Some Revisions of Fatigue Crack Growth Characteristics of Rubber

Fatigue crack growth (FCG) characteristic of rubber materials is a very important factor in determining the durability of the rubber products. Slight variations in compounding ingredients, mixing and the curing process or even in the loading conditions and several physical factors have an impact on the final FCG behaviour of rubber vulcanisates. Thus, possible inaccuracies in the experimentally determined FCG characteristics can have direct consequences on the development of durable rubber compounds. Therefore, the aim of this work is focused on the experimental validation of the FCG characteristics of rubber in comparison with the recently customary theoretical background and functions describing the relationship between the FCG rate and the tearing energy. From the literature survey, the weak points directly influencing the accuracy of the FCG characteristics in the experimental approach were identified. The first weak point is the transient point or discontinuity of the FCG characteristics within the region of the stable FCG. To follow on, a visible deviation of the experimentally determined data within the region of the stable FCG from the theoretical function is necessary to be validated. FCG analyses of plane strain tension samples based on ethylene propylene diene monomer (EPDM) rubber filled with a varied content of carbon black were performed using a Tear and Fatigue Analyzer (TFA©, Coesfeld GmbH & Co. KG, Germany). The FCG characteristics were plotted for a broad range of tearing energies. The intrinsic strength and the ultimate strength were determined. The region of the stable FCG was studied in detail. The continuous function of the stable FCG within the region was found, and thus, the presence of a transient point was refuted. Moreover, a specific equation was validated to fit the data into the region of the stable FCG compared to a previously preferred power-law with a higher accuracy.