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

Abstract

A homemade stretching machine has been developed to perform fatigue tests on natural rubber in the synchrotron facility Soleil. Strain induced crystallisation is investigated by wide angle X-ray diffraction during in situ fatigue tests of different minimum and maximum strain levels. The index of crystallinity χ 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 λ_M. On the contrary, when the stretch ratio is maintained higher than the critical stretch ratios for melting λ_M and crystallisation λ_C, χ increases with the number of cycles. The size of the crystallites has the same evolution during fatigue testing as χ. On the contrary, the misorientation of the crystallites does not depend on the minimum strain level reached and decreases with the number of cycles for all the fatigue tests.