Mechanisms of deformation in crystallizable natural rubber. Part 2: Quantitative calorimetric analysis

This paper deals with the calorimetric analysis of deformation processes in natural rubber. Infrared thermography is first used to measure the temperature evolution of specimens under quasi-static uniaxial loading at ambient temperature (see Part 1). Then the heat sources produced or absorbed by the material due to deformation processes are deduced from the temperature variations by using the heat diffusion equation. Different main results are obtained from cyclic and relaxation tests. First, no mechanical dissipation (intrinsic dissipation) is detected during the material deformation. Second, strain-induced crystallization leads to significant heat production, whereas the melting of crystallites absorbs the same heat quantity with different kinetics. This difference in kinetics explains the mechanical hysteresis. Finally, relaxation tests show that crystallite melting does not systematically occur instantaneously.