Agricultural holdings: hindsight and foresight

In France, the concept of the agricultural holding is a result of a lengthy social construction in which the stages in classification and statistical work have proceeded in tune with the major political struggles and social debates of the 19th and 20th centuries. Some people argue that the “ agricultural holding ” is now just a term revived from the past for the modern “ agricultural enterprise ”. Sociologists and economists therefore need to reconsider the significance and relevance of this concept. The diversity of the ways of practising agricultural activities encountered in French households shows that the economic and social realities referred to in this concept are far too varied for its use in defining a productive sector having an institutional existence. Neither can it be used to demark the social groups that will be entitled to benefit from the support measures of agricul-tural and rural development policies. As a basic statistical unit, however the concept of the agricultural holding can provide a com-mon basic unit for measuring agricultural activity, and the land used for this activity, thereby permitting the integration of results concerning the different functions of agricultural activity (production, natural resource management, land use, socio-economic cohesion, etc.). From this angle, the statistical notion of the agricultural holding as presently defined is of increasing interest for the management of new agricultural and rural policies and for social sciences research.Knowledge, agricultural statistics,agricultural holding,history of concepts, multifunctionality

Modelling the influence of machined surface roughness on the fatigue life of aluminium alloy

The influence of machined surface roughness on the fatigue life of 7010 aluminium alloy has been investigated. Four-point bending specimen have been machined according to various machining conditions and tested in fatigue. In order to explain the high dependence of SN curves on the surface roughness of the specimen, an approach based on the finite element analysis of measured surface topography is proposed. Surface grooves due to machining are supposed to generate stress concentrations that are so calculated. A model of fatigue life prediction is developed, using this definition of local Kt

Simplified modelling of the behaviour of 3D-periodic structures such as aircraft heat exchangers

In this paper, experimental, analytical and numerical analysis are used to study and model the mechanical behaviour of a heat exchanger core consisting of a 3D-periodic structure. The purpose of the present investigation is not only to acquire knowledge on the mechanical behaviour of a given heat exchanger core but also to propose a simplified approach to model this behaviour. An experimental study is carried out in order to get an insight on the mechanical behaviour of this structure. Global static characteristics are obtained via analytical and finite element analysis of a unit cell of the core. Dynamic behaviour is studied by means of finite element calculations based on the results of the static modelling. The proposed approach is validated by comparison with experimental tests results

SPH method applied to high speed cutting modelling

The purpose of this study is to introduce a new approach of high speed cutting numerical modelling. A Lagrangian smoothed particle hydrodynamics (SPH)- based model is arried out using the Ls-Dyna software. SPH is a meshless method, thus large material distortions that occur in the cutting problem are easily managed and SPH contact control permits a "natural" workpiece/chip separation. The developed approach is compared to machining dedicated code results and experimental data. The SPH cutting model has proved is ability to account for continuous to shear localized chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Thus, comparable results to machining dedicated codes are obtained without introducing any adjusting numerical parameters (friction coefficient, fracture control parameter)

A predictive fatigue life model for anodized 7050 aluminium alloy

The objective of this study is to predict fatigue life of anodized 7050 aluminum alloy specimens. In the case of anodized 7050-T7451 alloy, fractographic observations of fatigue tested specimens showed that pickling pits were the predominant sites for crack nucleation and subsequent failure. It has been shown that fatigue failure was favored by the presence of multiple cracks. From these experimental results, a fatigue life predictive model has been developed including multi-site crack consideration, coalescence between neighboring cracks, a short crack growth stage and a long crack propagation stage. In this model, all pickling pits are considered as potential initial flaws from which short cracks could nucleate if stress conditions allow. This model is built from experimental topography measurements of pickled surfaces which allowed to detect the pits and to characterize their sizes (depth, length, width). From depth crack propagation point of view, the pickling pits are considered as stress concentrator during the only short crack growth stage. From surface crack propagation point of view, machining roughness is equally considered as stress concentrator and its influence is taken into account during the all propagation stage. The predictive model results have been compared to experimental fatigue data obtained for anodized 7050-T7451 specimens. Predictions and experimental results are in good agreement

Surface characterization and influence of anodizing process on fatigue life of Al 7050 alloy

The present study investigates the influence of anodizing process on fatigue life of aluminium alloy 7050-T7451 by performing axial fatigue tests at stress ratio ‘R’ of 0.1. Effects of pre-treatments like degreasing and pickling employed prior to anodizing on fatigue life were studied. The post-exposure surface observations were made by scanning electron microscope (SEM) to characterize the effect of each treatment before fatigue testing. The surface observations have revealed that degreasing did not change the surface topography while pickling solution resulted in the formation of pits at the surface. Energy dispersive spectroscopy (EDS) was used to identify those constituent particles which were responsible for the pits formation. These pits are of primary concern with respect to accelerated fatigue crack initiation and subsequent anodic coating formation. The fatigue test results have shown that pickling process was detrimental in reducing the fatigue life significantly while less decrease has been observed for anodized specimens. Analyses of fracture surfaces of pickled specimens have revealed that the process completely changed the crack initiation mechanisms as compared to non-treated specimens and the crack initiation started at the pits. For most of the anodized specimens, fatigue cracks still initiated at the pits with very few cracks initiated from anodic coating. The decrease in fatigue life for pickled and anodized specimens as compared to bare condition has been attributed to decrease in initiation period and multi-site crack initiations. Multi-site crack initiation has resulted in rougher fractured surfaces for the pickled and anodized specimens as compare to bare specimens tested at same stress levels

Modelling High Speed Machining with the SPH Method

The purpose of this work is to evaluate the use of the Smoothed Particle Hydrodynamics (SPH) method within the framework of high speed cutting modelling. First, a 2D SPH based model is carried out using the LS-DYNA® software. SPH is a meshless method, thus large material distortions that occur in the cutting problem are easily managed and SPH contact control allows a “natural” workpiece/chip separation. The developed SPH model proves its ability to account for continuous and shear localized chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Then, The SPH model is used in order to improve the general understanding of machining with worn tools. At last, a milling model allowing the calculation of the 3D cutting forces is presented. The interest of the suggested approach is to be freed from classically needed machining tests: Those are replaced by 2D numerical tests using the SPH model. The developed approach proved its ability to model the 3D cutting forces in ball end milling

Metal cutting modelling SPH approach

The purpose of this work is to evaluate the use of the smoothed particle hydrodynamics (SPH) method within the framework of high speed cutting modelling. First, a 2D SPH based model is carried out using the LS-DYNA® software. The developed SPH model proves its ability to account for continuous and shear localised chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Then, the SPH model is used in order to improve the general understanding of machining with worn tools. At last, a hybrid milling model allowing the calculation of the 3D cutting forces is presented. The interest of the suggested approach is to be freed from classically needed machining tests: Those are replaced by 2D numerical tests using the SPH model. The developed approach proved its ability to model the 3D cutting forces in ball end milling

Étude thermomécanique d’une nouvelle géométrie d’éprouvette de fatigue en environnement sévère

De nombreuses pièces mécaniques sont soumises à des variations de chargement dans des environnements agressifs. Pour évaluer la tenue des matériaux les constituant, a été développée une nouvelle géométrie d’éprouvette. Il s’agit d’une éprouvette tubulaire, dont le fût constitue la zone utile, munie d’un noyau fabriqué dans le même matériau qui fait office de demi ligne. Dans cet article, sera présenté le bon comportement mécanique de cette éprouvette en fatigue et en flambage. Pour vérifier ce dernier point, un modèle tridimensionnel complet a été réalisé. Les résultats étant concluants, l’étude du comportement en cyclage thermique a débuté. Un modèle a été développé au moyen d’un code par éléments finis qui montre des gradients inférieurs à 40K pour des amplitudes de cyclage de l’ordre de 850 K. Ce modèle une fois validé expérimentalement permettra d’optimiser le système d’essai pour minimiser les gradients tout en augmentant la fréquence des cycles thermiques

Building collectives via the Web? Information and mobilization on cancer websites

International audienceIn this presentation, we analyse the construction of cancer patient profiles through websites offering information on the disease. We characterize the profiles of cancer patients as they appear on a large number of French websites. Many sites belong to non-profit organizations; others are initiatives by the medical profession; others still are produced by professional organizations linked to the media sphere. Apart from a general review of the competencies and rights associated with patients, on the role of information in determining their capacities to act, and on the place granted to patients and their families to express themselves, the sites related to patient organizations raise specific questions. For instance, what are the forms of engagement pertaining to cancer, in the French non-profit organization movement? In particular, how can the division of tasks that each organization institutes between doctors, patients and itself be characterized, and how does it articulate its support activities with its activism?In parallel, we examine the role of the Internet in shaping this engagement, and the forms of writing peculiar to the Web. This writing has the characteristic of affording the possibility of a multiplication of enunciators and thus of facilitating encounters and the formation of collectives, that is, individuals talking in the same voice with specific aims. In what way do the uses to which the various "authors" of websites put these possibilities allow for the creation of new knowledge, the emergence of new collectives, and the performation of new actor configurations?To answer these questions, our presentation is divided into three parts:- First, we consider the status and format of medical information, as delivered on websites. In particular, we examine the designated enunciators, the authority on which their information is based, and the mise en scène of the context of enunciation. What position is assigned to the recipients of this information? Is there space for uncertainty and debate?- In the second part we characterize the presence of laypersons' and patients' talk. In particular, we examine its possible link with that of professionals, and that of "science". Are there any forms of articulation between individual experiences and collective forms of expression?- Finally, in the third part, we analyse the patient profiles that each website constructs in its public, both through the proposed content and through the modalities of action afforded by the site itself. We consider the "patients", their possibilities to act and the competencies attributed to them. How does the site describe a patient's relations with healthcare professionals? What choices does the patient have? What leeway does he or she have to define him- or herself through the site itself? What are the relations between the patient profile, that of the activist and that of the donor of funds