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  • 1
    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 incorporation of continuous, uniaxial oriented, nylon and polyethylene terephthalate fibres into isotactic polypropylene leads to the expected increase in tensile strength as predicted by the rule of mixtures. The elongation to break, however, is found to be significantly in excess of those of the fibres and the matrix and increases with fibre volume fraction. The increase in ductility of the composites is attributed to decrease in spherulite size of the polypropylene and to restrained necking of the fibres due to transcrystalline growth at the fibre surface.
    Type of Medium: Electronic Resource
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  • 2
    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 Injection-moulded bars made from poly(methyl methacrylate) (PMMA) polystyrene (PS), polycarbonate (PC) and poly(vinyl chloride) (PVC), have been weathered outdoors in Jeddah, Saudi Arabia, for varying periods. The residual stresses in the bars have been found to vary considerably with exposure and in some cases the surface stress has reversed, becoming tensile. With PS and PVC, significant surface damage developed on exposure and the presence of surface flaws together with tensile residual stresses at the surface can be expected to reduce the resistance to fracture, especially in the case of PS which suffers considerable molecular weight reduction near the surface. The changes in residual stress in PMMA and PC were smaller, and the surface deterioration, examined by scanning electron microscopy, was much less than with PS and PVC. The performance of PMMA and PC in fracture tests generally declined less with weathering than did that of PS and PVC but the materials used were all commercial grades designed for use in Europe and the results obtained here should not be taken to indicate the relative weatherability of the different polymers. The significance of the results relate to the mechanism of failure involving the interaction of reversed residual stresses and surface flaws.
    Type of Medium: Electronic Resource
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  • 3
    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 Injection-moulded bars made from polypropylene (PP), polyacetal (POM) and nylon 6,6 (N6, 6), have been weathered outdoors in Jeddah, Saudi Arabia, for varying periods. In POM and N6, 6 the residual stresses became tensile near the surface, though this happened even with unexposed bars. Prolonged ageing or weathering of PP caused the residual stresses to fall to very low values. With POM and N6, 6 significant surface damage developed on weathering, and multiple surface cracks opened up during uniaxial tensile testing. With N6,6 these developed into the form of diamond-shaped ductile fracture cavities, and the failure mechanism appeared quite different to that obtained with unexposed mouldings. With weathered PP no significant surface damage was visible even in the scanning electron microscope, but prolonged weathering caused a change in the failure mechanism, with fracture usually occurring without necking and drawing with specimens weathered for two years or more.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 129-144 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polycarbonate injection moldings have been conditioned for various times in (i) hot water (40, 60, 80, and 100°C) or (ii) in a temperature gradient (with hot surface/cold surface temperatures 80/25, 100/25, 120/35, and 140/60°C). Water absorption occurred in hot water and caused the formation of disc-shaped flaws, which were located at all depths within the bars and at all orientations. The presence of the flaws caused severe embrittlement and cracks were nucleated by them during uniaxial tensile testing. Residual stress levels were found to be diminished by hot water conditioning more than those in bars conditioned at the same temperatures in air. The sense of the residual stresses reversed in a bar that was allowed to cool slowly in the water bath, an observation attributed to desorption. It was generally found that the flaws near the surface healed on allowing the bars to stand in air at room temperature. Temperature gradient conditioning caused reversal of the sense of the residual stresses near to the hot surface at the two higher temperatures used and significant reduction in magnitude at the lower temperatures. Fracture nucleated at this surface during uniaxial tensile testing.
    Additional Material: 23 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The isothermal crystallization of isotactic polypropylene at different temperatures in the presence of fibrous substrates has been investigated. It is shown that preferential transcrystalline growth occurs at the fiber surface and that changes in nucleation density in the bulk material adjacent to the fibers also occur, the extent of which is dependent on temperature and fiber volume fraction. The effects are discussed in terms of the diffusion of heterogeneities in the bulk due to interaction and the adsorption on the fibers.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 11 (1990), S. 24-31 
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Glass-fiber-reinforced polystyrene (GFPS1) and polyethersulfone (GFPES) injection-moldings containing 20 wt% glass have been weathered in Jeddah, Saudi Arabia, for up to one year. The retained strength and ductility were, generally, better than in the corresponding unreinforced polymers. The tensile strength fell to ca 73% of the initial, unexposed value, (GFPS1) and ca 77% (GFPES), whereas the extension to break values fell to ca 50% and 76%, respectively, after one year of weathering. The inclusion of carbon black in reinforced polystyrene (GFPS(B)) resulted in a barely perceptible drop in strength (to ca 98%) and a greatly improved reduction in extension to break, dropping only to ca 81% after one year. Residual stress levels were measured and were found to be insufficient to have a significant influence on fracture behavior. In GFPES they were generally less than 2MN/m2 except at a location ≃0.3 mm from the surface, where compressive stresses of up to 4 MN/m2 were present. No significant change in residual stress occurred with exposure in GFPES. With GFPS1 the stress levels were insignificant ( 〈1 MN/m2) through most of the bar both before and after exposure. With unexposed GFPS(B) the stresses were 〈1 MN/m2 except within 0.2 mm of the surface, where they rose steeply, though probably not above 5 MN/m2. After weathering the stresses were everywhere 〈1 MN/m2, but the sense of the residual stresses had reversed near to the exposed surface. This is attributed to radiant heating, and is undesirable because it may lead to distortion.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0360-6384
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 28 (1983), S. 2033-2051 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Birefringence measurements have been made on six glassy polymers during stress-relaxation and recovery experiments at temperatures below Tg. Of the six polymers tested only one pair, poly(ethylene terephthalate) and a glassy polyamide (“Trogamid”), show a strong mutual resemblance in the behavior of birefringence under these conditions. The results are discussed with reference to molecular structure, and, although detailed interpretations are not offered, it is observed that the behavior is less complex for polymers which possess their most polarizable groups in the main chain or attached rigidly to it than for those polymers having polarizable side groups with relaxations which do not involve the main chain. All six polymers have been tested in injection-molded form, and the possible consequences of this are considered. The major differences observed to occur between the different materials do not appear to be related to processing, however, and some results obtained using specimens prepared in other ways are also presented to illustrate this.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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