Isotropic pyrolyric graphite (IPG) is a new kind of brittle material, it can be used for sealing the aero-engine turbine shaft
and the ethylene high-temperature equipment. It not only has the general advantages of ordinal carbonaceous materials
such as high temperature resistance, lubrication and abrasion resistance, but also has the advantages of impermeability
and machinability that carbon/carbon composite doesn't have. Therefore, it has broad prospects for development.
Mechanism of brittle-ductile transition of IPG is the foundation of precision cutting while the plastic deformation of IPG
is the essential and the most important mechanical behavior of precision cutting. Using the theory of strain gradient, the
mechanism of this material removal during the precision cutting is analyzed. The critical cutting thickness of IPG is
calculated for the first time. Furthermore, the cutting process parameters such as cutting depth, feed rate which
corresponding to the scale of brittle-ductile transition deformation of IPG are calculated. In the end, based on the theory
of micromechanics, the deformation behaviors of IPG such as brittle fracture, plastic deformation and mutual
transformation process are all simulated under the Sih.G.C fracture criterion. The condition of the simulation is that the
material under the pressure-shear loading conditions .The result shows that the best angle during the IPG precision
cutting is -30°. The theoretical analysis and the simulation result are validated by precision cutting experiments.