Investigation of mode III fatigue crack growth in rubber based on the pioneering work of Alan N. Gent and coworkers

• We revisit the work of A.N. Gent on mode III fatigue crack propagation in rubber.
• We develop new sample and methodology to conduct well-controlled experiments.
• We demonstrate that mode I and mode III coincide for high fracture energies.

From 1998 to 2003, Alan N. Gent and some co-workers published a series of papers devoted to the first measurements of fatigue crack growth properties in rubber in mode III loading conditions (Rubber Chemistry and Technology, vol. 71, pp. 76–83; vol. 71, pp. 84–94; vol. 76, pp. 1276–1289). The present paper proposes to revisit this seminal work benefiting from the capabilities of new multiaxial fatigue machines. Then, a new mode III fatigue test for elastomers is developed. A thin bonded disk of rubber with a circumferential cut is subjected to cyclic torsion to investigate the fatigue crack growth in mode III. The corresponding measurement methods for the crack growth rate and the fracture energy are proposed. As a constant small axial extension can be applied and controlled to prevent the cracking surfaces from abrasion and to ensure almost mode III loading conditions, the quality and the relevance of the experimental data are highly enhanced. As a results, the method is applied to an unfilled natural rubber and the crack growth rate is related to the fracture energy for several loading cases. The effects of axial extension, alternate cycles and positive minimum angle cycles are examined. In particular, it is shown that for fully unloaded cycles the crack growth rate laws in modes I and III coincide in the regime of high fracture energies.