Experimental Modification Of Boundary Conditions And Constitutive Relationship In Finite Element Model Under High Speed Loading

The use of finite element numerical simulation technology has gradually become one of commonly methods in the process of powder pressing.In order to obtain correct simulation results,parameters such as velocity and quality of the die must be set reasonably according to actual conditions.At present,constant velocity is used as the boundary condition when the powder particle simplified model is constructed by finite element software,and quality of the die is ignored simultaneously.But in the actual high energy powder pressing,speed of the die is not stable,and so the problem of which how to set speed and quality of the die in the model need to be solved.Besides,rational constitutive equation of material is considerable to analyze the numerical results of powder suppression.Therefore,the simulation was carried out with initial velocity as the boundary condition,and parameters such as the quality of the die was modified based on the experiment in the study.Meantime,constitutive equation of powder was studied to provide guidance for building a finite element model.ABAQUS was used to establish simplified transverse and longitudinal models based on SHPB experiment firstly.The quality of die was got under a certain relative density.Ratio between the quality of die in the simulation and quality of punch in the experiment was taken as the equivalent quality simultaneously.Thereby,relationship between particle rows and the quality of the die were obtained through the results of simulation.Relative quality of discrete density volleyball accumulation model was 0.224.The relationship built was applicable for other materials by comparing the experimental results of copper powder with the simulation results.Different initial velocity was set in models of simulation to obtain relationship between the equivalent quality of the die and the relative density.Then formula of equivalent quality of the two sets models,the initial velocity and the number of particles was received afterwards.Based on the formula obtained,assumed relationship between equivalent quality of the die,the initial velocity of the die,the number of transverse particles and the number of longitudinal particles was inferred.Then new particle model was simulated to get the specific form of the model,and the accuracy of the model was verified by comparison.Finally,the constitutive equation of powder high energy rate was discussed.Bernstein Polynomial was used as shape function to describe strain effect in metal powder high energy rate compression process.Then constitutive equation was obtained by the combination of JohnsonCook model.Ultimately,the specific form of the shape function was obtained by fitting the experimental data of copper powder SHPB,and strain rate sensitivity coefficient under the experimental conditions was 0.285.Besides,the stress-strain curves and SHPB curves were obtained by using the constitutive equation,and the results showed good agreement.In a word,the parameters of the simplified model are modified based on the experiment in the paper,the problem of which how to set speed and quality of the die in the model was solved.The constitutive equation was obtained at the same time to provide guidance for building a finite element model.