板材成形FEMシミュレーションにおける板厚方向応力を考慮したシェル要素-スプリングバック予測精度向上に関する研究 第1報

摘要

Shell elements are most commonly employed in FEM stamping simulations. It is clarified that conventional shell elements based on the Mindlin-Reissner assumption give rise to significant problems in springback prediction, because the displacement function does not allow sheet normal strain and sheet normal stress is neglected. In order to overcome the problems, a new shell element considering sheet normal stretchability is proposed. "Pseudo nodes" are added on the upper and lower surfaces of the conventional quadrilateral 4-node shell element. "Pseudo nodes" have only one degree of freedom in the direction normal to the midsurface, which makes it possible to calculate sheet normal strain. It is possible to treat the boundary conditions under which both surfaces are constrained or loaded. The calculation results indicate that the sheet normal stress distribution is compatible with both surface conditions, and the bending moment is reduced considerably by applying sheet normal pressure. These suggest that the proposed element can simulate the effect of overpressing on springback.