In the analysis of sheet metal forming, constitutive equations are examined for the prediction of breakage strains. Breakage initiation is numerically evaluated by Gotoh's method in which the onset of the localized necking is adopted as a breakage condition. The commercial elastic-plastic FEM code is improved by using J2-Gotoh's corner theory and biquadratic anisotropic yield function. The evaluation function for breakage is also introduced into this code. The friction coefficient on dies are measured by a model test, and the actual pressure distribution on the blank-holder is considered. The square-cup drawing process is numerically analyzed using the improved code. Numerical results with respect to the distribution of displacement and strain along the die surface, the punch load, the breakage location, and the punch stroke at the onset of breakage are in good agreement with the experimental results. The ring-shaped cup press working process is also numerically analyzed. The yield function is modified so as to consider the effect of the pressure on breakage. Numerical results for the strain, the breakage site, and the breakage depth are in good agreement with the experimental results. �@
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