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

Laser Shock Adhesion Test (LASAT) of electron beam physical vapor deposited thermal barrier coatings (EB-PVD TBCs)

International audienceDamage prediction, adhesion strength and remaining lifetime of TBC are highly important data for understanding and preventing TBC spallation on blades. LAser Shock Adhesion Test (LASAT) is a powerful method to measure adhesion of coating due to its rapidity, simplicity and capabilities to distinguish different strength levels and the easy damage observation in case of TBCs. A new protocol of LASAT has been introduced in order to measure the adhesion level of the ceramic coating from the exploitation of the two-dimensional effects that promotes a shock wave pressure-dependent size of the damage. Finite element modeling, taking into account the TBCs dimensions, showed the edges effect on interfacial stress applied by laser shock

Etude par choc laser de l'adhérence de barrières thermiques aéronautiques

National audienceL'estimation de la durée de vie des barrières thermiques aéronautiques (BT) déposées sur les aubes de turbines haute pression nécessite de comprendre les mécanismes induisant l'endommagement entre la sous-couche et la zircone. Le LASAT, LAser Shock Adhesion Test ou essai d'adhérence par choc laser, est une technique exploitant tout son potentiel dans le cas des BTs, en particulier par sa rapidité, simplicité et au comportement optique de la couche de zircone. Ce dernier avantage permet de dimensionner l'endommagement généré sans réaliser de coupes métallographiques. Un nouveau protocole de l'essai LASAT a été mis en place utilisant les ondes de choc bidimensionnelles et exploitant la dépendance entre l'intensité du choc appliqué, le niveau d'adhérence du dépôt, et la dimension de la fissure générée

State-of-the-art laser adhesion test (LASAT)

This paper proposes a state-of-the-art laser adhesion test. It consists of testing material interfaces with laser-driven shock wave. Since the first demonstration in the 1980s by Vossen, many studies and developments have been done. This paper presents recent experiments and developments on the basic physics involved. Results show the ability of the technique to perform a quantitative adhesion test for a wide range of materials and configurations. Edge effect principle and ultra-short shock wave give perspectives for new applications for multi-layer combination of material. Fundamental principles are evidenced through experiments on bulk ductile materials before demonstrating their application to coated systems

Etude du comportement dynamique de matériaux sous choc laser subpicoseconde

Laser driven shocks allow to investigate materials behavior at high strain rate and presents a great interest for research applications, but also for industry fields. The latest laser technologies evolutions provide an access to shorter regimes in durations, going below the picosecond. This work, which results from a collaboration between the P' institute, the PIMM laboratory and the CEA‐DAM, is dedicated to characterize the metallic material behavior in this ultra‐short mode, (aluminium, tantalum), leading to extreme dynamic solicitation in the target (>107s‐1). The study includes the validation of experimental results obtained on the LULI 100TW facility by comparison with numerical model. First, the study is orientated to the femtosecond (fs) laser‐matter interaction, which is different from what happens in nanosecond regime. Indeed, the characteristic duration scale is comparable to several molecular phenomena like non‐equilibrium electrons‐ions states. The aim is to determine the equivalent pressure loading induced by the laser pulse on the target. Then, we have studied the shock wave propagation within the target and particularly its pressure decay, particularly strong in this regime. In this configuration, the spalls observed are thin, a few μm order, and show a planar rupture morphology. The results obtained by post‐mortem observation show that the spall thickness is thinner if the target thickness is reduced. The spalls are characterized by the VISAR measurement. Within the framework of dynamic damage modeling and rupture criteria dimensioning, particularly those which have been validated in the ns regime as Kanel, shots with different thicknesses have been carried out to determine the damage properties in function of strain rate and validate the parameters by prolongation to the ultra‐shorts modes. Then, the study has been generalized to the 2D propagation waves, which can explain the spall diameter evolutions. Meanwhile, microscopic simulations of ultra‐short laser driven shock on micrometric single‐crystal metals have been performed by using the CEA‐DAM molecular dynamic codes. This method, complementary to continuum models, provides an analysis the microscopic processes related to damage (ductile pore nucleation and growth). The high strain rates involved, around 109s‐1, allow to approach the inter‐atomic theoretical cohesion threshold. By the end, the results obtained in both ultra‐short and 2D regimes are of great interest for applications such as the adhesion test of thin coating by laser driven shock (LASAT), open the way to news LASAT extensions. As example, various fields in the industry (optics, electronics...) use micrometric coatings, but there are actually few ways to characterize their mechanical properties precisely. The transposition of the LASAT process to the fs regime has been tested on multi‐layer solar‐cell‐like, and has confirmed the possibility to debond sub‐micrometric layers and determine its adhesion threshold.Les chocs induits par laser de puissance permettent d'investir le comportement hautement dynamique des matériaux, d'un grand intérêt tant pour la recherche fondamentale que pour l'industrie. L'évolution des technologies laser ces dernières années a permis d'accéder à des régimes plus courts, en dessous de la picoseconde. L'objectif de ce travail, résultat d'une collaboration entre l'institut P', le PIMM et le CEA‐DAM est de caractériser le comportement sous choc de matériaux métalliques (Aluminium, Tantale,...) dans ce régime ultra‐bref, conduisant à des sollicitations dynamiques extrêmes (>107s‐1). L'étude repose sur la comparaison et la validation de modèles numériques à des résultats expérimentaux obtenus sur la chaîne 100TW du LULI. Cette caractérisation passe dans un premier temps par l'étude de l'interaction laser‐matière afin caractériser le chargement équivalent en pression sur la cible. Les processus en régime ultra‐bref sont différents de ce qui est connu en régime nanoseconde : en effet, l'échelle de temps, quelques picosecondes, est du même ordre que bon nombres de phénomènes moléculaires tel que le déséquilibre électrons‐ions. Ensuite, nous avons étudié l'évolution de l'onde de choc et son amortissement, très prononcé dans ce régime. L'écaillage dans une telle configuration se produit par couches très minces (quelques μm) et régulières dans ce régime. L'endommagement obtenu est caractérisé par la mesure VISAR. Les résultats obtenus par observations post‐mortem jusqu'à présent montrent que plus l'épaisseur de cible est faible, plus l'épaisseur d'écaille diminue, pouvant atteindre l'échelle du micron. Dans le cadre de la modélisation de l'endommagement et le dimensionnement des critères d'endommagement utilisés et éprouvés en régime nanoseconde (Kanel), des essais à différentes épaisseurs de cible ont été réalisés afin d'observer les conséquences d'une variation de vitesse de déformation sur l'endommagement, et généraliser le modèle de Kanel au régime ultra‐bref, et plus généralement en fonction de la vitesse de déformation. L'ensemble des résultats relatifs à l'endommagement est généralisé à des configurations 2D, permettant notamment de caractériser l'évolution du diamètre d'écaille. En parallèle, des simulations microscopiques par dynamique moléculaire de choc laser ultra‐bref sur des cibles monocristallines de Tantale à l'échelle du micron ont été menées au CEA‐DAM donnent un point de vue complémentaire des processus microscopiques liés à l'endommagement à des vitesses de déformation aux abords de la limite de cohésion théorique. Les résultats obtenus sur les chocs ultra‐brefs et 2D présentent un grand intérêt pour le développement du test d'adhérence de revêtements par choc laser (LASAT), offrant la possibilité de nouvelles extensions pour le procédé LASAT. Par exemple, de nombreux domaines industriels utilisent des revêtements micrométriques (optique, électronique, ...) mais il existe peu de méthodes pour caractériser leurs propriétés avec fiabilité. Des essais de transposition de LASAT en régime femtoseconde sur des cellules photovoltaïques ont démontré la possibilité d'éjecter des revêtements submicrométriques et caractériser leur seuil d'adhérence

Experimental and numerical study of the tantalum single crystal spallation

Using X-microtomography and non equilibrium classical molecular dynamics, we present a study of the elementary processes of spallation of single crystal tantalum. The single crystal is illuminated by a laser pulse which induces the propagation of a strong unsustained shock. The analysed data mainly are number and shape of pores resulting from the tensile inside the material when the incident shock reflects on the opposite face. Experimental pores size distribution exhibits two power laws attributed to the growth and the coalescence stages. The average pore shape is ellipsoid with main axis along the shock axis propagation. This first part is completed by a large scale molecular dynamics simulation mimics at reduced scale the real experiment. After preliminary calculations validating the chosen potential function the formation and shock propagation is detailed. Then we extract from the simulation similar data than in experiment. The pores size distribution shows three power laws identified as the nucleation, the growth and the coalescence stages. The slopes of the two last stages are very similar to the experimental one, confirming the scale invariance of this data as suggested by their analytical form. The general pore shape also is close to the experiment shape but with a different orientation (perpendicular to the shock propagation axis)

Behaviour of metals at ultra-high strain rate by using femtosecond laser shockwaves

The mechanical behavior of materials under extreme conditions can be investigated by using laser driven shocks. Actually, femtosecond (fs) technologies allow to reach strong pressures over a very fast duration. This work is dedicated to characterize metals behavior in this ultra-short mode, (aluminum, tantalum), leading to an extreme dynamic solicitation in the target (>107s−1). The study includes the validation of experimental results obtained on the LULI 100TW facility by comparison with numerical model. Three modeling steps are considered. First, we characterize the pressure loading resulting from the fs laser-matter interaction, different from what happens in the classical nanosecond regime. Then, the shock wave propagation is observed through the target and particularly its pressure decay, strong in this regime. The elastic-plastic influence on the shock attenuation is discussed, particularly for tantalum which has a high elastic limit. Dynamic damage appears with spallation. Experimentally, spallation is characterized by VISAR measurements and post-test observations. Shots with different thicknesses have been carried out to determine the damage properties in function of strain rate. We show in this work that a simple instantaneous rupture criterion is not sufficient to reproduce the damage induced in the sample. Only the Kanel model, which includes damage kinetics, is able to reproduce experimental data (VISAR measurements, spall thickness). A generalization of this model to any strain rate can be performed by confronting these results to other shock generators data (ns laser driven shocks, plate impacts). One remarkable result is that every Kanel parameters follows a power law with strain rate in dynamic regime (105 to 108s−1) for both aluminum and tantalum

Etude du comportement dynamique de matériaux sous choc laser sub-picoseconde

Le travail présenté a pour objectif d'étudier le comportement de métaux soumis à un choc laser femtoseconde, amenant à des sollicitations dynamiques extrêmes (>107s-1). Dans ces conditions, on peut découpler les phénomènes en 3 parties : l'interaction laser-matière ultra-brève donnant naissance à l'impulsion en pression, la propagation de l'onde et sons atténuation dans la cible, très prononcée en raison de la brièveté du chargement et l'endommagement en face arrière par écaillage. Les modèles utilisés pour restituer ce comportement ont été validés dans ce régime par comparaison avec des données expérimentales de tirs effectués sur le laser fs 100TW du LULI (VISAR, post-mortem). En raison des ordres de grandeurs expérimentaux impliqués, proches de ceux employés en Dynamique Moléculaire ( m et ps), une étude microscopique de l'écaillage ductile a été effectuée au CEA-DAM. Les résultats obtenus, cohérents avec la physique des chocs et de l'endommagement, permet d'explorer des régimes ultra-dynamiques (>109s-1) où le seuil d'endommagement approche la force théorique de décohésion interatomique. Toutes les données déduites permettent de décrire le comportement d'un modèle en fonction de la vitesse de déformation, dans notre cas Kanel. L'ensemble de l'étude a ensuite été généralisé à des configurations 2D, permettant notamment de caractériser l'évolution du diamètre d'écaille, source complémentaire d'informations sur l'endommagement. Ce type d'approche peut être transposé à des cibles multicouches pour déterminer l'adhérence de revêtements (Procédé LASAT). Les sources ultra-brèves ont permis de provoquer la décohésion des couches sub-micrométriques et mesurer leur adhérence.This work consists in studying the behavior of metals submitted to femtosecond laser driven shocks, leading to highly dynamic solicitations (>107s-1). In these conditions, phenomena can be separated into 3 parts : ultra-short laser matter interaction which generates the pressure pulse, wave propagation and decay, very strong because of brief loading duration, and finally damage mechanics induced by spallation close to the target free surface. The numerical models used to reproduce this behavior have been validated in this regime by comparison with experimental data obtained on the LULI 100TW fs laser facility (VISAR, sample microscopy...). By considering the involved space-time characteristic scales, close to those actually available in molecular Dynamic approach ( m and ps), a microscopic study of ductile spallation has been performed with CEA-DAM. The related results are consistent with both shock and damage physics. Moreover, they allow to explore ultra-dynamic regimes (>109s-1) where the damage threshold is close to the theoretical interatomic decohesion force limit. All the data obtained make possible to describe a damage model behavior in function of strain rate, Kanel in this work. The study has been then generalized for 2D configurations, giving access in particular to the spall diameter evolution characterization which constitutes a complementary information source about damage mechanisms. This kind of approach can be transposed to multilayer targets in order to determine coatings adhesion (LASAT process). The ultra-short lasers allowed to debond sub-micrometric layers and then deduce their adhesion strength.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Behaviour of metals at ultra-high strain rate by using femtosecond laser shockwaves

The mechanical behavior of materials under extreme conditions can be investigated by using laser driven shocks. Actually, femtosecond (fs) technologies allow to reach strong pressures over a very fast duration. This work is dedicated to characterize metals behavior in this ultra-short mode, (aluminum, tantalum), leading to an extreme dynamic solicitation in the target (>107s−1). The study includes the validation of experimental results obtained on the LULI 100TW facility by comparison with numerical model. Three modeling steps are considered. First, we characterize the pressure loading resulting from the fs laser-matter interaction, different from what happens in the classical nanosecond regime. Then, the shock wave propagation is observed through the target and particularly its pressure decay, strong in this regime. The elastic-plastic influence on the shock attenuation is discussed, particularly for tantalum which has a high elastic limit. Dynamic damage appears with spallation. Experimentally, spallation is characterized by VISAR measurements and post-test observations. Shots with different thicknesses have been carried out to determine the damage properties in function of strain rate. We show in this work that a simple instantaneous rupture criterion is not sufficient to reproduce the damage induced in the sample. Only the Kanel model, which includes damage kinetics, is able to reproduce experimental data (VISAR measurements, spall thickness). A generalization of this model to any strain rate can be performed by confronting these results to other shock generators data (ns laser driven shocks, plate impacts). One remarkable result is that every Kanel parameters follows a power law with strain rate in dynamic regime (105 to 108s−1) for both aluminum and tantalum