3D-Numerical Simulation Study Of BP-ECAP Of Magnesium Alloy Based On Smoothed Particle Hydrodynamics

The mechanical properties of metal materials can be improved effectively by Equal Channel Angular Pressing,(ECAP),while for materials which are difficult to plasticize at room and low temperatures,the cracks in the large plastic deformation process can be eliminated by the Equal Channel Angular Pressing with Back Pressure(BP-ECAP),which can realize the equal-channel extrusion process of metal which is difficult to deform at room or low temperature By means of numerical simulation,the deformation of the materials in the closed mould can be obtained,which is helpful to reduce the experimental cost and time.In view of the shortcomings of the current mesh method,such as finite element method,for the simulation of large plastic deformation and crack propagation,this paper uses particle SPH method to simulate the back-pressure-ivalent channel extrusion process of magnesium and magnesium alloys.The main research contents are as follows:Firstly,based on the basic theory of SPH method,the formula of SPH method applied to elastoplastic mechanics is deduced.In order to realize the uniform motion of the boundary and prevent the internal particles from penetrating the boundary,the repulsive force model of penalty function is introduced.It was then developed to apply The SPH method of metal plastic deformation process is simulated and the correctness of the SPH method is verified by a classical example of Taylor bar,which lays a foundation for the introduction of a new constitutive model of SPH method.Secondly,in order to improve the simulation accuracy of the SPH method,three plastic constitutive models are introduced.by simulating the unidirectional compression process of magnesium alloy,and comparing with the Deform-3D simulation results,the correctness of the proposed coupling program between the SPH method and the constitutive model is verified.Two damage models describing crack initiation and particle approximation is carried out to convert them into a suitable form for coupling with the SPH method program.the correctness of the SPH method damage constitutive coupling program is verified by simulating different fracture patterns of pure magnesium during equal channel extrusion at room temperature and comparing with the finite element method simulation results and experimental results.Finally,the program of back pressure application module is written,and the SPH simulation of Equal Channel Angular Pressing with Back Pressure process is realized.The equal-channel extrusion process of magnesium alloy with different back pressure of AZ31magnesium at200?and 10mm·s^-1 was simulated by SPH method.The SPH method is analyzed from the angles of equivalent plastic strain and damage value distribution,and compared with the finite element method simulation results and experimental results,which verifies the correctness of the SPH back pressure program compiled in this paper and provides a new method for the numerical simulation of Equal Channel Angular Pressing with Back Pressure process.