Michel Boustie

Experimental investigation of liquid spall in laser shock-loaded tin

When a metal is shocked above its melting pressure or melted on release, the tensile stresses generated upon reflection of the compressive pulse from a free surface are induced into a liquid state. Instead of the well-known spallation process observed in solid targets, cavitation is expected in the melted material, and liquid fragments are ejected from the free surface. Their size, velocity, and temperature distributions are issues of increasing interest, as well as their impact on other nearby materials, but data are limited on the subject. Here, we present an experimental study performed on tin samples subjected to high pressure laser shocks (ranging from about 50to200GPa) of short duration (∼5ns). The results include post-test observations of the ejecta recovered after impact on a polycarbonate shield and time-resolved measurements of the free surface velocity through the shield. For shock pressures below some 80GPa, the velocity profiles are compared to the predictions of one-dimensional simulations i...

Spallation generated by femtosecond laser driven shocks in thin metallic targets

Spallation induced by a laser driven shock has been studied for two decades on time scales of nanosecond order. The evolution of laser technologies now opens access to sources whose pulse duration is under the picosecond, corresponding to characteristic times of numerous microscopic phenomena. In this ultra-short irradiation regime, spallation experiments have been performed with time-resolved measurements of the free surface. These measurements, complemented with post-test observations, have been compared with numerical simulations to check the consistency of modelling of the laser–matter interaction, shock propagation and to the study of dynamic damage at this ultra-short time scale, inducing strong tensile stress states at very high strain rates.

Physical approach to adhesion testing using laser-driven shock waves

This paper deals with an adhesion test of coatings using laser-driven shock waves. Physical aspects concerning laser–matter interaction, shock wave propagation and interface fracture strength are described. This comprehensive approach using two numerical codes (HUGO and SHYLAC) allows the determination of mechanisms responsible for coating debonding and a quantitative evaluation of fracture strength. From this description, a coating test protocol is also designed. To diagnose coating debonding, it is based on the analysis of experimental rear free surface velocity profiles measured by velocity interferometer system for any reflectors (VISAR). Ni electrolytic coating (70–90 µm) deposited on a Cu substrate (120–190 µm) is used for the experimental validation of the test. The fracture strength is 1.49 ± 0.01 GPa for a laser pulse duration of 10 ns at 1.064 µm.

Investigating impact demagnetization through laser impacts and SQUID microscopy

Understanding demagnetization by hypervelocity impacts is crucial for the interpreta- tion of planetary magnetic anomalies and remanent magnetization in meteorites. We de- scribe an innovative approach for investigating the effects of impacts on the remanent magnetization of geologic materials. It consists of the combination of pulsed laser impacts and Superconducting Quantum Interference Device (SQUID) microscopy. Laser impacts are nondestructive, create shocks with peak pressures as high as several hundred GPa, and allow well-calibrated modeling of shock wave propagation within the impacted sam- ples. High-resolution SQUID microscopy quantitatively maps the magnetic field of room- temperature samples with an unprecedented spatial resolution of ;100 mm. We present shock modeling and magnetic field data obtained for two laser impacts on a magnetite- bearing basalt sample. Magnetic measurements show a demagnetized area at the impact locations. We also show that high-resolution magnetic measurements combined with im- pact modeling provide a continuous relation between the demagnetization intensity and the peak pressure undergone by the sample. This promising technique will allow for the investigation of the demagnetization behavior of a variety of geological materials upon impacts, with implications for our understanding of the magnetization of extraterrestrial materials and of terrestrial impact structures.

Spallation in laser shock-loaded tin below and just above melting on release

Spall damage in solid materials has been one of the most widely studied shock-induced phenomena for several decades, for both applied and basic scientific motivations. Comparatively, very little data can be found yet about spallation in liquid metals. In a recent paper, we have reported an exploratory investigation of liquid spall in tin samples melted upon laser shocks of very high intensities. Here, we present further experimental results obtained over a lower pressure range, where we focus on the transition from the ductile fracture behavior of solid tin to the cavitating spall expected above melting. This transition is clearly evidenced from both time-resolved free surface velocity measurements and post-test examination of the recovered targets. The drop in tensile strength associated with melting is evaluated from the velocity profiles. Detailed views of the fracture surfaces in the spall craters provide an insight into the cavitation process. Experimental data are compared to preliminary computation...

Absolute equation of state measurements of iron using laser driven shocks

First absolute equation of state measurements obtained for iron with laser driven shock waves are presented. The shock velocity and the free surface velocity of compressed iron have been simultaneously measured by using a VISAR diagnostic, and step targets. The pressure range 1–8 Mbar has been investigated, which is directly relevant to planetary physics. The experiments have been performed at the Laboratoire pour l’Utilisation des Lasers Intenses of the Ecole Polytechnique.

Bond strength determination of hydroxyapatite coatings on Ti-6Al-4V substrates using the LAser Shock Adhesion Test (LASAT)

An adhesion test procedure applied to plasma-sprayed hydroxyapatite (HA) coatings to measure the LASAT threshold (LAser Shock Adhesion test) is described. The good repeatability and minimal discrepancy of the laser-driven adhesion test data were ascertained for conventional plasma sprayed HA coatings. As a further demonstration, the procedure was applied to HA coatings with diverse characteristics on the ceramic/metal interface. Different preheating and grit blasting conditions and the presence of a thick plasma-sprayed Ti sublayer or a thin TiO(2) layer prepared by oxidation were investigated through LASAT. It was assessed that a rough surface can significantly improve the coatings bond strength. However, it was also demonstrated that a thin TiO(2) layer on a smooth Ti-6Al-4V substrate can have a major influence on adhesion as well. Preheating up to 270°C just prior to the first HA spraying pass had no effect on the adhesion strength. Further development of the procedure was done to achieve an in situ LASAT with in vitro conditions applied on HA coatings. To that end, different crystalline HA contents were soaked in simulated body fluid (SBF). Beyond the demonstration of the capability of this laser-driven adhesion test devoted to HA coatings in dry or liquid environment, the present study provided empirical information on pertinent processing characteristics that could strengthen or weaken the HA/Ti-6Al-4V bond.

Study of damage phenomena induced by edge effects into materials under laser driven shocks

Spallation of materials induced by laser driven shock waves is generally produced under uniaxial (one-dimensional (1D)) deformation by irradiating a spot of diameter much greater than the sample thickness. Here, two-dimensional (2D) effects are introduced in shock wave propagation by drastically reducing the loaded spot. Experiments performed on aluminium samples detect the effect of lateral wave propagation, both on recovered samples and on time-resolved VISAR measurements. Damage zones are localized completely differently from that under uniaxial condition, according to the presence of 2D effects, and the signature of these 2D effects can be read on VISAR signals. Numerical simulations provide a full understanding of wave propagation and resulting damage in 1D or 2D configuration. Comparisons with experimental VISAR signals show the possibility of validating more accurately the dynamic damage criteria, including the 2D effects.

On the dynamic fragmentation of laser shock-melted tin

Dynamic fragmentation in liquid metals is an issue of increasing interest in shock physics, both for basic and applied scientific motivations. In a recent paper, we have reported an exploratory study of liquid spall in tin samples melted upon laser-driven shocks. The need for further experiments and analyses to answer some questions raised by that work had been pointed out. Thus, we present here some complementary results, including specific recovery tests as well as high speed transverse shadowgraphy to visualize both the expanding cloud of fast droplets and the late motion of large fragments that had been inferred from postshock observations.

PDV MEASUREMENTS OF NS AND FS LASER DRIVEN SHOCK EXPERIMENTS ON SOLID TARGETS

We present a new heterodyne velocimeter setup embedding a second low‐power frequency‐tunable laser acting as a local oscillator. We thus double the overall bandwidth of the system and we make the tuning of the laser power levels easier, to achieve good matching between the electric signal matching and the dynamics of the detector. Recently, we used this velocimeter onto metallic target shock driven by high power laser. The aim is to test the ability of this means to reveal shock propagation and effects into materials under extremely high strain rate with fast variations into the loading evolution. Spallation and fragmentation experiments carried out on aluminum samples were performed on the LULI2000 laser (800 J, 3 ns) and on the 100 TW laser (30 J, 300 fs) of the Ecole Polytechnique, with both VISAR and HV diagnostics. Comparisons reveal a very good consistency of experimental results.