Sémantique des spécifications géométriques : Classification des éléments géométriques — Calibre à Mobilités Internes

The imperfections, inherent in the manufacturing processes, involve a degradation of the functional characteristices, and thus, of the quality of the product. From a geometrical point of view, a part is seen as a non-ideal surface, modeling the physical interface between the part and its environment. To ensure a certain level of quality, we define the limits of the geometrical variations of the parts. To do so, we express functional geometrical specifications. In this paper, we present the definition of features used to express the geometrical specifications and the functional expression of the virtual gauge with internal mobilities.     

La mécatronique dans la formation d'ingénieurs généralistes

This paper presents an approach adopted since 2 years in the training of general background engineers, to contribute to the global view of a mechatronic process. The distinctive feature of this approach, based within a project type organisation, is to bring knowledge via a horizontal approach (working group) and no longer via a vertical approach (lectures illustrated by tutorials and practical works for each subject). It allows students to address a problem from every angle while integrating, as the study progresses, the technological aspects playing a part in the elaboration of an industrial solution. The course so proposed, entitled “Applied Mechatronics Design”, allows one to synthesise the whole project progress (concurrent engineering). It implies a pluridisciplinary pedagogical team, working with the students as a project-team. The study and the design of an autonomous mobile platform will be used to illustrate the overall approach.     

Un dispositif pour la caractérisation des propriétés amortissantes de matériaux viscoélastiques non-linéaires en cisaillement

Viscoelastic materials are widely used in passive antivibration mounting design. In order to optimize their use, designers have to take into account the non-linearities caused by the large strain amplitudes these systems are subjected to. In this paper we present an apparatus designed to characterize the mechanical behavior of some viscoelastic materials used for this application. Simple shear deformation under sinusoidal load is used. The results are displayed as an extension of the complex moduli linear concept. The highly non-linear behaviour of the samples is underlined. A large scale of frequency and strain amplitude can be studied using this apparatus, without any restrictive assumption regarding the material model. This apparatus was designed in order to validate the design of an aerospace antivibration equipment.     

Méthodes adaptatives pour les déformations localisées

Structure materials carry the loads that are applied to them, often by developing very localized behaviour near geometric singularities like joints (welds, rivets, etc.), thickness variations or various notches. Computations accuracy requires then meshes that would be prohibitive if they were uniformly refined without knowing a priori the aforementioned areas. Adaptive methods with shape functions enrichment allows to focus the computational cost in these regions. Herein, the error estimation problem is addressed as well as various mesh and model enrichment possibilities in particular hierarchical enrichment, for example for joints between three-dimensional and shell structure. The interest of such an analysis for crack propagation in ductile material is examined. Finally several numerical examples are presented to emphasize the efficiency of the approach.     

Analyse théorique et expérimentale des effets thermiques dans les butées hydrodynamiques à géométrie fixe

Theoretical and experimental analysis of thermal effects in fixed geometry thrust bearings. This paper deals with both theoretical and experimental analyses of thermal phenomena in thrust bearings. The test allowed us to measure the pressure and the temperature fields and the minimal film thickness separating the two surfaces in relative motion. The experimental data are obtained on a hydrodynamic thrust bearing with eight fixed pads. The influence of operating conditions (applied load and rotational speed) on the thrust bearing performance is also analysed. The numerical simulation is done using a thermohydrodynamic computer code taking into account the local thermal effects.     

Conception Inversée Intégrée : prédimensionnement de produits par satisfaction de contraintes

Mechanical design is based on aims of schedule of conditions. Design is an inverted integrated process: designers use aims to do design choices. This process, which requires a translation of all objectives, allows the synthesis of ideal dimensions (choices of materials, dimensions and shapes) from explicit and implicit rules. Rules translate all process laws and mechanical laws: mechanical calculus is integrated in design. Inverted Integrated Design (IID) process is modelized from a constraint based representation and a qualitative valuation. Constraints are analytical or are build from neural networks. Consistency techniques are used in CSPs to seek all consistent dimensions. We apply our work to the design of some pressure apparatus.     

Spécification et simulation des imperfections géométriques en CFAO

The dimensioning and tolerancing model presented in this paper allows the functional tolerancing of a class of mechanicals parts. This model is based on the use of the TTRS concept and on relative positioning constraints. Moreover, this paper presents some improvements in the modeling of the assembly process and describes a sensitivity analysis approach to identify the key characteristics of the assembly.     

Caractérisation expérimentale de paramètres thermomécaniques liés au frottement

Technological progress in infrared thermography has changed the way to study thermal effects in mechanics and, in particular, in contact problems in the presence of friction where a direct measurement is difficult. The method discussed here consists, during wear tests, of estimating simultaneously the evolution of the friction coefficient and the temperature, the latter varying because of the heat generated by friction. The observations are made on a plane, parallel to the plane of contact where the temperature increases because of conduction through the thickness of the specimen. The temperature change is assessed by an infrared thermo-system. This method has great potential especially in the presence of damage in the vicinity of the zone of contact.     

Aspects expérimentaux et numériques du frottement latéral des pieux

Experimental and numerical aspects of side friction of piles. Piles are foundations widely used for the construction of civil engineering works and buildings. Numerous studies have shown the fundamental role of friction at the soil–pile interface in the load bearing capacity. This paper gives the practical design rules as well as examples of numerical modelling for research purposes (finite element calculations). Finally, comparisons with site measurements (full scale piles submitted to axial loads) show that these approaches lead to satisfactory results in predicting the load–displacement behaviour of piles.     

Influence de la microstructure des aciers sur leur propriétés mécaniques

The development of physical approaches describing the effects of the microstructures on the mechanical properties are essential first to understand the effects of the process parameters on the final product, second to rapidly find ways of optimising the process of these products and last but not least to conceive new products. Therefore ARCELOR has been developing for a few years physical models and experimental methods (TEM, image analysis, non-destructive in-situ evaluation) to describe monotonous behaviour, as well as fatigue and fracture mechanisms. Chemical composition, volume fraction of the different phases (ferrite, martensite, pearlite and bainite) and their morphology (grain size, diameter of the martensitic islands, etc.) are taken into account. The aim of the present article is to review a part of these experimental and modelling studies concerning ferritic, dual-phase and bainitic steel grades.     

Intégration de méthodes sur un processus industriel de conception mécanique

The work presented in this paper deals with the definition of a mechanical design process built from the integration of industrial methods used by mechanical designers. The paper is divided into four parts. We first position our work through a bibliographical analysis. The mechanical design process is considered and we describe its various forms of representation. Design methods are then approached under the point of view of their mode of classification. We discuss in the second part about the principles of determination of a specific mechanical design process. We show in particular that a fine decomposition of a process can lead to a natural positioning of the methods towards certain elementary phases. We highlight the existence of methods directly related to the mechanical design process and other methods indirectly associated with it by the means of methodological supports they communicate with. Within the framework of the third part, we study the way the design process call direct methods. In the last part an application is made on the basis of a group of design methods classically used in industrial fields.     

Mécanismes physiques et modélisation mécanique du frottement entre corps solides

Physical mechanisms and mechanical models of solid friction. First we present the theory of solid friction due to Bowden and Tabor and its extension by the junction growth theory which provides some theoretical support of Coulomb's friction law. After a brief discussion of its experimental validation, we present some theoretical works developed for a validation or an extension of Bowden–Tabor's model from various points of view: the plasticity index of Greenwood and Williamson, the mechanical characteristics of the solids, the theory of elastoplastic indentation and the theory of the plastic wave of Oxley. Finally we state more precisely the possibilities offered by the recent developments in numerical simulation.     

Modélisation,identification et simulations éléments finis des phénomènes de délaminage dans les structures composites stratifiées

Modelling, identification and finite element predictions of delamination in laminated composite structures. In order to forecast the delamination initiation and propagation in a finite element context, a previously defined damage meso-modelling of composite laminates is used. At the meso-level, the laminate is described as an assembly of damageable layers and interlaminar interfaces. The present work concerns the modelling, the identification and the finite element predictions of delamination phenomena in composite structures. Finite element predictions are conducted with non-linear geometric and material hypothesis. The interface modelling is implemented in the finite element code Castem 2000 developped by CEA. Classic edge delamination tension and propagation tests are conducted in order to improve the interface damage model approach in the finite elements context.     

Génération de bruit par appariement de tourbillons dans les zones cisaillées

Noise generation by vortex pairings in shear flows. Noise generation in a bidimensional subsonic mixing layer is investigated. In order to obtain the acoustic radiation directly from the filtered Navier–Stokes equations, a large eddy simulation code (ALESIA, Appropriate Large Eddy SImulation for Aeroacoustics) is built up using specific numerical techniques of computational aeroacoustics, and especially for boundary conditions. The mixing layer is excited at its fundamental frequency and its first sub-harmonic frequency to fix the location of vortex pairings. The successive pairings generate an acoustic radiation at the frequency of pairings. The sound generation mechanism corresponds to the rotating quadrupole associated to two co-rotative vortices. The dynamics of vortex pairings is also analysed to explain the whole acoustic field.     

Influence de la découpe d'éprouvettes en composite sur leur tenue mécanique

The preparation of composite coupons by cutting alters their mechanical properties according to the composite specificities, cutting conditions and test methods. This study shows this dependence through the coupons preparation, made from three polymer matrix composites, by different edge machining techniques (routing, endmilling, grinding or sawing) and using number of cutting tools (PCD, carbide, coated carbide and diamond wheel). The mechanical responses of both the tensile test on a ring specimens and the Iosipecu test coupons (ASTM D 5379) are correlated to the cutting conditions and the microscopic damage observations due to the cutting actions.     

Récents développements de la mesure des contraintes résiduelles par méthode ultrasonore. Les principales sources d'erreurs

Recent developments in measurements of the residual stresses by ultrasonic method. The main sources of errors. . Welding causes deformation of welded joints leading to the occurrence of residual stresses. Now, it is possible to evaluate the field of residual stresses, whether experimentally, or by calculation. The knowledge of the distribution and level of the residual stresses in welded components is an important factor, particularly for predicting the damaging and ruin phenomena of these components. This paper presents recent advances obtained in the field of an ultrasonic method for stress measurements. This method is potentially advantageous because it is nondestructive, easy and fast to use in situ. In the paper are presented the results obtained with ultrasonics on steel welded plate, and comparison is made with stress measurements obtained by incremental step-by-step hole drilling method. These results are also discussed after offset and “microstructure” corrections. The paper discusses also the influence of the principal sources of errors and the precision obtained.     

Modélisation du contact lubrifié—exemple de la mise en forme des métaux

Lubricated contact modelling — the example of metal forming processes. The theory of hydrodynamic (HD) lubrication was developed after the derivation of the Reynolds' equation in 1886. It allowed us to understand firstly low pressure lubricated contacts, then, when coupled with elastic deformation equations, high pressure lubricated contacts in elasto-hydrodynamic (EHD) lubrication. In the 60's, the same techniques were transposed to plasto-hydrodynamic lubrication (PHD), where one of the solids in contact is under plastic deformation, such as in metal forming processes. With the example of wire-drawing, the application of PHD models to metal forming is recalled. The importance of temperature effects on film formation and evolution was then an incentive to transposing thermo-EHD models into thermo-PHD. The roughness–lubricant flow coupling is then described, in EHD then in PHD. Finally, models of the mixed lubrication regime are addressed, whereby average contact pressure is borne partly by solid–solid, or micro-EHD, or boundary films, and partly by the hydrodynamic or hydrostatic pressure in the lubricant. Following a discussion of a few results on strip cold rolling, perspectives for evolution of these mixed regime PHD models are presented, in view of recent mixed-EHD models from the literature.     

Moulage par injection de poudres métalliques. Expérimentation,modélisation et simulation

Metal injection moulding. Experiment, modelling and simulation. The metal injection moulding process is used to produce small and complex metallic components. The first step is the injection of a mixture composed by a metallic powder and a thermoplastic binder. The binder is eliminated by a thermal or catalytic debinding. The last step is the sintering in order to obtain a part with the correct size and required mechanical properties. The metal injection moulding process is analysed using both experiments and computational modelling. A numerical approach for biphasic mixtures has been developed to analyse the flow of the feedstock during injection. The solution of the Navier–Stokes equations is made by an implicit finite element method. The mould filling simulation uses an Eulerian formulation with a VOF method. The simulation gives the density field in order to detect the segregation zones leading to an anisotropic shrinkage. The modelling of the solid state sintering is based on a viscoplastic model. The results obtained by experiments and numerical simulations are compared and reveal a good agreement. Furthermore, the components obtained after injection, debinding and sintering have the correct size and required mechanical properties.     

Représentation et échange de données techniques

Representation and exchange of industrial data. With the concept of digital mock up, and with all the software tools that generate and use technical data, the extended enterprise needs concepts, methods and tools for exchanging and for long term archiving the digitally-represented knowledge about its products. The aim of this paper is to present an overview on industrial data modeling and exchanging, both for representing enterprise products and for describing libraries of pre-existing components intended to be used in enterprise products. We first introduce the EXPRESS language, developed within the context of the STEP project (officially ISO 10303), for modeling highly structured industrial data. Then, we outline the information models developed in STEP for the computer-interpretable representation and exchange of product data, throughout the life cycle of products and for any kind of industry. In a third section we present the concepts and information models developed within the PLIB project (officially ISO 13584) for representing and exchanging digital libraries of industrial components. We discuss the achievements of both projects, developed in the same ISO committee. Then we present recent developments, performed first to integrate the data-oriented view (EXPRESS) and the document-oriented view (HTML/XML) on component libraries and/or electronic catalogues for the web, and, second, to integrate the STEP and PLIB models and capabilities.