Effect of temperature, strain, and strain rate on the flow stress of aluminum under shock-wave compression

Abstract

The evolution of elastic-plastic shock waves with the propagation distance has been studied in 99.99% purity aluminum and in annealed 6061 aluminum alloy. The free surface velocity histories of shock-loaded samples, 0.1–2.0 mm thick and with initial temperature from 296 to 932 K, have been recorded using velocity interferometer system for any reflector (VISAR). The measured amplitudes of the elastic precursor waves have been approximated by power functions of the propagation distance, and these data have been converted into relationships between the shear stress at the top of elastic precursor wave and the initial plastic strain rate. The latter was found to decrease from 106 to 104 s−1 over 0.1 to 2-mm precursor traverse, while the density of mobile dislocations corresponding to these strain rates varied from 2 × 108 to 5 × 106 cm−2. At fixed strain rates, the flow stress of aluminum grows linearly with temperature. An analysis of the rise times of the plastic shock waves has shown that, for the same level of shear stress, the plastic strain rate at the shock front is by an order of magnitude higher and the density of mobile dislocations is 2-3 times higher than their initial values behind the elastic precursor front.