Ejection of Micron-Scale Fragments from Triangular Grooves in Laser Shock-Loaded Copper Samples

When a material is submitted to a dynamic compression, a shock wave propagates through the bulk and potentially interacts with a free surface. If this surface has geometrical defects such as grooves, some material ejection can occur. The energy of the high velocity ejecta is an area of concern for many applications, such as industrial safety, pyrotechnics or inertial confinement fusion. We have studied this phenomenon of microjetting from calibrated grooves in laser shock-loaded Cu samples, combining complementary experimental, numerical and analytical approaches, in order to investigate the formation and the fragmentation of the jets over ranges of small spatial (~µm) and temporal (~ns) scales and extremely high strain rates (~107 s−1). Various grooves were used with different depths and aperture half-angles (20°, 30°, 45°). The velocities measured by fast shadowgraphy and heterodyne velocimetry were compared to numerical predictions using the finite element or the smoothed particles hydrodynamics formulations with the Radioss code. Size distribution of the ejecta was inferred from rough measurements of the debris sizes and compared to analytical predictions from a probability law.