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  • 1995-1999  (5)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 30 (1995), S. 655-660 
    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 environmental stress cracking behaviour of polycarbonate in ethanol was studied with the aim of critically evaluating craze initiation criteria. A combination of constant strain-rate tensile tests and creep tests were conducted in air and ethanol. The onset of crazing was determined by the use of departure points, which were shown to correlate well with the formation of optically visible crazes. Samples with different states of physical ageing and hence different relaxational behaviour were used to test out various initiation criteria. It was found that crazing occurred when the slower α relaxations had accumulated a certain amount of strain, in this case, 0.1%, and that a criterion based on critical inelastic strain was the most appropriate. Post-immersion tests showed that the development of craze precursors occurs independently of the environment.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 34 (1999), S. 417-422 
    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 Elastomer seals are widely used to contain high-pressure gases and can suffer from decompression damage when the contained gas is depressurized. The generally accepted mechanism for the damage is that there is a considerable degree of dissolution of the gas into the elastomer which cannot diffuse out quickly enough when the contained pressure is reduced; hence bubbles and fissures occur in the bulk of the elastomer. Attempts to model this behaviour typically assume the elastomer material properties are measured in the absence of the dissolved gas. In this study, a standard dumb-bell test piece tensometer has been developed which allows the elastomer material properties to be measured while saturated with CO2 and N2 (two gases with markedly different solubilities) at pressures of up to 4 MPa. The equipment was shown to be capable of providing accurate measurements under these conditions and various fluorocarbon, nitrile and silicone elastomers were tested. These tests showed that the high-pressure CO2 induced a slight reduction in initial modulus compared to tests in air, accompanied by a more significant loss in both strength and ultimate extension. The reduction was greater than 50% in some cases. Electron micrographs of the samples showed that the fracture surfaces were of a smoother nature for the samples tested in CO2, suggesting a mechanism of disruption of interchain forces. The implications of these results for models of decompression damage are noted.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 33 (1998), S. 5193-5204 
    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 Slow strain rate tensile tests were conducted on un-notched PMMA samples in a range of liquid environments in order to assess the effects of diffusion on craze formation. The environments were selected to have a spread of diffusion rates and consisted of water,methanol, propan-2-ol, 355 trimethylhexanol and ethylene glycol.Absorption tests in these environments showed that methanol had the fastest diffusion rate and greatest degree of swelling, followed by water. Ethylene glycol and trimethylhexanol showed no weight gain,and propanol caused a steady dissolution of the PMMA. Tensile tests were conducted after the samples had been pre-immersed in the liquid environments for times ranging from 1 minute to 14 days. These were compared with equivalent tests in air, with the point at which the environment curve departed from the air curve being used to establish where crazing commenced. Tests were also conducted in methanol and ethylene glycol at a range of strain rates. It was found that with methanol and to a lesser degree with water and trimethylhexanol,crazing was delayed in tests with longer pre-immersion. This is due to mechanisms of flaw blunting and/or the introduction of surface compressive stresses. Similar effects were seen with the methanol tests at slower testing rates. It was found that these effects can occur very locally to the sample surface, where no weight gain could be measured and in the very early stages of craze development.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 165-169 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: The effects of physical aging on the failure behavior of a typical brittle polymer, polystyrene, have been studied. Properties examined were creep rupture lifetimes, fatigue lifetimes, and environmental stress cracking in ethanol. Fractured samples were examined both optically and by scanning electron microscopy to determine the degree of crazing. It was found that a longer physical aging time produced shorter lifetimes in all cases. The main reason for this is the reduction in craze strength caused by a reduced toughness due to physical aging. A long aging time was found to delay craze formation, but once formed, these crazes were much less stable than those formed with a short aging time. The effects of aging are important on failure prediction criteria and on testing methodologies, and the implications are discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 1995-02-01
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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