William W Predebon - Academia.edu (original) (raw)

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Papers by William W Predebon

Journal of Thermal Stresses, 1980

ABSTRACT An analysis of thermal and mechanical loads acting on an inertial confinement fusion (or... more ABSTRACT An analysis of thermal and mechanical loads acting on an inertial confinement fusion (or fusion/fission) reactor is presented. It is shown that, as a result of the pulsed mode of operation, quasi-steady-state temperatures and stresses can be separated into static and dynamic components. Numerical results are presented for a specific design of a spherical fusion/fission reactor with a lithium-wetted wall. For the purpose of scaling, materials selection, and fatigue damage assessment, approximate formulas for temperatures and stresses are also given.

Journal of Applied Mechanics, 1969

A vacuum hot pressed alumina material having small, isometric grains; a uniform distribution ther... more A vacuum hot pressed alumina material having small, isometric grains; a uniform distribution thereof; relatively low, predominantly transgranular porosity; and a density approaching the theoretical density of pure alumina produced by vacuum hot pressing alumina powder which contains at least 98.0% alumina, is substantially free of any sintering aids or any other additives, and has a median particle size less than about 3 microns, in a vacuum hot press operated at a temperature of at least about 1350° C. and a pressure of at least 28 MPa (3500 PSI) for a sintering period of at least 1.5 hours. The vacuum hot pressed alumina material also has compressive strength, flexural strength, impact strength, and wear resistance superior to that for most conventional sintered alumina materials.https://digitalcommons.mtu.edu/patents/1072/thumbnail.jp

1996 Annual Conference Proceedings

AIP Conference Proceedings, 1994

ABSTRACT Alumina disks which were vacuum hot pressed from a 99.99&percnt; pure Al2O3 powd... more ABSTRACT Alumina disks which were vacuum hot pressed from a 99.99&percnt; pure Al2O3 powder were subjected to flyer-plate impact testing. VISAR techniques were used to measure rear surface velocities. The Hugoniot elastic limit (HEL) for this alumina was 11.9 GPa. At a precompression of three times the HEL, a remarkably high spall strength of 1.2 GPa was observed. However, a negligible spall strength was found when the alumina was shocked to approximately 1.3 times the HEL. These results indicate that the spall strength of pure polycrystalline alumina goes through a transition, first decreasing in value near the HEL and then increasing again above the HEL. In other flyer-plate impact tests, manganin stress gauges were used to measure the decay of the HEL with specimen thickness. The HELL for this alumina decreases slightly when the thickness of the specimen was increased but stabilized for specimens thicker than about 9 mm.

Scripta Metallurgica, 1988

Acta Metallurgica, 1985

ABSTRACT The compressive yield strength of directionally solidified Co-CoAl eutectic alloys was m... more ABSTRACT The compressive yield strength of directionally solidified Co-CoAl eutectic alloys was measured in specimens containing a range of lamellar termination densities but at approximately a constant interlamellar spacing. The yield strength was found to decrease as the transverse lamellar termination density increased. A linear dependence of yield strength on the distance between the terminations is observed provided the spacing between terminations is less than 500 μ. For spacings greater than this, the yield strength is approximately constant. These observations are attributed to a relaxation in constraint on deformation between the two phases due to the initiation of enhanced slip in the vicinity of the terminations.RésuméNous avons mesuré la limite élastique en compression d'alliages eutectiques Co-CoAl solidifiés uni direction ellement dans des échantillons présentant une gamme de densités de terminaisons de lamelles, mais dont l'espacement interlamellaire était approximativement constant. La limite élastique diminuait lorsque la densité de terminaisons lamellaires transverses augmentait. Nous avons observé une variation linéaire de la limite élastique en fonction de la distance entre les terminaisons à condition que l'espacement entre les terminaisons soit inférieur à 500μm. Pour les espacement supérieurs, la limite élastique est approximativement constante. Nous attribuons ces observations à une relaxation de la contrainte de déformation entre les deux phases due au début d'un glissement favorisé au voisinage des terminaisons.ZusammenfassungDie Flieβspannung von gerichtet erstarrten eutektischen Co-CoAl-Legierungen wurde im Druckversuch gemessen. Die Legierungen enthielten verschiedene Dichten an Lamellenenden, jedoch in näherungsweise gleichem Abstand zwischen den Lamellen. Die Flieβspannung sank mit ansteigender transversaler Dichte der Lamellenenden. Die Flieβspannung hing linear vom Abstand zwischen den Enden ab, wenn dieser Abstand unter 500 μm lag. Oberhalb dieser Grenze bleibt die Flieβspannung näherungsweise konstant. Diese Befunde werden einer Erleichterung in den Einschränkungen der Verformung zugeschrieben, die zwischen den beiden Phasen durch verstärkte Gleitung an den Enden bedingt wird.

$Research paper thumbnail of The fracture toughness of a high-strength alumina: compact tension versus indentation fracture techniques$

Journal of Materials Science Letters, 1994

ABSTRACT The indentation fracture method is widely used for assessing the fracture toughness of c... more ABSTRACT The indentation fracture method is widely used for assessing the fracture toughness of ceramic materials. In one technique, the surface traces of cracks formed about a Vickers microhardness indentation are measured, and the toughness value is determined knowing the applied load as well as the hardness and elastic modulus of the material (Vickers indentation technique) [1-3]. In a second method, the Vickers indentation forms the critical flaw on the surface of a three- or four-point bend specimen. Two applications of the method are then possible: the fracture toughness value is calculated knowing the load used to produce the flaw and the fracture stress of the indented bar [4] or by actually measuring the flaw size and shape after fracturing the bar at a known stress [5] (indentation strength technique). The former procedure has the advantage in that no direct measurement of the flaw is required.

$Research paper thumbnail of Deformation and fracture in directionally solidified Co-CoAl eutectic$

Journal of Materials Science, 1993

Journal of Engineering Materials and Technology, 1987

Yielding in a crystal structure occurs with plastic slip on preferential planes. It is similar to... more Yielding in a crystal structure occurs with plastic slip on preferential planes. It is similar to yielding on maximum shear planes in an isotropic continuum, but in this case the slip is anisotropic. The anisotropic slip is described by 24 piecewise, continuous yield functions, also known as the generalized Schmid’s law for FCC crystals. The plastic strain increment for any one slip mechanism is assumed given by the potential flow law of plasticity. However, there are combined slip situations where two or more slip mechanisms are activated simultaneously. In this paper, the plastic strains for all the possible intersections in FCC crystals are derived, i.e., for intersections of two, four, and eight yield surfaces of compatible stress states. A strain hardening modulus H′ is included by defining an equivalent shear stress τ and an equivalent plastic shear strain γp for each slip system. The analysis is programmed for finite-element solution on the computer, by defining a strain “vec...

Journal of Applied Physics, 1988

It is shown through numerical simulations that the gap between performed fragments closes during ... more It is shown through numerical simulations that the gap between performed fragments closes during explosive launch, trapping the detonation products until radial expansion of the fragments is sufficient to separate the fragments. Circumferential strains from the numerical calculations are in good agreement with the plastic strains from recovered fragments. Additionally, considerable insights into the dynamics of the explosive launch process