13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- the banded structure in the apparent yy ε . Moreover, the axial splitting may be driven by the buckling induced delamination between the columns. Thus it is likely deformation of the present sandstone under compression can be described by force chain model as applied in mechanics of granular materials [16]. However, more detailed experiments are required to confirm it and whether such a failure mechanism is applicable to other brittle rocks under uniaxial compression remains for future study. (a) (b) (c) (d) (e) Fig. 5 Visualization of the deformed profile by zooming out displacement by 50 times at load level of 40, 55, 62, 62.7 and 64.5 kN (The difference in width and height is caused by different display ratio) 4 Concluding remarks Samples of sandstone under uniaxial compression were studied experimentally by combing the conventional compressive test with DIC technique. Deformation field and its evolution with loading have been obtained with the aid of DIC technique. It has been found the sandstone deformed in an inhomogeneous manner and failed via axial splitting. However the failure mode cannot be attributed to the wing crack formation and nucleation. Instead, the macroscopic crack formed via coalescence of some local axial splitting microcracks and the micromechanism may be the buckling of force chains that induces delamination. Although more detailed experiments are required to verify it, the present results may cast new light on understanding the failure mechanism in brittle materials under compression. Acknowledgements This work was supported by the National Natural Science Foundation of China under Grant Nos.11072170 and 11127202. References [1] J. Gramberg, Axial cleavage fracturing, a significant process in mining and geology. Eng. Geol., 1(1965) 31-72. [2] S. Peng, A. M. Johnson, Crack growth and faulting in cylindrical specimens of Chelmsford granite. Int J Rock Mech Min Sci., 9(1972) 37-86. [3] M. S. Paterson, Experimental deformation and faulting in Wombeyan marble. Bull. Geol. Soc. Am. 69(1958) 465-76. [4] B. T. Brady, Theory of earthquakes. I. A scale independent theory of rock failure. Pure Appl Geophs. Res., 112(1974) 701-25. [5] E. Z.Lajtai, Brittle failure in compression. Int. J. Fract., 10(1971) 525–536. [6] H. Horii, S. Nemat-Nasser, Brittle failure in compression: splitting, faulting and brittle-ductile transition. Phil. Trans. R. Soc. Lond. A., 319(1986) 337-374. [7] A. Bobet, H. H. Einstein, Fracture coalescence in rocktype materials under uniaxial and biaxial compression. Int. J. Rock Mech. Min. Sci., 35(1998) 863-888.
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