In-situ synchrotron X-ray diffraction study of strain-induced crystallization of natural rubber during fatigue tests

A home made stretching machine has been developed to perform fatigue tests on natural rubber in the synchrotron facility Soleil. Strain-Induced Crystallization (SIC) is investigated by Wide-Angle X-ray Diffraction (WAXD) during in-situ fatigue tests of different minimum and maximum strain levels. The index of crystallinity chi decreases with the number of cycles when the minimum strain level reached during the fatigue test is lower than the critical stretch ratio for melting lambda(M). On the contrary, when the stretch ratio is maintained higher than the critical stretch ratios for melting lambda(M) and crystallization lambda(C),chi increases with the number of cycles. The crystallites size and orientation have the same evolution during the different fatigue tests: the crystallites have a constant size but their orientation is enhanced with the number of cycles.