NETWORK STRUCTURE AND MECHANICAL-PROPERTIES OF ELASTOMERS .2. INFLUENCE OF STRESS-INDUCED CRYSTALLIZATION ON STRESS-STRAIN DATA

Uniaxial stress-strain properties of thiuram-cured natural rubbers are discussed in the framework of a non-Gaussian network model. The finite extensibility component of the reduced stress is evaluated by using a series expansion of the inverse Langevin function. From the resulting Gaussian contribution to the reduced stress, the effect of stress-induced crystallization on stress-strain data Is extracted by comparing measurements at room temperature (24-degrees-C) and 80-degrees-C, It is seen that at 24-degrees-C stress-induced crystallization leads to positive deviations from the linear behavior of the Gaussian contribution to the reduced stress in Mooney-Rivlin plots for extensions larger than about 100 %-200 %. At extensions larger than about 400 %, the observed deviations increase very rapidely and stress-induced crystallization becomes dominant A qualitative different picture is found for the measurements at 80-degrees-C, which means that stress-induced crystallization is not significant at this temperature.