발간논문

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Vol.29, No.4, 379 ~ 389, 1991
Title
Blow Forming of Superplastic 7475 aluminum Alloy Sheets
정성규S . K . Jeong, 최준환J . H . Choi, 이동녕D . N . Lee, 이혁모H . M . Lee, 홍순형S . H . Hong, 홍성석S . S . Hong, 이종수J . S . Lee
Abstract
The 7475 aluminum alloy sheets were subjected to a thermornechanical treatment to have superplastic characteristics. The superplastic specimens were tested in an Instron testing machine at constant cross head speeds to obtain a constitutive equation for an optimum superplasticity. The constitutive equation which offers the reference data for a constant-apex-strain-rate blow forming was established at 516℃ in the form of 0=K·ε˙^m. The equation was applied to the analyses of blow forming into cylinderical and conical dies. The theoretical models mainly followed Ragab`s analytic model about a constant-pressure blow forming but were modified into the models relevant to a constant-apex-strain-rate blow forming. A number of experiment have been conducted, involving the blow forming of superplastic 7475 Al alloy sheets into cylinderical and conical dies at 516℃ with the apex-strain-rate, 1.15 × 10^(-3)/sec. The theoretical results and experiments were compared and the problems such as cavity occurrence and dynamic grain growth were discussed.
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