A critical local energy release rate criterion for fatigue fracture of elastomers

Using Digital Image Correlation on high-resolution images, the full strain field near the tip of a crack propagating under cyclic loading in an elastomer was characterized. We show unambiguously, and for the first time, the existence of a strongly localized and highly oriented process zone close to the crack tip and propose a simple physical model introducing a local energy release rate glocal = WunloadingH0, where Wunloading is the unloading strain energy density in uniaxial tension at the maximum strain measured at the crack tip, and H0 is the undeformed size of the highly stretched zone in the loading direction. Remarkably, the crack growth rate under cyclic loading is found to fall on a master curve as a function of glocal for three elastomers with different filler contents and crosslinking densities, while the same crack growth rate as a function of the applied macroscopic energy release rate G, differs by two orders of magnitude for the same three elastomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1518–1524, 2011