Abstract
The bulging behavior of circular aluminum sheets was investgated by the electro-hydraulic discharge free-forming method, which was chosen as an example of high strain rate metal forming. Dynamical strains and strain rates were measured from the strain of punched pieces taken from a part of the polar circle at different polar deflections during forming. The stress-strain curves at the pole were obtained by measuring the working pressure from the movement of the piston which was interposed as a damper between the blank and explosive wire in order to uniform the pressure. The forming velocity was obtained by pin contacts in each forming condition.
The obtained results are as follows: (1) The relation between the polar deflection and the strain during forming was not very different from the relation obtained from each final polar deflection below the critical energy for failure. (2) The maximum strain rate reached to 2 × 103 sec-1 in O-temper sheet and 3 × 103 sec-1 in 1/2H sheet. (3) Above the critical energy, the strain rate reached to 8 × 103 sec-1 at failure in the polar circle. However, the forming velocity increased and the strain and strain rate with respect to the polar deflection decreased with an increase of the energy. It was found to fail in the die shoulder rather than in the polar circle, especially in 1/2H sheet. (4) In the stress-strain curves at the pole, the stress was higher in dynamical testing than in hydrostatical testing, especially in 1/2H sheet. (5) These tests of the forming behavior are thought to be applicable to other materials and forming conditons.
