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

•The dynamic behavior of Al with helium bubbles at room temperature and at 600 °C is studied.•Near melting the HEL becomes substantially higher than its value at room temperature.•Near melting the spall of Al with helium is significantly reduced in comparison to Al without helium.•From simulation: the helium bubbles become dominant in the spallation at pre-heating conditions.

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 °C and near melting at 600 °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.10B and Al + 0.15%wt.10B with helium. The Hugoniot Elastic strength limit (yHEL) for the target with helium at room temperature is smaller than the appropriate target without helium. The yHEL for all targets becomes substantially higher at 600 °C preheating temperature. Furthermore, the preheated (600 °C) pure Al has yHEL significantly larger than all other targets. For the preheated Al–10B 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 °C. The preheated pure aluminum has significantly higher spall strength in comparison to all other preheated targets. However, at 600 °C the spall strength of Al–10B with helium bubbles is significantly reduced in comparison to Al–10B without helium, while at 25 °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.