The Applied Program Development Of DYNAFORM Based On Forming Limit Stress Diagram Criterion

The finite element numerical simulation analysis is an important method to predict sheet metal instability in the sheet metal forming process. And the current general-purpose finite element codes all choose the strain-based forming limit diagram as the instability criterion, which has the limitation of correlative to the strain path. Thus it is very inconvenient to study sheet metal forming under complex strain paths. In view of the above reason, this thesis adopts the forming limit stress diagram as the instability criterion due to its independence of strain paths, which is acknowledged at home and abroad in the field of sheet metal forming, and develops the applied software for the special purpose finite element analysis code DYNAFORM in order to provide it with a new instability criterion.This thesis briefly analyzes some yield criteria and instability criteria to the sheet metal forming first. Then according to the transformation rule from ultimate strain to ultimate stress, it establishes the mathematical calculation models of the forming limit stress diagram for the software development according to Hill48,Hill79 and Hosford yield criterion irrespectively.According to the former mathematical calculation models, the applied software, which uses the forming limit stress diagram as its instability criterion, is developed based on the sheet metal forming finite element code DYNAFORM using Visual C++. First read in the calculation result file i.e. D3plot, then input the correlative material parameters and ultimate strain from experiments, and the developed software will produce the forming limit stress diagram used as sheet metal instability criterion and the stress contour of the part. The goal of analyzing the instability in complex sheet metal forming is reached using the forming limit stress diagram as criterion in this thesis. Some different sheet metal forming parts are analyzed with the developed software, whose results show that the developed software is satisfying for technological analysis of sheet metal forming and the applied module attains the anticipated goal. At the same time, the module is applicable to other FEM codes that use LS-DYNA as solver.