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  • 1980-1984  (14)
  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 296 (1982), S. 59-61 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Upper Barremian sample has an organic carbon content of 9% and was Soxhlet extracted with toluene/methanol (1/3, v/v; 20 h). The hexane-soluble part of the extract was separated by column chromatography over silica/alumina using hexane, toluene and toluene/methanol (1/1, v/v). The saturated ...
    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] The shale sample was taken from an exposure (4333'N, 1241' E) near the cemetery of Moria, a small village near Cagli, province of Pesaro and Urbino, Italy8. The sediment, which has an organic carbon content of 13.3%, was Soxhlet-extracted with toluene/methanol (1:3 v/v; 20 h). The hexane-soluble ...
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 43 (1981), S. 397-408 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The possibility of generating an occupation inversion n(E) 〉1/2 in a nonequilibrium superconducting state by tunnel injection is discussed. By investigating the combined densities of states of the processes involved, a condition on the occupation function n(E) for sound wave amplification is derived, which generally is more restrictive than occupation inversion. It is shown that occupation inversion can be generated only in nonsymmetric superconductorinsulator-superconductor tunnel junctions where the super-conducting layers are of different thicknesses. The thickness of the amplifying layer must not exceed the diffusion length of the quasiparticles. The estimates suggest that sound wave amplification should in principle be possible.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 17 (1981), S. 483-491 
    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 Des calculs numériques de la relaxation d'énergie de déformation dans le cas de fissure se propageant au voisinage de l'interface entre une particule sphérique et une matrice ont été utilisés en vue de déterminer la fonction de relaxation de vitesse d'énergie de déformation dans le cas où les contraintes sont créées par une contraction thermique différentielle. Cette fonction a été trouvée telle qu'elle présente un maximum suivant la longueur de fissure et que ce maximum est compatible avec les conditions théoriques d'extension de fissure et d'arrêt de fissure proposées par Lange. Les calculs montrent qu'il existe une dimension critique de particule en-dessous de laquelle l'extension de fissure ne se produit pas pour en système donné de contrainte thermomécanique. La dimension critique de particule que l'on peut prédire est en bonne corrélation avec les résultats expérimentaux.
    Notes: Abstract Numerical computations of the strain energy release rate for cracks propagating around the interface between a spherical particle and a matrix have been used to determine the strain energy release rate function for the case where stresses arise due to differential thermal contraction. The strain-energy release rate function was found to exhibit a maximum as a function of crack length consistent with the theoretical conditions for crack extension and arrest proposed by Lange. The calculations show that a critical particle size exists below which crack extention does not occur for a given thermalmechanical stress. The predicted critical particle size correlates well with experimental results.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 17 (1982), S. 225-234 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The thermodynamics of the constrained phase transformation is presented with particular reference to size effects introduced by surface phenomena concurrent with the transformation, e.g., the formation of solid-solid surfaces (twins, etc.) and solid-vapour surfaces (microcracks). It is shown that these surface phenomena not only introduce a size-dependent energy term into the total free-energy change, but also reduce the strain energy associated with the transformation, which can result in a transformation at a temperature where ¦ΔGc¦, the chemical free energy change, is less thanU se, the unrelieved strain energy associated with the constrained transformation. The results of this analysis lead to a phase diagram representation that includes the size of the transforming inclusion. This diagram can be used to define the critical inclusion size required to prevent the transformation and/or to obtain the transformation, but avoid one or more of the concurrent surface phenomena.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 17 (1982), S. 235-239 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Two approaches are taken to determine the contribution of a stress-induced phase transformation to the fracture toughness of a brittle material. Both approaches result in an expression for the critical stress intensity factor,K c, of $$K_c = \left[ {K_0^2 + \frac{{2RE_c V_i (|\Delta G^c | - \Delta U_{se} f)}}{{(1 - v_c^2 )}}} \right]^{1/2} ,$$ whereK 0 is the critical stress intensity for the material without the transformation phenomenon, (¦ΔG c¦−U se f) is the work done per unit volume by the stress field to induce the transformation,E c andν c are the elastic properties,V i is the volume-fraction of retained, high-temperature phase andR is the size of the transformation zone associated with the crack. It is assumed that only those inclusions (or grains) close to the free surface of the crack will contribute to the fracture toughness; thus,R the inclusion size. The chemical free-energy change associated with the transformation, ¦ΔG c¦, will govern the temperature and alloying dependence of the fracture toughness.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 17 (1982), S. 240-246 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Materials in the ZrO2-Y2O3 system (with ⩽7.5 mol % Y2O3) were fabricated to investigate the conditions required to retain the metastable, tetragonal phase and to determine the contribution of the stress-induced martensitic reaction to fracture toughness. Retention of the tetragonal phase was optimized by minimizing porosity and maintaining the grain size below a critical valve. The critical grain size increased from 0.2 to 1μm for compositions ranging between 2 and 3 mol %, respectively. These results are consistent with the theories developed regarding the thermodynamics of the martenistic reaction in a constrained state. In the tetragonal plus cubic phase-field (compositions between 3.0 and 7.5 mol % Y2O3), the critical stress-intensity factor decreased from 6.3 to 3.0 MPa m1/3 as the volumefraction of the retained, tetragonal phase decreased to zero. Theoretical results, derived from the concept that the stress field of the crack does work to unconstrain the transformation, are in good agreement with the experimental results.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 17 (1982), S. 247-254 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Three Al2O3-ZrO2 composite series, containing 0, 2 and 7.5 mol % Y2O3, were fabricated for fracture toughness determinations. Without Y2O3 additions, tetragonal-phase ZrO2 could only be retained up to approximately 10 vol % ZrO2; additions of 2 mol % Y2O3 allowed full retention of the tetragonal phase up to 60 vol % ZrO2. Cubic ZrO2 was produced with additions of 7.5 mol % Y2O3. Significant toughening and strengthening was achieved when tetragonal ZrO2 was present.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 17 (1982), S. 255-263 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The critical stress-intensity factor,K c, of materials containing tetragonal ZrO2 was found to decrease with increasing temperature and CeO2 alloying additions, as predicted by theory. The temperature dependence ofK c was related to the temperature dependence of the chemical free-energy change associated with tetragonal-monoclinic transformation. Good agreement with thermodynamic data available for pure ZrO2 was obtained when the size of the transformation zone associated with the crack was equated to the size of the ZrO2 grains. TheK c against CeO2 addition data was used to estimate the tetragonal, monoclinic, cubic eutectoid temperature of 270° C in the ZrO2-CeO2 binary system.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 15 (1980), S. 616-618 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A comparison of “creep” resistance in as-fabricated and pre-oxidized specimens of different Si3N4/MgO alloys shows that pre-oxidation not only significantly reduces the apparent steady-state creep rate, but can also change the stress dependence from a non-linear to a linear behaviour. This phenomenon is discussed in terms of compositional changes induced by oxidation.
    Type of Medium: Electronic Resource
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