Study On Hardening Behavior And Fracture Prediction Of 7075-T651 Aluminum Alloy Sheet Under Proportional Loading

In the field of aviation industry manufacturing and application,aluminum alloy has higher strength and good recycling performance compared with other metals under the same density condition,so it is widely favored.7075 aluminum alloy is widely used in the aviation industry.The research on the aluminum alloy is mainly focused on the field of hot forming and corrosion resistance,and the mechanical behavior of its cold forming is rarely involved.Therefore,this paper studies the mechanical behavior of 7075-T651 aluminum alloy sheet under the condition of cold forming proportion loading,which has important significance.In this paper,by means of mechanical properties experiment,hardening model theory research and finite element simulation,a hardening model was constructed and a ductile fracture criterion was selected.The hardening model can accurately describe the hardening behavior of 7075-T651 aluminum alloy sheet under proportional loading condition.The ductile fracture criterion is suitable for describing the fracture behavior of the material under proportional loading condition.The main contents and conclusions are as follows:1)The proportional loading experiments under different loading conditions were carried out at room temperature and quasi-static strain rates.The mechanical properties of different orientations were obtained.The fracture sections and the strain evolution process of characteristic points of samples under different loading conditions was analyzed.The results show that the initial yield strength and tensile strength of 7075-T651 aluminum alloy are not obvious,and the anisotropy of thickness anisotropy coefficient R value and fracture elongation is weak.There is no obvious necking phenomenon in the forming process of the six samples under different loading conditions,and the fracture occurs along the direction of the maximum shear stress of the material.2)Considering the influence of different loading conditions on the hardening behavior of the specimens,the VTL hardening model was established by introducing the stress triaxiality T and Lode parameter L to represent different loading conditions on the basis of the Voce hardening model.The simulation results of VTL,Swift and Voce hardening models on the hardening behavior of 7075-T651 aluminum alloy sheet were compared and discussed.The results show that the VTL hardening model has a higher accuracy in describing the hardening behavior of 7075-T651 aluminum alloy compared with Swift and Voce hardening models.3)A non-coupled ductile fracture criterion calibration system based on Python was developed.The DF2015 ductile fracture criterion,which considered the influence of large stress state range and maximum shear stress on the fracture behavior of the material,was applied to the fracture behavior prediction of 7075-T651 aluminum alloy sheet,and was compared with Oh,Rice-Tracy and DF2012 ductile fracture criterion.The results show that,based on the comprehensive analysis of the fracture displacement simulation results of samples under different loading conditions,the simulation accuracy of DF2015 ductile fracture criterion considering the influence of large stress state range and maximum shear stress on the fracture behavior of materials is higher than that of Oh,Rice-Tracy and DF2012 ductile fracture criterion.