Parameter identification of yield functions using hourglass-shaped tensile specimens

The use of higher-order yield functions, such as Yld2000-2d, is useful for improving the accuracy of stamping simulations, and biaxial tensile tests have been used to identify their parameters. However, biaxial tensile testing machines are not widely used, and material testing is difficult. Therefore, we developed a specimen with a special geometry (hourglass-shaped specimen) that can generate an equibiaxial stress state using a uniaxial tensile testing machine. A uniaxial tensile test was conducted on various steel sheets using this specimen, and the strain distribution in the specimen was measured by digital image correlation. The parameters of the Yld2000-2d yield function were identified from the test results using inverse analysis and from the results of ordinary uniaxial and equibiaxial tensile tests using cruciform tensile specimens. The yield curves obtained using the two methods were in good agreement. The parameters identified by the hourglass-shaped specimens were validated.