Stress-strain curves and yield loci of auto steel sheet
汽车薄钢板应力应变曲线及屈服轨迹的研究

On the basis of biaxial tensile experimental system, two types of steel sheet were studied under different loading paths using optimized cruciform specimens with slots in the arms. According to the experimental true stress-logarithmic strain curves, the stress-strain curves of steel sheet vary with the stress state, and the strain-hardening exponent become larger when the load ratio is near the ratio 1:1. The contours of experimental yield loci for two steel sheets from 0.2% to 2% plastic strain were determined based on the equivalent plastic work principle. It is found that the shape of yield loci does not show symmetry along equibiaxial stretching path because of anisotropic mechanical properties. The geometry of the experimental yield loci were compared with the yield loci calculated from several existing yield criteria and the analytical result shows that the Hosford yield criterion describes the general trends of experimental yield loci of steel sheets very well, whereas the Hi1148 yield criterion overestimated the yield stress in all the contours. In addition, the Mises yield criterion that is generally used in isotropic materials also gives good fitness to the experimental yield loci.