Thermal and calorimetric evolutions of natural rubbers under cyclic loadings
Résumé
The aim of this study is to characterize and to interpret both the thermal and the calorimetric responses of unfilled natural rubber subjected to a cyclic loading test. For this purpose temperature variations of specimens are measured by infrared thermography during the test at ambient temperature. 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 results are obtained. First, the heat source due to thermoelastic (entropic) coupling increases with the stretch ratio at constant stretch rate. Second, under the assumption that the mean of thermo-mechanical couplings vanishes on one cycle, no mechanical dissipation (intrinsic dissipation) is detected during the material deformation even if a hysteresis loop is observed in terms of the mechanical response. Finally, the crystallization of the polymer chains under tension leads to a temperature increase of the order of several degrees Celsius.
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