Theoretical modelling and experimental study of the fatigue of elastomers under cyclic loadings of variable amplitude

Deviations from Miner's linear law of cumulative damage have been modelled and observed many times for the fatigue of metals, but almost no analogous studies have been performed for elastomers. Such a study is reported here.A simple phenomenological model, applicable to any type of material and able to quantitatively reproduce such deviations, is presented first. This model is based on continuum damage mechanics. It relates the fatigue damage of the material to the number of cycles through some suitable evolution law, in which the derivative of damage is expressed as a non-factorizable function of the instantaneous load cycle and the damage itself.Fatigue experiments performed on “diabolo” specimens made of two different elastomeric materials and subjected to two successive cyclic loads of different amplitudes are then reported. Significant deviations from Miner's rule are observed: Miner's “total cumulated damage” may be lower or larger than unity by a small or large amount, depending on the sequence of loadings and the type of material. As a rule, the deviation from Miner's rule systematically changes sign upon reversal of the sequence of loadings. The model is shown to allow an acceptable reproduction of the experimental results, and especially of this systematic change of sign.