Unraveling the simultaneous shock magnetization and demagnetization of rocks

International audienceIn the natural case of an hypervelocity impact on a planetary or asteroidal surface, two competing phenomena occur: partial or complete shock demagnetization of pre-existing remanence and acquisition of shock remanent magnetization (SRM). In this paper, to better understand the effects of shock on the magnetic history of rocks, we simulate this natural case through laser shock experiments in controlled magnetic field. As previously shown, SRM is strictly proportional to the ambient field at the time of impact and parallel to the ambient field. Moreover, there is no directional or intensity heterogeneity of the SRM down to the scale of ∼0.2mm. We also show that the intensity of SRM is independent of the initial remanence state of the rock. Shock demagnetization and magnetization appear to be distinct phenomena that do not necessarily affect identical populations of grains. As such, shock demagnetization is not a limiting case of shock magnetization in zero field

On the crystal lattice parameters of graphite-like phases of the B-C system

The structure of graphite-like BCx phases (x = 1, 1.5, 3, 4, 32) has been studied using conventional X-ray diffraction. The results have been obtained, which unambiguously point to turbostratic (one- dimensionally disordered) structure of all phases under study. The crystal lattice parameters, sizes of coherent scattering domains, and microstrain values have been defined, which have allowed us to find a correlation between the structure and stoichiometry of the phases synthesized at the same temperature

Effects of the α-ε phase transition on wave propagation and spallation in laser shock-loaded iron

International audienc

Influence of elevated temperature on the wave propagation and spallation in laser shock-loaded iron

International audienceLaser shock experiments have been performed on preheated iron samples to address the role of initial temperature on the elastic limit, wave propagation, and spall fracture in this metal over the temperature range 300–1000 K at very high expansion rates of the order of 3×106 s−1. Time-resolved measurements of the free-surface velocity indicate a slight, roughly linear decrease of the spall strength with increasing temperature, accompanied by a clear change from brittle to ductile fracture behavior evidenced from post-shot examination of the recovered samples. The results are discussed on the basis of simulations accounting for laser-matter interaction, pressure wave propagation, and subsequent polymorphic transformations throughout the sample thickness. Over the explored range of loading conditions, the occurrence of such transformations prior to spallation, which takes place near the free-surface under tensile loading after reversion to the α phase, does not seem to strongly affect dynamic fracture

DYNAMIC FRACTURE OF GLASS MATERIALS UNDER SHOCKWAVES INDUCED BY PULSED LASER IRRADIATION AT VERY SHORT DURATIONS

The study of fracture induced by a laser-driven shockwave loading of solid targets leads to an unusual range of stress (hundreds of GPa) and pulse duration (a few ns). The present paper deals with the spallation of glass materials in this specific range. An analytical and numerical study reveals the influence of various parameters upon dynamic fracture, which is essentially characterized by the thickness of the spalled layer. Preliminary experimental results on glass targets irradiated by laser pulses are presented. The observed behaviour is very different from the one of ductile materials like aluminum or copper

ÉTUDE DE L'ÉCAILLAGE DANS DES MATÉRIAUX DUCTILES ET FRAGILES SOUS L'ACTION D'UNE ONDE DE CHOC DE DURÉE TRÈS FAIBLE INDUITE PAR UNE IMPULSION LASER

L'utilisation des ondes de choc générées par irradiation laser permet d'étendre l'étude de l'endommagement dynamique à des amplitudes de choc élevées (jusqu'à quelques centaines de GPa) et des durées de maintien très courtes (quelques nanosecondes). Ce travail, consacré aux matériaux de type fragile en comparaison avec les matériaux de type ductile, présente une étude analytique et numérique des effets des différents paramètres (durée de l'impulsion, pression induite, épaisseur de la cible, ...) et une étude expérimentale de l'écaillage de cibles de verre irradiées par impulsion laser.Laser induced shock wave technique provides a useful means for studying the dynamic fracture in an unusual range of stress and loading duration : respectively up to few hundreds of GPa and less than 10 ns. This paper presents the results of an experimental and numerical study of laser-shock spallation in brittle materials with the comparison with ductile material behaviour. The present investigation has two objectives : first, to study the effect of various parameters (pulse duration, induced pressure, target thickness, ...) and, second, to show preliminary experimental results on glass targets irradiated by laser pulses

Ballistic properties of debris produced by laser shock-induced micro-spallation of tin samples

International audienceDynamic fragmentation in the liquid state after melting under shock compressionor upon release leads to the ejection of a cloud of droplets. This phenomenon, called microspallation,remains essentially unexplored in most metals. We present laser shock experimentsperformed on tin, to pressures ranging from about 60 to 220 GPa. Experimental diagnosticsinclude skew Photonic Doppler Velocimetry (PDV) measurements of the droplets velocities,transverse observations of the expanding cloud of droplets, and soft recovery of ejecta withina low density gel. Optical microscopy of the gel reveals the presence of droplets whichconfirm shock-induced melting prior to fragmentation. To quantify size distribution of thedebris, 3D X-ray micro-tomography has been performed at the ESRF synchrotron facility inFrance (similar to US Advanced Photon Source), where sub-micrometer resolution could beachieved. In this paper, the resulting velocity and size distributions are presented andcompared with theoretical predictions based on a one-dimensional description accounting forlaser shock loading, wave propagation, phase transformations, and fragmentation.Discrepancies between measured and calculated distributions are discussed. Finally,combining size and velocity data provides estimates of the ballistic properties of debris andtheir kinetic energy, which are key issues for anticipating the damage produced by theirimpacts on nearby equipments