Design Of Diamond Wire Saw For Nuclear Facility Demolition And MD Simulation For Cutting Mechanism

With the development of human society,the traditional ways to obtain energy are difficult to meet the needs of human beings.As a clean and efficient energy,nuclear power is widely used in the world.Nuclear power plants built in the last century are facing decommissioning at the beginning of this century.The decommissioning of nuclear facilities will pose a threat to the surrounding environment and staff,which is an obstacle to the disposal of nuclear facilities in China.As the protective cover of nuclear facilities,the containment adopts reinforced concrete structure,which is extremely difficult to remove.How to remove the containment safely and efficiently is a problem that needs to be solved in our country.This thesis designed a diamond wire saw that can change the cutting direction.According to the particularity of the working environment and the main operation requirements,this thesis determined the basic structure of the wire saw,analyzed the strength of the key components,and planed the work flow of the diamond wire saw.The cutting operation of the diamond wire saw is mainly realized by the diamond grains on the bead surface.Molecular Dynamics can analyze the interaction between the tool and the workpiece from the micro-nano perspective.In this thesis,the MD simulation model of diamond cutting iron was established based on FFP boundary conditions using LAMMPS software.The microscopic stress calculated by LAMMPS was converted into the macroscopic stress in solid mechanics,and the transformation relationship between microscopic and macroscopic was established.As the cutting progresses,the temperature will increase gradually,the cutting stress fluctuates around 50000 bars.By using the OVITO visualization software,the common neighbor analysis(CNA)and centro symmetric parameter(CSP)of iron atoms were observed,and the micro mechanism of cutting process was clarified.This thesis studied the effects of rake angle,crack on the flank face and diamond crystal orientation on temperature and cutting stress.It is found that when the rake angle is 15° and the crystal orientation of flank face is(110),the wear of diamond tool is the minimum.The feasibility suggestions for the manufacture of beads were also put forward.By observing the change of the radial distribution function(RDF)during the cutting process,the rule of the transformation from diamond structure to graphite structure was analyzed.The cutting experiments of single diamond grain was carried out by using modified SFT-2M pin-disc friction and wear tester.In this thesis,the single-factor method was used to study the influence of speed and load on temperature and friction coefficient.By comparing the friction coefficient between experimental results and MD simulation results,the correctness of molecular dynamics simulation is verified,which will play a guiding role in the subsequent molecular dynamics research.Based on the dry cutting simulation,using TIP4 P water molecular model,considering the long-range interaction and electrostatic interaction between water molecules,this thesis established the wet cutting simulation model with water molecular layer as lubrication.By comparing the temperature and friction coefficient under wet cutting and dry cutting,the cooling and lubricating effects of water molecules were studied during the cutting process.It is found that under wet cutting,the tool temperature is reduced from 800 k to 550 k,and the friction coefficient is reduced from 0.7 to 0.4.It can be seen that the cutting efficiency and the service life of diamond particles under wet cutting can be greatly improved.