Investigation On Texture Simulation And Friction Characteristics Of Machined Surface Of Titanium Alloy

Titanium alloy is an important metallic material,and has been widely used in many fields,such as aeronautics and military industries.At present,the investigation on the machining of titanium alloy at home and abroad mainly focuses on the surface integrity and process optimization at the macroscopic level,and the study on the plastic deformation at the mesoscopic level is less.Therefore,this thesis investigates the plastic deformation and the relationship between the crystal orientation and the macroscopic friction behavior of the machined surface of titanium alloy.This thesis firstly carried out orthogonal cutting experiment on the end face of cylindrical titanium alloy bar,and studied the influence of cutting parameters on surface integrity.The principal cutting force and chips were collected and sorted for further work.A two-dimensional finite element simulation model for orthogonal cutting of titanium alloy was established.The J-C constitutive model was used to simulate the material flow and the strain separation criterion was used to describe the formation of the chip and material failure.The validity and reliability of the simulation was verified by the principal cutting force and chip shape characteristics obtained from experiments and simulations.The plastic deformation was analyzed,and the results showed that the shear strain is the main strain on the machined surface.The variations of shear strain and strain rate with time in the cutting process were also obtained.Finally,the effects of cutting speed and feed rate on shear strain and maximum strain rate were studied.Based on the variation of shear strain and strain rate with time,the crystal orientation of the machined surface was simulated by VPSC program,and the pole figure and ODF diagram were made and analyzed.The results showed that the typical shear textures were formed on the machined surface:B,P,Y,C1 and C2 fiber textures.In addition,the shear texture density decreased with the increase in cutting speed and feed rate.This is mainly due to the weakening of shear strain.The friction experiments were carried out on the machined surfaces of titanium alloy in cutting direction and in the direction perpendicular to cutting direction.The results showed that the friction coefficient decreased with the increase in cutting speed and increased with the increase in feed rate.The friction coefficients in the cutting direction were lower than those in the direction perpendicular to the cutting direction,This is due to the existence of the typical shear textures,which lead to the anisotropy of the macroscopic property.It was also found that the difference increased with the increase in cutting speed,and the difference decreased with the increase in the feed rate.This is the result of the interaction of grain refinement and shear texture.Finally,the variation of wear width with cutting speed was studied.