Study On Deformation And Fracture Behavior Of 6 Series Aluminum Alloy Based On Digital Image Correlation Method

Automobile lightweight is the need to solve energy consumption and environmental pollution problems and economic development.Aluminum alloy has become one of the most important materials for the lightweight of automobile body due to its low density,good plasticity,high specific strength and good corrosion resistance and formability.In this paper,6016 plates and 6061 extruded profiles were selected as the research object.Through a large number of experimental studies to characterize the stress and strain changes of aluminum alloy materials in the tensile process and to analyze the effect of stress triaxiality on the fracture failure behavior of6 series aluminum alloys.The stress and strain changes of aluminum alloy during the tensile process were characterized and the effect of stress triaxiality on the fracture failure behavior of 6 series aluminum alloys was analyzed through a large number of experimental studies.The main contents and conclusions of this article are:(1)For the 6016-T4,the baking heat treatment method was used to simulate the actual production process of the baking process to obtain a 6016-T6 aluminum alloy sample with improved strength.For the 6061 profile,o ffline quenching and artificial aging heat treatment were used to obtain 6061-T6 aluminum alloy tensile samples with basically the same initial properties.(2)In the mechanical property test,to avoid the many drawbacks of the traditional grid strain test,combined with the digital image correlation method(DIC)to obtain the baked 6016 plate and 6061-T6 aluminum alloy stress field changes during the entire tensile process.The stress field changes of the baking 6016 plate and 6061-T6 aluminum alloy during the entire tensile process were obtained combined with the digital image correlation method(DIC).At the same time,the flat,notched R5,notched R20,shear 0°and shear 45°tensile specimens were designed to obtain the stress-strain curves of the tensile specimens with a wide range of stress triaxiality under quasi-static conditions,combined with fracture scanning to analyze and study the fracture mode of tensile specimens und er different stress states;The fracture mode of tensile specimens under different stress states was analyzed and studied by combining the fracture scanning.(3)Combining the experimental results of mechanical properties and numerical simulation of the static flat tensile specimen,the parameters in the Johnson-Cook constitutive equation and the Swift-Hockett-Sherby(SHS)weighted hardening criterion were obtained.The parameters in the Johnson-Cook constitutive equation and the Swift-Hockett-Sherby(SHS)weighted hardening criterion were obtained by combining the experimental results of mechanical properties and numerical simulation of the static flat tensile specimen.By comparing the simulation and experimental results,it is found that the Johnson-Cook constitutive equation and the SHS weighted hardening criterion can describe the changes of stress and strain before necking during the stretching process of baked 6016 sheet and 6061-T6 profile.The simulation and experimental results were compared,and it is found that the Johnson-Cook constitutive equation and the SHS weighted hardening criterion can describe the changes of stress and strain before necking during the stretching process of baked 6016 sheet and 6061-T6 profile.At the stage of necking to fracture,for 6016 plate and 6061-T6 profile,when the weighting coefficient ? is 0.25 and 0.75 respectively,it can best reflect the changes of the flow stress of the material during the stretching process;(4)Use LS-DYNA finite element to extract the fracture s train,stress triaxiality and Lode angle of samples with different stress states,analyze and study the effect of stress triaxiality on the fracture behavior of baked 6016 sheet and 6061-T6 aluminum alloy and get the MMC breaking curve.LS-DYNA finite element was used to extract the fracture strain,stress triaxiality and Lode angle of samples with different stress states.The effects of stress triaxiality on the fracture behavior of baked 6016 sheet and 6061-T6 aluminum alloy was analyzed and studied.The MMC breaking curve was obtained.The corresponding numerical simulation mo del was established using the GISSMO fracture failure criterion,and the simulation results were in good agreement with the experimental results.