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American Journal of Science, Vol. 303, December 2003, P.956-971

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Instabilities in Stress Corrosion and the Transition to Brittle Failure

Daniel Koehn*,**, Jochen Arnold**, Bjørn Jamtveit* and Anders Malthe-Sørenssen*

* Physics of Geological Processes, Postbox 1048 Blindern, N-0316, Oslo, Norway

** Institut fuer Geowissenschaften, Tectonophysics, University of Mainz, 55099 Mainz, Germany; koehn{at}mail.uni-mainz.de

Studies on the dissolution of stressed crystals have shown that stress corrosion can lead to roughening of interfaces. The corrosion pattern develops due to gradients in elastic energy along a free crystal surface with an initial roughness. Dissolution will cause further increase in elastic energy, which in turn will speed up dissolution, the so-called Asaro-Tiller-Grinfeld instability. We present a numerical model in order to study the effect of stress corrosion that is observed in physical experiments of interface roughening of brittle salt crystals. In the simulations a salt crystal that is immersed in saturated brine is stressed and dissolution patterns develop. Stress corrosion can lead to an Asaro-Tiller-Grinfeld instability that develops into cusp instabilities and crack-like structures or anti-cracks. The system breaks its symmetry and produces a secondary instability where the number of growing anti-cracks is reduced. This coarsening of the surface roughness is due to stress-shielding effects of growing anti-cracks. Finally, one single anti-crack remains on each side of an initial hole as a "superstructure". The large anti-crack grows at an almost constant speed and eventually leads to brittle failure of the crystal. This mechanism may be important not only for dissolution-precipitation creep but also other phase-transitions and may lead to large scale brittle failure that can be associated with earthquakes.






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