Dynamic Testing under Nonsinusoidal Conditions and the Consequences of Nonlinearity for Service Performance

Abstract

Abstract In this work, nonlinearity in the dynamic behavior of rubber has been considered. In order to understand its effects in a service environment involving complex patterns of vibration, it has been necessary to clarify the derivations of dynamic properties for the sinusoidal excitation that is conventionally used in testing. Using the fundamental frequency components as a basis, non-linearity can be quantified by the harmonic components that it produces. A dynamic test system has been developed which incorporates the ability to perform a harmonic analysis, and the usefulness of this has been demonstrated. Harmonic analysis has enabled the dynamic behavior of rubber to be quantified under complex, periodic waveforms. This is necessary for filled rubbers, because their nonlinearity means that a superposition on their properties from sinusoidal tests is incorrect. Examples of this approach for assessing dynamic behavior range from shock mounts to tire treads. Dual-sine tests on a nonlinear rubber indicate that for complex vibrations, consisting of many amplitudes and frequencies, the overall dynamic behavior will tend toward that obtained in single sine tests at a strain amplitude which corresponds to the largest amplitude that occurs in the time history. A similar conclusion is drawn from random vibration tests with a continuous spectrum of vibrations. The result of this is that under a more complex system of vibrations, nonlinear rubbers will behave in a more linear fashion and will exhibit higher damping than indicated by their dynamic properties measured in conventional sinusoidal tests. Therefore, when the service environment of many components is taken into account, the dynamic behavior of nonlinear rubbers may give better performance characteristics than expected from conventional testing.