Dyskin, AV & Pasternak, E 2008, 'Rotational Mechanism of In-Plane Shear Crack Growth in Rocks Under Compression', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium
, Australian Centre for Geomechanics, Perth, pp. 99-110.
In-plane growth of shear fractures in rocks in the presence of high magnitude compression routinely observed in both laboratory testing and in the field so far eludes explanation. Indeed, in-plane growth of shear crack is difficult to explain based on the Linear Elastic Fracture Mechanics. We propose here a mechanism that reconciles the observations and the theory. We assume that what presents itself as a Mode II crack is in fact a crack driven by relative rotations of grains at the crack tip. The relative rotations are created by the conventional shearing of the crack faces, which leads to a concentration of moment stresses at the crack tip. The moment stress – the bending moment per unit area created in the intergranular bonding due to the relative rotation of the grains – ruptures the bonds in front of the crack creating en-echelon formation. This affects the in-plane growth when the conventional out-of-plane growth (kinking) caused by the concentration of tensile stress is suppressed by the high ambient compression.
Atkinson, C. and Leppington, F.F. (1977) The effect of couple stresses on the tip of a crack, International Journal of Solids Structures, Vol. 13, pp. 1103–1122.
Bobet, A. (2000) The initiation of secondary cracks in compression. Engineering Fracture Mechanics, 66, pp. 187–219.
Dyskin, A.V., Jewell, R.J., Joer, H., Sahouryeh, E. and Ustinov, K.B. (1994) Experiments on 3-d crack growth in uniaxial compression. International Journal of Fracture, 65 (4), pp. R77–R83.
Dyskin, A.V., Jewell, R.J., Joer, H., Sahouryeh, E. and Ustinov, K.B. (2003) Influence of shape and locations of initial 3-D cracks on their growth in uniaxial compression. Engineering Fracture Mechanics, 70(15), pp. 2115–2136.
Garajeu, M. and Soós, E. (2003) Cosserat models versus crack propagation. Mathematics and Mechanics of Solids, pp. 189–218.
Gourgiotis, P.A. and Georgiadis, H.G. (2007) Distributed dislocation approach for cracks in couple-stress elasticity: shear modes. International Journal of Fracture, 147, pp. 83–102.
Kobelev, V. (2006) Mircopolar model of fracture for composite material. Meccanica, 41, pp. 653–660.
Landau, L.D. and Lifshitz, E.M. (1959) Theory of Elasticity, Oxford. London. Edinburgh. New York. Toronto. Sydney. Paris. Braunschweig, 165 p.
Morozov, N.F. (1984) Mathematical Issues of the Crack Theory, Nauka, Moscow (in Russian), 255 p.
Nakamura, S. and Lakes, R.S. (1988) Finite element analysis of stress concentration around a blunt crack in a Cosserat elastic solid. Computer Methods in Applied Mechanics and Engineering, 66, pp. 257–266.
Nowacki, W. (1974) The linear theory of micropolar elasticity. Micropolar Elasticity, W. Nowacki and W. Olszak (editors), Wien, New York: Springer Verlag, pp.1–43.
Pasternak, E., Mühlhaus, H.-B. and Dyskin, A.V. (2004) On the possibility of elastic strain localisation in a fault. Pure and Applied Geophysics, 161, pp. 2309–2326.
Pasternak, E. and Mühlhaus, H.-B. (2005) Generalised homogenisation procedures for granular materials, Engineering Mathematics, 52(1), pp. 199–229.
Pasternak, E., Dyskin, A.V. and Mühlhaus, H.-B. (2006a) Cracks of higher modes in Cosserat continua. International Journal of Fracture, 140, pp. 189–199.
Pasternak, E., Dyskin, A.V. and Estrin, Y. (2006b) Deformations in transform faults with rotating crustal blocks. Pure and Applied Geophysics, 163, pp. 2011–2030.
Pasternak, E., Dyskin, A.V. and Mühlhaus, H.-B. (2006c) Cracks of higher modes in Cosserat continua. International Journal of Fracture, 140, pp. 189–199.
Shmoylova, E., Potapenko, S. and Rothenburg, L. (2007) Boundary element analysis of stress distribution around a crack in plane micropolar elasticity. International Journal of Engineering Science, 45, pp. 199–209.
Sternberg, E. and Muki, R. (1967) The effect of couple stress on the stress concentration of a crack. International Journal of Solids Structures, 3, pp. 69–95.
Tada, H., Paris, P.C. and Irwin, G.R. (1985) The stress analysis of cracks. Handbook. Third edition. New York: ASME Press, 512 p.