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This paper describes the dependence on test parameters of the fatigue resistance of EPDM. Fatigue was investigated using dumbbell specimens under load control at 1 Hz until failure. Tests were made in order to create a common Wö hler (S-N) curve while increasing the stress amplitude and also to show the influence of increasing minimum stress at constant stress amplitude on fatigue properties. The results of these tests confirmed the well known amplitude dependence of fatigue life in filled rubbers. An additional significant influence on fatigue life is seen to be the minimum stress applied during each cycle to these materials. Fatigue life is not dependent on strain crystallisation in EPDM as it is for natural rubber. The results of this research give component designers the opportunity to increase the fatigue lives of components made from this material.PRC/1743

Fatigue tests on ethylene propylene (EPDM) and styrene-butadiene (SBR) rubber reveal physical behavior that is not seen in conventional linear elastic solids. Uniaxial cyclical tests, using cylindrical dumbbell specimens, with the same minimum stress of zero (Smin=0) and varying stress amplitude (sa), predictably gave decreased fatigue life with increased stress amplitude and hence maximum stress (Smax). However, tensile uniaxial cyclic tests where Smin was increased in successive tests while alternating stress (sa) remained constant, produced longer fatigue lives for higher values of Smax. EPDM and SBR compounds were chosen for the tests because they do not strain crystallize during deformation. Consequently, this phenomenon has no influence. The results show that Smax can not be used as criterion to predict fatigue life of elastomers. Preliminary evaluation of recorded data of stress vs. strain gave evidence that energies control the fatigue life rather than stress and strain. Experimental results on filled and unfilled rubber materials are evaluated and discussed as well as the consequences on predictions of component properties.

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