JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, B04406, doi:10.1029/2005JB003948, 2006

Dynamic fracture of granular material under quasi-static loading

Amir Sagy

Institute of Earth Sciences, Hebrew University of Jerusalem,
Jerusalem, Israel

Now at Department of Earth and Space Sciences, University of California,
Los Angeles, California, USA

Gil Cohen

Racah Institute of Physics, Hebrew University of Jerusalem,
Jerusalem, Israel

Ze'ev Reches

Institute of Earth Sciences, Hebrew University of Jerusalem,
Jerusalem, Israel

Now at School of Geology and Geophysics, University of Oklahoma,
Norman, Oklahoma, USA

Jay Fineberg

Racah Institute of Physics, Hebrew University of Jerusalem,
Jerusalem, Israel

Abstract

[1]   The dynamics of rapid fracturing of heterogeneous grainy media are studied in laboratory experiments in which artificial rock slabs are fractured under uniaxial tension. By performing detailed measurements of the instantaneous fracture velocity and the fracture surface topography, we quantitatively relate fracture morphology with the dynamics of the surface formation. We show that fracture dynamics in these materials is strongly influenced by the interaction of the fracture front with material heterogeneities and by the formation of microbranches. The instantaneous fracture velocity is characterized by abrupt fluctuations, whose amplitudes increase with the average velocity and which are correlated with the surface roughness. The surfaces of the fractures display aligned grooves and ridges, which extend large distances in the propagation direction and are localized in the transverse direction. These features, interpreted as lines of aligned microbranches, are observed solely when the fracture velocity is above 0.3 of the Rayleigh wave speed. In addition, small-scale striations corresponding to fracture front waves are identified. The overall similarity between fracture dynamics in these heterogeneous materials and those in ideal amorphous materials suggests that universal processes control the dynamics. The heterogeneity of the grainy medium, however, strongly amplifies the velocity fluctuations and enhances both the deflection and segmentation of fracture fronts.

Received 19 July 2005; revised 14 December 2005; accepted 12 January 2006; published 13 April 2006.

Keywords: dynamic fracture, crack velocity, branches.

Index Terms: 7209 Seismology: Earthquake dynamics (1242); 8004 Structural Geology: Dynamics and mechanics of faulting (8118); 8010 Structural Geology: Fractures and faults; 8030 Structural Geology: Microstructures.


AGU

Citation: Sagy, A., G. Cohen, Z. Reches, and J. Fineberg (2006), Dynamic fracture of granular material under quasi-static loading, J. Geophys. Res., 111, B04406, doi:10.1029/2005JB003948.