Unraveling the Effect of Laser Fluence and Loading Orientation on the Spallation of Cu and Al microstructures at Atomic Scales.

The spall response of metals under laser shock loading conditions is investigated using a hybrid approach that combines molecular dynamics (MD) simulations with a continuum two-temperature model (TTM). This hybrid methodology is able to accurately model the laser energy absorption, electron heat conduction, and electron-phonon interaction that results in the ablation/melting of the material and the generation of a shock wave that travels through the metal followed by wave reflections and interactions to initiate spallation failure. The hybrid MD/TTM simulations are carried out to investigate the role of laser fluence on the laser shock loading induced spall failure of single crystal Cu and Al systems for a range of laser fluences from 0.5 to 13 kJ/m2. In addition, MD/TTM simulations are also carried out to investigate the role of loading orientation on the defect/damage nucleation and evolution behavior for Cu and Al single crystal systems. The simulations suggest a correlation between the spall strength and the density of dislocations generated in the metal at the spall plane. The microstructure response and the role of solid-liquid interfaces, defects and voids evolution, and shock wave structure on the spall strength and Hugoniot Elastic Limit of these systems are presented.