Yield Behavior Study And Finite Element Simulation Of Ultra High Strength Steel QP1180 Under Local Heating

Vehicle lightweight is the development direction of today's automobile industry.Variable section members of the advanced high strength steel can reduce the quality under certain load conditions.As the third generation of advanced high-strength steel,Q&P steel has the characteristics of high strength and high plasticity.In this subject,QP1180 super high strength steel is taken as the object.In order to reduce the residual stress of the formed specimen,the forming process of the metal sheet is optimized and the forming quality of the specimen is improved.The yield criterion is proposed for QP1180 high strength steel under high temperature.The mechanical properties and stress-strain curves were obtained by quasi-static uniaxial tensile test about QP1180 ultra high strength steel at room temperature.Under the strain rate of 0.002s-1,the uniaxial tensile tests at different temperatures were carried out.The results showed that the plastic forming of QP1180 super high strength steel was better at 350? by the comparison of plastic strain ratio,flexion ratio,strong flexion and elongation.Based on the thermal biaxial tensile test machine which developed by our the project group.At 350?,the tensile test of QP1180 tenth shaped specimen was carried out with different loading paths.The biaxial tensile stress-strain curves were obtained under different loading paths of 1:4,2:4,3:4,4:4,43,4:2 and 4:1 at this temperature.In order to explore the yield behavior of QP1180 at 350?,according to the principle of Mises,Hill'48,Gotoh and Hosford yield criterion,and the principle of equal plastic work of per unit volume,the average error is calculated by comparing the theoretical yield track with the experimental plastic work.The results show that the Hill'48 yield criterion is suitable for description of QP1180 ultra high strength steel,the average error is 43.76%.In order to further explore the temperature dependent yield criterion to reduce the error value.The Yld2000-2D yield criterion is chosen to fit the curve of the five polynomial of the temperature of each strain point,which is in high agreement with each strain point under different loading proportions.The error value is reduced to less than 10%.Therefore,the temperature dependent Yld2000-2D yield criterion can accurately describe the yield behavior of QP1180 at high temperature.The constitutive model and yield criterion of QP1180 super high strength steel coupling deformation resistance and temperature are embedded into ABAQ US software,and the finite element model is established about variable cross section roll forming of QP1180 super high strength steel.The simulation results show that the web of the forming piece is smooth,and there are no defects such as side wave,warpage and arch.The maximum stress 916Mpa,the maximum stress is about 25.71%lower than that at normal temperature after QP1180 sheet forming;the maximum angle of rebound is 3.7 degrees,the minimum is 1.7 degrees,and the angle of forming springback is reduced about 84.61%.Therefore,the QP1180 super steel sheet can reduce the internal stress of the forming part and improve the forming quality under the local heating condition.