2004 Volume 90 Issue 12 Pages 1016-1022
Work hardening behavior of IF and low carbon Al-killed steel sheets (SPCE and SPHC) under biaxial tension is investigated using biaxial tension tests and hydraulic bulge tests. The test materials have different r-values: an average r-value, r, is 1.87 for the IF steel, and 1.76 and 0.95 for SPCE and SPHC, respectively. In the biaxial tension tests detailed measurements are made of the initial yield locus, contours of plastic work for different levels of work hardening, and the directions of the incremental plastic strain vectors for linear stress paths. Only the IF steel and SPCE, which have relatively large r-values, exhibit the differential hardening, while SPHC work-hardens almost isotropically. The results are consistent with the author's earlier research. True stress-logarithmic thickness strain curves measured in the bulging tests are also consistent with the biaxial tension test results. Accordingly, it emerges that the differential hardening is characteristic of steel sheets with large r-values (about 1.5 or more). The work-hardening behavior of the test materials predicted using Yld2000 yield function (Barlat et al., Int. J. Plasticity, 19 (2003), 1297) agrees closely with the observations.