Abstract
The effects of matrix constitutive behavior and nonmetallic inclusions on forming limit strains have been examined with five laboratory heats of Fe-42 pct Ni alloy. The inclusion volume fraction was varied between approximately 0.01 and 1.59 pct by proper selection of Mn, S, and O contents. Each ingot was processed into 0.38-mm-thick sheets and heat treated to the recovered or the recrystallized condition. Forming limit strains were obtained from uniaxial tensile, plane-strain tensile, and hydraulic bulge tests by circle grid analysis. In any strain path, the limit strain increased with increasing the strain hardening exponent, n. The forming limit strains on the right-hand side of the forming limit diagram (FLD) decreased with inclusion volume fraction, while no effects of the inclusion volume fraction were observed on the left-hand side. A decrease in the slope of the FLD on the right-hand side due to an increase in the inclusion volume fraction qualitatively agrees with the theoretical calculation by Graf and Hosford, which was conducted on the basis of the Marciniak-Kuczynski (M-K) theory.
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