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DYNAMIC MECHANICAL PROPERTIES OF STRETCHED NATURAL RUBBER
PENNSYLVANIA STATE UNIV UNIVERSITY PARK
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Dynamic shear compliance measurements on a vulcanized natural rubber stock have been carried out from 50 to 5000 c as a function of static elongation in the range 0-400. Above 300 elongation several very large resonance dispersions appear in the region 1000-2000 c, but at lower elongations no such resonances are observed. The appearance of mechanical resonance dispersion coincides with the development of oriented crystallinity in the stretched rubber as shown from X-ray diffraction data. The magnitudes of the dispersions decrease with increasing elongation above 300 whereas X-ray measurements indicate the amount or extent of crystallinity increases with stretching above 300 elongation. The resonances clearly decrease as the crystallinity becomes more perfect or more extensive and appear to reflect the imperfections of the crystalline regions formed by elongation rather than the crystallinity itself. Observed changes in the compliance spectrum with time at each elongation also favor this view. Author
APPROVED FOR PUBLIC RELEASE