THREE-DIMENSIONAL NAVIER-STOKES PREDICTION OF HEAT TRANSFER WITH FILM COOLING

Three-dimensional Navier-Stokes calculations have been performed on various geometries in the presence of discrete-hole injection. The quality of the aerodynamic and thermal predictions of the flow is assessed by comparison . to experiments. The code used for the calculations is developed at ONERA and haS previously been presented by various authors . It solves the unsteady set of three-dimensional Navier-Stokes equations, completed by a mixing-length turbulence model, using a finite volume technique. The multi-domain approach of the code has facilitated the treatment of this type of geometry. The injection holes are discretized on cylindrical subdomains which overlap the mesh of the main flow. Two applications of the code are presented in this paper. First, a calculation was performed on a row of hot jets injected into a flat plate turbulent boundary layer. Secondly, the code was tested on a plane nozzle guide vane grid with multiple injections. Heat transfer rates, temperature and velocity profiles are compared to experimental data

River histories : A thematic review

Peer reviewe

Early stages of fatigue damage in aluminium and aluminium alloys

In this paper fatigue damage initiation is considered as both microcrack nucleation from microheterogeneities within fatigued material and microcrack growth over distances corresponding to the size of the microstructure. A brief review of the literature shows that, depending on fatigue conditions and microstructure three different types of nucleation sites exist in aluminium and aluminium alloys : slip bands, grain boundaries and brittle particles. In the last part of this paper tentative to obtain a general view of fatigue damage initiation is made from theoritical considerations taking into account incompatibility problems between matrix and microheterogeities

PART 1‐Casting and Solidification‐Pore Characterization in a Model Cast Aluminum Alloy and its Quantitative Relation to Fatigue Life Studied by Synchrotron X‐Ray Microtomography

International audienceno abstrac

Mechanical properties of aluminium-based metal matrix composites reinforced with α-alumina platelets

The tensile properties of an aluminium-based metal matrix composite reinforced with [MATH]-alumina platelets were investigated from an experimental and a theoretical point of view. An increase in Young modulus, 0,2% proof stress, flow stress and ultimate tensile strength was observed over the unreinforced metal. These improvements were obtained at the expense of the tensile ductility. The experimental results were analyzed using both a dislocation model and a continuum model based on an iterative Eshelby method

INTERACTIONS BETWEEN DISLOCATIONS AND CRYSTALLINE DEFECTS DURING THE CYCLIC DEFORMATION OF A 0.7 Wt% Al-Li ALLOY

In the aerospace industry requirements for new materials with high mechanical properties and low density has stimulated research works in Al-Li alloys. For ten years numerous studies have been developed in order to promote complex alloys having convenient mechanical and physical properties, and able to replace conventional alloys /1/ and /2/. From a fundamental point of view basic researchs to study the microscopic mechanisms controlling the mechanical behauiour of Al-Li alloys have to entered upon because several microscopic mechanisms are not well understood. Such investigations were first conducted on binary Al-Li alloy in solid solution state or having a fine distribution of δ' (Al3Li) precipitates, according to the amount of lithium atoms. Tensile properties /3/ or cyclic behaviour /4/, /5/ have been investigated. The ain of this paper is to determine in terms of dislocation-crystalline defect interactions the microscopic mechanisms involved in the cyclic deformation of a solid solution of a binary Al-Li alloy, containing 0.7 Wt % of lithium. This work is a part of a whole research program devoted to Al-Li binary alloys in our laboratory and therefore is complementary to studies presented in reference /5/

THE PHENOMENON OF STRESS INSTABILITIES IN Al-Li BINARY ALLOYS AND MICROSCOPIC MECHANISMS CONNECTED

For several years it has been well established that aluminium alloys with lithium additions are very attractive for aerospace applications, since they offer interesting combinations of high specific strength and high specific modulus /1/, /2/. Numerous studies were carried out in order to obtain optimum mechanical properties by modifying suitably microstructures /3/, /4/, /5/. Mechanical properties are mainly dependent on interactions between dislocations and precipitates, especially δ' (Al3Li) precipitates. Fundamental studies were carried out on Al-Li binary alloys exhibiting only δ' precipitates /6/. We have entered upon a study concerning the identification of microscopic mechanisms which control the cyclic deformation of Al-Li binary alloys. During fatigue tests, we have discovered an interesting substructure in hysteresis loops corresponding to stress instabilities in fatigue behaviour which are rigorously coupled with a strain age hardening phenomenon. The aim of this paper is to describe this phenomenon which is typical of the fatigue behaviour of Al-Li binary alloys with small δ' precipitates. In the last part of this paper, this unstable behaviour is compared to the PORTEVIN-LE CHATELIER (PLC) phenomenon. In addition, microscopic mechanism that control stress instabilities and strain age hardening are analysed in terms of interactions between dislocations and δ' precipitates

A model for damage in a clustered particulate composite

International audienceno abstrac