ABSTRACT
Fatigue damage in elastomers causes eventual rupture, as well as gradual degradation of the stiffness prior to rupture. The mechanisms of this degradation seem to have origins in both molecular and mesoscopic processes in the material (Mars and Isasi 2013, Jago 2012, Le Saux et al 2011, McKenna and Zappas 1998). Whether the stiffness degradation results in reduced stresses or increased strains depends upon the mode of control of the fatigue test (stress-, energy-, or strain-control). The usual forms for describing fatigue behavior (Wohler curves or crack growth rate curves) do not explicitly address this aspect of the behavior, although the coupling to stiffness degradation can be significant. The lack of analysis approaches that deal with stiffness loss as an integral part of the fatigue process is particularly felt in the design world, where rubber part end-of-life definitions are frequently written in terms of stiffness loss, rather than crack growth or complete rupture (Brieu et al 2010, Diani et al 2011, Lorenz et al 2011). Accordingly, the purpose of this work is to show how stiffness degradation effects can be rationalized and computed via modest additions to the classical framework for fatigue analysis in rubber.
