Comprehension of chip formation in laser assisted machining

Laser Assisted Machining (LAM) improves the machinability of materials by locally heating the workpiece just prior to cutting. Experimental investigations have confirmed that the cutting force can be decreased, by as much as 40%, for various materials. In order to understand the effect of the laser on chip formation and on the temperature fields in the different deformation zones, thermo-mechanical simulations were undertaken. A thermo-mechanical model for chip formation was also undertaken. Experimental tests for the orthogonal cutting of 42CrMo4 steel were used to validate the simulation. The temperature fields allow us to explain the reduction in the cutting force and the resulting residual stress fields in the workpiece.Contrat Plan Etat Région (CPER) Pays de la Loir

Remarques sur les symbolismes du Commentaire sur la République de Proclus

De part en part traversé par le mythe, le Commentaire sur la République du Néoplatonicien Proclus accorde forcément une attention soutenue au symbole. Cet article se propose de mettre en lumière deux types de symbolisme que l’on trouve dans ce Commentaire. Le premier, « non imitatif », reconfigure significativement l’héritage des Formes intelligibles platoniciennes ; le second, tiré des Oracles chaldaïques, consiste en une « intériorisation » du symbole. Les deux symbolismes se rejoignent en ce qu’ils impliquent une sympathie profonde entre toutes choses, et présupposent la communication préalable des symboles tant dans la genèse que dans l’interprétation du mythe inspiré.Given the importance awarded to myth in the Commentary on the Republic by the Neoplatonist Proclus, it should come as no surprise that symbolism is a central issue in that work. This article aims to shed some light on two kinds of symbolism found in the Commentary : the first, “non-imitative” kind, significantly reconfigures the symbolism implied by the Platonic Forms ; the second kind, which comes from the Chaldean Oracles, consists in what we call the “interiorization” of the symbol. These symbolisms converge in that they point to the sympathy that exists between all things, just as they assume the prior communication of the symbols in both the genesis and the interpretation of the inspired myth

Mythe et éducation : Proclus et la critique platonicienne de la poésie

Le présent article se propose de mettre en lumière non seulement la critique platonicienne de la poésie telle qu’elle se déploie dans les livres II, III et X de la République, mais aussi — et surtout — la lecture qu’en fait le néoplatonicien Proclus dans son vaste Commentaire sur la République. Le principal enjeu de cette lecture est le lien entre le mythe et l’éducation. Nous verrons d’abord comment Platon s’emploie à lier ces deux éléments, puis comment Proclus cherche pour sa part à relativiser ce lien, au point où mythe et éducation en viennent, sinon à s’exclure mutuellement, du moins à n’entretenir qu’un faible commerce.This article aims to shed some light not only on the Platonic critique of poetry as it is articulated in books II, III and X of the Republic, but also — and chiefly — on the Neoplatonist philosopher Proclus’ very personal reading of that critique in his vast Commentary on the Republic. The crux of this reading is the link between myth and education. We will first witness how Plato tries to tie those two elements together, and then how Proclus attempts to minimize this relationship, to the point where myth and education, although they do not exclude one another, come to share very little common ground

Experimental and numerical analysis of micromechanical damage in the punching process for High-Strength Low-Alloy steels

Sequential sheet metal forming processes can result in the accumulation of work hardening and damage effects in the workpiece material. The mechanical strength of the final component depends on the “evolution” of these two characteristics in the different production steps. The punching process, which is usually in the beginning of the production chain, has an important impact on the stress, strain and damage states in the punched zones. It is essential that the influence of these mechanical fields be taken into account in the simulation of the forming sequence. In order to evaluate the evolution of each phenomenon, and in particular damage accumulation in the forming process, it is essential to characterize the punching process. The objective of this work is to understand and identify the physical damage mechanisms that occur during the punching operation and to establish relevant numerical models to predict the fracture location. The effect of the punch–die clearance on mechanical fields distribution is also discussed in this work

Numerical integration of an advanced Gurson model for shear loading: Application to the blanking process

A new extension of the Gurson damage model has been proposed recently to predict ductile fracture under shear dominated loads. The aim of this work is to verify the ability of this approach to simulate, in an accurate way, the damage evolution in shearing processes. An implicit stress integration algorithm is then developed to implement the new model in a finite element code. The numerical procedure is checked through simulations of shear and uniaxial tension tests on a single elements. The extended Gurson damage model is tested and applied to the punching process to compare its predictive ability with the original approach. The obtained numerical results are in good agreement with experimental results of the punching process, showing better ductile fracture predictions compared to the original Gurson model

Experimental characterization and numerical modeling of micromechanical damage under different stress states

The use of HSLA steels for the manufacture of automotive components is interesting from an engineering point of view. This family of steels, while possessing high strength, also has good formability and can be used in forming manufacturing processes. In some forming processes such as blanking, shear strain localization occurs, which causes damage and results in the final fracture of the material. This paper presents an experimental study based on in situ tests to understand and identify the physical mechanisms of ductile damage under two stress states: tension and shear. Different macroscopic tests were performed to calibrate a damage model based on a micromechanical approach. This damage model is based on the Gurson–Tvergaard–Needleman theory and presents recent improvements proposed by Nahshon and Hutchinson and by Nielsen and Tvergaard so as to better predict fracture under a wide range of stress states, especially with low levels of stress triaxiality. These extensions have made the identification of the material parameter more complicated. In this work an identification strategy has been proposed using tests on specimens with different shapes. The identified parameter values are validated and the fracture model show good predictive capability over a wide stress state range

REAL-TIME DETECTION OF THE ACTIVITY OF A DOG

International audienceThis paper introduces our preliminary work with assistance dogs. Even when dogs are very well trained some problems may occur in practice, typical examples are dog escaping or running after a cat. Our long term objective is to take advantage of the technology to increase the safety of the dog and its owner. Our first work focuses on the activity classification of the dog. This paper presents preliminary results for recognizing four types of activity: walk, run, lay and sit down. Experiments and results on real data collected with low-cost gyroscopes and accelerometers are presented and discussed