Effect of pre-torsion strain on impact compression behavior of FCC metals
Hasebe Tadashi; Imaida Yutaka; Nakamoto Hitoshi
Abstract:This paper systematically studies the effect of nonproportional strain history on the flow behavior of FCC metals at high strain rates. Impact compression tests with pre-torsion strain ranging from 0% to 10% are performed at several rates up to 103s-1 by using a split Hopkinson pressure bar method. Two kinds of materials with different stacking fault energy, i.e., pure aluminum and pure copper, are employed to examine also the material dependency. The experimental results demonstrate that there exists significant interaction between strain history and strain rate effect, which is strongly material dependent. The strain history effect tends to disappear at high strain rates for pure Al, whereas it becomes large under impact loading for Cu. The controlling micromechanism which describes both the above positive and negative interactions is extensively, discussed based on dislocation interaction. The effect of pre-straining path is also discussed, where reversed torsion is introduced following 10% pre-torsion. The reversed pre-torsion straining tentatively reduces the strain history effect for Al, while no reduction in flow stress is observed in Cu. These trends are found to become strong for both the materials as the strain rate increases. Key Words:impact compression, pre-torsion strain, nonproportional loading, FCC metal, high strain rate, split Hopkinson pressure bar method