A pragmatic approach to accommodate in-plane anisotropy in forming limit diagrams

The traditionally used forming limit diagram (FLD), a locus of limit strain states under different linear strain paths is usually determined from the blanks along the rolling direction. The effect of in-plane anisotropy on the forming limit diagram is neglected for engineering applications. However, the in-plane anisotropy effect is significant when the FLD is used to estimate forming limit stress diagram (FLSD). The available models to account for the in-plane anisotropy are reviewed and their limitations are discussed. A simpler and more pragmatic approach to account for the in-plane anisotropy in forming limit diagrams is proposed. The new method calculates the change in the plane strain limit using constitutive models of plasticity theory. The orientation specific FLD is then calculated by interpolating between the limit strains along the uniaxial, plane and biaxial strain paths. The proposed methodology is discussed by comparing the experimental FLDs for three different grades of low carbon steels and an aluminum alloy. The calculation of FLSD using the predicted anisotropic FLD, assuming Hill48 yield criterion is illustrated for one of the materials. (C) 2014 Elsevier Ltd. All rights reserved.