Sheet bulk metal forming is widely used for medium-thick metal plate due to its convenience in the manufacture of accurately finished 3Dfunctional components.To obtain precise anisotropy and flow curve of metal plate is aprerequisite for correct simulation of sheet bulk metal forming processes.Inverse analysis of compression test was introduced here to evaluate the sensitivity of different flow curve models and geometric influence of compression test specimen.Besides,a methodology was proposed to compute plastic anisotropic coefficients of Hill quadratic yield criterion,which is based on the ratios of flow curves obtained by inverse analysis of compression tests using specimens cut in six directions on the medium-thick metal plate.The obtained flow curves and anisotropic coefficients were compared with those calculated from tensile tests.Flow curves based on inverse analysis of compression tests cover the curves of the tensile tests well,while the anisotropic coefficients are different,especially for the coefficient related to the RT45 direction.To estimate the effectiveness of the proposed method,the calculated material properties and those based on the traditional tensile tests were applied in a rim-hole process simulation.The simulation results based on the material properties from inverse analysis of compression tests accorded with the tested properties better.
Various microstructure-level finite element models were generated according to the real microstructure of DP590 steel to capture the mechanical behavior and fracture mode.The failure mode of the dual-phase(DP)steels,mainly resulting from microstructure-level inhomogeneity and initial geometrical imperfection,was predicted using the plastic strain localization theory.In addition,dog-bone-type tensile test specimens with different edge qualities were prepared and the deformation processes were recorded using a digital image correlation system.When the steel exhibited no initial geometrical imperfection,void initiation was triggered by decohesion between martensite and ferrite which was predicted based on the severe strain concentration,or tensile stress in areas where stress triaxiality and strain values were high.Final failure was caused by shear localization in the vicinity.Moreover,the initial geometrical imperfections severely affected the overall ductility and failure mode of the DP590steel.When initial geometrical imperfections were deeply ingrained,an incipient crack began at the site of initial geometrical imperfection,and then caused progressive damage throughout the microstructure,from the area of shear localization to the final fracture.Overall,the depth of the geometrical imperfection was the critical factor in determining whether internal decohesion or a local crack plays a dominant role.
