Papers by Philippe Picart
Wear, 2012
This research on punch wear resulting from the blanking of copper alloy thin sheet has been condu... more This research on punch wear resulting from the blanking of copper alloy thin sheet has been conducted by means of experimental and numerical analyses. Firstly, the experimental method has consisted in measuring punch worn profiles from replicas, and secondly in obtaining the wear coefficient by using a specific tribometer. The numerical modelling of blanking process has been developed with the finite element method to compute the mechanical fields necessary to calculate wear. Thus, the Archard formulation for abrasive wear has been programmed to compute the wear depth and the resulting punch geometry. Finally the simulation results of wear prediction have been compared to experimental ones.
L'objectif du travail présenté est de proposer un outil numérique efficace pour simuler le p... more L'objectif du travail présenté est de proposer un outil numérique efficace pour simuler le procédé de découpage et pour déterminer les caractéristiques géométriques et mécaniques d'une pièce découpée. Le critère de rupture de Freudenthal a été utilisé pour prédire l'amorçage de la ...
L'etude innovante porte sur le micro fraisage d'un acier inoxydable 316L avec des micro f... more L'etude innovante porte sur le micro fraisage d'un acier inoxydable 316L avec des micro fraises cylindriques en carbure de tungstene de diametres inferieurs au millimetre, et avec des broches tournant jusqu'a 160 000 tr/min. Les investigations menees traitent de l'effet d'echelle (macro-micro) et sur la comprehension des phenomenes de coupe au travers de 'observation des micro outils, des copeaux, etats de surfaces, bavures et variations d'energies specifiques de coupe. L’etude presentee constitue une premiere etape dont l’objectif final est l’elaboration d’une approche instrumentee de la coupe en micro fraisage, ouvrant a la comprehension les phenomenes intervenant dans la coupe a l’echelle micro d’acier inoxydables type 316L.
Key Engineering Materials, 2003
Journal of Materials Processing Technology, 2009
ABSTRACT A numerical formulation of the blanking process in 2D is presented in this article. A fi... more ABSTRACT A numerical formulation of the blanking process in 2D is presented in this article. A finite element software called BlankForm has been developed to simulate the blanking process. Several approaches to model ductile damage and fracture have been investigated and are presented in this paper. In particular, some details are provided about a discrete cracking method that has been developed to take the propagation of one or several cracks into account. Our formulation is evaluated on an axisymmetric blanking experiment. The importance of remeshing is demonstrated. Coupled and uncoupled damage models are benchmarked, and two methods for fracture simulation are analysed, namely the previous discrete cracking method, and a widely used method in blanking applications, the element kill method. It is shown that more realistic results are obtained when the discrete cracking method is used.
Precision blanking process is widely used by electronic and micromechanical industries to produce... more Precision blanking process is widely used by electronic and micromechanical industries to produce small and thin components in large quantities. To take account of the influence of strain rate and temperature on precision blanking of thin sheet in copper alloys, we have proposed a thermo-elasto-visco-plastic modelling. In addition, dynamic recrystallization takes place in Cual copper alloy during the blanking process of thin sheet. A new modelling of dynamic recrystallization based on the thermodynamics of irreversible ...
Revue européenne de mécanique numérique, 2007
L’objectif du travail présenté est de proposer un outil numérique efficace pour simuler le procéd... more L’objectif du travail présenté est de proposer un outil numérique efficace pour simuler le procédé de découpage et pour déterminer les caractéristiques géométriques et mécaniques d’une pièce découpée. Deux stratégies distinctes sont proposées pour simuler la propagation de fissures : une méthode d’élimination des éléments finis et une approche de fissuration discrète. En premier lieu, ces deux méthodes ont été évaluées sur l’exemple-test d’une plaque asymétrique en traction. En second lieu, la capacité de ces deux méthodes de propagation à prédire un profil de rupture réaliste est analysée dans le cadre du découpage. Les courbes effort-déplacement du poinçon obtenues par ces deux méthodes de propagation de fissures sont comparées à des courbes expérimentales.
Nickel based alloys are extensively used in the aerospace industry due to the excellent corrosion... more Nickel based alloys are extensively used in the aerospace industry due to the excellent corrosion resistance and high mechanical properties that are maintained up to elevated temperatures (600-800 °C). However, these superalloys are classified as difficult-to-cut and therefore modelling and simulation of the machining processes has become a key in the machinability assessment of nickel based alloys. The reliability of Finite Element Models (FEM) largely depends on the quality of input parameters, one of the most relevant being the constitutive material model representing work material behavior under high strain, strain rate and temperatures. In order to develop a reliable material model, the present work deals with a complete characterization of Inconel 718. Uniaxial compression tests at testing temperatures close to those found in machining (21-1050 °C) and high strain rates (10°−10 2 s −1) were performed on the Gleeble 3500 testing machine. Moreover, the microstructural analysis and microhardness measurements of the testing samples were performed, in order to correlate the microstructural state with the mechanical properties of the Inconel 718. Based on this experimental work, a new coupled empirical model is proposed to describe the particular behaviour of nickel based alloys at elevated temperatures and high strain rates. This material behaviour model introduces softening phenomena as well as the coupling between the temperature and the strain rate known to occur experimentally, for machining FEM simulations with Inconel 718 superalloy.
Journal de Physique …, 2002
Résumé. Les travaux présentés concernent l'analyse du comportement des métaux fins en découp... more Résumé. Les travaux présentés concernent l'analyse du comportement des métaux fins en découpage. Un dispositif expérimental a été réalisé au LMARC Il permet de découper des échantillons d'épaisseur comprise entre 0. 1 mm et 0. 5 mm. Une méthodologie de caractérisation ...
Large Plastic Deformations
Communications in Applied Numerical Methods
ABSTRACT
International Journal of Material Forming
The development of cold metal forming processes for very small mechanical components by forging, ... more The development of cold metal forming processes for very small mechanical components by forging, coining, stamping, extrusion is limited by the understanding of geometric and material effects due to the size reduction of the components. In this study a set of experiments is performed on a copper alloy (CuZn10) where the diameter of the cylinder is scaled down from 5mm to 1mm, in order to evaluate the size effects on the flow stress. Compression tests were carried out by reducing the height of the cylinder by 80% at a constant rate of 0.03 mm/s and without lubricant. During these tests, the load-displacement curve can be plotted. For each specimen size the material behaviour is obtained. The material parameters were identified by an inverse method using the code LS-Dyna. Then, considering the results, a new model of the constitutive behaviour is proposed which takes into account size effects. This model is function of a semi-intrinsic parameter, the share of surface grains.
International Journal of Damage Mechanics
A radial return algorithm is developed for large strain elasto-plastic struc tures in order to ea... more A radial return algorithm is developed for large strain elasto-plastic struc tures in order to easily compute microvoid volume fraction rates. The basic feature subroutines are described in detail and forwards four typical problems are analysed: Q4 element tensile test, Q4 element compression test, notched cylinder tensile test and pipe bulging. The influence of microvoids volume fraction is clearly enhanced, mainly in regard to hydrostatic stress.
AIP Conference Proceedings, 2007
ABSTRACT In microforming, the so-called size effects can be observed in the material flow behavio... more ABSTRACT In microforming, the so-called size effects can be observed in the material flow behaviour as well as in the frictional behaviour. In order to study the frictional behaviour a preliminary numerical characterization of the surface tribology has been carried out. A numerical design of experiments (DOE) is based on cylinder upsetting tests to define the influence of surface geometric properties on the resultant force. The simulations have been performed with the finite element software LS-Dyna by using an axisymmetric model. The mechanical behaviour of the cylinder specimen was described by an elastic-plastic material law, whereas the upsetting plates were assumed to be rigid. The workpiece is considered to be a copper alloy (CuZn10). The average roughness Ra and the average mean spacing Sm have been chosen to describe surface roughness properties. The tool and workpiece surfaces have been modelled using a sinusoidal profile. The five input parameters of the DOE are the amplitude and the period of the two sinusoidal profiles and the phase displacement between them. The analysis of variance shows the statistically significant parameters or interactions.
AIP Conference Proceedings, 2007
ABSTRACT Blanking process is widely used by electronic and micromechanical industries to produce ... more ABSTRACT Blanking process is widely used by electronic and micromechanical industries to produce small and thin components in large quantities. To take into consideration the influence of strain rate and temperature on precision blanking of thin sheet in copper alloy, a thermo-elasto-visco-plastic modelling has been developed in [1]. Furthermore the blanking of thin sheet in Cual copper presents dynamic recrystallization. A new modelling of dynamic recrystallization based on the thermodynamics of irreversible processes is proposed. Blanking simulations of Cual copper sheet are performed to analyze the softening effect induced by dynamic recrystallization.
International Journal of Material Forming, 2008
Journal of Materials Science and Engineering A, 2015
The study focuses on micro-milling of a hardened tool steel with micro ball-end mills. The purpos... more The study focuses on micro-milling of a hardened tool steel with micro ball-end mills. The purpose is to observe the capability of a set of these mills to machine hard steels used for tooling applications. Different cutting configurations are here tested in order to evaluate their performance and finally enhance their design in this context. Experimental data, in terms of cutting forces, surfaces integrity and machining errors, is obtained from machining tests on a 40NiCrMo16 hardened steel with 0.5 mm diameter coated tungsten carbide micro-tools. The results allow highlighting some cutting, wear and dynamical phenomena related to the process. They are mainly associated to the types of mill and cutting conditions, as feed or tool/surface inclination. In this paper, the tool geometry and its dynamical behavior are mainly discussed.
L'amélioration de la productivité des découpeurs de leadframes (supports pour composants électron... more L'amélioration de la productivité des découpeurs de leadframes (supports pour composants électroniques) repose sur plusieurs axes de recherche. La découpabilité des alliages cuivreux, c'est-à-dire leur faculté à être découpés, est le thème de cette étude. Dans cet article, nous cherchons à établir quels sont les paramètres de la matière découpée qui sont influents vis-à-vis du profil de découpe, de l'effort de découpe et de l'usure des parties actives du poinçon. Pour ce faire, des essais de découpe d'alliages de cuivre couramment utilisés ainsi que de nuances originales, notamment en terme de microstructure, nous ont permis de montrer que le profil de découpe était fortement influencé par les caractéristiques mécaniques et la microstructure des alliages et que la bavure de découpe ainsi que l'usure des poinçons étaient eux uniquement conditionnés par la microstructure, et en particulier par les précipités présents dans la matrice de cuivre.
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Papers by Philippe Picart