Coupling of fatigue crack growth and crack nucleation fatigue approach for non-crystallising rubber under fully relaxing uniaxial loading with multiaxial stress–strain state of 3D dumbbell test specimen

Abstract

Coupling the two main approaches for characterizing the fatigue life of rubber materials, crack nucleation and crack growth approach, provides the opportunity to find a more universal approach to fatigue characterization since both approaches characterize the same intrinsic material property.

In this work, we have investigated the possibility of coupling the fatigue tests on planar tension, uniaxial and 3D dumbbell specimens. As is common in fatigue testing, the tests were performed at variable frequencies depending on the magnitude of the load and the limits of the testing machine. Fatigue test data for planar tension and 3D dumbbell specimens were taken from our previous works, whereas fatigue tests results on uniaxial specimens are presented herein.

First, the fatigue crack growth curve is converted into a crack nucleation fatigue life curve for room temperature and, in the next step, into an isothermal fatigue life curve for the 3D dumbbell specimens to check the applicability of the method. These represent a more complex three-dimensional geometry with a multiaxial stress–strain field that also exhibits considerable internal heat generation and could, in practice, be replaced with a product of arbitrary geometry. With an additional transformation, the room temperature isothermal fatigue curve can be used to estimate the fatigue life for any rubber product regardless of its geometry and loading condition/level.

The results presented herein show that the coupling provides a promising basis for the development of a universal method that opens the way to a faster and more versatile fatigue characterization of new rubber compounds.