Material ejection from surface defects in laser shock-loaded metallic foils (original) (raw)
Related papers
Ejection of Micron-Scale Fragments from Triangular Grooves in Laser Shock-Loaded Copper Samples
Journal of Dynamic Behavior of Materials, 2016
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 (*lm) and temporal (*ns) scales and extremely high strain rates (*10 7 s-1). Various grooves were used with different depths and aperture halfangles (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.
Velocity and mass density of the ejecta produced from sinusoidal grooves in laser shock-loaded tin
Journal of Applied Physics, 2020
When a shock wave of several tens of GPa breaks out at a free surface, material is ejected ahead of this surface. The amount and velocity of such ejecta depend on the breakout pressure, state of the released material (solid, liquid, or mixed), whether the shockwave is supported or unsupported and the initial geometrical perturbation (or roughness) of the free surface. If surface defects consist of small grooves, pits or scratches, material ejection occurs in the form of jets breaking up into tiny particles (so-called microjetting), with jet tip velocities up to several times higher than the free surface velocity. The laser-based experiments presented in this paper focus on microjetting in shock-melted tin with periodic surface perturbations. Several complementary diagnostics are combined to measure the velocity and mass of ejecta during the early stages of the jetting process. One relevant advancement is the use of ps-laser X-ray radiography to probe the density of the ejecta in distinct jets a few tens of µm-wide. The effects of the depth and wavelength of the initial perturbation are investigated in both linear and near-linear growth regimes. The results are compared with predictions derived from the Richtmyer-Meshkov Instability (RMI) theory.
Laser-induced shock waves from structured surfaces
Laser Sources and Applications, 2012
We present our results on the expansion dynamics of laser induced plasma created shock wave from stainless steel alloy propagating into ambient air that are characterized by time resolved shadowgraphic imaging. A machinist's scale with periodic surface structures of 30 µm depth and 240 ± 20 µm width having 25 and 64 lpi (lines per inch) is used as a target surface. Laser pulses from frequency doubled Nd:YAG (7ns, 532 nm) with 45 mJ energy per pulse focused to a beam diameter of ~ 1 mm on the target surface are used to generate laser induced shock waves. A fast ICCD camera (DH-734U, ANDOR) with 1.5 ns gating resolution is used to capture the time evolution of SWs into air. The properties of shock waves from structured surfaces are compared to that from a flat surface to understand the contribution of structured surface to shock wave dynamics. The SWs from a flat surface are observed to follow Sedov-Taylor solution during time delay of 0.2 to 20 μs. Contact front discontinuity dynamics were studied at different time scales for flat and structured surfaces The maximum velocity of the SWs has increased from 2.75 to 4 km/s with increasing number of surface structures from 25 to 64 lpi. From the measured radius of curvature of SW's (R SW ), the velocity, pressure and temperature associated with the micro explosion of metal surface is estimated using Counter Pressure Corrected Point Strong Explosion Theory.
Picosecond x-ray radiography of microjets expanding from laser shock-loaded grooves
Journal of Applied Physics, 2018
Material ejection upon the breakout of a shock wave at a rough surface is a key safety issue for various applications, including pyrotechnics and inertial confinement fusion. For a few years, we have used laser driven compression to investigate microjetting from calibrated grooves in the free surface of shock-loaded specimens. Fast transverse optical shadowgraphy, time-resolved measurements of planar surface and jet tip velocities, and post-shock analysis of some recovered material have provided data over ranges of small spatial and temporal scales, short loading pulses (ns-order), and extremely high strain rates. In the new experiment reported here, picosecond laser irradiation of a thin copper wire generates an ultrashort x-ray burst which is used to radiograph the microjets expanding from plane wedged-shape grooves in tin and copper samples shock-loaded by a longer, nanosecond laser pulse. Such ultrafast radiography provides estimates of the density gradients along the jets and of the total ejected mass at different times after shock breakout. Furthermore, it reveals regions of low density inside the samples deep beneath the grooves, associated with subsurface damage due to tension induced by the interaction of rarefaction waves. Thus, combining this x-ray probe with our former experimental techniques provides a more complete insight into the physics of microjetting at very high loading rates and the ballistic properties of the resulting ejecta.
Ejection of spalled layers from laser shock-loaded metals
2010
Dynamic fragmentation of shock-loaded metals is an issue of considerable importance for both basic science and a variety of technological applications, such as inertial confinement fusion, which involves high energy laser irradiation of thin metallic shells. In this context, we present an experimental and numerical study of debris ejection in laser shock-loaded metallic targets ͑aluminum, gold, and iron͒ where fragmentation is mainly governed by spall fracture occurring upon tensile loading due to wave interactions inside the sample. Experimental results consist of time-resolved velocity measurements, transverse optical shadowgraphy of ejected debris, and postshock observations of targets and fragments recovered within a transparent gel of low density. They are compared to numerical computations performed with a hydrodynamic code. A correct overall consistency is obtained.
Ballistic properties of ejecta from a laser shock-loaded groove: SPH versus experiments
The interaction of a shock wave with a rough free surface may lead to the ejection of high velocity (~ km/s) particles of small size (~ µm). This process is a safety issue for various applications such as pyrotechnics or inertial confinement fusion. To complement data obtained by other groups under explosive loading or plate impacts, we use laser driven shock loading to study microjetting from V-shaped grooves of various angles in copper and tin samples, with a combination of complementary experimental techniques. To simulate such experiments, we have chosen to use the Smoothed Particles Hydrodynamics formulation, well-suited for the very high strains involved in jet expansion and subsequent fragmentation. In this paper, we report some advances in this modelling effort, then we compare computed predictions with new experimental results including fragments size distributions inferred from post-test microtomography after soft recovery in a low density gel. Special focus is made on the dependence of the ejecta ballistic properties (velocity and mass distributions) on numerical parameters such as the initial inter-particular distance, the smoothing length and a random geometrical noise introduced to simulate inner irregularities of the material. Shock Compression of Condensed Matter -2017 AIP Conf. Proc. 1979, 080012-1-080012-5; https://doi.
Laser and Particle Beams, 2015
The effect of laser intensity on characteristics of the plasma ablated from a low-Z(CH) planar target irradiated by a 250 ps, 0.438 µm laser pulse with the intensity of up to 1016W/cm2as well as on parameters of the laser-driven shock generated in the target for various scale-lengths of preformed plasma was investigated at the kilojoule Prague Asterix Laser System (PALS) laser facility. Characteristics of the plasma were measured with the use of 3-frame interferometry, ion diagnostics, an X-ray spectrometer, andKαimaging. Parameters of the shock generated in a Cl doped CH target by the intense 3ω laser pulse were inferred by numerical hydrodynamic simulations from the measurements of craters produced by the shock in the massive Cu target behind the CH layer. It was found that the pressure of the shock generated in the plastic layer is relatively weakly influenced by the preplasma (the pressure drop due to the preplasma presence is ~10–20%) and at the pulse intensity of ~1016W/cm2the...
Debris ejection upon shock breakout at a rough surface is a key issue for many applications, including pyrotechnics and inertial confinement fusion. For a few years, we have used laser driven shocks to investigate microjetting in metallic samples with calibrated grooves in their free surface. Fast transverse optical shadowgraphy, time-resolved measurements of both planar surface and jet tip velocities, and post-shock analysis of recovered material have provided data over ranges of small spatial and temporal scales, short loading pulses (ns-order) and extremely high strain rates. The new experiment presented here involves two laser beams in a pump-probe configuration.
Spatial distribution of laser-ablated material by probing a plasma plume in three dimensions
Applied Surface Science, 1996
A Pb,, Bi,,,Sr,Ca,Cu,O. target has been irradiated with 30 ns FWHM KrF excimer laser pulses having a wavelength of 248 nm and an energy density of = 8 J/cm*. An intensified charge coupled device camera was used to measure the overall luminescence of the resulting plume in three dimensions as it moved from the target to the substrate. For small enough laser spots the plumes were found to have an ellipsoidal shape with two distinct axes. On the other hand, for a large rectangular laser spot (3.0 X 1.2 mm* or 2.4 X 1.0 mm') the plumes were found to have an ellipsoidal shape with three distinct axes. For example, at a time delay of 1000 ns the extensions were z = 34 mm (normal), y/2 = 12 mm, and x/2 = 8 mm, the lateral dimensions (x and y axes) being rotated at 90" with respect to the laser spot. The z extension is sufficiently greater than those for x/2 and y/2, and the z expansion-front velocity is sufficiently high, that both normal vaporization and normal boiling can be excluded as the mechanisms of the laser sputtering. Subsurface explosion can be eliminated on the grounds that the analysis demonstrating its existence was wrong. It follows that either an electronic process or else phase explosion (also termed explosive boiling) or else another still-to-be-defined but violent process may be involved. The results were finally compared with numerical solutions of the two-dimensional flow equations and a rotation effect was found essentially as observed. For example, it was largely absent at 200-700 ns, fully developed at 600-2000 ns, and, interestingly, starting to disappear at 3000-9000 ns.
Optical Measurement of a Laser Induced Micro Shock Wave on a Metal Surface
Journal of Fluid Science and Technology, 2008
Laser induced streaming is one of the interesting phenomena. When we provide a highly concentrated energy in a small region with laser beam, an induced streaming, such as micro shock wave or laser induced thermal acoustics is observed in the region. In the present paper, a micro shock wave in air which was induced by laser irradiation was observed by the optical techniques. The shock wave was generated on the metal surface due to the laser ablation. In the present experiment, we focused on a relatively low irradiation intensity region. As the laser power decreased, the plasma plume was not observed clearly on the metal target, but a strong micro shock was still induced. The trajectory of shock front was recorded with the shadowgraphic measurement and the Mach number was calculated experimentally. Alternatively, the induced density behind the shock wave was measured by speckle photographic technique. The shock Mach number and density distribution was analyzed and discussed with self-similar theory.