Microjetting from grooved surfaces in metallic samples subjected to laser driven shocks

Abstract

When a shock wave propagating in a solid sample reflects from a free surface, geometrical effects predominantly governed by the roughness and defects of that surface may lead to the ejection of tiny jets that may breakup into high velocity, approximately micrometer-size fragments. This process referred to as microjetting is a major safety issue for engineering applications such as pyrotechnics or armour design. Thus, it has been widely studied both experimentally, under explosive and impact loading, and theoretically. In this paper, microjetting is investigated in the specific loading conditions associated to laser shocks: very short duration of pressure application, very high strain rates, small spatial scales. Material ejection from triangular grooves in the free surface of various metallic samples is studied by combining transverse optical shadowgraphy and time-resolved velocity measurements. The influences of the main parameters (groove angle, shock pressure, nature of the metal) on jet formation and ejection velocity are quantified, and the results are compared to theoretical estimates.

Hydrodynamic simulations of microjetting from shock-loaded grooves

“…2a). Spall fracture due to release wave interactions is fully consistent with analytical predictions [1]. It leads to the ejection of planar spalled layers, and deeper cracks on both sides of the groove, while the region just below the groove bottom is less (or not) damaged (Fig.…”

“…As predicted by the 2D theory [1], the oblique interaction of the shock wave with the edges of the groove produces their collapse toward the bisecting plane of the groove, leading to jet formation (Fig. 2).…”

“…Complementary diagnostics including transverse shadowgraphy and Photonic Doppler Velocimetry permitted to measure the velocities of the jet tips and of the free surface. Experimental details and results can be found elsewhere [1,2].…”

Ejecta from periodical grooves in tin foils under laser-driven shock loading

“…KiloJoule-laser driven shocks are powerful tools for studying micro-jetting [1,2]. Because they are not very destructive, all the diagnostics can be very close to the ejecta area (down to a few mm), they allow several experiments in the same day (up to 10), the shock pressure is adjustable (the laser fluence or the spot diameter), all the delays are adjustable (unlike the guns).…”

Exploration of the fragmentation of laser shock-melted aluminum using x-ray backlighting

“…This process, referred to as microspalling by some authors, 1,2 has been of increasing interest because of its scientific and engineering significance. [3][4][5][6][7][8][9] However, high-quality experimental work on the subject remains limited and experimental data, such as the mass distribution of the fragmentation products in space, particle size distribution, successive evolution of the fragmentation product topology and the thermodynamic states, are quite sparse. These data are essential for developing predictive models of the phenomenon.…”