Molecular Dynamics Simulation Of Acoustic Emission Response To Nano-cutting

With the high-end manufacturing entering the field of nano manufacturing,nano-cutting,a high-end manufacturing method,is widely used in aerospace,semiconductor and other manufacturing fields due to its simple,feasible,low-cost,wide application etc.In the process of nano-cutting,it is inevitable to introduce subsurface defects such as vacancy,dislocation and crack,which seriously affect the surface quality,strength and service life of products.Therefore,it is of great significance to study the deformation mode of materials and the formation and expansion of defects in the process of machining for the on-line monitoring and improvement of machining quality.Acoustic emission?AE?,a kind of transient elastic wave released when the internal structure of materials changes,is highly sensitive to the defects such as dislocation nucleation,phase transformation and formation of micro cracks.Therefore,based on the molecular dynamics method,this paper studies the deformation mechanism and the AE response mechanism of defects of different crystal system materials while revealing the defect evolution of brittle and plastic materials in the process of nano machining at the atomic scale.The study has of great significance in improving the accuracy and reliability of AE detection,expanding its application scope,and improving the quality of nano machining.The results of this study include three aspects:1.Through nano-cutting of superplastic superalloy Ni₃Al at room temperature and low temperature,the formation mechanism of super dislocation and anti-phase boundary in cutting process was studied,and the frequency-domain characteristics and AE source of AE signal in the cutting process at low temperature were analyzed.The results show that there are both brittle deformation and plastic deformation in the process of cutting at low temperature,and the main type of subsurface defect distribution is vacancy cluster without pinning phenomena occurs,and a far lower level of the residual stress in subsurface in comparison with normal temperature,which gets as close to 0 GPa.In the process of low temperature cutting,AE sources are mainly classified as lattice vibration,dislocation motion and higher energy level dislocation activity such as twinning.2.The nano-cutting of single crystal copper with hard particles at room temperature is simulated,and the effect of the position,size and number of hard particles on the dislocation in the cutting process is studied.The results show that the hard particles can reduce the cutting force during the plastic cutting process,and the Case with hard particles at surface is the most significant.When the tool acts directly on the hard particles,the Case with hard particles below the surface can effectively block the movement of dislocations,while the surface hard particles reduce the generation of dislocations.In the process of room temperature cutting,the main sources of AE are lattice vibration and dislocation motion,in which lattice vibration is more obvious;while the effect from hard particles increase the AE power and energy integration of dislocations,which increase with the increasing number of hard particles as well.3.The brittle cutting process and AE response of brittle material 6H-SiC at low temperature are investigated.Results show that the crack forms under brittle cutting when the cutting depth is 77 nm.Before the crack formation,4 times of dislocation propagations occur in sequence and the part of workpiece in front of the tool is divided into pieces.In addition,three AE sources during the brittle cutting process mainly include lattice vibration,dislocation propagation and crack propagation.