Abstract
The fatigue crack growth of natural rubber reinforced with various grades of carbon black has been studied across a wide range of tearing energies. Carbon blacks differ significantly in structure and surface area, influencing the mechanical and dynamic properties of the compounds. High-structure carbon black compounds exhibit an abrupt and significant step change in crack growth rate. Above the point of this step change, the different carbon black compounds have similar crack growth rates. Prior to this step change, high-structure carbon black compounds show a better crack growth resistance of up to two orders of magnitude compared to low-structure carbon black compounds. These step changes are attributed to strain-induced crystallisation effects. Before the step change, high-structure carbon black compounds nucleate and grow enough crystals at the crack tip to suppress crack growth. Above the step change, the crack tip velocity is too rapid for substantial strain-induced crystallisation to occur, as it is a time-dependent phenomenon. The step change aligns with the crack tip velocity where strain-induced crystallisation is reportedly absent. Understanding these step changes in crack growth can help rubber compounders design materials with improved crack growth resistance, leading to more durable components.