Fatigue resistance of natural rubber in seawater with comparison to air

•Fatigue life and crack propagation tests are performed.•Fatigue damage is analyzed by scanning electron microscopy.•Fatigue behavior is the same as in air under relaxing loading conditions.•Fatigue life is longer in seawater under non-relaxing large strain amplitudes.•Non-classical cracking features are observed in seawater.

Fatigue properties of filled natural rubber in seawater environment are investigated by uniaxial fatigue and crack propagation experiments, and the damage is analyzed by scanning electron microscopy. The behavior under relaxing and non-relaxing loading conditions is studied and the results are compared to those obtained in air environment. For relaxing loading conditions, fatigue behavior is the same in both environments. Under non-relaxing conditions at large strain levels, for which the influence of strain-induced crystallization is important, fatigue life is longer in seawater. Such behavior could be explained by increased internal temperatures of specimens tested in air due to lower heat conductivity of air as compared to seawater. Such conclusion is also supported by the damage mechanisms observed under non-relaxing loading conditions.