Effect Of Size Effect On Mechanical Properties And Deformation Behavior Of OFHC Copper At Multiple Strain Rates

The fast development of microsystem technology and MEMS has put forward higher demand on the machining accuracy and molding quality of micro parts.Oxygen-free highconductivity(OFHC)copper is widely used in electronic components,communications and other industries because of its good thermal conductivity,electrical conductivity,and processability.The mechanical properties and deformation behavior of OFHC copper at the micro/meso-scale are affected by the stain rate effect and size effect,which is different from the traditional machining characteristics at the macroscopic scale.It is significant to analyze the influence of size effect on mechanical properties and deformation behavior and to establish a constitutive equation that can predict the material deformation behavior for machining micro parts.In this paper,the effects of size effect and strain rate effect on mechanical properties and deformation behavior of OFHC copper were studied.The mechanical properties and deformation behavior of OFHC copper at micro/mesoscopic scale were analyzed through quasistatic and split Hopkinson pressure bar(SHPB)mechanical experiments.The constitutive equation for predicting the deformation behavior of the material was established.The modified constitutive equation is brought into ABAQUS by the VUMAT subroutine,and the proposed modified constitutive equation is verified by finite element simulation.Firstly,the original samples of OFHC copper were annealed at three temperatures by vacuum furnace.Therefore,the samples were not affected by the original state during the experiment,and the compressed samples of OFHC copper with different grain sizes were obtained.The quasi-static and dynamic mechanical properties of samples with different grain sizes and geometric sizes were tested.The true stress-strain curves during the compression process of OFHC copper samples were obtained and analyzed.The experimental results show that the size effect and strain rate effect of OFHC copper samples are not significant at the macroscopic scale.At micro/mesoscopic scale,the size effect and strain rate strengthening effect are obvious.It is found that the grain has elastic deformation and severe plastic deformation by the metallographic diagram of the deformed specimen.The grain boundaries of some grains in dynamic compression samples are almost compressed together.Microcracks even appeared in dynamic load samples.It can be observed from the micromorphology that microcracks appear on the circumferential surface of the OFHC copper samples after the experiment,and the shear slip phenomenon on the surface is greatly affected by the size effect and strain rate effect.Then,considering the mesoscopic scale size effect on the mechanical behavior and deformation behavior of oxygen-free copper,with surface layer model and Hall-Petch equation of hybrid model replaces the first item of J-C constitutive equation,and strengthening coefficient C is established and the relationship between grain size d,obtained considering the size effect of modified J-C constitutive equation.The fitting results of standard J-C constitutive model and modified J-C constitutive model were compared with the experimental results,and the average relative error was analyzed.Finally,the modified constitutive equation is embedded into ABAQUS by VUMAT subroutine,and the modeling and simulation of SHPB and right-angle cutting are carried out.The micro-cutting test of oxygen-free copper was conducted,and the simulation results were compared with the experimental results.It is further verified that the prediction accuracy of the modified J-C constitutive equation considering the size effect is higher than that of the standard J-C constitutive equation at the micro/meso-scale.