Generation of laser-driven flyer dominated by shock-induced shear bands: A molecular dynamics simulation study

High-power pulsed lasers provide an ingenious method for launching metal foils to generate high-speed flyers for high-pressure loading in material science or aerospace engineering. At high-temperature and high-pressure laser-induced conditions, the dynamic response of the metals and the mechanism of flyer formation remain unclear. In this study, the overall process of the laser-driven aluminum flyer, including laser ablation, rupture of metal foil, and the generation of the flyer was investigated by molecular dynamics combined with the two-temperature model. It was found that under high laser fluence (over 1.3 J/cm2 with 200-fs laser pulse duration), the laser induced a shock wave with a peak pressure higher than 25 GPa, which led to shear bands expanding from the edge of the laser ablation zone in the foil. Compared with the cases of low laser fluence less than 0.5 J/cm2, the shear band induced by high laser fluence promotes the rupture of the foil and results in a high-speed flyer (> 1 km/s) with better flatness and integrity. In addition, the shock wavefront was found to be accompanied by aluminum crystal phase transformation from face-centered cubic (FCC) to body-centered cubic structure. The crystal structure reverts with the decrease of pressure, therefore the internal structure of the generated flyer is pure of FCC. The results of this study provide a better understanding of the laser-induced shock effect on the foil rupture and flyer quality and forward the development of the laser-driven flyer.