Rubber Fatigue is really about degradation of the polymer network which allows a tear to start. The degradation can start with one or many repeated strains, or it can be an environmental effect such as high heat or ozone attack plus high strains. Some even say that a microcrack is always present in the rubber network due to discontinuities between the carbon black particles and the polymer chains.
Sometimes rubber fatigue is a manufacturing problem, for example the wrong durometer rubber is used, or not cured long enough or cured for too long of a time. Trapped air can cause voids in the rubber.
Then there is the problem with adhesion to the inner and outer metal. Whatever the cause we need a way to evaluate the finished product. In this section we will go over several methods available to fatigue test rubber bushings.
Some are very cheap and fast, probably good for quick production type checks but not very good for development information. These would include Standard Bushing Life Test and Wahl Joint type machines. Better test are available for bushing development and are also good for standard fatigue testing. They include Single Axis, Multiaxis Block Cycle and Real Time RPC tests.
