The effect of two different types and particle sizes (micronized cryo-ground 74 μm or ambient-ground 400 μm) of recycled rubber powder (RRP) was studied during fatigue crack growth (FCG) in a natural rubber/butadiene rubber (NR/BR) compound using a fracture mechanics approach. Absolute and relative hysteresis losses using single-edge notch tensile specimens were determined with a displacement-controlled strain compensating for the permanent set of the samples throughout the FCG experiments. Differences in relative hysteresis loss showed that additional energy dissipation, due to multiple new crack surfaces at the crack tip, contributes to the FCG of the RRP compounds. At higher tearing energy, beside other factors affecting the FCG performance of the RRP compounds, both higher absolute and relative hysteresis loss are slightly detrimental to the crack growth rates. At lower tearing energy, the larger RRP-filled compound showed slower, but not significant, different crack growth rates than the NR/BR control compound. Fracture morphologies for NR/BR and RRP-filled compound were associated with different fracture surface topographies at various tearing energies, which revealed the dependency of the crack growth microstructure on the tearing energies.

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