Thibaut de Resseguier

Investigation of laser shock induced ductile damage at ultra-high strain rate by using large scale MD simulations

Laser driven shocks allow an investigation of materials behavior at very high strain rate (107s-1) and present a great interest for research applications. Microscopic simulations of ultra-short laser driven shock on micrometric Tantalum single-crystals have been performed by using the CEADAM Classical Molecular Dynamics code. This method, complementary to continuum models, provides an analysis the microscopic processes related to damage (ductile pore nucleation and growth) which occurs during spallation. These results are compared to spallation experimental data (VISAR signals, micro-tomography) obtained with the LULI100TW femtosecond laser in order to validate the MD behavior. Moreover, in the framework of a multi-scale approach, we show the possibility to use MD simulation to fit macroscopic damage models. This method is illustrated with an application to the parameters determination of Kanel damage model parameters. This also shows the high strain rates involved during damage process, around 109s-1, ca...

Damaging of materials by bi-dimensional dynamic effects

Laser shocks are most often used to produce uniaxial stress and strain into materials by irradiating a spot diameter conventionally admitted at least three times larger than the thickness of the shocked sample. By reducing the laser spot versus the sample thickness, 2D lateral waves are created earlier and their crossing during propagation stages generates traction which can yield to voids into materials (near the front loaded face). This phenomenon has been evidenced by an experimental study, including VISAR measurements which exhibit the signature of the fracture generated by these 2D effects. Numerical simulations with the explicit finite element code RADIOSS clearly evidence the origin of the 2D effects on VISAR measurements. This different mode of damaging materials by laser lateral waves can act simultaneously with the classical laser spallation produced by the uniaxial propagation (shock wave reverberation crossing the unloading). This opens new discussed prospects for the development of 2D damage ...

Laser-driven quasi-isentropic compression experiments and numerical studies of the iron alpha-epsilon transition in the context of planetology

The iron alpha-epsilon transition is one of the most studied solid-solid phase transition. However, for quasi-isentropic compression, the dynamic and the influences of this transition on the high-pressure states of iron are still unknown. We present experimental results and numerical simulations to study these effects. Experiments performed at LULI2000 and the Janus laser facility (LNLL), using two different ramp shapes and different compression rates allowed to study the dynamic of the alpha-epsilon transition. We have observed the transition at particle velocity ranging from 0.25 km/s to 0.52 km/s depending on the compression rate. Depending on the ramp, either a shock formation was observed (high compression rate) at the transition or a flat plateau whose duration is function of compression rate. Increasing the compression rate leads to a smaller plateau duration. These results are important for reproducing Earth and Super-earth core conditions (2-15Mbar, 5- 15000K) on laboratory where the quasi-isentropic compression is the most promising experimental scheme.

Wave Propagation and Dynamic Fracture in Laser Shock-Loaded Solid Materials

Shock wave loading of solid materials results in specific damage processes at high strain rates. The most widely studied of these processes is probably spall fracture (e.g. Antoun et al., 2002, and references therein), which arises from tensile stresses generated by the interaction of release waves within the material upon reflection of a compressive pulse from a free surface or from an interface with a layer of lower acoustic impedance. If such tensile stresses exceed the dynamic strength of the material, they cause the nucleation and growth of micro-voids or micro-cracks which may eventually coalesce to form a macroscopic fracture and lead to the ejection of one or several fragments (spalled layers) from the sample. Spall damage and wave propagation are tightly coupled. On one hand, the creation of new free surfaces accompanying damage development induces stress relaxation which gives rise to recompression waves. Such waves can be detected in time-resolved velocity (Antoun et al., 2002; Tollier et al., 1998) or piezoelectric (De Resseguier et al., 1997) measurements, and their analysis provides very rich data on the fracture process (location, time and tensile stress at damage initiation, rate of the damage growth, thickness of the spalled layer...). On the other hand, spall fracture results from wave interaction, so that post-test observations of the residual damage in recovered samples (location, sizes and shapes of the damages zones, fracture surface morphology...) may provide key information on the propagation of compression and release waves prior to failure. In this chapter, we illustrate this second, more original statement with experimental results obtained under laser driven shock loading. Intense irradiation of an absorbing target by a high power pulsed laser produces the vaporization of a thin layer of material, transformed into a plasma cloud, whose expansion toward the laser source induces by reaction a compressive pulse into the solid target. The main specificity of this technique is the very short time of pressure application (typically a few ns) compared to other shock generators such as plate impacts or explosive loading, where the duration of the pressure load is usually of μs-order. This difference makes laser shocks less destructive than those more conventional techniques, and favours sample recovery for post-shock analyses of residual damage. In a first example, spall fracture observed in laser shock-loaded single crystal quartz provides very clear evidence of the strong effect of crystal anisotropy on stress wave Source: Wave Propagation in Materials for Modern Applications, Book edited by: Andrey Petrin, ISBN 978-953-7619-65-7, pp. 526, January 2010, INTECH, Croatia, downloaded from SCIYO.COM

Behavior of basalt under laser-induced shock-wave application to the planetary hypervelocity impact effect

This paper presents the results of an investigation of the impact of laser-induced shock on basalt samples in a water confinement regime. In order to observe the effect of laser shock-wave propagation, in this material, the rear free surface velocity is measured by a velocimetry interferometer system for any reflector under various specified conditions. Parameters for an elastoplastic constitutive law and the Kanel’s damage model are provided and have been set up in such a way to ensure good correlation between numerical simulations and laboratory experiments. These resultant material properties, identified for the basalt sample studied here, could be used in future investigations looking to further correlating residual effects in material with pressure levels induced by water confined laser-matter interaction. This is of particular importance in meteoritics and planetary science due to the fact that hypervelocity impacts represent a major event taking place in the solar system, and shock waves generated ...

Gel versus aerogel to collect high velocity ejectas from laser shock-loaded metallic targets for postrecovery analyses

Soft recovery of fast objects is an issue of considerable interest for many applications involving shock wave loading, such as ballistics, armor design, or more recently laser-driven inertial confinement fusion, where the characterization of the debris ejected from metallic shells subjected to intense laser irradiation conditions the design of the experiments. In this work, we compare the high velocity ejecta recovery efficiency of two materials: silica aerogel (density 0.03 g/cm3), which has been used as fragment collector for many years, and “varagel” (density 0.9 g/cm3), which we have tested recently in laser shock experiments. Ejected fragments have been recovered in both types of collectors. Then, samples have been analyzed by X-ray tomography at the European Synchrotron Radiation Facility (ESRF). Three-dimensional reconstructions of the fragments populations have been achieved, and quantitative comparisons between both collecting materials, used in the same conditions, have been performed.

Behaviour of basalt under shock-wave induced by laser: Application to planetary hypervelocity impact effect

This paper presents the study of basalt under shock induced by laser in water confinement regime. A model is developed to reproduce rear free surface velocity measured by Velocimetry interferometer for any reflector. Computation is in agreement with experiments. Material properties of basalt could be used for works aiming to correlate residual effects in material with pressure levels induced by water confined laser-matter interaction.This paper presents the study of basalt under shock induced by laser in water confinement regime. A model is developed to reproduce rear free surface velocity measured by Velocimetry interferometer for any reflector. Computation is in agreement with experiments. Material properties of basalt could be used for works aiming to correlate residual effects in material with pressure levels induced by water confined laser-matter interaction.