Study On The True Stress-strain Curve And Hardening Characteristics Of Q235 Material With Large Deformation

The establishment of an accurate constitutive equation is an important prerequisite for solving the problem of metal plastic forming,and the relationship between the equivalent stress and the equivalent strain is an indispensable complement to the plastic constitutive.According to the single condition curve,the relationship between the equivalent stress and the equivalent strain of the metallic material in any stress state can be replaced by the true stress strain curve of the material.Over the years,national researchers have used a variety of methods to explore the real stress and strain curve of the production method to explore the results of various studies,but the real strain is too small.Moreover,for the hardening properties of metal materials,the quantitative description of the hardening degree and the plasticity index change can not be obtained on the curve from its real stress strain.In view of the above problems,this paper takes Q235 as the research object,and proposes a method to combine the one-way compression experiment and the tensile experiment to make the real stress-strain curve under the condition of large deformation.Firstly,under the condition of lubrication,the cylinder of Q235 material is deformed at different deformation levels,and the relationship between the radial displacement and the amount of reduction of the contact surface mesh node is tested.The establishment of the sample and the finite element analysis model for upsetting,measured the amount of pressure and contact surface radial displacement as boundary conditions by the finite element model,the finite element calculation of the upsetting process of the specimen internal uniform deformation zone and uniform deformation within the area of the equivalent strain size.Then the specimen in the upsetting deformation zone after the uniform cut take tensile specimens were tensile experiments with different upsetting deformation amount(including reduction of 0)to obtain the yield limit of tensile material(or 0.2 sigma)even a curve,the equivalent can be obtained under the condition of large deformation degree stress strain(true stress-strain curve).The numerical results show that due to the influence of friction test,etc.effect evenlyin the deformation zone is slightly larger than the average variable true strain of specimens,with the increase of deformation degree,the difference between the two increase,when the reduction is 50%,the difference between the two is 6%.The hardness test results of upsetting specimens showed that with the increase of the amount of pressure,the specimen core and edge hardness value is increasing,but the amount of pressure increases to a certain value,the hardness values tend to be constant.This fact shows that work hardening material has its limit value.From the tensile tests with different upsetting the amount of specimen after the elongation and contraction rate,upsetting deformation degree on subsequent tensile test residual plastic is not affected,the fact that clarified the fuzzy concept of the plastic index decreased the deformation hardening concept.