Study On Experiment And Prediction Of The Forming Limit Diagram Of High Strength Steel Laser Tailor Welded Blanks

Owning to the advantages such as reducing body weight, enhancing vehicle safety, cutting down the fabricating cost and etc, high strength steel laser tailor welded blanks has become the mainstream technique to fabricate lightweight vehicle.High strength steel laser tailor welded blanks whether can be applied successfully due to their formability. Forming limit diagram (FLD) is a synthetical index that is applied to assess the formability of sheet. It always has been applied in metal forming industry broadly. Study on the FLD of high strength steel laser tailor welded blanks is import guidance significance to lightweight body design, finite element analysis, industry producation and etc.In this thesis, the researches focus on fabricating the FLD of high strength steel laser tailor welded blanks through experimental and finite element simulation.In the second chapter, the finite element simulation process concerning sheet metal forming and simulation model set-up about laser tailor welded blanks forming are presented. The simulation process for high strength steel laser tailor welded blanks forming is obtained at last.In the third chapter, the Nakazima test is performed to generate the limit strains ofhigh strength steel laser tailor welded blanks. Owning to gain the limit strains broadly under different strain states, the forming limit specimens are designed base on finite element simulation. The ARGUS strain measuring system is adopted to measure the limit strain, and the FLD of tailor welded blanks is plotted subsequently.In the forth chapter, finite element simulation method is used to calculate limit strains of high strength steel laser tailor welded blanks. A novel criterion for predicting forming limits of tailor welded blanks is presented, namely, thickness gradient criterion. FLD of tailor welded blanks was obtained by finite element calculation based on thickness gradient criterion. Results show that the FLD obtained by using this method are good correlation with experimental results.