J.P. ROMAIN

Publications (26)28.38 Total impact

• Article: Effects of inside spallation of a coating on the debonding of its interface with a substrate subjected to a laser shock

  M Boustie, E Auroux, J P Romain, M Jeandin
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  ABSTRACT: When applying a laser shock to a substrate with a coating in order to test the adhesion strength of the interface, traction can be generated not only at the interface, but also within the materials. The effects of a possible rupture of these materials prior to the debonding is analysed by shock wave propagation mechanisms and experimentally evidenced for plasma sprayed coatings of alumina on an aluminium substrate. An estimate of the bond strength and the spall strength of the coating is obtained by numerical simulation.
  Journal of Physics Condensed Matter 10/2002; 14(44):10839. · 2.55 Impact Factor
• Article: Pressure measurements and analytical model for laser-generated shock waves in solids at low irradiance

  J.P. Romain, F. Bonneau, G. Dayma, M. Boustie, T. de Rességuier, P. Combis
  Journal of Physics Condensed Matter 01/2002; 14:10793. · 2.55 Impact Factor
• Article: Investigation of the response of a porous steel to laser driven shocks

  T. de Rességuier, J.P. Romain
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  ABSTRACT: Laser-driven shocks have been performed to investigate the dynamic response of a sintered porous steel to uniaxial compressive loading at very high strain rates. The water-confinement technique has been used to increase both amplitude and duration of the laser shocks. Two steels of different initial porosities have been studied. Time-resolved wave profiles have been measured with thick piezoelectric transducers stuck at the back of the steel targets. The residual porosity has been evaluated by post-shock examination of the recovered samples. A simple constitutive material model, based on a macroscopic description involving the equation of state of the compact steel and a traditional P- compaction model, has been adapted and introduced in a one-dimensional hydrocode to simulate the experiments. A correct overall agreement has been obtained between measured and computed wave profiles. Finally, the residual model has been compared to that observed along the direction of wave propagation. Both distributions show a significant densification of the samples over a depth of a few hundreds m below the irradiated surface.
  Shock Waves 06/2001; 11(2):125-132. · 0.95 Impact Factor
• Article: Application of the laser spallation technique to the measurement of the adhesion strength of tungsten carbide coatings on superalloy substrates

  M. Boustie, E. Auroux, J.-P. Romain
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  ABSTRACT: High power pulsed lasers are used to induce shock waves in Hastelloy X targets coated with tungsten carbide of 70 μm and 50 μm thickness. In suitable irradiation conditions, a debonding of the substrate/coating interface due to the generation of tensile stresses is observed. Experimental results are analyzed with the use of numerical simulations yielding the stress history at interface and its dependence on laser pulse intensity up to 600 GW/cm2 with 1 ns and 3 ns durations under direct irradiation, and 23 ns with water confinement. As a consequence of shock decay during the propagation through the substrate, a strong variation of incident intensity results in a small variation of tensile stress. This allows an accurate determination of the debonding threshold which is found in the range of 1.0 to 1.3 GPa for short laser pulses (1 and 3 ns) and 0.5 to 0.6 GPa for long laser pulses (23 ns confined).
  The European Physical Journal Applied Physics 09/2000; 12(01):47 - 53. · 0.77 Impact Factor
• Article: Coating debonding induced by confined laser shock interpreted in terms of shock wave propagation

  M. Boustie, C. Seymarc, E. Auroux, T. de Rességuier, J. P. Romain
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  ABSTRACT: Debonding of coatings on a substrate is currently achieved by the so-called laser spallation technique. Here, we give an interpretation of the debonding by laser shock based on the impedance mismatch between the substrate and the coating rather than on the spallation process. An analysis in the (pressure-particle velocity) plane coupled with (space-time) diagrams provides the stress history at the interface and shows the possible traction history, depending on the applied pressure loading and the nature of the target. From this study, the different configurations that can lead to a separation of the layers under laser confined irradiation are evidenced according to the impedance mismatch between both components. A case of this analytical survey is experimentally studied. Free surface velocity measurements by the electro-magnetic technique are performed on a 75 μm-thick aluminum coating stuck on a 1.5 mm-thick copper plate irradiated by various laser intensities in water confined geometry. A debonding threshold is observed on the records. © 1998 American Institute of Physics.
  AIP Conference Proceedings. 07/1998; 429(1):985-988.
• Article: Shock profile induced by short laser pulses

  S. Couturier, T. de Resseguier, M. Hallouin, J. P. Romain, F. Bauer
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  ABSTRACT: Standard 25‐μm‐thick polyvinilydene fluoride (PVDF) piezoelectric gauges and new 450‐μm‐thick P(VDF 70%, TrFE 30%) piezoelectric copolymer have been used to record shock profiles at the back face of metallic targets irradiated by laser pulses of 2.5 and 0.6 ns duration at a 1.06 μm wavelength. The records are fully explained with simplified space–time diagram analysis. The pressure profile applied at the front face of the target has been determined from these records combined with numerical simulations of wave propagation through the target. A numerical code describing the interaction of laser with matter (FILM) has also been used for computing the applied pressure. Both methods lead to very close results. The peak pressure dependence on incident laser intensity is determined up to 30 GPa at 10¹² W/cm². © 1996 American Institute of Physics.
  Journal of Applied Physics 07/1996; · 2.17 Impact Factor
• Article: Some applications of laser-induced shocks on the dynamic behavior of materials

  M. Boustie, T. De Rességuier, M. Hallouin, A. Migault, J.P. Romain, D. Zagouri
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  ABSTRACT: High-power pulsed lasers are used widely nowadays as shock generators. They settle as a complementary technique to the conventional shock generators by the high peak pressure and short duration shocks they deliver. They are used to investigate the feasibility of new industrial processes and to get information on the behavior of matter in specific conditions of extremely high strain rate. In this paper, some studies about typical applications of laser shocks are presented: surface densification of porous materials, spallation in ductile and brittle materials, α-ε phase change in iron, and an estimate of the relaxation time for this transition. Laser shock experiments provide additional data on the dynamic behavior of materials at the nanosecond time scale.
  Laser and Particle Beams 05/1996; 14(02):225 - 235. · 1.62 Impact Factor
• Article: Shock pressure and free surface velocity measurements in confined interaction — Response of new VF2/VF3 piezoelectric gauges

  M. Boustie, S. Couturier, J.P. Romain, D. Zagouri, H. Simonnet
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  ABSTRACT: To determine the peak pressure induced versus the incident intensity of a neodymium (Nd) glass pulsed laser, with a duration of 25 ns in glass confined geometry, two methods have been comparatively used. Free surface velocity measurements have been performed using an electromagnetic gauge. The results are compared with pressure measurements realized at the back of irradiated aluminum targets with the use of polyvinylidene fluoride (PVDF) gauges. Both diagnostics provide consistent results. The measurements of peak pressure as a function of laser irradiance are used to determine the calibration curve (current density versus loading pressure) for new VF2/VF3 copolymer shock gauges used in this lasermatter interaction configuration. These experimental set-up deliver time resolved measurements that are interpreted by the shock-propagation phenomena.
  Laser and Particle Beams 05/1996; 14(02):171 - 179. · 1.62 Impact Factor
• Article: Laser driven shock pressure measurements by VF2/VF3 and PVDF gages for pulses of 2.5ns up to 1012 W/cm2

  S. Couturier, M. Boustie, T. de Résséguier, M. Hallouin, J. P. Romain
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  ABSTRACT: Thick 450 μm piezoelectric VF2/VF3 copolymer and thin 25 μm PVDF gages have been used to measure the induced pressure history at the back face of aluminum and copper targets irradiated by infra-red laser pulses† of 2.5 ns with intensities up to 7.1011 W/cm2. The measured pressures in the gages infer pressures up to 200 kbar on the front face of the target. The whole shock pressure temporal pressure profile applied on the front face of the targets is determined roughly by using the laser matter interaction hydro-code FILM. The modifications to bring to this profile in order to fit the experimental record via the simulation of the propagation of the applied profile into the set-up are very limited. The comparison of the applied peak pressure given by simulation of laser matter interaction and the experiment deduced one is also rather good. These results give the peak pressure versus the incident intensity under these laser irradiation conditions and assess the possibility to use this kind of gages as a measurement device for high amplitude with rapid evolution shocks. © 1996 American Institute of Physics.
  AIP Conference Proceedings. 05/1996; 370(1):1097-1100.
• Article: Microstructural investigation of quartz submitted to ultra-short shock loading

  P. Cordier, J. C. Doukhan, A. Migault, J. P. Romain
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  ABSTRACT: A high-energy pulsed laser was used to induce very short (2 ns) pressure pulses in quartz single crystals. The microstructure of recovered specimens was characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy. Whatever the peak pressures (20–90 GPa), the shocked materials showed no shock defects (amorphous lamellae, Brazil twins, etc.). The microstructure was dominated by fracturing. The present study thus suggests that for very short pulse durations, quartz can be loaded at pressures well above the Hugoniot elastic limit without undergoing solid-state amorphization. The behaviour of quartz is purely elastic-brittle.
  Journal of Materials Science 12/1994; 30(16):4009-4013. · 2.02 Impact Factor
• Article: Shock waves and acceleration of thin foils by laser pulses in confined plasma interaction

  J. P. Romain, P. Darquey
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  ABSTRACT: The process of shock wave generation and shock evolution in a solid target by confined laser plasma, in the range 10⁸–10¹⁰ W/cm² incident intensity, is analyzed with the use of computer simulations. Predicted variations of plasma pressure are consistent with theoretical results from simple analytical models and with experimental data. The simulations also provide a complete description of various effects such as target or confinement thickness and acceleration of thin foils.
  Journal of Applied Physics 09/1990; · 2.17 Impact Factor
• Article: Two‐dimensional study of shock breakout at the rear face of laser irradiated metallic targets

  F. Cottet, L. Marty, M. Hallouin, J. P. Romain, J. Virmont, R. Fabbro, B. Faral
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  ABSTRACT: The two‐dimensional propagation dynamics of laser‐driven shock waves in solids is studied through the analysis of the shock breakout at the rear face of the target for a set of materials and laser intensities. The laser shock simulations were carried out by means of a two‐dimensional hydrodynamics code in which the laser‐ablation pressure is replaced by an equivalent pressure pulse. It is shown that the two‐dimensional code is a very useful tool to analyze laser‐shock experiments where two‐dimensional effects arise from a finite laser‐spot size or a heterogeneous energy deposition.
  Journal of Applied Physics 12/1988; · 2.17 Impact Factor
• Article: Experimental evidence of the generation of multi-hundred megabar pressures in 0.26 μm wavelength laser experiments

  R. Fabbro, B. Faral, J. Virmont, H. Pepin, F. Cottet, J. P. Romain
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  ABSTRACT: A 9 μm thick aluminium foil is accelerated to a velocity of about 160 km/s by a laser of 0.26 μm wavelength and intensity of 1015 W/cm2 and collides with an aluminium impact foil. The measurement of the velocity of the induced shock wave in the impact foil, using a step method at the rear of the impact foil, gives pressures in the multi-hundred megabar range. The dynamics and constraints of this shock wave are presented and the effect of X-ray preheating, which can be important at this laser wavelength, is discussed.
  Laser and Particle Beams 07/1986; 4:413 - 419. · 1.62 Impact Factor
• Article: Enhancement of a laser‐driven shock wave up to 10 TPa by the impedance‐match technique

  F. Cottet, M. Hallouin, J. P. Romain, R. Fabbro, B. Faral, H. Pepin
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  ABSTRACT: We have used the impedance‐match technique to increase the shock pressure induced in an aluminum‐gold target by a laser of 0.26 μm wavelength and intensity of 10¹⁵ W/cm². With incident pressures of 4.5 TPa in aluminum, transmitted pressures of 10⁺⁴ -3.5 TPa in gold are inferred from shock velocity measurements. Experiments on gold‐aluminum targets, with the same irradiation conditions, verify the shock pressure decrease due to the reverse impedance‐match effect.
  Applied Physics Letters 11/1985; · 3.84 Impact Factor
• Article: Experimental study of laser acceleration of planar targets at the wavelength 0.26 μm

  R. Fabbro, B. Faral, F. Cottet, J. P. Romain
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  ABSTRACT: The main characteristics of accelerated aluminum targets, which are the target velocity, the uniformity of the acceleration and the backside temperature have been studied in laser experiments performed at wavelength 0.26 μm with an absorbed flux of a few 10¹³ W/cm², in 400‐ps pulse duration by using the double‐foil technique and an optical pyrometry diagnostic: The ablation pressure was inferred from the velocity measurements. The uniformity of the acceleration was shown to be controlled by the hot spots in the focal spot, and the importance of studying the smoothing of laser inhomogeneities for accelerated targets with large ablated fractions was emphasized. The observed dependence of the backside temperature as a function of the initial foil thickness is discussed in the light of shock wave heating and radiative heating.
  Journal of Applied Physics 01/1985; · 2.17 Impact Factor
• Article: Measurements of laser shock pressure and estimate of energy lost at 1.05‐μm wavelength

  F. Cottet, J. P. Romain, R. Fabbro, B. Faral
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  ABSTRACT: Laser‐driven shock pressures at 1.05‐μm wavelength have been evaluated from measurements of shock transit time through aluminum foils by streak camera records of shock luminosity at the back face of the foil. An ablation pressure of 0.3 TPa is obtained for 1.2×10¹⁴ W/cm² laser pulses focused on 300‐μm spot diameter and 0.55 TPa for 3.5×10¹⁵ W/cm² laser pulses focused on 60‐μm spot diameter. These results, compared with theoretical values, show an important loss of energy, attributed to two‐dimensional effects. The ratio of effective energy for compression to incident energy is estimated to be 12% for 1.2×10¹⁴ W/cm² experiments and only 1% for 3.5×10¹⁵ W/cm² experiments.
  Journal of Applied Physics 07/1984; · 2.17 Impact Factor
• Article: Formation and decay of laser-generated shock waves

  F. Cottet, J. P. Romain
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  ABSTRACT: The process of formation and decay of laser-generated shock waves is described by a hydrodynamic model. Measurements of shock velocities are performed on copper foils for incident intensities between 3×1011 and 3×1012 W/cm2, with the use of piezoelectric detectors. Maximum induced pressures are found between 0.5 and 1.2 Mbar in the intensity range considered. Analysis of the results with the shock-evolution model outlines the importance of the decay process of laser-generated shocks.
  Phys. Rev. A. 25(1).
• Article: Laser shock experiments with nanoseconds pulses: a new tool for the reproduction of shock defects in olivine

  F. Langenhorst, M. Boustie, A. Migault, J.P. Romain
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  ABSTRACT: Laser shock experiments with olivine have been carried out in order to test the capability of this new experimental approach to produce known shock defects in olivine. To determine the shock conditions, numerical simulations of experiments have been undertaken, indicating the generation of a rapidly decaying shock wave with an initial pressure of 60 GPa and a duration of 5 ns. The pressure prevailed thus distinctly shorter than in conventional shock experiments with explosives or light gas guns (0.1–1 μs). Despite this shorter pressure pulse in our laser experiment, TEM revealed that a high density of dislocations and planar fractures was activated in olivine up to a depth of 30 μm. A drastic decrease of dislocation and fracture densities observed deeper in the sample is attributed to the decay of the shock wave. The dislocation systems and the orientations of planar fractures in our experiment are identical to those found in naturally shocked olivine. The TEM observations indicate furthermore that fractures in olivine are the sources of dislocations and that the stress field around fractures determines which slip system is activated. Our study demonstrates that laser shock experiments are not only a powerful new tool in the reproduction of shock defects but also an indispensable tool to understand better the role of time in impact processes and the formation mechanisms of shock defects.
  Earth and Planetary Science Letters.
• Article: Simulation laser d'impacts de particules de très grande vitesse

  J.-P. Bibring, F. COTTET, M. HALLOUIN, Y. Langevin, J.P. ROMAIN
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  ABSTRACT: Silicated micrometeorites (mass : 1/10 μg) impacting aluminium target are simulated with a neodyme pulsed laser, producing a maximum laser pulse energy of 100 in a few ns. The simulated micrometeorites velocities are in the range of 5 km/s-45 km/s; the mass loss ratio, Km, is related to particle velocity Vp by Km = 1.17 V1.52 p. Le laser au néodyme du GRECO I.L.M. délivrant des impulsions de l'ordre de 100 J en quelques ns, nous a permis de simuler des impacts de micrométéorites silicatées de quelques dixièmes de μg, de vitesse comprise entre 5 et 45 km/s, sur une cible d'aluminium. Les cratères produits dans la cible sont hémisphériques, et le rapport Km, de la masse éjectée sur la masse de la particule incidente simulée, varie avec la vitesse d'impact Vp selon la loi Km = 1,17 V 1,52p.
  http://dx.doi.org/10.1051/jphyslet:01983004405018900.
• Article: Influence des conditions initiales sur l'évolution d'une onde de choc induite par impulsion laser

  F. COTTET, J.P. ROMAIN
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  ABSTRACT: The evolution of a high amplitude laser-generated shock in a solid target is described by the use of a hydrodynamic model. In comparison with a previous model, this one takes into account the front face target propagation due to the ablation pressure effect. This model is also used to study the initial pressure profile effect on the shock wave decay. L'évolution d'un choc de forte amplitude induit par une impulsion laser dans une cible solide est décrite à l'aide d'un modèle hydrodynamique, précisant un modèle antérieur par la prise en compte du déplacement de la surface avant de la cible sous l'effet de la pression d'ablation. Ce modèle est également utilisé pour étudier l'influence du profil initial de pression sur l'amortissement de l'onde de choc au cours de sa propagation.
  http://dx.doi.org/10.1051/jphyslet:01983004407023500.