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  • 1970-1974  (10)
Material
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1972), S. 131-141 
    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 When polyethylene single crystals are mounted on a substrate less rigid than the usual evaporated carbon, they undergo considerable dimensional changes in the electron beam. In particular, crystals mounted on collodion expand by 22±2% in every direction in the plane of the lamellae. No induction period is observed and the expansion continues after all crystalline order has been destroyed. Since irradiation increases the density of bulk polyethylene, it is presumed that the lamellae become thinner as they expand. A similar but lesser expansion occurs on irradiation in the electron microscope at liquid helium temperatures, and when crystals are mounted on formvar films. In a solution grown lamellar crystal of polyethylene, most of each molecule is straight and aligned along thec axis, which is nearly perpendicular to the plane of the lamella. Radiation damage in the electron microscope introduces disorder, and these results imply that the effect of this disorder is to reduce the mean molecular dimension alongc, and increase it in the plane perpendicular toc. Polymer chains are generally highly oriented in crystalline regions, so this qualitative explanation would imply similar effects in other systems. These effects have important implications for the contrast observed in the electron microscopy of polymers.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1972), S. 131-141 
    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 When polyethylene single crystals are mounted on a substrate less rigid than the usual evaporated carbon, they undergo considerable dimensional changes in the electron beam. In particular, crystals mounted on collodion expand by 22±2% in every direction in the plane of the lamellae. No induction period is observed and the expansion continues after all crystalline order has been destroyed. Since irradiation increases the density of bulk polyethylene, it is presumed that the lamellae become thinner as they expand. A similar but lesser expansion occurs on irradiation in the electron microscope at liquid helium temperatures, and when crystals are mounted on formvar films. In a solution grown lamellar crystal of polyethylene, most of each molecule is straight and aligned along thec axis, which is nearly perpendicular to the plane of the lamella. Radiation damage in the electron microscope introduces disorder, and these results imply that the effect of this disorder is to reduce the mean molecular dimension alongc, and increase it in the plane perpendicular toc. Polymer chains are generally highly oriented in crystalline regions, so this qualitative explanation would imply similar effects in other systems. These effects have important implications for the contrast observed in the electron microscopy of polymers.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1972), S. 427-434 
    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 transverse rupture strength of hot-pressed and annealed composites of magnesium oxide and dispersed metallic phases (nickel, iron, cobalt) increases with increasing volume fraction of metal and annealing temperature. The strengthening effect of the metal is attributed to an inhibition of grain growth while flaw healing occurs during the annealing of the composites. The strength of magnesium oxide hot-pressed with nickel fibres is not affected by the volume fraction of fibre or the annealing temperature, and is comparable to the strength of porous magnesia. However, the work of fracture, though insensitive to heat-treatment, increases by at least two orders of magnitude for a moderate volume fraction of randomly oriented fibres. Mechanisms of energy absorption during the fracture of composites containing weakly bonded, non-aligned fibres are discussed. They include the work done in plastically deforming the fibre as it is withdrawn from its socket. It is concluded that this mechanism may be of importance in composites containing very weakly bonded ductile fibres.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1972), S. 427-434 
    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 transverse rupture strength of hot-pressed and annealed composites of magnesium oxide and dispersed metallic phases (nickel, iron, cobalt) increases with increasing volume fraction of metal and annealing temperature. The strengthening effect of the metal is attributed to an inhibition of grain growth while flaw healing occurs during the annealing of the composites. The strength of magnesium oxide hot-pressed with nickel fibres is not affected by the volume fraction of fibre or the annealing temperature, and is comparable to the strength of porous magnesia. However, the work of fracture, though insensitive to heat-treatment, increases by at least two orders of magnitude for a moderate volume fraction of randomly oriented fibres. Mechanisms of energy absorption during the fracture of composites containing weakly bonded, non-aligned fibres are discussed. They include the work done in plastically deforming the fibre as it is withdrawn from its socket. It is concluded that this mechanism may be of importance in composites containing very weakly bonded ductile fibres.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1972), S. 422-426 
    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 MgO crystals containing up to 40% by volume of magnesioferrite and up to 2% by volume of iron and nickel were produced by a diffusion technique followed by appropriate heat treatments. Magnesioferrite precipitate did not significantly change the effective surface energy of a crack as measured by the double cantilever beam technique. Iron and nickel precipitate was produced in the form of platelets lying on {100}MgO planes whose orientation relationships were [001]MgO ∥[001]Fe, [110]MgO ∥[100]Fe with a spread of +10°, approximately, and [001]MgO ∥[001]Ni, [010]MgO ∥[010]Ni with negligible spread. Despite the crystallographic orientation relationships, the metal-MgO interface appeared to be very weak; the reasons for this are discussed. The effect of the metal precipitate on crack propagation was to markedly increase the density of cleavage steps. For a volume fraction of precipitate of 0.02, this led to a small increase in the effective surface energy, on the order of 1 Jm−2.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1972), S. 422-426 
    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 MgO crystals containing up to 40% by volume of magnesioferrite and up to 2% by volume of iron and nickel were produced by a diffusion technique followed by appropriate heat treatments. Magnesioferrite precipitate did not significantly change the effective surface energy of a crack as measured by the double cantilever beam technique. Iron and nickel precipitate was produced in the form of platelets lying on {100}MgO planes whose orientation relationships were [001]MgO ∥[001]Fe, [110]MgO ∥[100]Fe with a spread of +10°, approximately, and [001]MgO ∥[001]Ni, [010]MgO ∥[010]Ni with negligible spread. Despite the crystallographic orientation relationships, the metal-MgO interface appeared to be very weak; the reasons for this are discussed. The effect of the metal precipitate on crack propagation was to markedly increase the density of cleavage steps. For a volume fraction of precipitate of 0.02, this led to a small increase in the effective surface energy, on the order of 1 Jm−2.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 9 (1974), S. 1436-1445 
    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 effect of the orientation of metal wires on the opening of a crack in a brittle-matrix composite has been studied. The force arising from the plastic bending of a wire which is weakly bonded to the matrix and which crosses the matrix crack at an angleθ to the crack face normal has been measured in model resin-wire composites and good agreement is found with a simple theory based on the calculation of the force needed to produce a plastic hinge in a cantilever beam. The force passes through a maximum at a small crack opening, of the order of one wire diameter, and decreases with further crack opening. The The largest force is obtained for a value ofθ of approximately 45°. For wires whose length approaches the critical length, the force and the total work of fracture arising from the bending of the wire are small compared to the values arising from the interfacial shear stress resisting pull-out; the contributions due to bending and interfacial shear stress are of comparable magnitudes for wires which are approximately one-fifth of the critical length.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 8 (1973), S. 71-78 
    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 Polypropylene, oriented by hot-drawing, has been deformed in tension and compression, at various angles to the initial draw direction. The behaviour in tension is described well by a three-part criterion of the type applied in previous work to fibre-composites [8, 9]. The Hill-von Mises treatment of the plasticity of an anisotropic metal, which has been previously extended successfully to polymers [1], can be applied to describe the tensile yield stresses but is unsatisfactory in its prediction of the form of the strain in polypropylene. In compression, the variation of the yield stress with the angle of the stress axis is much less than in tension, and the modes of deformation are different from those operating in tension at the same angle. In particular, compressing at right angles to the molecules produces shear in a direction normal to the molecules (transverse shear). The critical stress for transverse shear in compression is approximately the same as the critical stress for shear parallel to the molecules in tension.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 8 (1973), S. 1012-1022 
    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 Polypropylene and high-density polyethylene, oriented by hot drawing, have been tensile testedin situ in a low angle X-ray camera. Two orientations of polypropylene,Θ 0=31° andΘ 0=60°, and one orientation of polyethylene,Θ 0=30°, were examined. (Θ 0 is the initial angle between the tensile axis and the molecular axis.) Low-angle and wide-angle X-ray patterns were taken at successive stages of increasing strain up to approximately 100%. The rotations of the molecular axis and lamellar normal for both materials oriented nearΘ 0=30° were quantitatively consistent with predominantly intermolecular shear, occurring within the lamellae. In the case of polypropylene, it is proposed that small amounts of interlamellar and interfibrillar shear were also present. AtΘ 0=60°, the polypropylene was shown to deform by void opening or fibril separation, followed by intermolecular shear. The behaviour of polypropylene was consistent with the yield criterion based on a fibre reinforced composite model which was presented in a previous paper [1].
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 8 (1973), S. 1238-1246 
    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 Sapphire filament oriented within 2 1/2° of the crystallographic c-axis underwent creep by a mechanism other than slip on the basal planes at temperatures above 1600° C. There was a stress below which creep could not be detected; this decreased from 180 MNm−2 at 1600° C to 65 MNm−2 at 1800° C. The total tensile strain obtained never exceeded 5%. Fracture occurred during a linear stage of creep in which the stress exponent of the strain-rate was approximately 6. The creep mechanism appeared to be slip on {20¯2¯1} 〈01 T2〉 (morphological unit cell). A filament in which the c-axis lay at 6° to the filament axis deformed by localized basal slip. The accompanying local latice rotations produced fracture at a small overall strain, usually less than 0.5%. The results demonstrate extreme anisotropy of creep in sapphire crystals.
    Type of Medium: Electronic Resource
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