Warm tensile tests of B340/590DP dual phase steel and tailor welded blanks(TWBs) are carried out by using the testing machine CMT5205.The flow stress behaviors of base metal and TWBs are investigated in the temperatures range form 550 ℃ to 700 ℃ and strain rates from 0.000 1 s-1 to 0.1 s-1.Stress-strain curves for welding zone are obtained by calculation of equal jigging strain method.The models of base metal and tailor welded blanks are established by the improved model contained softening factor.The results show that the dynamic recovery and dynamic recrystallization occur obviously during warm tensile tests of base metal and TWBs.The flow stress increases with the increase of strain rates and decreases with the increase of temperature.The flow stress predicted by the proposed models well agrees with experimental results,which is reliable.

In order to realize numerical simulation of warm forming and establish the warm formation process parameters for Al5083-O aluminum alloy,the warm forming behaviors of Al5083-O aluminum alloy were investigated under different temperature range and strain rate.The relationship between the flow stress in warm forming and the deformation temperature or strain rate was described correctly using the hyperbolic sinusoid function of Zener-Hollomon parameter,a mathematical model was established to predict the stress-strain curves of this Al5083-O aluminum alloy during warm deformation.The stress-strain curves obtained by this model are in good agreement with experimental results,which confirm that the established models are accurate.

Necking or fracture caused by the non-uniform deformation is the problem that affects the forming of laser tailor-welded blanks(LTWB), thus the formability of LTWB needs to be known urgently.Forming limit diagram(FLD), which can be established by experiment or theoretical calculation, is an important method to evaluate the formability of sheet metal.However, the FLD obtained by experiment costs much and takes more time.And the method of theoretical calculation is not yet perfect and needs further improvement.A new theoretical model is developed to compute the FLD of same gauge laser tailor-welded blank.Base on the theoretical model, the FLD of same gauge laser tailor-welded blanks made of high strength interstitial free(HS-IF) steel is calculated by using the Hosford's yield criteria.Good correlation between the calculation result and experimental data is indicated.The FLD of laser tailor-welded blanks can be obtained conveniently through this method after the material performance parameters of welding zone are given.

Based on the numerical simulation and torque equilibrium theory,an optimal method was applied to calculate the torque difference between both sides of the center line;and the offset distance was obtained.The data got from the method applied in a progressive die for an electronic shell part was compared with the calculating results from the conventional analytical method and it shows effective and accurate in optimizing the pressure center of progressive dies.

In order to predict when and where the rupture of multi-gauge high strength steel of laser tailor-welded blanks(LTWB) happens,new failure criteria are proposed based on the research of failure behavior.In the established criteria,for the left side of forming limit diagram,LTWB ruptures when the punch load achieves maximum;for the right side of forming limit diagram,rupture happens when the strain path drifts to plane strain state.On the basis of the failure criteria,combined with the FE simulation of forming limit test,the forming limit diagram(FLD) of high strength steel LTWB is established.Good correlation between simulation and experimental results is obtained,which also verifies the validity and reliability of the failure criteria.By combining the failure criteria with FEM,the FLD of multi-gauge high strength steel LTWB can be calculated accurately and conveniently.