A criterion for the generation of internal cracks normal to and astride the central axis in a drawing or extrusion process has been based on the conditions requiring less driving force with such cracks than without. Application of the upper bound theorem of limit analysis to approximate these forces yields a criterion for central burst. However, use of the lower bound theorem indicates that the cracked work-piece will always deform with less force, so that such a criterion would always predict the occurrence of this forming defect. Energy required to initiate and extend the crack must be included for a correct analysis.

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