Stéphanie Beurrot

In situ synchrotron wide-angle X-ray diffraction investigation of fatigue cracks in natural rubber.

Natural rubber exhibits remarkable mechanical fatigue properties usually attributed to strain-induced crystallization. To investigate this phenomenon, an original experimental set-up that couples synchrotron radiation with a homemade fatigue machine has been developed. Diffraction-pattern recording is synchronized with cyclic loading in order to obtain spatial distributions of crystallinity in the sample at prescribed times of the mechanical cycles. Then, real-time measurement of crystallinity is permitted during uninterrupted fatigue experiments. First results demonstrate the relevance of the method: the set-up is successfully used to measure the crystallinity distribution around a fatigue crack tip in a carbon black filled natural rubber for different loading conditions.

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 λM. On the contrary, when the stretch ratio is maintained higher than the critical stretch ratios for melting λM and crystallisation λC, 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.