6. How Does Cristallizable Rubber Use Mechanical Energy to Deform?

Strain-induced crystallization (SIC) is responsible for the hysteresis loop observed in the mechanical response of Natural Rubber (NR). The present paper aims at determining the physical origin of such mechanical energy dissipation. For that purpose, temperature variations are measured by using infrared thermography during cyclic uniaxial tensile tests at ambient temperature. Heat sources (heat power densities) produced or absorbed by the material due to deformation processes are deduced from temperature fields by using the heat diffusion equation. Energy balance performed for each deformation cycle shows that crystallization/melting process does not produce intrinsic dissipation. The crystallization/melting process dissipates mechanical energy without converting it into heat. Hence, the whole dissipated mechanical energy corresponds to energy used by the material to change its microstructure. The demonstration that NR is able to dissipate mechanical energy without converting it into heat explains its ability to resist the crack growth and the fatigue loading.