Abstract
Hole expansion using a flat-bottomed cylindrical punch was carried out to clarify the effects of piercing conditions on the fracture behavior of high-strength steel sheets. The results showed that the hole expansion rate λ negligibly changed with the piercing conditions in the case of a small initial hole diameter because of fracture from the inside of the edge of the hole. On the other hand, λ drastically changed in the case of a large initial hole diameter because of fracture from the edge of the hole. Moreover, by investigating the correlation between the quality of what around the hole and λ for a large initial hole diameter, it was clarified that λ of ferrite single-phase steel is affected by hardening behavior, and λ of ferrite-pearlite dual-phase steel is affected by the number of microvoids.
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