High-power laser shock-induced dynamic fragmentation of iron foils

High-power laser shots were performed on 100-μm -thick iron foils, leading to shock loading pressures ranging from about 100 to 300 GPa. Free surface velocities were measured by interferometry. Ejected fragments recovered on polycarbonate shields were analyzed using scanning electron microscopy. Particle-size distributions were extracted from backscattered electrons images. These distributions, as well as the morphologies of fragments and the values of the tensile strength, change abruptly with increasing laser intensity. One-dimensional hydrodynamic simulations were performed in order to interpret these evolutions. By comparison with recent static measurements and calculations of the iron phase diagram, the BLF (Bushman, Lomonosov and Fortov) equation of state was inferred to provide more realistic predictions than SESAME 2150 at the highest pressures investigated. The calculated decompression paths show that spall fracturation took place in the solid state, either in α or in γ iron, this phase difference being the simplest hypothesis for explaining the changes observed in the fragmentation behavior.