavior of perforated sheets containing a large number of holes. The limit or failure strains in sheet metal forming are best represented by a forming limit curve (FLC) which indicates the onset of necking over all possible combinations of strains in the plane. A number of theoretical treatments have been developed to predict the FLC of continuum materials. However, there are few reports on the experimental and theoretical studies on FLC for a perforated sheet. The purpose of this paper is to propose a model which can explain the FLC of a perforated sheet for dot-type shadow mask.

T-Jz model on the Cayley tree and the square lattice.

Candidates for the ground state of the anisotropic t-${\mathit{J}}_{\mathit{z}}$ model at low hole doping are studied within two related lattices: the Cayley tree and the square lattice. The Cayley tree allows for the evaluation of the single hole as well as the hole-pair ground states to arbitrary precision. Threshold values for the formation of bound hole pairs appear to be similar for both lattices. We show that the main contributions to the binding of a hole pair on the Cayley tree comes from the excess number of frustrated bonds (``spinons''). Considering systems with a larger number of holes, we establish high stability of configurations with holes forming straight domain walls between nonequivalent antiferromagnetic domains. In particular, for the Cayley tree we find that domain-wall-like configurations have lower energy than separate hole pairs. For the square lattice, however, there exists at low but finite doping a parameter interval 0.18J/t0.56 where, in the ground state, holes are paired.

Experimental setup for monitoring the parameters of holes in perforated vanes

A setup for noncontacting measurement of diameters and spacing of holes in rows is described. The setup is used to measure holes in perforated vanes but can also be employed to inspect other similar parts having large numbers of holes.

Submicron Particles Observed during Etching Process

Submicron particle counts were taken by monitoring hole etching in the RIE (reactive ion etching) process for approximately 30 days. One particle sensor was installed in the exhaust pipe from a process chamber and the second one in the exhaust pipe from loadlock chambers. More than 1000 wafers were processed using five different etching processes. Differences in the particle count per minute were observed among the etching processes. Reactive gas pressure, 13.56 MHz rf power and gas composition significantly influenced the generation of particles. The particle count rate increased as the etching time for one wafer increased. A large number of holes were observed on the etched photoresist surface with a scanning electron microscope (SEM) after prolonged etching time.

Fatigue crack growth in unidirectional metal matrix composite : Ghosn, L.J., Telesman, J. and Kantzos, P.NASA Lewis Research Center Report No NASA TM-103102 1990 8 pp

Multi-hole parts made of difficult-to-cut materials like discs, blisks and casings are common and require high surface quality in aero engines. In workshops, a large number of holes in these parts are drilled successively in one process to ensure their positional accuracy. Due to the fast time-varying drill wear, the surface roughness of the holes is unstable and difficult to be satisfied. To this end, this paper presents a varying-parameter drilling (VPD) method to improve machining efficiency and hole surface roughness for multi-hole parts made of Ni-based superalloy. This method uses varying cutting parameters for each hole to adapt to the varying drill wear. The main issue of this method lies in an optimization problem in which the optimal sequence of cutting parameters need to be found, with the objective of the processing time and the constraint of the hole surface roughness. As the cutting parameter sequence has a high dimension and the surface roughness of all the holes must be guaranteed, the challenge of this optimization problem is the strict constraint with a complicated non-linear boundary of the feasible zone. To address the convergence difficulty of the searching algorithm, a soft computing method based on particle swarm optimization (PSO) algorithm with a self-adaptive penalty method (SAPM) is applied. The hole surface roughness is predicted with a radial basis function (RBF) neural network. Different types of drill wear comprising flank wear, crater wear, chisel wear and outer corner wear are considered, and the grey relational analysis (GRA) is employed to select the input drill wear parameters to the network. The PSO algorithm coupled with the SAPM is used to search the global optimal solution of the optimization problem. It is found that the satisfied solutions can be searched in all the three trials with the proposed algorithm, even though the proportion of feasible solutions is severely fluctuant during the searching process. The drilling experiment confirm that, when compared with the fixed-parameter drilling, the proposed VPD and the soft computing method for solving the optimization problem can effectively improve machining efficiency and surface quality for drilling Ni-based superalloy multi-hole parts.

ChemInform Abstract: Neutron Scattering Studies of Magnetism in High Tc Superconductors

Results of neutron scattering studies of the magnetic properties of YBa2Cu3O6+x materials are reviewed. At low oxygen concentration, anti-ferromagnetic ordering in the CuO2 sheets has been evidenced. The Neel temperature is around 415 K. With increasing oxygen content, the ordered magnetic moment and the Neel temperature are reduced. Finally, the long range magnetic order disappears for xc = 0.41, which indicates the appearance of a large number of holes in the CuO2 layers. Inelastic neutron scattering measurements of spin waves have established the two-dimensional character of the magnetic couplings in the antiferromagnetic phase. Increasing the hole concentration reduces the spin wave stiffness and close to xc the in-plane spin fluctuations become diffusive.

Stressed state of axially loaded turbine journal lips

1. In loading a gently sloping conical shell of average thickness (h/R=0.0.08; 0.11) with an axial force, its stress-strain state is characterized mainly by bending in the meridional and circumferential directions. This state can be taken as two-dimensional. 2. Thin cylindrical ribs on the shell surfaces cause meridional stress concentration and practically do not affect the circumferential stress distribution. 3. The strses concentration around a hole in a gently sloping conical shell of average linearly variable thickness should be compared qualitatively with the stress concentration around a hole in a bending plate. 4. The stress concentration factor for the stresses around a hole, the axes of which is parallel to the shell axis (in case of conical shells loaded with an axial force), is less than that for stresses around a hole perpendicular to the shell surface. 5. The presence of ribs and a large number of holes significantly changes the stressed state of a shell. Therefore, based on data on shells, the stressed state of such a complex model, like that of a turbine journal-lip, can be estimated only approximately.

Shear Layer Mixing for Low Emission Gas Turbine Primary Zones

Shear layer turbulent fuel and air mixing has been utilised in a simulated gas turbine primary zone combustor. Two methods of fuel injection and two values of the number of air injection holes have been investigated at a constant pressure loss of 4% at a reference Mach number of 0.047. The method of fuel injection and the number of air injection holes was found to influence the flame stability and NOx emissions. A large number of holes produced much higher NOx emissions which was not compensated for by the ability to operate at weaker equivalence ratios due to the greater flame stability. An optimum primary zone operating condition, for very low NOx and high combustion efficiencies involving a flame temperature of approximately 1600K was identified and there was a wide flame stability margin on this condition.Copyright © 1984 by ASME

Estimating the acid concentration in spinning viscose complex yarn through a spinneret with a large number of holes

Estimating the acid concentration in spinning viscose complex yarn through a spinneret with a large number of holes

Elastoplastic analysis of thick perforated plates with application to prestressing anchor heads

The elastoplastic finite element stress analysis of a prestressing anchor head is described. The anchor head constitutes part of an unbonded tendon system for a prestressed concrete nuclear reactor vessel. The anchor head, which is a thick plate with a central region perforated by a large number of holes, is analyzed using an equivalent homogeneous material with numerically determined effective elastic constants and yield stress. Maximum inelastic tensile strains are calculated as a function of anchor head load level, and related to observed failure modes.

On-Line Hole Quality Evaluation for Drilling Composite Material Using Dynamic Data

Aircraft manufacturing involves the drilling of a large number of holes for structural joints. The life and proper functioning of the joint can be critically affected by the quality of the hole which generally deteriorates with drill wear. In the use of composite material for the aircraft structure, the “lamination frequency,” associated with the laminated fiber of the material, can be considered to represent the waviness of the hole surface (an aspect of hole quality). The variance associated with this frequency, present in the dynamic nature of the drilling thrust and the hole surface profile, was found to change with the use of the drill. This study presents the possibility of using this change in the lamination frequency content of the drilling thrust for on-line monitoring of the drill condition, through analysis by the Dynamic Data System (DDS) technique.

An experimental test of equations predicting the load bearing capacity of squeeze films of elastico-viscous liquid

A form of squeeze film apparatus was recently described in which the movement of one plate towards the other was simulated by the continuous volume generation of liquid over the plate area. The liquid exuded from a large number of holes in the lower plate surface and formed a “continous flow” version of squeeze film apparatus with no moving parts [1]. A later paper gave derivations of equations from which squeeze film load bearing capacity could be evaluated, taking into account viscous, inertial and normal stress effects in the liquid film [2].In order to find the total load in a squeeze film system, it was necessary to obtain the relationship between the first normal stress difference and shear rate for the liquid in use, using an experimental method. At high shear rates, the jet thrust method provided these data [3,4] and from them the load bearing capacity of squeeze films of hot, polymer-thickened oil were predicted [2].A more complete test of the method is possible with a highly elastic liquid because considerable load enhancement due to extra stress is present at moderate deformation rates in squeeze film systems [1,5,6,7]. Thus a 0.1 per cent aqueous polyacrylamide solution gives well-defined load enhancement and (quite independently) the jet thrust method gives the relationship between normal stress and shear rate from which predictions of load enhancement may be made. Furthermore, convergent nozzles may be used in the jet thrust apparatus [3] to measure the stress development in an elastic liquid which is being simulateneously sheared and stretched, a situation which more closely resembles the squeeze film case than that of steady shear.

Suction flow drainage in head and neck surgery. A new principle for postoperative suction drainage.

Suction drainages are used all over the world in head and neck surgery. Especially in large resections with rather thin skin flaps, it is of great value to try to avoid postoperative hematomas and local infections. A good functioning suction drainage is a valuable factor to eliminate these risks. A careful investigation of most of the drainage types in use, however, shows that a large number of holes in the tube are blocked very soon after wound closure, and the suction capacity is diminished and in many cases insufficient. In order to overcome this disadvantage a new type of drainage with suction and possibilities of a continuous slow flow of Ringer solution has been worked out. This new drainage has been in use for five years and has proved to be superior to the common ones. A correlation between the old and new type of drainage system concerning percentages of blocked holes has also been made.

Vertical gradients of heat production in the continental crust 1. Theoretical detectability from near-surface measurements

The linear relation between heat flow and heat production suggests that in a gross sense the vertical distribution of crustal heat production beneath granitic rocks has a simple generalized form. Knowledge of the vertical gradient of heat production near the surface would permit selection between alternative simple models. However, attempts to determine a generalized gradient from heat-production measurements from boreholes are complicated by the occurrence of inhomogeneities on all observable scales. Variations in heat production typically observed on the hand-sample scale preclude meaningful estimates (even of the sign) of the generalized gradient in holes a few hundred meters deep, the depth typically drilled for heat-flow-heat-production measurements. In holes 3 km deep, the uncertainty in the gradient due to small-scale perturbations is generally reduced to acceptable levels with 100 or so samples. However, perturbations with wavelengths greater than 1 km and amplitudes sufficiently small to permit the linear heat-flow relation, can still preclude meaningful estimates of gradient if the phase is unfavorable. Confident determinations of the trend of heat production with depth in granitic rock will require observations in several holes to depths of a few kilometers or in very large numbers of holes drilled to lesser depths.

Use of nozzles in spinning fibre through spinnerets with a large number of holes

It has been established that the use of nozzles, when spinning fibres through spinnerets with a large number of holes, enables the mass transfer between a roving of fibres and the coagulation bath to be increased. This makes it possible to raise the spinning rate, the coagulation bath concentration and the uniformity of properties of the resulting fibre.

Large conductance molecular leak for gas sampling at high pressure

A thin metal sheet perforated with a large number of holes by means of laser techniques, and constituting a molecular leak for special purposes is described.

Diode Array Camera Tubes and X-ray Imaging

A modification of the silicon diode array camera tube has been carried out which permits X-ray images to be displayed on a television monitor. The silicon target, 50 to 150 μm thick, serves as the tube's vacuum window. Each X-ray photon generates a large number of holes in the silicon substrate. Most of these can be usefully collected, and effective quantum efficiencies over 1000 have been measured. Absolute measurements of the spectral sensitivity have been made and show good agreement with theoretical predictions made using values of hole lifetime and surface recombination velocity obtained from optical measurements on the same target. The silicon diode array offers a number of inherent advantages in X-ray imaging compared with the conventional amorphous selenium target. Among these are greater quantum efficiency, high sensitivity, and temperature stability. The diode array sensitivity greatly exceeds that of film in this X-ray energy range (5 to 20 keV). Moreover, because the video signal current is linear as a function of X-ray photon flux over a wide dynamic range, relative intensities may be compared directly rather than necessitating densitometer measurements as does film. The performance of the many types of X-ray imaging systems in different applications is compared in some detail.

A thin walled tube for core sampling of soils

A new core-sampler for sails is described-A thin-walled steel tube is driven into the soil by a sliding weight arrangement. The tube with its enclosed core is extracted with a hydraulic jack. For a sampling programme of either a large number of holes or very deep ones an electric hammer is very suitable for driving the tubes. Modifications enable the tubes to be used in saturated sands and wet sticky clays.

The Hole Theory of Liquids

RECENTLY, Furth1, in a series of papers, has developed the hole theory of the liquid state. A liquid is regarded as a continuum permeated by a large number of holes, the number of holes being comparable to the number of particles in the liquid. The motion of the holes in the material continuum is similar to that of particles in a gas, and the hole theory on this account has a formal similarity with the kinetic theory of gases. A hole has four degrees of freedom, three of translation and one corresponding to a change in its radius. The average period for radial oscillation of holes is found to be which is of a far smaller order of magnitude than the meanlife Γ of the hole, σ represents the surface tension of the liquid, ρ its density, T the temperature and k is Boltzmann's constant. The meanlife as discussed by Furth is the time for which a hole lasts before it is destroyed by evaporation of molecules into it. In determining the meanlife, Furth has neglected the effect of curvature on the rate of evaporation. When this is taken into account, the hole theory affords a simple though, because of its inherent defects, not quantitatively accurate description of the variation of viscosity of liquids with pressure. For example, for pressures smaller than p2, the internal pressure of the liquid, we have where q is the ratio of the viscosity under pressure p(kgm./cm.2) to that under atmospheric pressure, M the gram molecular weight, and R the gas constant. For most liquids pi is of the order of 103 kgm./cm.2.