Fatigue crack propagation characteristics of rubbery materials under variable amplitude loading

Fatigue failure is a critical issue frequently encountered by the rubber components in service. In this work fatigue crack propagation experiments with an edge-notched pure shear specimen under variable amplitude loading, which brings effectiveness in experiment time, are carried out. Based on the dispersed data of measured crack lengths versus number of cycles, an alternative method for dealing with the dispersed data is proposed and compared with two conventional methods used in constant amplitude loading. The comparisons of the three types of methods shows that the secant method and the incremental polynomial method are not applicable whereas the proposed method with one power function is superior to characterize the crack propagation characteristics of rubbery materials. The crack propagation rate (crack propagation length per cycle) is then calculated from the determined power function, and a fatigue life prediction model for filled natural rubbery materials is established as well as applied to calculate the fatigue life of dumbbell specimens under uniaxial tension fluctuating loading. The consistence between the calculated fatigue lives and the measured lives of the dumbbell specimens validates the proposed data processing method for dealing with the dispersed measured data of crack length versus number of cycles.