Figure 12. The yield loci for the high-exponent criterion (Equation 8) for a = 6 (bcc) and for a = 2 Hill's quadratic criterion (Equation 7) for (a) R = 0.5 and (b) R = 2. Note that with the high exponent criterion, the stress ratio for plane strain (dashed line) remains close to 0.5 regardless of the R-value.
 
12a

Figure 12a

12b

Figure 12b

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This figure is a component of the on-line article "Sheet Metal Forming: A Review", which appears in the November 1999 Issue of JOM.