Research On The Stress And Strain Distribution Of The Main Stress Surface Of The Ductile Material Necking Based On The Aramis Three-dimensional Strain Observation System

With the continuous development of the construction industry,ductile metal materials,especially steel,are becoming more and more widely used in building structures.It is well known that the mechanical properties and failure laws of materials have a direct impact on the safety and durability of building structures.Meanwhile,as a sign of material fracture failure,the stress-strain distribution of the necking state plays an important role in understanding ductile fracture.As the result,it is important to study the stress-strain distribution of the necking section of the material to understand the nature of the fracture failure.To study this problem deeply,based on Bridgman and Chen’s study,combined with the results of fracture electron microscopy,the results show that there is a defect in the stress distribution in the neck.To overcome the defect and improve the calculation accuracy,Chen’s necking principal stress surface assumption was introduced into the equilibrium equation to derive the modified stress distribution solution in this study.Afterwards,to discuss the accuracy of this correction,the Aramis three-dimensional strain observation system(Aramis system)was introduced to conduct uniaxial tensile experiments at room temperature on aluminum,Q235,Q345,45#steel,40Cr steel and brass.Moreover,the material parameters of the modified stress distribution solutions for the four materials Q235,Q345,45#steel and 40Cr steel were calibrated and the accuracy was discussed based on the experimental results.Finally,combined with the experimental results,the uniaxial tension finite element models were established by Abaqus,and the accuracy of the modified principal stress surface stress distribution in the neck was further verified by the finite element model.The specific work is as follows:Firstly,a comprehensive overview of the research on necking was given at first.A large number of study have shown that the main reason for the traditional stress-stressing solution of the necking stress--Bridgman solution and Chen Chi solution,are the large calculation errors,because the common strain uniformity assumptions have large errors.To prove this point,uniaxial tensile experiments at room temperature were carried out on aluminum,Q235,Q345,45#steel,40Cr and brass.The whole process was observed by Aramis system.Meanwhile,the surface of the fracture was observed under scanning electron microscopy.The distribution and size of the dimples at different locations of the fracture were analyzed,and the deformation of the point was inferred.Secondly,in order to overcome the error caused by the strain uniformity assumption,this paper starts from the shear strain assumption of the necking principal stress surface of Chen Chen,and combines the equilibrium equation to derive the stress and strain distribution on the modified necking principal stress surface.The material parameters were compared with the measured values observed by the Aramis system and the material parameters of the modified stress distribution solutions of the four metals Q235,Q345,45#and 40Cr were checked.The accuracy of the formula was discussed.Finally,combined with experimental data,a uniaxial tensile model was established in Abaqus/Explicit and its correctness was tested.Combined with the results of finite element calculation,the stress-strain distribution on the modified principal stress surface of the neck is compared with the accuracy of the traditional solution.It proves the correctness of the solution proposed in this paper.This results can provide a new method for further understanding the nature of material necking fracture;it simplifies the calculation of the plastic deformation stage of ductile materials.At the same time,it provides a more effective way to study the plastic constitutive relationship of materials.