2,126 research outputs found

    Stress redistribution due to creep in nimonic 90 ministry of aviation contract no. PD/28/021 report for the period June, 1965 to July, 1966: part 2

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    Part I of this report, dated September 1965, deals mainly with the design and construction of the special apparatus to simulate the stress redistribution occurring during the creep of a cooled turbine blade. It reported some preliminary experiments using aluminium alloy test specimens. During the past year, the period covered by this report, a series of experiments have been completed using specimens machined from nimonic 90 alloy. Experience gained in operating the apparatus, have resulted in several modifications both to the apparatus and the associated instrumentation. These are detailed within this report

    Stress redistribution due to creep in nimonic 90 ministry of aviation contract no. PD/28/021 report for the period January 1964 - June 1965: part 1

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    The period covered by this report has been devoted to the design, construction development and calibration of a special apparatus to simulate the stress redistribution conditions occurring during the creep of a cooled turbine blade. The experimental assembly consists of two creep machines, each operating at a different temperature, so controlled that a load is shared between them. maintaining equal creep strains (and in consequence equal creep rates) in each specimen. The stress in each specimen and the creep strain of the pair are automatically measured and recorded by a specially developed unit. Some preliminary results on an aluminium alloy are presented

    The development and evaluation of an ultrasonic fatigue unit

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    A fatigue test apparatus operating at 20 kc/s is described. The unit is based on a standard magnetostrictive drive system as used in high energy stresswave generators. An automatic counting device has been developed and incorporated in the final equipment, resulting in improvements in accuracy and reproducibility of results. Some typical results of tests on aluminium alloys are presented

    The Method of Images in Cosmology

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    31 pages, 18 figures31 pages, 18 figuresWe apply the method of images to the exact initial data for cosmological models that contain a number of regularly arranged discrete masses. This allows us to join cosmological regions together by throats, and to construct wormholes in the initial data. These wormholes allow for the removal of the asymptotically flat "flange" regions that would otherwise exist on the far side of black holes. The method of images also provides us with a way to investigate the definition of mass is cosmology, and the cosmological consequences of the gravitational interaction energies between massive objects. We find evidence that the interaction energies within clusters of massive objects do indeed appear to contribute to the total energy budget in the cosmological regions of the space-time

    The design and construction of a weld heat-affected zone simulator

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    Investigation of the structure and properties of the heat-affected zones in welded joints is usually limited by their small size and their complexity. One method of overcoming this problem is to simulate the structure at a particular point in the heat-affected zone in a specimen of larger size by imposing on it the thermal cycle sustained at that point. The equipment described in this note uses a.c. resistance heating and water cooling to impose thermal cycles on 2.5" x O.W' x O.W' specimens, the thermal cycle being chosen by adjustment of a bank of variable resistors to construct a voltage analogue. Control of specimen temperature is achieved using a thyristor and two ignitrons to control the input at 44ov. to a welding transformer. Feedback is applied from a thermocouple welded to the specimen hot-zone. The equipment has been shown to produce the desired thermal cycles in a reproducible manner

    Push-pull fatigue properties of wires in an iridium - 5% tungsten alloy

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    Introduction This memorandum reports a series of tests to determine the fatigue properties of an iridium - 5% tungsten alloy at 600┬░c and 700┬░C. A previous memorandum, Memo. Mat. 61, reports the fatigue properties at room temperature of the same alloy

    Dynamics of a lattice Universe

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    We find a solution to Einstein field equations for a regular toroidal lattice of size L with equal masses M at the centre of each cell; this solution is exact at order M/L. Such a solution is convenient to study the dynamics of an assembly of galaxy-like objects. We find that the solution is expanding (or contracting) in exactly the same way as the solution of a Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average density as our model. This points towards the absence of backreaction in a Universe filled with an infinite number of objects, and this validates the fluid approximation, as far as dynamics is concerned, and at the level of approximation considered in this work.Comment: 14 pages. No figure. Accepted version for Classical and Quantum Gravit

    Chandra Observation of PSR B1823-13 and its Pulsar Wind Nebula

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    We report on an observation of the Vela-like pulsar B1823-13 and its synchrotron nebula with Chandra.The pulsar's spectrum fits a power-law model with a photon index Gamma_PSR=2.4 for the plausible hydrogen column density n_H=10^{22} cm^{-2}, corresponding to the luminosity L_PSR=8*10^{31} ergs s^{-1} in the 0.5-8 keV band, at a distance of 4 kpc. The pulsar radiation likely includes magnetospheric and thermal components, but they cannot be reliably separated because of the small number of counts detected and strong interstellar absorption. The pulsar is surrounded by a compact, 25''x 10'', pulsar wind nebula (PWN) elongated in the east-west direction, which includes a brighter inner component, 7''x 3'', elongated in the northeast-southwest direction. The slope of the compact PWN spectrum is Gamma_comp=1.3, and the 0.5-8 keV luminosity is L_comp~3*10^{32} ergs s^{-1}. The compact PWN is surrounded by asymmetric diffuse emission (extended PWN) seen up to at least 2.4' south of the pulsar, with a softer spectrum (Gamma_ext=1.9), and the 0.5-8 keV luminosity L_ext~10^{33}-10^{34} ergs s^{-1}. We also measured the pulsar's proper motion using archival VLA data: \mu_\alpha=23.0+/-2.5 mas yr^{-1}, \mu_\delta=-3.9+/-3.3 mas yr^{-1}, which corresponds to the transverse velocity v_perp=440 km s^{-1}. The direction of the proper motion is approximately parallel to the elongation of the compact PWN, but it is nearly perpendicular to that of the extended PWN and to the direction towards the center of the bright VHE gamma-ray source HESS J1825-137, which is likely powered by PSR B1823-13.Comment: 13 pages, 8 figures and 3 tables; submitted to Ap
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