Eva Héripré

French National Centre for Scientific Research | CNRS · Section de Mécanique des matériaux et des structures

Sample-return missions allow the study of materials collected directly from celestial bodies, unbiased by atmospheric entry effects and/or terrestrial alteration and contamination phenomena, using state-of-the-art techniques which are available only in a laboratory environment—but only if the collected material stays pristine. The scarcity of outer...

The effects of dynamic predeformation on the dynamic behaviour of metallic glasses (MG) are investigated through split Hopkinson pressure bar (SHPB) tests. The results obtained on samples fractured in a single test are compared with those on samples fractured in two successive SHPB tests. They show a reduction in data scatter and an increase in max...

Al/Mo/SiC periodic and aperiodic multilayers were optimized and deposited on high groove density gratings to achieve broadband efficiency in the extreme ultraviolet (EUV). Grating efficiencies were measured by monochromatic synchrotron radiation under 5° and 45° incident angles in the wavelength ranges 17-25 nm and 22-31 nm, respectively. We study...

Silicon oxycarbide film deposited on a silicon substrate has shown superior electrical conductivity relative to its monolithic counterpart. In this work, the evolution of different microstructures detected on the SiOC film reveals its hierarchical microstructure. The existence of sp2‐hybridized carbon domains has been unambiguously confirmed by mea...

A liquid metal embrittlement specificity of three austenitic steels with increasing nickel content (304 L, 316 L and 316L(N)) is studied in liquid mercury in the axisymmetric notched geometry. Only the low nickel alloys are susceptible to LME. The crack path of an austenitic steel fracture induced by liquid mercury has been elucidated at microstruc...

Sample-return missions allow the study of materials collected directly from celestial bodies, unbiased by atmospheric entry effects and/or Earth alteration and contamination phenomena, using state-of-the-art techniques - but only if the collected material stays pristine. The scarcity of outer-space unaltered material recovered until now makes this...

Sample-return missions allow the study of materials collected directly from celestial bodies, unbiased by atmospheric entry effects and/or terrestrial alteration and contamination phenomena, using state-of-the-art techniques which are available only in a laboratory environment - but only if the collected material stays pristine. The scarcity of out...

Surface topographies can be reconstructed from backscattered electron (BSE) images captured from different detector orientations. This article presents a very general approach to this problem, in the spirit of photometric stereo methods, allowing for arbitrary BSE detector number (at least 3) and shapes. The general idea is to both determine the (n...

In this paper, we report the results of a campaign of measurements on four fragments of the CM Aguas Zarcas (AZ) meteorite, combining X‐ray computed tomography analysis and Fourier‐transform infrared (FT‐IR) spectroscopy. We estimated a petrologic type for our sampled CM lithology using the two independent techniques, and obtained a type CM2.5, in...

During additive manufacturing of alloys, just after local heat-matter interactions, a molten material undergoes rapid solidification. Then, for the rest of the building time, it is subjected to cooling/heating cycles in the solid-state i.e., solid-state thermal cycling. The thermo-mechanical forces generated during solid-state thermal cycling can t...

Diffusion bonding with Au, Cu and Sn is a technique that can be used to manufacture printed circuit boards. The mechanisms of reactive diffusion and Kirkendall void formation were studied in the Cu–Au–Sn–Cu sandwich system. The initial thickness of the Au and Sn layers was a few micrometers, corresponding to 57 mol.% Au and 43 mol.% Sn. The experim...

Sclareol, an antifungal specialized metabolite produced by clary sage, Salvia sclarea, is the starting plant natural molecule used for the hemisynthesis of the perfume ingredient ambroxide. Sclareol is mainly produced in clary sage flower calyces; however, the cellular localization of the sclareol biosynthesis remains unknown. To elucidate the site...

Precipitates in an austenitic stainless steel fabricated via any Additive Manufacturing (AM), or 3D printing, technique have been widely reported to be only Mn-Si-rich oxides. However, via Transmission Electron Microscopy (TEM) studies on a 316L stainless steel, we show that non-oxide precipitates (intermetallics, sulfides, phosphides and carbides)...

Precipitates in an austenitic stainless steel fabricated via any Additive Manufacturing (AM), or 3D printing, technique have been widely reported to be only Mn-Si-rich oxides. However, via Transmission Electron Microscopy (TEM) studies on a 316L stainless steel, we show that non-oxide precipitates (intermetallics, sulfides, phosphides and carbides)...

The measurement of thin-layer mechanical properties, like compounds generated by thermo-chemical nitriding process, is a key issue to optimize and predict the endurance of surface treatment against contact fatigue and wear. An original FIB micro-tensile test strategy involving plain and micro-notched tensile specimens is proposed. These specimens w...

The objective of this work is to demonstrate that structures with low CTE’s can also be manufactured at the micrometric scale using tradintional milling and welding using a focused ion beam (FIB). In order to reach this target, we started from previous the- oretical work reported in [8] and experimental work at the large scale, e.g. Ref. [10] where...

Scanning Electron Microscopes (SEMs) often generate images with a shaded appearance which gives a natural 3D impression. Ergo, quite a few methods to reconstruct the 3D surface topography from these using shape-from-shading methods are available in the literature. Here, a novel approach is discussed which uses BackScatter Electron (BSE) images from...

Background : Stainless Steel Dissimilar Metal Welds (SS DMW) between low-alloy steel 18MND5 and austenitic 316L stainless steel are critical junctions in the currently operating reactors because of their heterogeneous microstructure and mechanical properties. The presence of a narrow hard layer of carburized martensite and austenite in the ferritic...

Coated sheets for car body are assembled by spot-welding and, more and more, by adhesive bonding. Thus, during life time, the coating endures stresses which can lead to the failure of the whole bonded assembly. The behavior of the zinc coating has then to be primarily studied during tension of flat samples. Several investigation techniques, includi...

Experiments in hydrogenated steam were performed on several U-bend specimens extracted from two Alloy 82 welds. Results demonstrated that Alloy 82 is susceptible to SCC in hydrogenated steam at 400 °C and its susceptibility depends on its chemical composition, welding process and thermal treatment. The microstructure was characterized in the apex o...

A joint experimental and modelling study of plastic strain and ensuing damage in a novel metal matrix composite (Fe-TiB2) is presented. Damage is observed and quantified using SEM images processing and Acoustic Emission (AE) analysis. The use of AE confirms that the surface damage observed is strongly correlated to damage in the bulk of the materia...

Alloy 82, used as weld metal in Pressurized Water Reactor (PWR), was exposed to hydrogenated steam at 400 °C and to simulated primary water at 340 °C. A comparative study of the oxide layer formed on the alloy surface in both environments was performed to confirm that steam conditions were representative of accelerated primary water conditions. For...

This paper reports on a micromechanical investigation of mudstones using a novel experimental method, based on a combination of environmental scanning electron microscopy (ESEM) and digital image correlation techniques. A specifically designed rig was developed, allowing in situ tests under combined hydric and mechanical loadings in the ESEM chambe...

Combining environmental scanning electron microscopy (ESEM) and digital image correlation techniques, the mechanical behaviour of mudstones is studied at the scale of their composite microstructure (that is, grains of carbonate and quartz embedded in a clay matrix). A specially designed apparatus is developed to allow insitu uniaxial compression te...

The mechanical behavior of mudstones strongly depends on humidity. In this paper, we present some microstructural insights into this phenomenon gained from a microscale investigation using a novel experimental method. The experimental method consists of combined hydric and mechanical loading tests in environmental scanning electron microscopy, as w...

Thick metallic or ceramic functional coatings onto polymers are of great interest for different domains such as the aerospace and medical industries. A vacuum plasma spray process has been developed to produce coatings on high- and low-temperature melting polymers including PEEK and polyethylene. This study reports the first experimental characteri...

This paper reports on a micromechanical investigation of mudstones using a novel experimental method, based on a combination of environmental scanning electron microscopy (ESEM) and digital image correlation techniques. A specifically designed rig was developed, allowing in situ tests under combined hydric and mechanical loadings in the ESEM chambe...

Some irreversible phenomena of argillaceous rocks during wetting and drying processes are experimentally investigated at the micrometric scale, by combining environmental scanning electron microscope (ESEM) imaging and digital image correlation (DIC) techniques. According to previous macroscopic experimental results, argillaceous rocks under a free...

The deformation of synthetic halite is investigated at the scale of its polycrystalline microstructure. Images recorded during compression test performed in the chamber of a scanning electron microscope on centimeter sized samples are analyzed by Digital Image Correlation techniques and reveal the combined contribution of crystal slip plasticity an...

Full-field strain measurement at microscale on geomaterials by means of hydromechanical in situ testing and imaging in an environmental scanning electron microscope and digital image correlation techniques is a challenging task because of both low magnitude of investigated strains (typically of the order of 10−3) and unfavourable imaging conditions...

Callovo–Oxfordian argillite is studied in France as a possible host rock for repository of high-level radioactive wastes. A new experimental procedure is proposed to quantify the free swelling of its main constitutive clay phase, which is a key parameter to model the hydromechanical behaviour of this rock. The material was pulverised finely enough...

An experimental study of the swelling anisotropy of the Callovo-Oxfordian argillaceous rock under hydration is presented. The investigation, which combines environmental scanning electron microscopy (ESEM) and digital image correlation techniques, has been carried out at the micrometric scale of the composite microstructure of the rock. Specimens w...

Halite is a commonly used analog polycristalline material. Compared to most rock forming minerals, halite exhibits extensively ductile behavior at even low temperatures and fast deformation rates. Therefore, it allows an easier study of the fundamental mechanisms of crystal plasticity, recrystallization, grain growth and texture development than an...

The hydromechanical behavior of argillaceous rocks, which are possible host rocks for underground radioactive nuclear waste storage, is investigated by means of micromechanical experimental investigations. Strain fields at the micrometric scale of the composite structure of this rock, composed of a clay matrix and other mineral particles (essential...

[1] There is a renewed interest in the study of the rheology of halite since salt cavities are considered for waste repositories or energy storage. This research benefits from the development of observation techniques at the microscale, which allow precise characterizations of microstructures, deformation mechanisms, and strain fields. These techni...

AB ST R ACT : An experimental study of the swelling anisotropy of the Callovo-Oxfordian argillaceous rock under hydration is presented. The investigation, which combines environmental scanning electron microscopy (ESEM) and digital image correlation techniques, has been carried out at the micrometric scale of the composite microstructure of the roc...

This work presents a numerical study of the intergranular crack propagation behavior of γ-TiAl. For this purpose, finite element simulations using remeshing techniques and crystal plasticity are carried out on a bidimensional γ-TiAl polycrystal. In order to evaluate the influence of crystal orientations, ten different random orientations are genera...

This paper presents a first validation of a novel methodology for identifying the parameters of a crystallographic elastoplastic constitutive law. This is accomplished by comparing simulation and experimental results at different length scales: the microstructure scale and the representative volume element scale. Experimentally, the microscopic str...

Halite is a rock forming mineral with geotechnical applications for storage in underground caverns (hydrocarbons, compressed air, wastes...). Halite is also a convenient analog polycristalline material, used to study deformation mechanisms (crystal plasticity, recrystallization, pressure solution ...). In this work we present an investigation of in...

Synthetic halite elaborated with different microstructures ( i.e. grain sizes and grain size distribution) has been deformed by uniaxial compression in a scanning electron microscope, with measure of the grain orientations, surface observation of slip lines, digital image correlation (DIC) to provide full-field estimates of displacements and surfac...

Experimental heating tests were performed on Volterra gypsum to study the micromechanical consequences of the dehydration reaction. The experimental conditions were drained at 5 MPa fluid pressure and confining pressures ranging from 15 to 55 MPa. One test was performed with a constantly applied differential stress of 30 MPa. The reaction is marked...

We observed with optical and scanning electron microscopy halite samples during uniaxial compression. Surface displacement fields were retrieved from digital images taken at different loading stages thanks to Digital Image Correlation (DIC) techniques, on the basis of which we could 1) compute global and local strain fields, 2) identify two co-oper...

We observed with optical and scanning electron microscopy halite samples during uniaxial compression. Surface displacement fields were retrieved from digital images taken at different loading stages thanks to Digital Image Correlation (DIC) techniques, on the basis of which we could 1) compute global and local strain fields, 2) identify two co-oper...

This study is devoted to the computation of realistic stress and strain fields at a local scale in fretting. Models are proposed to improve surface and volume modelling, by taking into account the heterogeneity of stress fields due to the irregular interface. This gives a new view toward damage mechanisms. The surface heterogeneity which is conside...

Mise en place d'un modèle de zone cohésive à base physique dans un bicristal de γ-TiAl. Résumé — Ces travaux proposent d'étudier numériquement l'effet d'une fissure intragranulaire modéli-sée par des éléments cohésifs dans un bicristal de γ-TiAl. Les effets de la fissure, insérée dans le premier grain, sont étudiés dans le second grain à la suite d...

Halite has been extensively studied both as a natural material (storage, diapirs, ...) and an analog material (tectonics, pressure solution, ...). In this work, we study the deformation of halite at room temperature, under uniaxial loadings in order to identify the different mechanisms of plastic deformation at the local scale. Halite is a ionic po...

Résumé : La déformation et l'endommagement des argilites sous sollicitation hydrique sont observés au MEB environnemental. La déformation est mesurée par corrélation d'images à l'échelle micrométrique des zones argileuses entre les grains carbonatés et de quartz et révèle un couplage hydromécanique complexe. On montre l'apparition d'une déformation...

Nous présentons les résultats expérimentaux de déformation à diérentes échelles obtenus à partir d'un polycristal de NaCl synthétique : essais de compression uniaxiale, couplés à des mesures de champs cinématiques, obtenus par corrélation d'images numériques acquises in-situ, sous MEB. Diérents mé-canismes de déformation plastique sont observés, gl...