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  • 1
    Electronic Resource
    Electronic Resource
    Fatigue mechanisms of thermoplastics (1966)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 6 (1966), S. 363-368 
    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: Failure in fatigue by the mechanism of crack initiation and propagation originationg at flaws and stress concentrations has been fairly well established. It explains the fatigue phenomena in highly elastic materials, namely metals and certain thermosetting plastics such as reinforced polyester and epoxy resins. We have found, however, that a different mechanism dominates the fatigue behavior of thermoplastics. Specifically, the mechanism involves the generationa of heat within the material due to viscous damping or hysteresis. This paper presents fatigue, damping data and temperature measurements during cyclic stress to support this conclusion on three themoplastic resins of widely different mechanical properties, polyetrafluouoethylene (PTFE), Nylon 6, and polymethyl-methacrylate (PMMA). In addition to the usual S-N fatigue curves, we wil show how surface temperature changes with fatigue life and how this change is affected by stress, Frequency, crystallinity, specimen geometry and other parameters. Alos, the loss compliance of the materials will be presented as afunction of temperature to show the relationship of fatigue to damping properties.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760060414
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanical behavior of polytetrafluoroethylene around the room-temperature first-order transitionThe data in this paper represent part of the Ph.D. thesis of G. P. Koo, submitted to the Department of Chemistry and Chemical Engineering, Stevens Institute of Technology, May, 1969. (1969)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 9 (1969), S. 268-276 
    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 effect of the room-temperature first-order transition on the plastic yield behavior of polytetrafluoroethylene (PTFE) has been investigated. Stress-strain curves were measured at different strain rates and temperatures. Tensile creep under constant dead load was also measured as a function of temperature and stress level. The effect of degree of crystallinity was investigated by using both a rapidly quenched and slow-cooled polymer. Observations were extended to large deformations, so that the phenomenon primarily observed was plastic yield rather than linear viscoelastic behavior.The curve of yield stress vs. temperature in the temperature range from -50 to +68°C was found to be almost identical with the curve of elastic modulus vs. temperature; the yield stress shows a marked local decrease at the first-order transition. The yield elongation was almost constant (at about 5%) over this same range, which is in accord with the above result. The more highly crystalline polymer is always more rigid than the less crystalline polymer at small deformations, but above 19°C its stress-strain curve shows a “cross-over” in stress level with the curve of the less crystalline polymer as extension increases. That is, above 19°C the less crystalline polymer shows a more rapid rate of “strain hardening”, even though the strain-hardening effect is pronounced in both polymers. Attempts to apply time-temperature superposition to creep data at different temperatures were partially successful; the lateral shifts required corresponded to an activation energy of approximately 80 kcal.The experimental observations suggest a model of the solid-state structure of PTFE which could be described as an “elastic-plastic network”, in which crystalline domains are connected by elastic amorphous regions, and in which the crystalline domains can flow plastically at sufficiently high stress or temperature.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760090406
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of cyclic loading on the morphology of polytetrafluoroethylene (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 1145-1152 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.160100616
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