Dynamic fracture feature in metals under very high strain rate induced by shock loading

The nucleation,growth and coalescence of micro voids in pure aluminum,OFHC copper and Ti-6Al-4V alloy have been studied experimentally, and here analyzed using numerical simulations based on the NAG(Nucleation And Growth) model. By means of electric gun and high power laser beam, loading techniques of very high strain rates in the range of 10(5) - 10(7)/s have been developed. The statistical data of voids in recovered specimens reveal that the void nucleation behaviors as well as the localization of damaged band are markedly different among the three tested metals. The results of NAG model show that the initial nucleation rate is material and strain rate sensitive, and can be spread over 3-4 orders of magnitude fi om aluminum to titanium alloy. The number of voids in aluminum is reduced and the damaged band becomes narrower as the strain rate is increased. However, the void nucleation behaviors of these materials can be quite different, even though aluminum and copper are usually regarded to be similar in many respects.