Shock compression and spall formation in aluminum containing helium bubbles at room temperature and near the melting temperature: Experiments and simulations

The influence of helium bubbles or boron inclusions in aluminum targets is studied by plane impact experiments with a gas gun. The experiments were done for targets with initial temperatures of 25 degrees C and near melting at 600 degrees C. The free surface velocity was measured with velocity interferometer for any reflector (VISAR) diagnostic. From these measurements the elastic yield strength and the spall strength were calculated. The experiments are analyzed by using a one dimensional (1D) hydrodynamic simulation coupled to a spall model. This model describes the time development of ensemble of growing voids or helium bubbles. The simulations of the VISAR free surface velocity are in a good agreement with the experiments. The impact experiments and the appropriate simulations are done for three distinct targets: pure Al, Al + 0.15%wt.B-10 and Al + 0.15%wt.B-10 with helium. The Hugoniot Elastic strength limit (y(HEL)) for the target with helium at room temperature is smaller than the appropriate target without helium. The y(HEL) for all targets becomes substantially higher at 600 degrees C preheating temperature. Furthermore, the preheated (600 degrees C) pure Al has y(HEL) significantly larger than all other targets. For the preheated Al-B-10 with helium, the shape of the velocity trace does not show a well defined Hugoniot elastic limit. The spall strength for all targets becomes substantially lower at 600 degrees C. The preheated pure aluminum has significantly higher spall strength in comparison to all other preheated targets. However, at 600 degrees C the spall strength of Al-B-10 with helium bubbles is significantly reduced in comparison to Al-B-10 without helium, while at 25 degrees C the spall strength is the same for both cases. The simulation revealed that this effect might be explained by a reduction of the viscosity in the aluminum with helium at the pre-heating conditions. (C) 2013 Elsevier Ltd. All rights reserved.