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| NIRE Annual Report | 
| 1998 |
Stress Corrosion Cracking of Rock in Chemical EnvironmentFracture Mechanics and Explosives DivisionSafety Engineering Department |
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Objectives
For silicate rocks, when cracks contain corrosive agents such as water, strong Si-O bonds are replaced by water hydrogen bonds -SiOH : HOSi-. The tensile stress at the crack tip accelerates the rate of hydration reaction. Such an environmentally induced weakening of a material is called stress corrosion.
The present report describes some of the experimental results of the subcritical crack growth in a granite rock. To evaluate chemically induced crack growth, double torsion tests have been performed on granite specimens in air, water and dodecyl trimethyl ammonium bromide (DTAB). And, zeta(
)-potential, which is an electric potential produced across solid-liquid interface, was also measured to investigate the relation between the strengths and
Results
The rate of crack velocity, V, and the stress intensity factor, KI, at the crack tip were measured using double torsion method. Specimens were made about 8cm × 4cm × 4mm in size. The rock samples used in the present study is an Ohshima granite.
The experimental results are shown in Fig.1, which is the relation between the rate of acoustic emission and the stress intensity factor. The rate of acoustic emission is consistent with the rate of crack velocity. This Fig. shows the significant effect of water and chemical solution on the stress corrosion cracking in the granite rock. Stress corrosion index, n, is significantly reduced in water and DTAB solution when compared to the one in dry condition. The decrease of stress corrosion index means that stress corrosion cracking is more likely to take place in the environment. It was also found out in the present study that the stress corrosion index is minimum in DTAB environment, when the zata potential is zero.
The present study shows that water and chemicals play an important role in the effect of crack propagation rate in the polycrystalline silicate rock, and also shows that the subcritical crack growth rate should be zeta-potential dependent, and that subcritical crack growth rate should be largest at zero zeta-potential.
Selected Publications
1) Fractal structure of the time distribution of microfracturing in rocks, submitted to Geophysical Journal International, 1997. 2) A new method of modelling the rock micro-fracturing process in double torsion experiments using neural networks, submitted to Int. J. Numerical Methods in Geomechanics, 1997.