Alternator | EPFL Graph Search

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines. An alternator that uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven by steam turbines are called turbo-alternators. Large 50 or 60 Hz three-phase alternators in power plants generate most of the world's electric power, which is distributed by electric power grids. History Alternating current generating systems were known in simple forms from the discovery of the magnetic induction of electric cur

Comportement en traction d'éléments en Béton de Fibres Ultra Performant combiné aces des barres d'armature

Eugen Brühwiler, Emmanuel Denarié, Julien Michels, John Wuest

L’objectif des interventions sur des ouvrages d’art est d’améliorer la durabilité et d’augmenter la résistance pour assurer la sécurité structurale. La combinaison de BFUP avec des armatures, peuvent répondre à ces exigences. Le comportement à la rupture de tirants en BFUP a donc été étudié. Deux paramètres ont été testés, il s’agit du taux d’armature et de la nuance d’acier. Les résultats montrent l’effet favorable de la combinaison d’armatures avec du BFUP que ce soit pour l’amélioration du comportement à la fissuration ou de la capacité portante de l’élément tendu. La conclusion de cette étude est que la combinaison BFUP-armature présente un potentiel élevé pour le renforcement d’ouvrage.

2005

Prediction of tantalum microstructure evolution during thermomechanical treatments using FEM calculations with a dislocation density based constitutive law

Roland Logé

In this paper, the behaviour of the tantalum subjected to a complex range of thermomechanical solicitations is studied and modelled. The objective of this work is the prediction of microstructure evolution of a tantalum part that is cold flow-formed, then stress-relieved and softened by heat treatments. Flow forming is a cold chipless process that elongates and thins the wall of a tubular part by applying a free rotating roller on the wall of the rotating part. (See Figure 1) This process leads to large strain up to 5 and one material point may be deformed at a fluctuating strain rate. To model this process, it is thus recommended to use a constitutive law that takes into account the history of the material. Microstructure evolution is controlled through the whole process by monitoring the state variable, that is, the dislocation density, within a FEM code. The 3D FEM software FORGE2007® is used to model the entire process. The code is enhanced with physical constitutive laws relative to the tantalum and derived from works of Klepaczko and Buy et al. [1,2,3]. The formalism of Klepaczko and Buy et al. is useful since it is based on laws regulating physical mechanisms of dislocations multiplication, annihilation and kinetics of glide depending on strain rate and thermal activation. Static recovery is modelled subsequently with an incremental approach where the softening is related to the dislocation density evolution. A set of thermomechanical experiments and treatments are done to identify the constitutive law and associated microstructure evolution. Compression, dynamic and static torsion tests covering a wide range of strain rates are used to fit the mechanical constitutive law and the dislocation density evolution law both inspired from Klepaczko and Buy et al. works. The same samples are then annealed with variable temperatures and times. Microstructure of annealed samples is characterized by means of micro-hardness. They give information to evaluate the dislocation density evolution. The data is used to model static recovery.0.

Hanrimwon Publishing Co.2008

Prediction of tantalum microstructure evolution during thermomechanical treatments using FEM calculations with a dislocation density based constitutive law

Roland Logé

Hanrimwon Publishing Co.2008