13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Using the DIC technique as handled in [12], we have obtained the displacement fields in the region indicated by the white rectangle in Fig. 1(a). Distributions of the displacements at load levels of 40, 55, 62, 62.7 and 64.5 kN have been presented respectively in Fig.3. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) Fig.3 The horizontal (a-e) and vertical (f-j) displacements on the sample surface at load levels of 40, 55, 62, 62.7 and 64.5 kN respectively (unit in the legend is micron) The displacement distributions clearly indicate uneven deformation has occurred especially when the applied load is close to the rupture load where the color pattern for the horizontal displacement is highly discontinuous at the middle of the sample. Partially the inhomogeneous deformation may be induced by the micro-structure in the sandstone. Observations by optical microscopy have indeed shown the sandstone is composed of grains of microns but the grain size is rather homogeneous (results not shown). It may also be the result inherent to the sandstone. To better analyze the deformation behavior, the apparent strain on the surface has been calculated since when there are cracks, displacement jumps may appear due to the crack faces sliding and opening and induce large apparent strain. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) (m) (n) (o) Fig. 4 apparent xxε (a-e), yyε (f-j) and xy γ (k-o) on the sample surface at load levels of 40, 55, 62, 62.7 and 64.5 kN respectively (The values are in percentage)
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