Parameter Identification For Macro-micro Coupling Constitutive Model And Its Application For Hot Forging Simulation Of Wheel Hub Bearing Flange

The overall performance of wheel hub bearing flange is highly related to the distribution of the grain. If the grain size evolution process of wheel hub bearing flange during hot forging can be simulated, then the hot forging process parameters can be optimized so as to achieve grain refinement, thus the quality of the product can be improved. In order to simulate the microstructure evolution of wheel hub bearing flange during hot forging, the macro-micro coupling constitutive model considering microstructure evolution must be given. Generally there are many unknown parameters, only when the specific values of the unknown parameters are decided can the related macro-micro variables of the deformed material be calculated.A systematic method is proposed in this paper to decide the parameter values for the macro-micro coupling constitutive model considering dynamic recrystallization. The goal of this method is to minimize the specific norm of the differences between simulated data and experiment data, genetic algorithm and sequential quadratic programming method are used to identify the parameters of the macro-micro coupling constitutive model. The genetic algorithm is used to search for a fair global solution, and this solution is further improved by using sequential quadratic programming method. Based on the above approach, the research of this paper contains these following steps:First, the parameter identification program is developed in FORTRAN language under Windows system based on the relevant theory of the macro-micro coupling constitutive model and the algorithms of parameter identification, the MPI(Massage Passing Interface) library is used to parallelize the parameter identification program.Secondly, to acquire the input data for the parameter identification program, hot compression test of 65 Mn, the material of wheel hob bearing flange, is taken and the metallographic analysis of the compressed samples is conducted. The required basic experiment data of the macroscopic and microscopic variables are achieved. The parameters of the macro-micro coupling constitutive model for 65 Mn are identified with the developed program based on the experiment data.Thirdly, redevelopment of the finite element simulation software DEFORM is conducted, the macro-micro coupling constitutive model after parameter identification is embedded into the user subroutine of DEFORM, enabling it to calculate the microscopic variables of the material. The redeveloped user subroutine of DEFORM is used to simulate the hot forging process of the wheel hub bearing flange, the results of the microscopic variables, such as the unrecrystallized grain size, recrystallized grain size, average grain size and the volume fraction of the recrystallized zone, are calculated.Finally, experiment is taken to manufacture the actual wheel hub bearing flange, then the metallographic analysis of the actual wheel hub bearing flange is conducted, and the experiment results are compared to the simulation results to verify the reliability of the simulation based on the macro-micro coupling constitutive model.