Experimental Studies on the Dynamic Quasi-Isentropic Compression of Oxygen Free-Copper

The experiments of quasi-isentropic compression of oxygen free-copper were performed in a two-stage light gas gun by means of the composite flyer, in which the shock impedance increased from the impact surface to the rear interface. The impact velocity was 2.51 km/s. The compression time attained was about 1 s. Using the Lagrangian analysis technique a quasi-isentropic stress-strain relation of oxygen free-copper was obtained from the laser interferometric measurements of the free surface velocity histories on the different thickness specimens. The preliminary results show that quasi-isentrope is located above the Hugoniot at stress lower than 32 GPa, which is contrary to the expectation, and falls back below the Hugoniot at the stress higher than 32 GPa. The phenomenon, which was similar to the results of aluminum and tungsten reported by Barker and Chhabildas et al., was attributed to the furth increasing of dynamic strength of the specimen with the lower strain rate, arising from the quasi-isentropic compressing process, at low stresses, comparing with the shock-loading condition.