Mechanistic Study of Fatigue Crack Growth in Natural Rubber Composites Governed by Crack Growth Rate

Fatigue failure of aircraft tires under high-impact loads during take-off and landing poses a critical challenge, with the crack growth rate of natural rubber (NR) composites serving as a key indicator of its fatigue performance. In this study, the crosslink density of NR composites was systematically tuned via vulcanization formulation to investigate its effect on fatigue crack growth behavior. Using a ramped fatigue testing method and in situ mechanical parameters, a non-monotonic dependence of crack growth rate on crosslink density of the NR composites was revealed, which is attributed to the competing effects of strain-induced crystallization and viscous hysteresis. A phenomenological model was developed by extending classical fracture theory, incorporating crosslink density and tear energy as governing variables. This model accurately captures the transition in the fatigue behavior of NR composites across different crosslinking regimes and enables rapid prediction of the optimal crosslink density for enhanced fatigue durability. These findings provide a mathematical model for improving the fatigue resistance of NR composites and new insights into the structure–property relationship of crystallizable rubber networks of the demanding aircraft tire.