Sheet Metal Forming Limits
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The maximum strain that the sheet metal can suffer in stretch-forming processes is limited by the phenomena of strain localization and fracture. Both are strictly connected with the stability loss of the workpiece. Different possible modes of instability are discussed in the paper. Also the post-stability stages of the forming process are analyzed. It is shown that the limit strain depends mostly upon the rate of strain-localization process that occurs in the unstable stage. The influences of stress ratio, material properties (strain hardening ability, strain rate sensitivity, temperature sensitivity, inhomogeneity) and the forming conditions (friction, surface pressure) on the strain concentration process and on the limit strain are analyzed.
KeywordsShear Band Sheet Metal Stress Ratio Strain Gradient Limit Strain
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