Investigation Of Mechanical Property Of Hot Stamping Component Based On Micro Damage

After hot stamping,the plasticity of high strength steel 22MnB5 decreases with the increase of its fragility.Therefore,it is of great importance to investigate the damage evolution and fracture of boron steel for hot stamping.As an important energy absorbing part,the thin-walled HAT-shaped component is commonly used.In this paper,the boron steel 22MnB5 is quenched following the hot stamping process of high strength steel.Then its mechanical property is tested by tensile test.GTN micro damage model is employed to depict the process of deformation and fracture of material.The damage parameters are calibrated by an integrate method of response surface model and genetic algorithm.However,because the parameter defined in GTN model for depicting damage evolution is the void volume fraction inside the material,which cannot predict the softening effect due to shear stress.Therefore,a shear modified term is included in the expression of void growth to improve the prediction accuracy of GTN model.To identify the new introduced parameters,specimens with rather low stress triaxiality during tensile test is newly designed in this paper.Furthermore,the shear modified parameters is calibrated by comparing experimental and simulated results and optimization method.Then the calibrated parameters are used for predictions of tests with shear-dominated specimens.The results shows that the accuracy of shear modified model is much higher than the original GTN model.Because the stress triaxiality during collapse test is rather low,even negative.So the shear modified GTN model mentioned above is adopted to predict the collapse test of HAT-shaped component with tailored property.The result shows that this model can predict the deformation and fracture very well.A two factors five levels design of experiment is employed and the peak crush force and energy absorption is used as two responses.With the developed response surface model,an optimized combination of hardness is obtained by the NSGA Ⅱ multi-objective optimization method.