Study On Mesoscopic Deformation Characteristic And Damage Mechanism Of Metallic Foil In Blanking Process

With the miniaturization of mechanical products,micro-blanking has become an important means of mass production of ultra-thin sheet metal parts in modern manufacturing,especially in the electronics industry.But so far,its process design is still highly dependent on previous production experience,and pre-research and parameter optimization mostly rely on experimental methods,so it is difficult to effectively promote low-cost simulation analysis.The fundamental reason for this phenomenon is that traditional mechanical models cannot reflect the microstructural sensitivity and size dependence of mesoscopic deformation and ductility failure of polycrystalline metal foils during the micro-blanking process.Given the above problems,under the framework of damage mechanics,plastic mechanics,and materials science,with the help of finite element calculations,mechanical tests,and common material characterization methods,this thesis reveals the deformation characteristics and damage mechanism of metal foils during the micro-blanking process and discusses the typical influence of process parameters and geometric miniaturization on forming quality and process stability.The main contents of this thesis are as follows:1)Combined with an extended Gurson-Tvergaard-Needleman theory,strain gradient plasticity,and Swift hardening relationship,a damage model suitable for multiple strain paths and considering the contribution of geometrically necessary dislocations is proposed.The incremental constitutive of this model is deduced in detail,and its numerical realization process based on the UMAT subroutine interface in the finite element platform ABAQUS is expounded.The proposed model can quantify the damage mechanism while reflecting the improvement of material strength caused by the reduction of geometric size,and there is no deformation path dependence.In addition to micro-blanking,it can also be extended to predict micro-forming processes such as micro-drawing and micro-extrusion.2)Two types of small notched plate specimens are designed,and in-situ tensile tests are carried out.By observing the section morphology using scanning electron microscopy and confocal laser microscopy,the differential failure mechanisms of metallic materials under tensile and shear conditions are revealed.In addition,based on numerical simulations,the evolution law of the damage parameter with the miniaturization of geometric size is obtained,which verifies the correctness of the proposed model.3)The macro-and micro-blanking tests were carried out on 304 stainless steel with the same clearance ratio.The size effect on the initial failure position,initial failure time,width of the shear band,and section morphology of the workpiece was expounded.Subsequently,micro-blanking experiments and corresponding simulation calculations under different clearances are carried out,and the clearance sensitivity of the above variables is discussed.The obtained results have reference significance in the design of the micro-blanking process.4)An uncoupled failure criterion is introduced into the crystal plasticity framework,and its numerical realization is completed.A series of finite element models reflecting the microstructure of real materials are developed,and simulations of the micro-blanking process of polycrystalline aggregates with different grain sizes are carried out,which broadened the engineering application scope of advanced numerical methods.In addition,a qualitative relationship between the grain size and the repeatability of micro-blanking is established.The indicators included:mesoscopic deformation,material flow,macroscopic mechanical response,and section hardness.Grain refinement is found to be beneficial to the quality control of finished products,which is consistent with many experimental phenomena reported in previous literatures.In summary,in this thesis,for the micro-blanking forming of metal foil,an numerical simulation scheme is established around the key scientific issue of the"size effect",which provides new ideas for mesoscopic deformation analysis and ductile failure prediction of polycrystalline materials.The obtained simulation and experimental results fully reveal the appearance and underlying mechanism of the size effect in foil blanking.