Abstract: For the purpose of realizing the brittle material’s turning in ductile mode on the basis of optimizing the diamond cutting tool’s geometrical parameters，the linear elastic fracture mechanics and finite element method are applied to stimulate the stress distribution and micro-cracks’ expanding in the cutting region generated under different rake angles and rounded cutting edge radius. The cutting experiments on single crystal silicon surface are then conducted to verify the stimulation results，which shows that the expanding of micro-cracks can be restrained from atomic-size cracks when utilizing the diamond cutting tools with -15°~-25° rake angles. As a result of increasing the value of the critical depth of cut of brittle-ductile transition，the goal of ductile-mode turning can be achieved. In addition，with a smaller cutting edge radius，the turning of brittle material in ductile-mode can be easily realized，resulting in good diamond turned surface quality.

Key words: Diamond cutting tool rake angle Rounded cutting edge radius FEM single crystal silicon Atomic force microscope