ネック形状変化の解析にもとづく超塑性変形における塑性安定性の検討

抄録

Plastic instability has been reanalyzed for superplastic materials with the strain rate sensitivity m and the flow hardening parameter γ. The condition under which a neck does not grow has been obtained as I≡(γ−1)⁄m≥0. Even though I<0, the neck broadens gradually provided I≥−1. In the case of −1>I>−2, the neck becomes initially sharper but it finally becomes broader. If I≤−2, the neck becomes sharp. Although the usual superplastic deformation is thought to proceed in an unstable state because I<0, a large elongation can take place provided that I>−2 and the neck becomes broader.