Isothermal and Adiabatic Stress-Strain Curves of Vulcanized Rubber

Abstract

Abstract The stress-strain diagram of rubber has been the subject of a large number of investigations, including those of Röntgen, Gough, and Joule in the nineteenth century, those on isothermal phenomena by Meyer and Ferri, and Wiegand and Snyder, and most recently those on adiabatic phenomena of Ornstein, Eymers, and Wouda. The investigations of Meyer and Ferri are concerned chiefly with the dependence of the stress-strain phenomena on the temperature, and they confirm experimentally the hypothesis that within a certain range of temperature and with highly vulcanized samples, the stress is proportional to the absolute temperature, i. e., S=aT+b. At lower states of vulcanization this proportionality does not hold true. The work of Ornstein and his collaborators, which is frequently cited in the literature, is concerned with the phenomena which take place when raw rubber and weakly vulcanized rubber are stretched adiabatically; that of Wiegand and Snyder is concerned chiefly with a thermodynamic interpretation of stress-strain curves obtained experimentally. Now in spite of the fact that stress-strain curves of rubber have been determined so frequently, particularly under isothermal conditions, these measurements are for the most part of limited value, since the chemical nature of the types of rubber employed is not described definitely. Then again in most cases little attention was paid to the difference between isothermal and adiabatic stretching. In view of these facts, it seemed desirable to throw further light on the problem by obtaining stress-strain curves of one particular well-defined material. The object of the present work was then: 1. To obtain true isothermal stress-strain curves as a function of the degree of vulcanization and as a function of the temperature, and thus to study stresses as a function of temperature. 2. To obtain data on the same vulcanizates under adiabatic conditions. 3. To compare the stress-strain results under isothermal conditions with those under adiabatic conditions.