Research On Plastic Wrinkle Of 304 Stainless Steel Sheet And Establishment Of Unified Wrinkling Limit Diagram

The wrinkling problem is one of the most important defects in the sheet metal forming process,especially with the continuous development of aerospace and other industrial fields,light-weight and high-strength thin-walled parts are increasingly widely used in various fields.The wrinkling problems have become more prone to occur,which gradually attracts the attention of the industry field.If the prediction of wrinkling instability can be achieved,wrinkles can be prevented or used to expand the forming limit of the thin-walled part during plastic forming.In this research,the square plate diagonal tensile test(YBT)model,the wedge tensile test model and the conical deep drawing test model were taken as the research objects,and numerical analysis models under the three kinds of processes were established by ABAQUS software.Based on the numerical simulation results,the establishment of universal wrinkling line diagram suitable for different forming conditions was explored.(1)The YBT test was designed and used as the research object of numerical simulation to establish the Buckle-Dynamic numerical analysis model.Comparing the bifurcation time of the stress path of the wrinkle elements with the bifurcation time of the strain path in the numerical simulation results,it is found that the bifurcation time of the stress path is easier to pick up,so the bifurcation time of the stress path is used as the critical time for determining wrinkle.It provides a basis for the judgment of the critical wrinkle time of the wrinkle elements under different processes.The critical wrinkle stress line and critical wrinkle strain line were established,and their morphologies and meanings were discussed.On this basis,the influence of the plate thickness on the critical wrinkle strain line was discussed.(2)Tensile wrinkle test of wedge pieces was designed,which was taken as the research object of numerical simulation to establish the Buckle-Dynamic numerical analysis model.The location of the critical wrinkle point was explored,and the critical wrinkle strain line of the wedge was established based on it.The critical wrinkle strain value of the middle wrinkle ridge region was extracted from the simulation results to establish the critical wrinkle strain line of the middle wrinkle ridge.By comparing the correlation between the critical wrinkle strain line of the wedge and the critical wrinkle strain line of the middle wrinkle ridge,the stress path law of the wrinkle element in the same specimen with different wrinkle ridge fegions was analyzed.A method was established to use the critical wrinkle strain value of the middle ridged element of the wedge to replace the stress and strain value of the critical wrinkle point to explore the critical wrinkle law of the wedge.Based on this,the critical wrinkle strain line of the same wrinkle ridge of different sizes of wedges was established,and the critical wrinkle stress and critical wrinkle strain law were discussed.On this basis,the differences of principal compressive stress paths between the wedge-shaped and square-plate wrinkle elements were compared.Through comparison,it is concluded that the main compressive stress path of the sheet under different loading conditions determines the process wrinkle resistance.The faster the compressive stress increases,the weaker the wrinkle resistance of process.(3)The wrinkle test of the conical part deep drawing was designed,and the BuckleDynamic numerical simulation model was established based on the test model.The selection method of the critical wrinkle point on the side wall of the conical parts was explored,and the critical wrinkle strain line of the side wall of the conical parts was established.On this basis,the distribution law of the critical wrinkle strain value of single wrinkle ridge on the side wall of the conical part was investigated,and the comparison with the critical wrinkle strain line of the side wall of the conical part showed that the critical wrinkle strain ratio of the side wall ridge element of the conical part could be used to replace the strain ratio of the critical wrinkle point to investigate the wrinkling instability of the conical part.According to this,the critical wrinkle strain line of the side wall wrinkle ridge element of the conical part with different diameters was established,and the morphological characteristics of the strain line were discussed.(4)The laws of critical wrinkle stress values and critical wrinkle strain values under the three working conditions were compared,and the relationship between the slope of the critical wrinkle strain line of specimens with different thicknesses under different working conditions and the wrinkle resistance of sheet metal was discussed.On this basis,the critical wrinkle stress ratio and the critical wrinkle strain ratio were used to establish a general wrinkling limit diagram under different load conditions based on the Matlab analysis software,and the morphological characteristics of the judgment line were discussed;Using the stress ratio and strain ratio between the wrinkled area and the unwrinkled area of the specimen,points are drawn in the figure,and the wrinkling limit diagram is judged to be accurate according to the distribution of each point.On this basis,the influence of plate thickness on the unified wrinkling limit diagram was explored.In summary,the Buckle-Dynamic numerical simulation method can be used to predict the wrinkling instability of the sheet under the above three conditions,it is found that there is a unified wrinkling limit diagram in the sheet metal forming process under different loading properties.