Identification Of The Slip System Parameters Of Steels By Using Nano-indentation Experiments And Crystal Plasticity Based Inverse Simulations

Due to the requirements of lightweight construction and environmental protection,the automotive industry is increasingly demanding advanced high-strength steels(AHSS)such as TRIP,DP and CP steels.In order to balance the strength and formability of materials,the composition and organization of the third generation AHSS is becoming more and more complex.At present,the research on the mechanical behavior and formability of the third generation AHSS is not enough,and the mechanism of the overall performance of the materials relative to each component needs to be further explored.Numerical simulation is an important way to study the deformation and mechanical behavior of materials,especially multi-scale simulations represented by crystal plasticity.It is widely used in simulation to predict the deformation behavior,anisotropy,microstructure evolution,and damage evolution of metal materials.The premise of numerical simulation modeling of AHSS is to master the mechanical properties and deformation mechanism of each constituent phase.Conventional experimental methods,such as compression and bending,can only provide macroscopic mechanical data of materials.Therefore,it is necessary to find a new method to identify the mechanical properties of advanced metal materials.In this regard,the application of nano-indentation and crystal plasticity is summarized in this paper.Electron backscatter diffraction(EBSD)was used to obtain the crystallographic information of the material;the atomic force microscope(AFM)was used to obtain the morphological information of the indentation surface,that is,the height and location of the stack.The crystal plasticity finite element simulation(CPFEM)was performed on the indentation process,and the load-displacement curves and indentation morphology were compared in the experiments and simulations.The objective function was constructed,and the constitutive parameters of the materials were back calculated using genetic algorithms and verified.Based on the above research results,this thesis substitutes the parameters extracted from a single indentation into the simulation.Using the crystallographic information of other single indentation points,comparing the load-displacement curve and morphology,we can draw the following conclusions: The crystal plasticity simulation and inverse analysis process can extract the key information of nano-indentation.However,there are multiple sets of solutions for the slip system parameters obtained by using only the load-displacement curve data.This thesis further considers the deformation information of indentation topography to optimize the parameter identification process.Finally,the DP980 is used as a verification object to identify the crystal plastic material parameters of the ferrite and martensite phases.Based on the load-displacement curve and indentation morphology,the proposed inverse analysis method determines the mechanical behavior of two phases.The results show that: for multi-phase advanced high-strength steels,the material parameters identified by the inverse analysis method can well describe the indentation mechanical behavior and indentation residual morphology of the material,so nano-indentation and simulated inverse analysis can also be used for identification Mechanical behavior and material parameters of each constituent phase of other metal materials.