Study On Shock-induced Phase Transition Of Iron By A Phase Field Model

Shock-induced phase transition is one of the important response characteristics of materials subjected to high strain rate loading,and the study on the mechanism of shock-induced phase transition is of important scientific value and application prospect in basic theory,industrial production and other fields.Phase field method is one of the powerful tools for studying the microstructure evolution of materials under external forces.Because of the conve nience of describing the interface,the microstructure evolution mechanism of the impact phase transition of the iron base material is studied by developing the phase fiel d under high strain rate loading.In this paper,the phase field control system of thermodynamic consistency is derived based on entropy functional,and the model adopted a diffusion interface,which made automatic tracking on interface possible.We added the density gradient term and order parameter to characterize the different phases of materials,and simulated the soften and phase transition under extreme physical conditions such as high temperature,high pressure and high strain rate,which are result from shock wave loading.According to the conservation theorems and principle of entropy increasing,we established the governing equations of shock-induced phase transition in metal dielectric.Then we discretized phase field model by using high order difference scheme,introduced the artificial viscosity,defin ed conditions of definite solution and local threshold conditions,and made program by using Intel Visual Fortran.Finally we obtained the numerical solution of the phase field model.Combined with the experimental data and theoretical analysis,the numerical valu e of thermodynamic quantities was in good agreement with the theoretical solution,and it indicated that the phase field model we have developed can simulate the propagation process of the strong shock wave in the medium.Based on the model described above,we studied the ??? polymorphic phase transition of iron-base alloy induced by one-dimensional shock wave.The numerical solution of equations obtained time and space distribution of pressu re,density,particle velocity,values of ,and internal energy.The Hugoniot curve could also be obtained,and the simulation results fitted well with the experimental results.We further analyzed the coupling effect of wave and phase transition by tracking the changes of pressure and speed in each unit.Analyzing the numerical simulation results,we found that the pressure for phase transition reduced compared with that under the static pressure and room temperature,which demonstrated the effect of temperature rise in shock-induced loading.Tracking the changes of pressure and speed in each unit under the different pressure s,we found out that when the shock wave pressure was less than the threshold of phase transition,there was only one wave in the me dium.As the shock wave pressure increasing(the particle velocity was also increased)over the threshold of phase transition,the phase transition wave appeared and the typical double wave structure was presented in the medium.If the impact pressure continued to increase,the phase transition wave would be combined with the shock wave.As the same time,we studied the phase transition relaxation time,and compared the result with the experimental data.The simulation results above fitted well with the exp erimental results,which indicated that the phase field model we developed was successful,and it would help people to understand the microstructural evolution of metallic materials under the shock wave.The influence of viscosity coefficient and interface parameters on shock wave propagation and phase transition interface was also studied.The results show that the parameters are closely related to the interface,and only choosing reasonable values under certain conditions,can established phase field model simulate the shock-induced phase transition process in metal well.