Comparison and evaluation of creep crack growth rate and fracture time for Alloy 800 by the Q* parameter

Creep crack growth tests were carried out under several temperature and stress conditions for Fe-based superalloy Alloy 800 and the Q* parameter was applied to an evaluation of the crack growth rate at elevated temperatures for DEN and CT specimens. Creep fracture times were evaluated with the parameter derived by integrating the creep crack growth rate formula expressed in terms of the Q* parameter for DEN, CT and smooth specimens of Alloy 800 under several temperature and stress conditions. It was found that the creep crack growth rate for CT specimens is represented as the different data bands by the Q* parameter for DEN specimens. However, it can be evaluated by parallel movement along the Q* axis in the Q* parameter-da/dt diagram for Alloy 800. The parameter {T(log₁₀t_f+20)×10⁻³} derived from the Q* parameter can compare and evaluate the difference in specimen shape and loading mechanism on creep fracture time using the identical parameter for Alloy 800.     

Abnormal Grain Growth in Alumina: Synergistic Effects of Yttria and Silica

Abnormal grain growth without strong anisotropy or faceting of the grains has been observed in high-purity yttria-doped alumina specimens, often starting at the surface and spreading right through the bulk at higher sintering temperatures. This appears to occur because of an interaction between Si contamination from sintering and the yttria doping; no such effect is seen for undoped samples. Similar microstructures were observed after deliberate Y/Si codoping. Analytical STEM showed that some grain boundaries bordering on large grains contained more Si than Y. HRTEM and diffuse dark-field imaging revealed thin (0.5–0.9 nm) disordered layers at some boundaries bordering large grains. It appears that Si impurities are accumulating at some boundaries and together with the Y inducing a grain boundary structural transformation that accounts for the dramatically increased mobility of these boundaries.     

Effect of exposure in vitro to ethanol and hypoxia on gamma-aminobutyric acid efflux in the hippocampus of the fetal and adult guinea-pig

The objective of this study was to determine the effects of acute direct exposure to ethanol, hypoxia or ethanol plus hypoxia on K+-stimulated gamma-aminobutyric acid (GABA) efflux (neuronal release minus uptake) in the hippocampus of the near-term fetal and adult guinea-pig. Transverse hippocampal slices were studied in a static-interface system. Exposure in vitro to ethanol or hypoxia involved 10-min incubation with 50 mM ethanol or 10-min incubation in a 95% N2/5% CO2 environment. GABA was quantitated by HPLC. Ethanol did not alter K+-stimulated GABA efflux; hypoxia augmented K+-stimulated GABA efflux three-fold in the near-term fetus and seven-fold in the adult; concurrent exposure to ethanol did not alter the effect of hypoxia. The data demonstrate that, for acute direct exposure to hypoxia and/or ethanol, only hypoxia increases K+-stimulated GABA efflux, the magnitude of which is dependent on the extent of development of the GABA system.     

Development of crystallinity and morphology in hafnium dioxide thin films grown by atomic layer epitaxy

The structural development of HfO₂ thin films grown from HfCl₄ and water onto glass substrates by atomic layer epitaxy at 500 °C was studied with X-ray diffraction, atomic force microscopy and scanning electron microscopy. The films were found to contain two regions of different crystallinity: a thin amorphous starting layer and a subsequent preferentially oriented polycrystalline layer. The films were built up of densely packed grains. Substantial surface roughening occurred along with increasing film thickness. The films were chlorine free as analyzed by Rutherford backscattering spectrometry.     

Phase stability,oxidation, and interdiffusion of a novel Ni−Cr−Al−Ti−Si bond-coating alloy between 900 and 1100°C

A novel, low-expansion experimental Ni–Cr–Al–Ti–Si bond-coating alloy was investigated in the as-cast state concerning its phase stability, oxidation resistance in air, and interdiffusion with single-crystal IN-100 at 900, 1000, and 1100°C. Isothermal oxidative thermogravimetry was employed up to 500 hr. Interdiffusion was compared to a commercial Ni–Co–Cr–Al–Y alloy on IN-100. Oxidized Ni–Cr–Al–Ti–Si specimens and diffusion couples were characterized by metallography, SEM, EDX, XRD, and XRF. The Ni–Cr–Al–Ti–Si alloy provides good oxidation resistance in air at least up to 1000°C. The alloy is an alumina former. Due to its coarse microstructure, other oxides (e.g., rutile) may form and considerably dominate the oxidation behavior. The kinetics of oxidation were correlated with temperature, formation of phases, and morphology of oxides. Interdiffusion fluxes between Ni–Cr–Al–Ti–Si and IN-100 were mainly directed to the superalloy. They were faster than in Ni–Co–Cr–Al–Y/IN-100 diffusion couples.     

Simulationsuntersuchungen zur Evaluierung der Kapazität eines neuen Fertigungssystems

Zusammenfassung In dieser Arbeit wird die Verwendung der diskreten Simulation zur Bestimmung von Kapazitäten und maximalen Produktionsmengen einer neu errichtenden Fertigungsanlage beschrieben. Aufgrund fehlender Erfahrungswerte ist es dabei notwendig, die Kapazität jeder einzelnen Maschine im Produktionsprozeß bzw. jeder Produktionsstufe zu bestimmen. Davon ausgehend wird die maximale Produktionsmenge der gesamten Fertigungsanlage ermittelt. Die Analyse des Fertigungssystems zeigt, daß die Lage der Engpässe sehr stark vom tatsächlichen Produktionsprogramm abhängig ist. Aus diesem Grund wird das maximale Kapazitätsangebot der einzelnen Produktionsstufen getrennt bestimmt und als Restriktionen bei der Einlastung der einzelnen Aufträge verwendet. Ein heuristisches Verfahren zum Festlegen des Produktionsprogramms unter Beachtung aller durch verschiedene Simulationsläufe ermittelten Restriktionen bildet den Abschluß der Arbeit.     

Entwicklung einer Dekompositionsstrategie für die Strukturoptimierung komplexer Bauteile

Zusammenfassung Der Einsatz von Finite-Elemente-Optimierungsprogrammen für die konstruktive Auslegung von Bauteilen ist mit gro?em Rechenaufwand und Speicherplatzbedarf verbunden. Die Dekompositionsstrategie stellt ein effizientes Verfahren dar, das zu einer drastischen Reduzierung der Rechenzeiten bei der L?sung von Problemen der Gewichtsminimierung führt. Darüber hinaus verringert sich der immens hohe Bedarf an Plattenplatz und nicht zuletzt wird ein schnelleres Konvergenzverhalten bei der Optimierung erreicht. Die in diesem Beitrag vorgestellten Arbeiten sind Gegenstand des von der Deutschen Forschungsgemeinschaft (DFG) gef?rderten Forschungsprojektes “Entwicklung von Dekompositionsstrategien für die Strukturoptimierung unter Einsatz von Parallelrechnern?     

Effet ďun champ magnétique sur les modes TMnmo ďune cavité cylindrique circulaire partiellement remplie de ferrite

The resonant modes of a circular cylindrical cavity resonator containing a coaxial circular ferrite rod are investigated. The ferrite sample is partially magnetized by means of a constant external magnetic field applied along its axis. A computer program for deriving the resoant frequencies of this system as a function of the externally applied magnetic field and of the sample radius has been developed. Results for the special cases of the tm₀₁₀ and tm110 modes are presented. The possible application of such a cavity resonator for the remote sensing of magnetic fields is discussed.