In-Situ Synchrotron Waxd Investigation of the Crystallized Zone At a Fatigue Crack Tip in Natural Rubber

In tire industry, fatigue crack propagation in elastomers is usually investigated to improve the service life of products. Natural rubber (NR) is a key compound in tires, because of its remarkable mechanical properties and more particularly its excellent resistance to fatigue crack growth as compared to synthetic rubbers. To explain these good properties, the literature often mentions the strain-induced crystallization phenomenon that takes place at the tip of fatigue cracks in NR.

In this study, an original experimental set-up that couples synchrotron radiation with a homemade fatigue machine has been developed to study strain-induced crystallization in the neighbourhood of fatigue cracks in NR. During uninterrupted fatigue tests, recording of X-ray diffraction patterns is synchronized with the cyclic loading to perform a “mapping” of WAXD measurements which leads to a 2D spatial distribution of crystallinity at the crack tip.

As results, we present the characteristics of the crystallized zone measured in front of a crack in natural rubber samples, filled with various amounts of N347 carbon-black (0, 30, 50 and 70 phr).  We investigate the influence of filler content and of loading conditions (non relaxing loading conditions) on the size of the crystallized zone, in order to relate it to the macroscopic measurements of crack propagation rates.