Mullins damage effect on rubber products with residual strain

In industry, the important design parameters of rubber products are currently based on only the loading part of loading–unloading histories, e.g. load–deflection and the fatigue requirement. Rubber-like materials exhibit an appreciable change in their mechanical properties during the loading–unloading process, especially in the first few cycles from a virgin state. There is neither a universally well-defined approach to evaluate the Mullins damage effect on design aspects in industry, nor a reliable criterion to evaluate it for rubber products. An approach based on rebound energy (resilience) change is proposed to predict the Mullins damage effect with residual strain. A rubber product, manufactured in industry, was selected for experiment and verification. A Mullins indicator, in term of the maximum loading forces over the accumulated residual deflections over the loading–unloading cycles, is proposed for a criterion to evaluate the Mullins damage effect. It is indicated that the first loading–unloading cycle removes the Mullins effect by approximately 80% and a typical three loading–unloading cycles in industrial practice can remove Mullins effect by approximately 94%. More than three loading–unloading cycles are suggested to reach a state for achieving the required accuracy on smaller tolerance of design parameters. The proposed approach provides the reliable prediction on the first loading–unloading and subsequent reloading–unloading cycles, and can be used for engineering design and industrial applications. Nevertheless, the proposed approach should be further verified using more industrial cases.