Calorimetric consequences of thermal softening in Johnson–Cook’s model

At high loading rates, the development of adiabatic shear bands in metals is conventionally attributed to the strong interactions induced by viscoplastic dissipation within the bands and thermal softening effects. The rheological equation proposed by Johnson and Cook takes both viscoplastic hardening and thermal softening into account. The present paper reviews and includes this equation into a thermodynamic framework in order to analyse the energy impacts of thermal softening. Indeed this latter implies the existence of a ther-momechanical coupling source, probably non-negligible and which must be considered when estimating temperature variations induced by shear band development

L'anthropologie du développement aux Etats-Unis : force et promesses d'une nouvelle profession

Au sein de la tradition "appliquée" de l'anthropologie américaine et, en dépit de nombreux obstacles (éthiques d'une part, politiques et institutionnels d'autre part), une discipline est devenue une profession à part entière : l'anthropologie du développement. Forte de nouveaux savoirs, savoir-faire et méthodes, décomplexée, extrêmement constructive, la nouvelle profession est de plus en plus considérée, au sein des organismes de développement, comme indispensable à la réussite effective (pour les organismes comme pour les populations) des projets de développement. Elle contribue de plus à l'élaboration et à l'enrichissement de nouveaux savoirs disciplinaires (théorie anthropologique de la pratique de développement, anthropologie dynamiste, savoirs spécialisés par types de projets). Encore fragile, cette nouvelle profession semble cependant bien armée désormais pour s'imposer véritablement dans le monde du développement. (Résumé d'auteur

High Speed Blanking: An Experimental Method to Measure Induced Cutting Forces

Lien vers la version éditeur: http://link.springer.com/article/10.1007/s11340-013-9738-1A new blanking process that involves punch speed up to 10 ms −1 has obvious advantages in increased productivity. However, the inherent dynamics of such a process makes it difficult to develop a practical high speed punch press. The fracture phenomenon governing the blanking process has to be well understood to correctly design the machine support and the tooling. To observe this phenomenon at various controlled blanking speeds a specific experimental device has been developed. The goal is to measure accurately the shear blanking forces imposed on the specimen during blanking. In this paper a new method allowing the blanking forces to be measured and taking into account the proposed test configuration is explained. This technique has been used to determine the blanking forces experienced when forming C40 steel and quantifies the effect of process parameters such as punch die clearance, punch speed, and sheet metal thickness on the blanking force evolution

Very high cycle fatigue of copper: Evolution, morphology and locations of surface slip markings

The surfaces of commercially pure polycrystalline copper specimens subjected to interrupted 20 kHz fatigue tests in the very high cycle fatigue regime were investigated. The stress amplitude needed to form the early slip markings was found twice lower than the stress amplitude required to fracture which confirmed the results obtained by Stanzl-Tschegg et al. (2007). Three types of slip markings were classified according to their morphology and their location in the polycrystalline material. They are compared to slip markings observed during fatigue tests at frequencies lower than 100 Hz and numbers of cycles lower than 107. For 20 kHz fatigue tests, stress amplitudes ranging from 45 MPa to 65 MPa produce straight and long early persistent slip markings located along twin boundaries. Stress amplitudes lower than 45 MPa produce clusters of fine early persistent slip markings mainly located at triple junctions

Protection biologique contre ravageurs aériens sur tomate sous abris : compte-rendu d'essai 2005

En agriculture biologique, les moyens de protection contre les ravageurs aériens sont coûteux et leur efficacité est parfois insuffisante. La pratique des brumisations sous abris réduit les températures et augmente l’hygrométrie, et peut améliorer la protection contre l’acarien Tetranychus urticae, comme l'ont montré les essais du GRAB conduits de 2002 à 2004 sur melon, aubergine et concombre. Cet essai a pour objectif d’étudier l’intérêt de la brumisation et de la lutte biologique contre l'ensemble des ravageurs aériens sur tomate : acariens, aleurodes, pucerons, thrips

Simulation of green wood milling with discrete element method

This work was carried out in LaBoMaP and PIMM at Arts et Metiers ParisTech. We acknowledge I2M laboratory for their technical support in Discret Element Method; Robert Collet, Louis Denaud, Guillaume Pot; PIMM and LaBoMaP technicians and Morgane Pfeiffer-Laplaud for their availability and advice.During the primary transformation in wood industry, logs are faced with conical rough milling cutters commonly named slabber or canter heads. Chips produced consist of raw materials for pulp paper and particleboard industries. The process efficiency of these industries partly comes from particle size distribution. However, chips formation is greatly dependent on milling conditions and material variability. Numerical simulation of chip fragmentation can allow some useful chip thickness prediction. In this complex situation in wood cutting, the utilization of the Discrete Element Method (DEM) is relevant. In this method, solids are modeled with spherical discrete elements linked by cohesive bonds. However the Discrete Element Method requires a previous calibration step with simple mechanical loading. For example the nature and the mechanical properties of the cohesive bonds must be determined. After an analysis of the different mechanical loadings in green wood milling, a complete study of green wood compression is carried out. This experimental study covers the strain rates range of 10-3 to 103 s-1 using a hydraulic compression machine and the Split Hopkinson Pressure Bar technique. Wood specimens at different moisture content states are compressed longitudinally. This study enables us to observe the viscoelastic and hygroscopic behaviour of wood. The experimental and qualitative simulation results show that elastic brittle beams are not well adapted to be used in quantitative green wood milling simulations