Ensuring the fatigue life of rubber components at high temperatures

Heat generation due to dynamic loading has been a major concern for rubber component manufacturers over many years. It is well known that the temperature of the rubber has to be kept in a certain limit to avoid early catastrophe failure. In engineering design and applications ccurrent practice is to monitor the component surface temperature in accelerated durability tests. However a number of unexpected early failures from heat generation during accelerated durability tests for rubber components have been observed and caused business loss even the surface temperature was well controlled

Fatigue failure hence becomes one of the critical issues in rubber components design for long term performance. In addition to the type of stress and??environmental factors, the fatigue life of elastomer is affected by basic polymer and compounding ingredients as explained below.

Fatigue life depends mainly on three factors: Base rubber, Cure system and Selection of fillers and anti-degradants.?

Rubber compounds based on natural rubber, chloroprene rubber, and??isoprene rubber show better fatigue properties than non-crystallising synthetic rubbers like butadiene rubber or styrene-butadiene rubber. However, under low strain, chloroprene rubber is superior to natural rubber in many cases.

Carbon black filled rubber shows increased fatigue life than corresponding gum rubber while finer grades give better fatigue properties. At a fixed volume fraction, low structure blacks results in more fatigue life compared to high?structure blacks. There is an optimum filler content above which the fatigue life drops due to the chance of occurrence of large filler agglomerates and grit in the rubber matrix.?

Anti degradants are critical at high temperatures. Elevated temperature, oxygen, and ozone affect the fatigue life of rubbers and therefore, incorporating suitable antioxidants or antiozonants in the formulation shall help to improve the product’s fatigue life.

Vulcanisation influences the fatigue life of rubbers by increasing the stiffness and reducing the hysteresis of the vulcanisate. There is an optimum crosslink density which results in maximum fatigue life in rubber components. This is due the dissipation of energy or heat with increasing crosslink density. Polysulphidic crosslinks are superior to monosulphidic or direct carbon-carbon crosslinks that are formed as a result of curing with peroxides. We shall should carefully select cure systems that do not bloom, as it can adversely affect the fatigue life leading to premature failure of components.

Both actual temperature mapping as well as simulation based on rubber heat transfer properties have been tried to assess the temperature and accordingly make the choice of material by appropriate compounding methods to ensure a good fatigue life under demanding high temperature conditions during usage