Study On The Critical Depth Of SiC Monocrystal In Ultrasonic Vibration

SiC monocrystal and other hard-brittle materials have been widely used in the aerospace and industrial production,with the special physical and mechanical properties,since the high hardness and brittleness make them difficult to process.In recent years,the proposition of ductile regime machining is an effective way to solve defects existing in the processing of hard-brittle materials,and the critical transition of brittle and ductile has been widely studied.The brittle and ductile transition mechanism for SiC monocrystal is studied based on the slip-line field theory,and the plastic deformation model of wedge-shaped tool scratches is established.Then the relationship between the fracture toughness,the yield strength of materials and the critical depth is studied.Also in the view of fracture mechanism,the deformation process of hard-brittle materials in the plastic deformation area is analyzed,and the mathematical expression of critical depth is derived.Aiming at the extreme precision demand in the micro-cutting system,a novel high-precision micro-adjusting platform is designed which was driven by piezo actuator and transmitted and supported by flexure hinge.The platform is analyzed and handled using the three-point levelling principle,and the motion trail is discussed.Simulations of the mechanism are conducted by Abaqus,the levelling experiments are carried out on the micro-adjusting platform.Then the results of simulation,experiment and theoretical analysis is compared to prove the feasibility of the levelling principle and method.The scratch experiments are carried out under ordinary conditions and ultrasonic vibration assisted conditions by four single point diamond tools with different tool angle and corner radius.The change of radial force is detected in the scratch process by force sensor,then the morphology and chip status of scratch surface is observed by Leica DCM3D and SEM to to obtain the impact of tool angle,the corner radius and ultrasonic vibration on the critical depth of cut as well as the corresponding values of critical depth of cut.