Effect of the r-value change on the forming limit analysis for a ultra-low carbon steel sheet

Abstract

The effect of the r-value change on the accuracy of the forming limits predicted using the Marciniak-Kuczynski-type (M-K) forming limit analysis for a cold rolled interstitial- free (IF) steel sheet is investigated. Uniaxial tensile tests with a digital image correlation system are used to measure the r-value change. A tube subjected to tension-expansion loading under linear paths in the first quadrant of the stress space are performed to measure the multiaxial plastic deformation behavior and the forming limits of the test material. The observed differential hardening (DH) behavior is approximated by changing the material parameters of the Yld2000-2d yield function (Barlat et al, 2003) as functions of the reference plastic strain. The M-K analyses are performed using the r-value change and r-value constant DH model. It is concluded that the DH model considering the r-value change leads to the more accurate predicted forming limits.