Parameter dependence and prediction of fatigue properties of elastomer products

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 (s_mm = 0) and varying stress amplitude (s_a), predictably gave decreased fatigue life with increased stress amplitude and hence maximum stress (s_max). However, tensile uniaxial cyclic tests where s_mm was increased in successive tests while allernating stress (s_a) remained constant, produced longer fatigue lives for higher values of s_max. 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 s _max 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.