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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2363-2367 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hardness and fracture toughness of aligned YBa2Cu3O7−δ obtained by melt processing was found to be highly anisotropic. Indentation measurements show that the (001), (100), and (010) planes are the preferred fracture planes in this material and that the critical stress intensity factor for propagating a crack on the (001) basal plane is the lowest, i.e., Kc001〈Kc100 or Kc010. Indentation crack length measurements on the (001) basal plane with the impression diagonals oriented parallel to the [100] and the [010] directions, indicate that the fracture toughness of these planes is K100/010air∼0.7 MPa m1/2. The hardness in this orientation was found to be 6.7 GPa. Measurements on a plane perpendicular to the basal plane resulted in a lower hardness of ∼3.8 GPa. This reduction in hardness is influenced by the extensive preferential cleavage of the (001) basal plane boundaries. The extremely low values of the fracture toughness suggest that considerable toughening would have to be achieved in melt-textured 123 for any practical bulk application. The presence of 211 phase and silver particles may serve to enhance the fracture toughness of aligned 123 by crack deflection and crack tip blunting respectively.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Variations in the amount of solar radiation reaching the Earth are thought to influence climate, but the extent of this influence on timescales of millennia to decades is unclear. A number of climate records show correlations between solar cycles and climate, but the absolute changes in solar ...
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Visual observations of the wall of Great Bahama Canyon indicate that ledges produced by differential submarine erosion occur at depths like reflectors on high-resolution seismic profiles, suggesting lithologic changes produce acoustic impedance contrasts and therefore reflectors. Quaternary-aged sediments in a core from Little Bahama Bank exhibit changes in lithology (and presumably acoustic impedance) associated with glacial-to-interglacial transitions, which also correspond in depth to seismic reflectors. This supports the concept that reflectors on high-resolution seismic profiles of Bahamian periplatform ooze correspond directly to changes in lithology and may be associated with climate/sea level fluctuations.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 4 (1993), S. 460-465 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Cholesterol is the major crystalline component of most gallstones found in the western hemisphere. Synthetic gallstones have been grown in our laboratory from cholesterol to study both growth morphology and kinetics. It is established that synthetic stones show characteristics of spherulitic crystallization. It is suggested that natural stones in vivo will also crystallize by spherulitic mechanisms. The microstructure of synthetic and natural stones consists of radiating arrays of cholesterol crystals emerging from a unique nucleation center. Impurities which are used to thicken the melt are segregated between the fibers. The radial growth of these fibers was observed to be a linear function of time. The radial growth rates are reported over a range of temperatures for support of a spherulitic model.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 18 (1999), S. 93-95 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 21 (1983), S. 229-240 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Résumé On analyse la zone libre de dislocation qui est située à l'extrémité d'une fissure de cisaillement de mode III. On solutionne à l'aide d'une distribution continue de dislocations le problème de l'empilement de dislocation-vis parallèle en front de fissure et situé, en cisaillement antiplanaire, dans le champ de contraintes d'une fissure. On suppose que l'extrémité de la fissure demeure aiguë et qu'elle satisfait au critère de rupture de Griffith, en recourant au facteur d'intensité de contraintes local à fond d'entaille. L'empilement de dislocations protège l'extrémité aiguë de la fissure contre l'influence du facteur d'intensité des contraintes appliquées, du fait d'une addition simple des contributions négatives de chaque dislocation à la valeur de l'intensité de contrainte appliquée. L'analyse diffère substantiellement de la théorie BCS bien connue en ce que les critères de rupture à l'extrémité de la fissure entrent dans la distribution de dislocation trouvée.
    Notes: Abstract The dislocation free zone at the tip of a mode III shear crack is analyzed. A pile-up of screw dislocations parallel to the crack front, in anti-plane shear, in the stress field of a crack has been solved using a continuous distribution of dislocations. The crack tip remains sharp and is assumed to satisfy Griffith's fracture criteria using the local crack tip stress intensity factor. The dislocation pile-up shield the sharp crack tip from the applied stress intensity factor by simple addition of each dislocation's negative contribution to the applied stress intensity value. The analysis differs substantially from the well known BCS theory in that the local crack tip fracture criteria enters into the dislocation distributions found.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 14 (1978), S. R73 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 16 (1980), S. R153 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 17 (1981), S. R7 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 13 (1977), S. 667-679 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Résumé La propagation stationnaire d'une fissure dans un solide est analysée en tant qu'un processus d'activation thermique. Le concept d'une force d'extension de la fissure, utilisé en mécanique de la rupture, est formellement introduit dans la théorie cinétique moléculaire. Cette représentation de la propagation d'une fissure apparaît, en maint aspects, similaire à celle du mouvement d'une dislocation sous l'effect d'une contrainte de cisaillement à traver des obstacles thermiquement franchissables. On dérive les relations thermodynamiques fondamentales pour la propagation stationnaire d'une fissure, à partir d'hypothèses simplificatrices similaires à celles couramment acceptées dans les théories de déformation basées sur le mouvement thermiquement activé des dislocations.
    Notes: Abstract Steady state crack propagation in solids is analyzed as a thermally activated process. The fracture mechanics concept of a crack driving force is formally introduced to molecular rate theory. This representation of crack propagation appears to be, in many aspects, similar to that of the motion of a dislocation under a shear stress across thermal obstacles. The basic thermodynamic relations are derived for steady state crack propagation using assumptions similar to those well accepted in theories of deformation based on thermally activated dislocation motion.
    Type of Medium: Electronic Resource
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