Tensile strength is an important mechanical property of rock. In Brazil test of a flattened disk specimen measuring tensile strength of rock

the central angle of the flats has great influence on measuring tensile strength．But there is no restriction in the test

which makes tensile strength of rock obtained by the test very scattering. Digital image processing methods are used as a measurement tool to construct a numerical representation for the actual spatial distribution of different materials and components in rock samples

which is introduced into rock failure process analysis (RFPA2D)

and numerical model of Brazil tests of granite flattened Brazilian disk specimen which considers the actual heterogeneity is established by processing its digital image. Using the numerical model

the influences of central angle of flats on stress distribution along axial line

splitting failure modes and tensile strength are analyzed; and reasonable range of central angle of flats is obtained

which should be in the range of 20??30?.