Finite Element Modeling And Size Effect Of Microplastic Forming Based On Voronoi Diagram Theory

With the rapid development of science and technology and the rapid increase of people's demand for micro-products,micro-forming technology has become the driving force of modern development and promoted the progress in the research field of micro-plastic forming of materials.Usually at least two dimensional scale,in the submillimeter range of the tiny parts under the action of a certain plastic deformation is often called micro plastic forming or micro forming.The technology is widely used in practical device processing,electronic industry,medicine and machinery and other fields.According to the study,the deformation characteristics of the micro plastic forming process are different from the traditional plastic deformation process due to the influence of the sample itself or the external conditions,and the size effect is obvious with the sample size or grain size.Therefore,the phenomenon of size effect in the process of micro-plastic forming studied in this paper has become a hot and difficult trend in the research field of plastic forming technology,and has an important impetus for the development of this technology in the future.In this paper,the experimental and simulation studies on the size effect in the micro-plastic process are carried out.First,the micro-tensile test is carried out,the size parameters are introduced,and the influence of the sample geometry and grain size on the flow stress is analyzed.Secondly,based on the Voronoi diagram theory,the three-dimensional polycrystalline geometric model was established in the finite element software ABAQUS by means of the plug-in POLARIS;based on the surface layer theory and crystal plasticity mechanics,a material polycrystalline constitutive considering the surface layer model and grain orientation was proposed Model,and fit the polycrystalline constitutive relationship of pure copper material according to the experimental data.Finally,using the established threedimensional polycrystalline geometric model and material constitutive model,the finite element software ABAQUS is used to realize the numerical simulation of the micro-upsetting and micro-stretching process.The simulation results are compared with the experimental results to verify the established model.At the same time,the size effect phenomenon in the micro-plastic process was further studied.The simulation results show that: the numerical simulation of the three-dimensional polycrystalline geometric model can more realistically show the grain shape of the specimen before and after deformation and the unevenness of deformation;The established material polycrystalline geometric model and constitutive model have certain reliability.The modeling method proposed in this paper is very suitable for analyzing the size effect phenomenon in the process of micro-plastic forming.The research results obtained have generalized significance and practical value for the numerical simulation of microplastic forming and the practical application of micro-plastic forming technology..