  Natural rubber (NR) is the most commonly used elastomer in the automotive
industry thanks to its outstanding fatigue resistance. Strain-induced
crystallization (SIC) is found to play a role of paramount importance in the
great crack growth resistance of NR [1]. Typically, NR exhibits a lifetime
reinforcement for non-relaxing loadings [2-3]. At the microscopic scale,
fatigue striations were observed on the fracture surface of Diabolo samples
tested in fatigue. They are the signature of SIC [2,4,5]. In order to provide
additional information on the role of SIC in the fatigue crack growth
resistance of NR, striations are investigated through post-mortem analysis
after fatigue experiments using loading ranging from-0.25 to 0.25. No striation
was observed in the case of tests performed at 90{\textdegree}C. This confirms
that the formation of striation requires a certain crystallinity level in the
material. At 23{\textdegree}C, two striation regimes were identified: small
striation patches with different orientations (Regime 1) and zones with large
and well-formed striations (Regime 2). Since fatigue striations are observed
for all the loading ratios applied, they are therefore not the signature of the
reinforcement. Nevertheless, increasing the minimum value of the strain
amplified the striation phenomenon and the occurrence of Regime 2.
