Jean-Pierre Meunier, Des images et des mots : Cognition et réflexivité dans la communication

Cet ouvrage du sémiologue, spécialiste des théories générales de la communication, Jean-Pierre Meunier, propose de poursuivre le projet de Saussure qui désirait, dans le prolongement de la linguistique, faire émerger une nouvelle science, plus grande encore, à travers la sémiologie. L’auteur s’engage ainsi à aller plus loin et à mettre en exergue, comme le titre du livre l’indique, le rôle majeur de la cognition et de la réflexivité dans les relations de communication. Il s’intéresse alors à ..

Comparaison entre les déformations représentatives de l'indentation Vickers et de l'indentation sphérique Comparison between representative deformations in Vickers indentation and spherical indentation

National audienceThe application of the concept of the representative strain is often used in the stress-strain curve determination from indentation test. A new methodology for determining the representative strain for spherical and for Vickers indentation is presented in this article. The results obtained from this methodology show that there is no universal value of representative strain independent of the mechanical parameters of materials indented by Vickers indentation and spherical indentation. It is also shown that the representative strain, obtained by Vickers or by spherical indentation, is much lower when it is obtained from the relationship between the applied force and the penetration depth, F-h, rather than from the relationship between the applied force and the contact radius, F-a. By choosing the same representative strain value in spherical indentation and in Vickers indentation, the results show that the same constraint factor is obtained. Hence, it is possible to determine a perfect analogy between the two types of indentation. For Vickers indentation, the values of the calculated representative strains show that simultaneous measurement of relationships F-a and F-h allows to characterize the hardening law with two unknown parameters. In the case of the spherical indentation, the identification of a material hardening law from simultaneous measurements relationships F-a and F-h should lead to a more accurate determination of the stress-strain curve

Identification of macroscopic hardening law through spherical indentation: definition of an average representative strain and a confidence domain.

The instrumented indentation test is widely used for the identification of the stress-strain curve. One of the disadvantages of the indentation test is that the plastic strain field in the deformed sample is not homogenous which makes it difficult to identify the hardening law of the material from an indentation curve. This difficulty can lead to some complications such as the uniqueness of the solution due to the sensitivity of the indentation test. The use of the concept of the representative strain can simplify the analysis of the indentation response and has often been used in the stress-strain curve identification. In the present work, a new method based on the definition of an “average representative strain”, εaR, is developed for the determination of the hardening law using the load displacement curve, F-h, of a spherical indentation test. The advantage of the proposed εaR is that it is directly obtained from the material’s response to the indentation test. This method consists to calculate the error between an experimental indentation curve and a number of FE simulation curves. For the smaller values of these errors, the error distribution shape is a valley, which is defined with an analytical equation. Based on a sensitivity study, the εaR and the corresponding value of stress σaR can be calculated for every penetration depth. Hence, the hardening law is constructed with no assumptions on its mathematical form. Because of the local aspect of the indentation test, materials heterogeneities can lead to differences between several indentation curves obtained under the same conditions. The proposed method allows the determination of a confidence domain that takes into account the experimental imprecision and the material heterogeneity using several indentation curves1, 2. The present method points out the limitation od the indentation test to characterize the mechanical behavior for large deformations. The uniqueness of the solution and the sensitivity of the indentation test are also discussed. The results obtained for a 20MnB5 steel alloy show that the identified hardening law (and confidence domain) is in agreement with the tensile test curve (Figure 1). A similar approach can be used for Vickers indentation for determining the representative strain3. Results obtained for Vickers indentation are discussed and compared to the literature. Please click Additional Files below to see the full abstract

Identification of the hardening law of materials with spherical indentation using the average representative strain for several penetration depths

International audienceThe identification of plastic properties with spherical indentation has been the subject of many studies in last decades. In the present work, a new method for the determination of the hardening law of materials using the load-displacement curve of a spherical indentation test is proposed. This method is based on the use of an average representative strain. The advantage of the proposed average representative strain is that it is strictly obtained from the material response to the indentation test. By using various values of penetration depth, the proposed method gives the range of strain for which the hardening law is precisely identified and allows determining a confidence domain that takes into account experimental imprecision and material heterogeneity. The influence of penetration depth and the error formula on the identified Hollomon hardening law are discussed in the present study. The present study clarifies many problems that were observed in previous studies such as the uniqueness solution and the sensitivity of the indentation test to the plastic parameters of the Hollomon hardening law

Revue bibliographique sur la caractérisation mécanique des matériaux utilisant la déformation représentative en indentation sphérique Literature review on mechanical characterization of materials using a representative strain in spherical indentation

National audienceThe instrumented indentation provides access to several mechanical properties of materials, leading in particular to the knowledge of their hardening law. In front of the lack of a standard procedure, many techniques have been proposed in recent decades. The present work is a literature review on the methods of mechanical characterization based on the instrumented indentation, and using a representative strain. There are two families of methods. The first, based on the Meyer hardness, includes methods of conducting hardness tests with different loads and determine, from the hardness and measuring the radius of the corresponding imprint, a representative deformation and the corresponding stress leading to the construction of the work hardenning curve "point by point" of the tested material. The second includes the methods giving the 2 plastic parameters of the Hollomon law that minimize the difference between the experimental indentation F(h) curve, and a model based on a representative deformation, linking the measured quantities (F, h) and the parameters of the Hollomon law. Each family of methods has advantages and disadvantages that should be known for choosing the most suitable method to the studied case and thus makes best use of instrumented indentation testing

Regulation of Mammalian Physiology by Interconnected Circadian and Feeding Rhythms.

Circadian clocks are endogenous timekeeping systems that adapt in an anticipatory fashion the physiology and behavior of most living organisms. In mammals, the master pacemaker resides in the suprachiasmatic nucleus and entrains peripheral clocks using a wide range of signals that differentially schedule physiology and gene expression in a tissue-specific manner. The peripheral clocks, such as those found in the liver, are particularly sensitive to rhythmic external cues like feeding behavior, which modulate the phase and amplitude of rhythmic gene expression. Consequently, the liver clock temporally tunes the expression of many genes involved in metabolism and physiology. However, the circadian modulation of cellular functions also relies on multiple layers of posttranscriptional and posttranslational regulation. Strikingly, these additional regulatory events may happen independently of any transcriptional oscillations, showing that complex regulatory networks ultimately drive circadian output functions. These rhythmic events also integrate feeding-related cues and adapt various metabolic processes to food availability schedules. The importance of such temporal regulation of metabolism is illustrated by metabolic dysfunctions and diseases resulting from circadian clock disruption or inappropriate feeding patterns. Therefore, the study of circadian clocks and rhythmic feeding behavior should be of interest to further advance our understanding of the prevention and therapy of metabolic diseases

Evaluation of the tensile properties of a material through spherical indentation: definition of an average representative strain and a confidence domain.

International audienceIn the present article, a new method for the determination of the hardening law using the load displacement curve, F-h, of a spherical indentation test is developed. This method is based on the study of the error between an experimental indentation curve and a number of finite elements simulation curves. For the smaller values of these errors, the error distribution shape is a valley, which is defined with an analytic equation. Except for the fact that the identified hardening law is a Hollomon type, no assumption was made for the proposed identification method. A new representative strain of the spherical indentation, called "average representative strain," ε aR was defined in the proposed article. In the bottom of the valley, all the stress-strain curves that intersect at a point of abscissa ε aR lead to very similar indentation curves. Thus, the average representative strain indicates the part of the hardening law that is the better identified from spherical indentation test. The results show that a unique material parameter set (yield stress σ y, strain hardening exponent n) is identified when using a single spherical indentation curve. However, for the experimental cases, the experimental imprecision and the material heterogeneity lead to different indentation curves, which makes the uniqueness of solution impossible. Therefore, the identified solution is not a single curve but a domain that is called "solution domain" in the yield stress-work hardening exponent diagram, and "confidence domain" in the stress-strain diagram. The confidence domain gives clear answers to the question of uniqueness of the solution and on the sensitivity of the indentation test to the identified hardening laws parameters

Influence of sample thickness and experimental device configuration on the spherical indentation of AISI 1100 steel

International audienceMost instrumented indentation theoretical studies and models consider bulk sample geometry, which implies no influence on the indentation response. In the particular case of thin samples, our previous studies have shown that the thickness has an influence on the experimental device behaviour as well as on the sample and material response. This work is a numerical and experimental illustration of this particularity. Spherical macroindentation tests are performed on AISI 1100 steel samples of thicknesses varying from 10 to 0.55 mm. Experimental and numerical results are compared. Experimental limitations are investigated and solutions to obtain results which are independent of the sample thickness and curvature are proposed. We show that the proposed solution, which is the object of an international patent, leads to a reliable identification of the material mechanical properties of thin and moderately bent samples

Mechanical characterization of carbonitrided steel with spherical indentation using the average representative strain

International audienceThis paper investigates the identification of mechanical properties of carbonitrided steels using the spherical indentation test. The proposed procedure consists in performing the Vickers microindentation hardness test across the carbonitrided steel in order to obtain the thickness of the hardened layers. Thus, with the assumption of a linear variation of the plastic properties in the intermediate layers between surface and substrate, two spherical macroindentation tests, performed on the substrate and on the surface of the carbonitrided steel, are necessary to identify the work hardening laws' variation through the thickness of the carbonitrided steel. The proposed method does not call for inverse analysis but is based on the use of a database of finite element simulation F–h curves obtained by simulating indentation tests on the surface of various pseudo-carbonitrided materials. The advantage of this method compared to those based on inverse analysis is that it allows a representative strain and a confidence domain of the solution to be determined. The confidence domain of the identified solution takes into account the experimental imprecision of the indentation test and of the case depth variability often encountered in carbonitrided parts

Clock-dependent chromatin topology modulates circadian transcription and behavior.

The circadian clock in animals orchestrates widespread oscillatory gene expression programs, which underlie 24-h rhythms in behavior and physiology. Several studies have shown the possible roles of transcription factors and chromatin marks in controlling cyclic gene expression. However, how daily active enhancers modulate rhythmic gene transcription in mammalian tissues is not known. Using circular chromosome conformation capture (4C) combined with sequencing (4C-seq), we discovered oscillatory promoter-enhancer interactions along the 24-h cycle in the mouse liver and kidney. Rhythms in chromatin interactions were abolished in arrhythmic <i>Bmal1</i> knockout mice. Deleting a contacted intronic enhancer element in the <i>Cryptochrome 1</i> ( <i>Cry1</i> ) gene was sufficient to compromise the rhythmic chromatin contacts in tissues. Moreover, the deletion reduced the daily dynamics of <i>Cry1</i> transcriptional burst frequency and, remarkably, shortened the circadian period of locomotor activity rhythms. Our results establish oscillating and clock-controlled promoter-enhancer looping as a regulatory layer underlying circadian transcription and behavior