Novel material characterization methods for sheet forming simulation

Abstract

In this study, novel material characterization methods for sheet forming simulation was investigated. Two topics were considered: (1) Expansion of DIC technology and (2) Geometry optimization technology. For the first topic, it was carried out the multipoint analysis and development of MATLAB code to deal with more characteristics within the gauge length of sheet type specimen of TRIP1180. From the analysis, Young’s modulus degradation due to the accumulation of plastic strain was calculated by generating multiple stress-strain curves from each ma-terial point. The repeated loading test was also conducted to compare the results from the proposed multipoint analysis and conventional test. It was found that the proposed method with uniaxial tension test could be employed to measure the Young’s modulus degradation on behalf of the repeated loading test. For the 2$^{nd}$ topic, geometry optimization of in-plane torsion test specimen (Twin bridge specimen) was conducted to measure the more accurate shear fracture strain with constant zero triaxiality and Lode parameter by introducing the integrated framework consisting of topology and shape optimization schemes. To consider the material anisotropy, User-defined MATe-rial (UMAT, Fortran code) was implemented in the framework. In addition, user-defined script (Python code) for constructing objective functions was also employed to deal with numerical output data and objective functions. The geometry of twin bridge area was optimized to achieve an exclusive shear deformation on the gauge area, and the actual experiment was performed for the verification purpose. From the experimental result, it was observed that the deformation up to onset of fracture on the area of interest was well evolved maintaining exclusively shear stress state.