Displacement-controlled fatigue testing of rubber is not strain-controlled

Abstract

Fatigue tests were performed on filled natural rubber (NR) and styrene butadiene rubber (SBR) materials, using die-cut dumbbells. A remarkable evolution of the strain occurs in the narrow section during fatigue even though the displacement amplitude was constant. Additional tests with different test piece geometries are evaluated. The effect of the changing strains depends on both the material and the test piece geometry. A method is introduced to transfer the changing strains into a Wöhler curve-compliant constant equivalent strain. Finally, results from finite element simulations are shown to indicate how the method could be applied to other test piece geometries or components.