Olivier Arnould | CNRS- Universite de Montpellier (original) (raw)

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Papers by Olivier Arnould

Les matériaux énergétiques présentent un caractère sensible aux sollicitations mécaniques, chimiq... more Les matériaux énergétiques présentent un caractère sensible aux sollicitations mécaniques, chimiques ou thermiques « faibles », dont l'origine est probablement liée à un endommagement microstructural progressif du matériau. La butalite analysée dans le cadre de notre étude est un propergol composite, constitué de grains de perchlorate d'ammonium et d'une matrice polymérique de type PBHT. Pour décrire la réponse thermo-mécanique sous faible choc de ce matériau à l'échelle mésoscopique, nous réalisons des essais d'impacts basse vitesse à la tour de chute, sous différentes configurations expérimentales, en couplant un enregistrement par caméra rapide à une analyse ante-et post-mortem de l'échantillon par microtomographie X. Plusieurs modifications d'une tour de chute classique ont été effectuées afin de mettre en oeuvre la vidéo rapide et d'explorer le maximum de configurations expérimentales possibles. Les résultats des essais de validation de la version modifiée du dispositif nous permettent d'envisager des campagnes d'essais permettant de récupérer les données nécessaires à l'identification et à la caractérisation des mécanismes d'endommagement pouvant servir de points chauds pour l'initiation d'une réaction sous faible choc.

IAWA journal / International Association of Wood Anatomists

Trees can control their shape and resist gravity thanks to their ability to pro- duce wood under ... more Trees can control their shape and resist gravity thanks to their ability to pro- duce wood under tensile stress. This stress is known to be produced during the maturation of wood fibres but the mechanism of its generation remains unclear. This study focuses on the formation of the secondary wall in tension wood produced in artificially tilted poplar saplings. Thickness of secondary wall layer (SL) and gelatinous layer (GL) were measured from cambium to mature wood in several trees sampled at different times after tilting. Measurements on wood fibres produced before tilting show the progressive increase of secondary wall thickness during the growing season. After the tilting date, SL thickness decreased markedly from normal wood to tension wood while the total thick- ness increased compared to normal wood, with the development of a thick GL. However, even after GL formation, SL thickness continues to increase during the growing season. GL thickening was observed to be faster than SL ...

Thuja (Tetraclinis articulata (Vahl.) Master) is a species endemic to the South-western coast of ... more Thuja (Tetraclinis articulata (Vahl.) Master) is a species endemic to the South-western coast of the Mediterranean Sea and especially Maghreb. The thuja burr is an outgrowth found at the collar of thuja trees. The burr wood of thuja is composed of dark growths of high density, mixed in a "matrix" of woody tissue of density close to that of thuja. When properly worked, the wood of thuja burr reveals a remarkable speckled pattern, leading to a real aesthetic value . In order to document the physical and mechanical properties behaviour of burr wood of thuja, we developed a method for determining the material symmetries for any material with unknown anisotropy, by combining ultrasonic experimental methods and numerical computation.

Composites Part A: Applied Science and Manufacturing, 2015

ABSTRACT Nowadays, the multi-scale modelling of wood has a great need for measurements of structu... more ABSTRACT Nowadays, the multi-scale modelling of wood has a great need for measurements of structural, chemical and mechanical properties at the lowest level. In this paper, the viscoelastic properties in the layers of a wood cell wall are investigated using the contact resonance mode of an atomic force microscope (CR-AFM). A detailed experimental protocol suitable for obtaining reproducible and quantifiable data is proposed. It is based on three main steps: sample preparation to obtain a good surface state, calibration of the contact modulus using reference samples, and image processing to produce the viscoelastic images. This protocol is applied on chestnut tension wood. The obtained topography and semi-quantitative viscoelastic maps are discussed with respect to the cell wall structure, sample preparation effects, and AFM measurement specificity compared with nanoindentation.

Plant cell walls are made of interacting networks of polysaccharides (cellulose, hemicelluloses, ... more Plant cell walls are made of interacting networks of polysaccharides (cellulose, hemicelluloses, pectins) and some structural proteins. Cellulose-xyloglucan networks are considered to be the main source of structural strength in primary cell wall. Little is known about the contribution of each polysaccharide network to mechanical properties. The aim of this work is to evaluate the role of hemicellulose, especially xyloglucans, by monitoring plant cell wall mechanical properties during targeted enzymatic degradation and establishing links with xyloglucan chemical composition and structure. Spatially homogeneous parenchyma from contrasted texture Golden Delicious (Go) and Granny Smith (Gr) apples were sampled and vacuum infused with enzymes in buffer solution aimed at maintaining and homogenising turgor pressure and limiting oxidation. Glucanases specific from xyloglucan and /or cellulose backbone and Glycoside hydrolases (α-fucosidase, and β-galactosidase) were used to study the impact of xyloglucan and its side chains on parenchyma mechanical properties.

Ultrasonics, 2010

In this work, we propose a study dedicated to the influence of the delay line nature in transvers... more In this work, we propose a study dedicated to the influence of the delay line nature in transverse ultrasonic sensors, dedicated to dynamic high frequency elastic moduli of viscoelastic materials estimation. In literature, these shear ultrasonic rheometers are using delay lines in glass or quartz and normal or oblique incidence of ultrasonic rays. The oblique incidence is used in order to improve the sensitivity of the measurements. We theoretically demonstrate in this work that the use of delay lines in polymers is recommended to improve the sensitivity. Due to modifications, performed on a 10 MHz commercial ultrasonic sensor, we experimentally show on glycerin (which is a Newtonian material) that it is possible to multiply by a factor 10 the sensitivity; compared to delay lines in quartz using a normal incidence of rays. Hence, we overpass the accuracy of the oblique incidence approach with a simpler experimental setup.

$Research paper thumbnail of Prevalent Material Parameters Governing Spalling of a Slag-Impregnated Refractory$

Key Engineering Materials, 2004

In steel ladle linings, bauxite refractories in contact with iron and steel slag are subjected to... more In steel ladle linings, bauxite refractories in contact with iron and steel slag are subjected to complex loadings. To identify the causes of degradation in different reactor linings, a coupling diagram made up of three poles is established: namely, slag Impregnation (I), Thermomechanics (TM) and Phase transformations (P). The variation of the microstructure and the gradient of the chemical composition resulting from the (I-P) coupling are characterized by microprobe analyses; a natural impregnation tracer is identified. The (I-T) coupling is studied by modeling the refractory lining behavior subjected to a cyclic thermal loading within the framework of the mechanics of porous continua. Parameters governing the location and amplitude of the maximum pore pressure are obtained and their influences are studied. The analysis of the (TM) pole leads to the identification of a thermo-elasto-viscoplastic model for bauxite in various states of slag impregnation. Numerical simulations show that the stress state developed during the heating stages can induce spalling, probably generated by a localized over-pressure of slag.

DYMAT 2009 - 9th International Conferences on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, 2009

Energetic materials are sensitive to "low" mechanical, chemical and thermal stresses, whose origi... more Energetic materials are sensitive to "low" mechanical, chemical and thermal stresses, whose origin is probably linked to their microstructural damaging. The present study focuses on a composite propellant composed of ammonium perchlorate grains in a polyurethane binder (HTPB). To describe the thermo-mechanical behavior of this material, at the mesoscopic scale under low impact, drop weight tests are carried out under various experimental configurations, adding a high speed camera recorder and ante-and post-mortem X-ray microtomographies. Several modifications of the usual device are developed in order to explore as many experimental configurations as possible. Results obtained during validation tests of the modified device enable us to consider that it can give the required data for the identification and characterization of the damage mechanisms that could be part of the hot spots initiation process and reaction ignition under low impact.

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