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Abstract Load-displacement curves of different offset notch positions and high-precision photos of crack extension are obtained through a three-point bending test by using scanning electron microscope(SEM) with loading system. As the mineral particles in the rock always exist in a certain three-dimensional scale，we analyze that the crack is not only nonlinear extension in the surface but also along the thickness direction. Surface energy expression is rewritten with the consideration of inhomogeneity of rock and crack nonlinear extension along the thickness direction. The new surface energy expression can well explain random phenomena of crack propagation. Through the analysis of load-displacement curves，we obtain that there are three typical stages and the mesomechanism of each stage has been explained by the new expression of surface energy in detail. A new parameter of offset notch crack influence coefficient is proposed to calculate the fracture properties of three-point bending specimens and its formula is given. According to experimental results，the changes of peak load and fracture energy with their offset amount are compared；and then their offset notch crack influence coefficients are obtainted.
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Received: 30 October 2012
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2013, Vol. 32 
