Effect of nature and type of flaw on the properties of a natural rubber compound

Fracture in rubber, like in all other materials, is initiated at imperfections inadvertently present or introduced in the body of the material or on the surface during processing. The point of initiation of fracture in the rubber is usually at flaws which are macroscopic or microscopic imperfections or inhomogeneities in the rubber. In order to investigate the effect of these flaws on the properties of a natural rubber compound, cuts to mimic weld lines were introduced before and near scorch at various cure temperatures, and the time for a complete healing of these cuts determined. The tensile properties were not significantly affected by the introduction of weld lines before scorch provided sufficient time was allowed for healing. Healing time reduced with increase in cure temperature. The intrinsic flaw sizes in a material inherently affect the material tensile properties and depend significantly on the size of the flaw. Pinhole flaws of varying sizes introduced after cure had a significant effect on both tensile strength and fatigue life with the pinhole equivalent intrinsic flaw size estimated to be about 200 μm.