Investigations of the formability of BCC steel sheets by using crystalline plasticity finite element analysis

Abstract

The effect of crystallographic texture on the formability of BCC steel sheets was studied by using crystalline plasticity finite element (FE) analysis. Three kinds of BCC steel sheets, mild steel, dual phase steel and high strength steel, were adopted as the examples in this investigation. At first, the crystal orientations of the three steel sheets were obtained by X-ray diffraction and orientation distribution function (ODF) analyses. The measured ODF results clearly revealed different preferred orientations — textures — of three kinds of steel sheets, featured by orientation fibers, skeleton lines and selected orientations in Euler angle space. Next, the crystal orientations were introduced into a FE model by using the orientation probability assignment method, which can be categorized as an inhomogenized material modeling. Huge numbers of integration points, which represent crystallites and can rotate individually, were employed to represent the textures for taking account of the initial and evolutional plastic anisotropy without introducing Taylor or Sachs homogenization assumption. The actual sheet metal forming processes, VDI benchmark and deep drawing problems, were adopted to assess the texture affects on the strain localization and failure. It was confirmed that the more {111} orientations — γ-fiber texture — and the less {001} orientations, the better the formability. Complex phase steel sheet (CP800), a high strength steel sheet, shows poor formability due to lack of γ-fiber texture.