Numerical Simulation Of Friction Stir Welding Based On Three-dimensional Monte Carlo Method

As a new solid-state joining technique,friction stir welding(FSW)is widely used in industry fields.The quality of welding are determined by the formation process of microstructure.In the process of welding,it is difficult to explore the microstructure of the welding area by experiment.With the rapid development of computer processing technology,the research on the numerical simulation of microstructure has gradually become the focus.In the first chapter,the development and application of FSW are introduced.At the same time,the research status of welding simulation method,stir head material,shape of stir head and residual stress analysis of welding materials are reviewed.Several commonly used methods for studying the microstructure are briefly introduced.In the second chapter,the basic theory and method for the finite element solution of friction stir welding are introduced,including the basic equations of fluid mechanics and the three most important methods in the numerical solution of finite element method.The CFD model of FSW is established,and the validity of the CFD model is further verified.In the third chapter,the basic theory of grain growth,including the theory of metal solidification and the theoretical deduction of grain growth correlation are introduced.Meanwhile,the Monte Carlo model,the MC calculation process and the driving mechanism are introduced.The grain growth index is close to 0.5,which verifies the reliability of the model.The combination of the MC model and the FEM model is also described.In the fourth chapter,the CFD model of FSW of aluminum alloy is established.Replacing the welding tool with flow boundary conditions.The flow velocity in the contact area is equivalent to the speed of the stirring head,and the boundary conditions are set according to the simulated material.The rotation speed of the welding tool from 400 rpm to 1500 rpm is simulated,and the relationship between the speed of the stirring head and the peak temperature is explored.The effective 3D Monte Carlo model was constructed which was used to predict the grain size and morphology distribution in the welding area.In the fifth chapter,on the basis of validation of the model,the influence of the rotating speed and the shoulder size on the welding temperature field and the grain size with morphology is further studied.Higher rotation speed or larger shoulder size can lead to the increase of the peak welding temperature.The increase of the shoulder size causes the increase of the welding area,and the influence of welding conditions on grain formation at different distances to shoulder and the weld line is further studied.