Soo Sik Han

A tension split Hopkinson bar for investigating the dynamic behavior of sheet metals

The dynamic response of sheet metals at high strain rate is investigated with a tensile split Hopkinson bar test using plate type specimens. The tension split Hopkinson bar inevitably causes some errors in the strain at grips with the plate type specimens, since the grip and specimens disturb the one-dimensional wave propagation in bars. To validate the experiment, the level of error induced from the grips is estimated by comparing the waves acquired from experiments with the Pochhammer-Chree solution. The optimum geometry of the specimen is determined to minimize the loading equilibrium error. High strain rate tensile tests are then performed with auto-body sheet metals in order to construct their appropriate constitutive models for use in crash-worthiness evaluation.

Optimum design of tailor welded blanks in sheet metal forming processes by inverse finite element analysis

Design of weld line in tailor welded blanks is indispensable for good manufacturing of stamped parts as assigned, since the initial weld line is distorted severely during the forming process. The initial weld line has to be determined such that desired weld line in a formed part can be obtained. The initial weld line can be predicted by inverse finite element analysis from the desired weld line in a formed part. In this paper, the multi-step inverse approach is employed to calculate more accurate initial blank shapes and initial weld line of tailor welded blanks for a cylindrical or square cup drawing. The applications demonstrates that the approach is useful for design of weld line in tailor welded blanks.