Nanocavitation Around a Crack Tip in a Soft Nanocomposite: A Scanning Microbeam Small Angle X-Ray Scattering Study

We explore nanocavitation around the crack tip region in a styrene-butadiene random copolymer filled with typical carbon black (CB) particles used in the rubber industry for toughening the rubber. Using quasistatic loading conditions and a highly collimated X-ray microbeam scanned around the crack tip, we demonstrate the existence of a damage zone consisting of nanovoids in a filled elastomer matrix. The existence of voids near the crack tip is demonstrated by a significant increase of the scattering invariant Q/Q(0) in front of both fatigued and fresh cracks. The size of the zone where cavities are present critically depends on the macroscopic strain epsilon(m), the loading history, and the maximum energy release rate G applied to accommodate the crack. Our findings show that nanovoiding occurs before fracture in typical CB-filled elastomers and that realistic crack propagation models for such elastomers should take into account a certain level of compressibility near the crack tip. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 422-429