True stress controlled fatigue life experiments for elastomers

As of present, fatigue life testing of elastomers in displacement control is extensively utilized in academic research and industry. However, there are limitations to this approach, if the tested elastomer behaves inelastically; it can be shown that the mechanical state parameters of the material, stress or strain, do not remain constant throughout the duration of an experiment carried out in displacement control. As such, application of various fatigue criteria is questionable and, moreover, a valid comparison of fatigue resistances of different materials cannot be carried out. In the present work, a procedure is developed that allows uniaxial fatigue life testing in true stress control and creation of the corresponding Wöhler curve. The procedure allows testing of single specimens and is then extended for several specimens in parallel. The procedure is validated by experiments on a synthetic rubber HNBR for three loading levels of true stress amplitude at a loading ratio R = 0. The results confirm the viability of the procedure for both individual and parallel testing.