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  • 11
    Electronic Resource
    Electronic Resource
    The mechanical properties of elastomers in high-pressure CO2 (1999)
    Springer
    Journal of materials science 34 (1999), S. 417-422 
    Details
    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
    URL: http://dx.doi.org/10.1023/A:1004442614090
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  • 12
    Electronic Resource
    Electronic Resource
    Environmental stress cracking behaviour of urethane methacrylate based resins (1994)
    Springer
    Journal of materials science 29 (1994), S. 3095-3101 
    Details
    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 kinds of cross-linked urethane methacrylate resins have been investigated using three-point bend tests to determine their environmental stress cracking (ESC) behaviour in a range of liquids (water, sodium hydroxide, ethylene glycol, acetonitrile, acetic acid, acetone, tetrahydrofuran, toluene, 3,5,5-trimethylhexanol and petrol). The resins were found to undergo ESC in organic liquids only, and the critical strains, ɛc, and critical stresses, σc, have been related to the solubility parameters, δ, of the liquid environments. The most severe ESC was observed in solvents with δ−19–20 MPa1/2, corresponding to minimum points in the plots of ɛc and σc against δ. Generally, the resin with the higher cross-link density had a greater resistance to ESC, but the effect of liquid diffusion complicated the situation and was found to play an important role in the ESC behaviour of these materials. The results confirmed that liquid diffusion into the resins lowered the critical strain (and stress), leading to earlier failure. In the case of the lower cross-link density resin, very fast diffusion was found to cause softening. However, it was noted that liquid diffusion can also blunt crazes and cracks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356650
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  • 13
    Electronic Resource
    Electronic Resource
    The effects of diffusion on environmental stress crack initiation in PMMA (1998)
    Springer
    Journal of materials science 33 (1998), S. 5193-5204 
    Details
    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
    URL: http://dx.doi.org/10.1023/A:1004431920449
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  • 14
    Electronic Resource
    Electronic Resource
    The use of flexural tests in the study of environmental stress cracking of polymers (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 665-670 
    Details
    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 use of bend testers for the determination of critical strains in the study of environmental stress cracking has been assessed. Using the combination of polystyrene in ethanol, various factors affecting the measurement of critical strains were investigated, including the strain applied during the bend testing, the time of immersion in the liquid prior to straining, the surface finish, and the extent of physical aging. It was concluded that the best determination of critical strain is the strain at which a sample just shows signs of crazing, rather than the strain at the outer edge of a band of crazes. The measured value of critical strain increases with increased prior immersion time, decreased surface roughness, and decreased physical aging time. Reasons for these variations are discussed. It is concluded that although the use of bend testers is valuable for qualitative testing, careful testing methodologies need to be adopted for it to be a useful quantitative test.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340808
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  • 15
    Electronic Resource
    Electronic Resource
    The effects of physical aging on the brittle fracture behavior of polymers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 165-169 
    Details
    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
    URL: http://dx.doi.org/10.1002/pen.760350207
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  • 16
    Electronic Resource
    Electronic Resource
    The influence of physical aging on the creep rupture behavior of polystyrene (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1451-1458 
    Details
    ISSN: 0887-6266
    Keywords: polystyrene ; postannealing aging time ; brittle fracture behavior ; creep rupture ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effects of postannealing aging time on the brittle fracture behavior of polystyrene were studied. A combination of mechanical properties, including creep and creep rupture under constant load and the behavior under constant extension rate deformation were examined for polystyrene samples of different prior aging times (from 1h to 2 months). The specimens and fracture surfaces were examined by optical microscopy and SEM to observe any change in the fracture behavior. It was found that longer aging times caused not only a change in the time-dependent modulus of the material but also a significant decrease in the creep rupture life and a decrease in strain to failure. It was found that the reasons for this are that although aging delays craze formation, craze breakdown and ultimate failure are accelerated by aging. The importance of these findings are discussed, particularly in relation to failure criteria involving the use of critical strains. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090311102
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