Study On Simulation And Experiment Of Micro Cutting Of Bone

Common bone cutting operations include orthopedics, traumatology and dental surgery, which nearly always involve milling, grinding and drilling. All these operations require high surface quality, good control of both cutting force and temperature, therefore applying appropriate cutting parameters, tool geometries and initial conditions has a direct impact on operation quality,damage of surrounding tissues and postoperative recovery. Finite element simulation for bone cutting takes both cost and efficiency into consideration,the equivalent homogeneous model has been applied to predict the cutting force, but few researches analyzed the bone structure, material peculiarity in micro cutting and failure mode which are also key and difficult problem of micro cutting of bone.Based on the thermodynamic characteristics and statistical geometry of bone,three structure models of bone describing the osteon arrangement h-ave been proposed and calculated the structure parameters. Simulation of orthogonal cutting has been conducted based on three arrangement pattern proposed and compared the cutting force to experiment, an appropriate arrangement pattern has been chosen and achieved by secondary development of ABAQUS using the Python.Based on the non-local strain gradient plasticity theory, the relation between strain gradient and flow stress was obtained, the constitutive equation in micro cutting was established by revising Johnson-Cook model. Based on arc deformation zone model and Boothroyd’s temperature model, the functional relation was established between cutting parameters, tool geometry, cutting force and effective strain, effective stress and mean temperature. Orthogonal narrow slot micro milling experiment was designed to match the micro cutting constitutive equations by the inverse model identification technology.Based on failure mode of the homogeneous material, the failure mode of heterogeneous material was proposed.The critical fracture energy release rate of which shear-crack mode transforms to crack mode was calculated, and obtained a governing equation for crack mode. Based on analyzing the traits of crack behavior of bone, the cohesive elements was utilized to model the cement line,and compiled the VUMAT subroutine of exponential type cohesive model.Based on ABAQUS software, an anisotropy model was utilized to simulate the orthogonal cutting process, to study the crack behavior on the transverse direction and the effect of osteon direction on cutting force. An isotropy model was utilized to simulate both the orthogonal cutting and drilling process, to observe strain and stress distribution in the first deformation zone, to study how the cutting parameters, tool geometry and initial conditions influence the cutting force and temperature, based on which to explore the reasonable operation conditions.Using the solid carbide drill to conduct a drilling experiments on bovine femur, the cutting force was measured under different cutting conditions and compared with simulation result, and measured the temperature with different initial conditions. Micro drilling orthogonal experiment was conducted by taking spindle speed, feed speed and bit diameter into consideration.