A Comparison of Two Different Cure Systems on the Age-Stiffening and Fatigue Crack Growth Characteristics in Natural Rubber and Polybutadiene

Natural rubber (NR) and polybutadiene (BR) elastomers are used in the manufacture of many vibration isolation devices in rotorcraft, including high-capacity laminate (HCL) rotor bearings and Fluidlastic™ blade dampers. Previously published investigations have shown that all conventionally-formulated NR and BR elastomers stiffen significantly over time during storage at ambient conditions and even more rapidly at elevated temperatures. At room temperature, increases in the elastic shear modulus G’ of 8% to 12% in six months is not out of the ordinary for a typical NR/BR blend, and the increase in stiffening continues for years. A proprietary chemistry that significantly reduces the magnitude of age-stiffening has been discovered. Although the specific chemistry is not disclosed, the data demonstrates that it is possible to greatly reduce both shelf age-stiffening and stiffening due to heat ageing associated with a conventional sulfur cure system. Fatigue Crack Propagation (FCP) testing was used to determine how crack growth behavior of rubber compounds changes after both ambient and high temperature aging.