Finite Element Analysis of Axisymmetric Hydrostatic Bulging

축대칭 정수압 벌징의 유한요소 해석

This paper examined strain distribution and radius of curvature of the bulge by finite element method and investigated limit polar thickness strain to predict the formability of sheet metal as we substituted effective strain and the radius of curvature obtained by FEM into instability condition equation successively. In experiment, the radius of curvature and limit polar thickness strainwere obtained by Moire method. Also, a concent- ric set of photogrid circles was used to measure the strain of arbitrary point and mild steel was used as material. This results obtained are as follows: 1) The radius of curvature obtained by FEM is in good agreement with the Moire experimental value. 2) The polar thickness strain is getting larger as the inside is approached from the edge. This means that fracture occurred near the ploe. 3) The circumferential strains agree closely with the meridian strains and the polar thickness strain is about twice the circumferential (or meridian) strain. This result agrees with the fact that anisotropy coefficient (R-value) obtained by tensile test is about one. 4) The theoretical results of limit polar thickness strain obtained by authors' method are better agreement with experimental results than other theoretical results. Therefore, we can better predict the formability of sheet metal with authors' method.