Research On The Prediction Of Crack In Plane Strain Deformation Of Aluminum Alloy Based On Bifurcation Theory

Plastic forming has a long history and many methods,and it is widely used in metal processing.Forming defects such as cracks may occur in the process of plastic forming.Before plastic forming,predicting its formability has a great significance to reduce the risk of die design failure,optimize die design and production process parameters,shorten die design and production cycle,and reduce production cost.Aluminum alloy is an ideal plastic forming material with high specific strength.It is widely used in transportation and other industries.In this paper,the prediction of cracks in plastic forming process of aluminum alloy is studied.The main work is as follows:(1)The theory and method of crack prediction in plastic forming are studied and summarized.(2)Based on the characteristic line theory of differential equation and the local bifurcation theory of plastic deformation,the crack prediction criterion in the form of plane strain deformation is established.(3)The constitutive equation of Prandtle-Reuss and the constitutive equation of Ito-Goya,which has a one-to-one relationship between strain increment and stress deviation increment,are derived for local bifurcation analysis of plane strain.Uniaxial tensile tests of A6061 aluminum alloy bar are carried out.The basic mechanical properties of the material and the constitutive relation of the material were obtained.(4)The finite element simulation of plane strain deformation of A6061 aluminum alloy bar is carried out by using ABAQUS software,and the crack prediction criterion is programmed by MATLAB software.The finite element simulation results are combined with the crack criterion to predict the crack occurrence,and the influence of constitutive relation on the crack prediction results is studied.(5)The experimental die for plane strain deformation of aluminum alloy bar under radial compression was designed,and the experimental results of variable path compression were carried out.The results of crack prediction were compared with the experimental results.The validity of this method and the importance of plastic constitutive form and parameters to the accurate prediction of crack are verified.(6)The plane strain extrusion of aluminum alloy and the rolling process of medium and thick plate are simulated,and the influence of processing parameters on the appearance of crack defects is studied.A set of extrusion experimental die is designed,and extrusion experiment is carried out.The effectiveness of the proposed crack prediction method in plane strain extrusion is verified.The effect of rolling reduction on the crack form in the center of plate is studied,and the crack form of head crack is predicted successfully.The method of crack prediction is proved to be useful in making rolling schedule of plate.In this paper,the research on the crack criterion of plane strain deformation and the dependence of plastic deformation local bifurcation analysis on plastic constitutive is of theoretical significance and practical application value.It is of significance for guiding the die design and process optimization of aluminum alloy forming.