Fatigue damage in carbon black filled natural rubber under uni- and multiaxial loading conditions

• Fatigue damage is investigated for both uni- and multiaxial loading conditions.
• Fatigue damage is described at both the macroscopic and the microscopic scales.
• Macroscopic crack initiation corresponds to crack growth at the microscopic scale.
• Results constitute database to validate criteria to predict fatigue crack initiation.
• Different fatigue striation shapes are observed: triangular and lamellar.

This paper deals with fatigue damage in carbon black filled natural rubber under uni- and multiaxial loading conditions. Fatigue damage is described at both the macroscopic (mechanical) scale and the microscopic (material) scale. The different fatigue damages observed at the macroscopic scale are presented according to the prescribed loading conditions. At this scale, five elementary fatigue damage patterns are defined, three correspond to external macroscopic cracks and two correspond to internal macroscopic cracks. These elementary fatigue damage patterns are investigated at the microscopic scale by distinguishing crack initiation and crack growth. Results show that the cracks initiate from microstructural defects, whose mean diameter does not exceed 400 μm and that crack initiation at the macroscopic scale corresponds to crack growth at the microscopic scale, which validates recent energetic approaches adopted to predict fatigue crack initiation in rubbers. The morphology of fracture surfaces exhibits two types of features: wrenchings and fatigue striations. In particular, results highlight that several shapes of fatigue striations can form, depending on the loading conditions, and that several mechanisms of fatigue striation formation could come into play.