Theoretical Determination of Forming Limit Stress Diagram for Steel 1021 Sheet

Abstract

Forming limit stress diagram represent the maximum acceptable limits of principal stresses in sheet metal forming. This diagram show the limits of major and minor true stresses for different strain paths (uniaxial tension, plane strain and equibiaxial stretching path) in sheet metal forming. It is confirmed that the Forming limit stress diagram and the Forming Limit Strain Diagram are two mathematically equivalent representations of forming limits in stress space and strain space respectively. The Forming limit stress diagram of the sheet metal is gained by the transformation relations between the strain state and stress state in deformation of sheet metal. In this paper, the Forming limit stress diagram is theoretically determined using Marciniak-Kuczynski analysis and Hosford yield criterion for steel 1021 sheet ,and compared with the experimental Forming limit stress diagram based on the experimental Forming limit strain diagram of steel 1021 sheet & theory of plasticity. The influence of normal anisotropic ratio, index of yield criterion, inhomogeneous factor and strength coefficient on the theoretical FLSD is also presented. It is shown that the limit stresses in theoretical Forming limit stress diagram is raised by increased values of the normal anisotropic ratio, the inhomogeneous factor and the strength coefficient. The limit stresses are lowered when the index of Hosford yield criterion increased.