The Thermodynamics of Rubber. II. Temperature Change of Rubber under Adiabatic Stretching
| Autor: | J. G. Eymers, J. Wouda, D. S. Ornstein |
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| Rok vydání: | 1930 |
| Předmět: | |
| Zdroj: | Rubber Chemistry and Technology. 3:403-408 |
| ISSN: | 1943-4804 0035-9475 |
| DOI: | 10.5254/1.3535502 |
| Popis: | In our first communication (Proc. Acad. Sci. Amsterdam, 32, 1235 (1929)) it was shown that the heating effect which takes place in stretched rubber must be due to hysteresis, because from thermodynamic considerations it is obvious that a substance with a positive coefficient of elongation shows a cooling effect. If this is true, rubber without hysteresis must obey the laws of thermodynamics. We have tested this for rubber of the following composition: which we got from Dr. van Rossem of Rijksrubberdienst, whom we heartily thank for his kindness also on this occasion. To determine whether this rubber is free from hysteresis, the following method was used: A piece of rubber was successively loaded more and more, till the elongation was about 250 per cent., and then the load was gradually removed. No hysteresis was shown by the substance. When the rubber is submitted to a force which gives a change of length of this amount, the length of the rubber does not alter with the time. When, however, the elongation is more than 250 per cent., the length changes slightly with the time up to an elongation of 370 per cent.; beyond this elongation no alteration in length takes place again. When, in the case of these large extensions, the force is gradually decreased, the elongations come to much larger values than before, when the same force was applied to the rubber from its zero state. However, this is not an effect of hysteresis, for, however great the force and however long the time might have been during which the force acted (even more than 24 hours), the rubber always momentarily assumed its original length when the weight was removed at once. In Fig. 1 the areas from O to E and from B to C must be ascribed to different phases, and the difference between the graph for increasing and decreasing force can be explained by a retardation of phase. Moreover, the slope of the curve AB can be much steeper as in this case, with a longer time between the application of different forces. Further, the rubber in the region DE is not in a stable state, for a slight impulse affecting the rubber causes the elongation to decrease at once. Since the second phase already shows itself above an elongation of 200 per cent., we have taken all our readings for thermodynamic relation below that elongation. It is known that from thermodynamical considerations one can get the formula for the change in temperature |
| Databáze: | OpenAIRE |
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