Abstract
The nucleation of internal cavities and their transition to cracks are examined at high spatial and temporal resolutions within polydimethylsiloxane (PDMS) elastomers of various cross-link densities under externally applied quasi-static mechanical loads. The focus here is on experiments where the initiation and propagation of internal damage are designed to occur in between two spherical glass beads that are firmly embedded within a matrix of the PDMS elastomer and are placed close to each other in order to generate a high triaxial stress state. An optical microscope is used to monitor the various processes of nucleation and growth of cavities and cracks at a spatial resolution of about \(1\,\upmu \hbox {m}\) and a temporal resolution of about 66.7 ms. In combination with corresponding full-field simulations, the experiments show that the nucleation of cavities—that is, the onset of cavitation—is an extremely fast process (involving stretch rates in excess of \(100\,\hbox {s}^{-1})\) that is controlled primarily by the stiffening at large deformations of the underlying elastomer and, more critically, by its fracture properties. The experiments and simulations also show that cavitation is followed by two distinct events upon further macroscopic loading: the transition of the nucleated cavities to micro-cracks, and the further transition of some micro-cracks to macro-cracks. These two distinct events are also controlled primarily by the fracture properties of the underlying elastomer.
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Notes
The experimental approach of high spatiotemporal resolution presented here can equally be applied to investigate cavitation in rubber confined between other geometries (not just spherical beads). Indeed, akin to the work of Cho et al. (1987), we have employed the same approach introduced here to study cavitation within a PDMS elastomer confined between two cylindrical fibers. The analysis of these experiments will be presented elsewhere.
We recall that the criterion (3) can be thought of (see Section 5 in Lopez-Pamies et al. 2011a) as a generalization of the classical elastic cavitation criterion of Gent and Lindley (1959a, b) for the case when: (1) the rubber contains a random isotropic distribution of vacuous defects (as opposed to just a single spherical vacuous defect) and (2) the rubber is subjected to arbitrary loading (as opposed to just purely hydrostatic loading).
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Acknowledgements
This work was performed during the course of a collaborative investigation into cavitation, fracture and damage in soft materials funded by the National Science Foundation Grants CMMI-1235352 and CMMI-1235138. This support is gratefully acknowledged.
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Poulain, X., Lefèvre, V., Lopez-Pamies, O. et al. Damage in elastomers: nucleation and growth of cavities, micro-cracks, and macro-cracks. Int J Fract 205, 1–21 (2017). https://doi.org/10.1007/s10704-016-0176-9
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DOI: https://doi.org/10.1007/s10704-016-0176-9