International audienceNatural rubber (NR) exhibits great fatigue properties which are usually explained by its ability to crystallize under strain. Nevertheless, strain-induced crystallization of NR in fatigue has never been investigated. We perform original in situ fatigue tests during which the degree of crystallinity, and the number and volume of crystallites are measured by synchrotron wide angle X-ray diffraction. For all loading conditions, the number of crystallites is constant. The evolution of their volume depends on the minimum stretch ratio achieved at each cycle. The results show that cyclic loading conditions modify the macromolecular structure of the material, in particular of its amorphous phase
, et al.. Multiaxial deformation and strain-induced crystallization around a fatigue crack in natural rubber. Engineering Fracture Mechanics, Elsevier, 2014, 123, pp.59-69. 10.1016/j.engfracmech.2014 Multiaxial deformation and strain-induced crystallization around a fatigue crack in natural rubber The study of fatigue crack propagation in elastomers is an essential prerequisite to improve the service life of tire products. Natural rubber is a key compound in tires, because of its unique mechanical properties and more particularly its remarkable resistance to fatigue crack growth as compared to synthetic rubbers. To explain this resistance, the literature often mentions the phenomenon of strain-induced crystallization which takes place at fatigue crack tips in natural rubber and then reinforces it. In the present study, an original experimental set-up that couples synchrotron radiation with a homemade mechanical fatigue machine is developed to investigate both strain-induced crystallization and deformation multiaxiality around fatigue cracks in natural rubber. During uninterrupted fatigue tests, recording of wide-angle X-ray diffraction patterns is performed in the crack tip region providing the two-dimensional spatial distribution of both crystallinity and principal strain directions. In particular, the influence of loading conditions on the size of the crystallized zone is investigated and related to fatigue crack growth rates. Finally, measurements of deformation multiaxiality, i.e. principal strain directions and change in thickness, obtained by this method are successfully compared with digital image correlation results.
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