| Popis: |
The effects of elongation on the audiofrequency dynamic mechanical properties of a natural rubber (Hevea) gum stock have been described previously in terms of the elastic (J') and the viscous (J') components of a complex shear compliance, J* equals J' - iJ'. In this prior work emphasis was on the changes in compliance levels and the frequency dependencies of the elastic and viscous components at static elongations from 0 to 400%, and after retractions to elongations below 300%. At elongations above 300%, several large, sharp resonances appeared in the compliance-frequency plots coincident with the well known stretch-induced, oriented crystallinity above 300% elongation for the initially amorphous rubber at room temperatures. In the present work attention is on the loss tangent, J'/J', which governs vibration damping, and for which no data were given in the earlier report. After extensions to 400%, as described above, followed by retraction to 275%, for example, values of loss tangent were two or three times those found at any of the first elongations from 0 to 400%. Current measurements using an automated measurement system yield similar results. Additional information on the effect of time at an elongation and the elongation-retraction sequence on enhanced damping has also been gathered. In any case, it is evident that natural rubber gum stocks, ordinarily with low damping, when treated smartly can be changed to high damping materials at some audio frequencies.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
