98 research outputs found
Multi-scale approach of the instrumented indentation technique on the fracture toughness estimation
Instrumented Indentation Technique (IIT) is widely used to determine the mechanical properties of materials. The elastic modulus is usually determined by applying the methodology proposed by Oliver and Pharr [1] who supposed that its value is independent of the indentation depth. However, some authors [2, 3] have observed a decrease of the elastic modulus when the indenter displacement increases which allowed them to introduce a continuous damage theory used afterwards to estimate the fracture toughness of ductile materials. The assumption made by the authors is that a damage in the region very close to the bottom of the indent results in the formation of microvoids which leads to the variation of the elastic modulus as a function of the indenter displacement. Starting from this observation, Lee et al. [2] proposed an energy model based on the Griffithâs theory and the continuous damage mechanics (CDM) which states that the elastic modulus variation is related to the fraction void volume through a variable damage, introduced by Kachanov [4], related to the surface density of the microdefects. On the other hand, the works carried out over ductile materials by Li et al. [3] have been performed only with nanoindentation data preventing a discussion on the scale-Ââeffect. (...
Exploitation of static and dynamic methods for the analysis of the mechanical nanoproperties of polymethylmetacrylate by indentation
The development of instrumented nanoindentation consists of non-destructive tests applied to miniature volumes of material (PMMA). The present research focuses on the factors explaining the variation in the trends of the mechanical properties studied. The evolution of Young's modulus (E) and contact hardness (H) with depth (h) and indentation force (P) shows the existence of an inflection point (2.77 nm) at low penetrations which separates two zones with the first increasing trend and the second decreasing. Explained respectively by the surface hardening induced by the preparation of the material surface and the existence of a surface hardness gradient denoted by the indentation size effect (ISE) observed at very low depths. In addition, on detection of a critical penetration depth below which the effect of the surface on the nanohardness dominates, the variation in the penetration charge is of the order of 9.71 nm. The differences in results of E and H between the dynamic and static modes are of the order of 8.46% and 6.44% inducing an overestimation of 35 MPa in value of E and an underestimation of 1.23 MPa in value of H. They tend to affect the expected nanoscale precision of the indentation to determine the nanomechanical properties of PMMA
AmĂ©lioration de lâintĂ©gritĂ© des surfaces plates usinĂ©e de lâalliage d'aluminium 2017A par l'application de six nouvelles stratĂ©gies de galetage Ă bille.
Le galetage Ă bille est un traitement mĂ©canique superficiel de finition et de parachĂšvement des surfaces mĂ©canique fonctionnelles [1]. Il est largement pratiquĂ© suite Ă lâusinage des surfaces de formes cylindriques [2-3-4], sphĂ©riques [5], concaves ou convexes [6], plates [7] ou de formes complexes [5] des piĂšces mĂ©caniques. GĂ©nĂ©ralement lâamĂ©lioration de la rĂ©sistance Ă lâusure est le rĂ©sultat de lâamĂ©lioration de lâintĂ©gritĂ© des surfaces traitĂ©es par la recherche, la maitrise et lâoptimisation des paramĂštres significatifs du procĂ©dĂ© du galetage Ă billes. Dans la prĂ©sente recherche nous rĂ©vĂ©lons lâinfluence de la variation de lâapplication des stratĂ©gies de galetage Ă bille sur lâamĂ©lioration de lâintĂ©gritĂ© des surfaces plates de lâalliage dâaluminium 2017A pour les valeurs optimum de lâavance latĂ©rale, la vitesse de galetage, la profondeur de pĂ©nĂ©tration. Le travail expĂ©rimental, menĂ© dans cette Ă©tude possĂšde comme objectif lâapplication de six stratĂ©gies de galetage Ă bille de la surface plate des Ă©chantillons en alliage dâaluminium 2017A. Lâusinage des surfaces Ă©chantillons et leurs traitement superficiel par galetage Ă bille ont Ă©tĂ© rĂ©alisĂ© sur le mĂȘme centre dâusinage Ă commande numĂ©rique SPINNER VC650 Ă trois axes
Caracterisation des proprietes mecaniques par nanoindentation dâun revĂȘtement de zinc pour differentes epaisseurs de tĂŽles galvanisees
La nano-indentation permet de connaĂźtre les propriĂ©tĂ©s mĂ©caniques des surfaces ou des couches minces, en particulier leur duretĂ© et leur module d'Ă©lasticitĂ© rĂ©duit. Ce travail porte sur la dĂ©termination des propriĂ©tĂ©s mĂ©caniques dâun revĂȘtement de Fer-zinc formĂ© sur un substrat en acier de construction laminĂ© Ă froid avec diffĂ©rentes Ă©paisseurs de tĂŽles. Ce revĂȘtement, typiquement dâune Ă©paisseur de lâordre 10-20 ÎŒm rĂ©sultant dâun traitement de galvanisation, est constituĂ© des phases ĂȘta, dzĂȘta, delta et gamma (interface substrat/revĂȘtement). Les Ă©chantillons sont issus de tĂŽles galvanisĂ©es dans les conditions dâArcelor Mittal Annaba. Les essais de nano indentation ont Ă©tĂ© menĂ©s en mode continu Ă lâaide dâun appareil Nano-Indenter XP ©. Lâavantage de ce mode (CSM), est de rendre possible la mesure du contact indenteur/Ă©chantillon et donc la duretĂ© (H) et le module de Young (E) tout au long de la phase de pĂ©nĂ©tration. Seize empreintes ont Ă©tĂ© rĂ©alisĂ©es sur diffĂ©rentes Ă©paisseurs de tĂŽle (0.4mm ; 0.7mm; 1mm et 1.5mm), sur chacun des deux constituants (couche Fe-Zn et substrat) ; celles rĂ©alisĂ©es sur le substrat servant Ă valider lâapproche inverse Ă Ă©tablir pour dĂ©terminer le comportement du revĂȘtement
Etude des proprietes mecaniques des couches galvanisees par nanoindentation
Les revĂȘtements industriels Fe-Zn constituent une large gamme des semi-produits de galvanisation en continu de tĂŽles minces destinĂ©es Ă lâindustrie de la carrosserie automobile. Ce revĂȘtement, typiquement dâune Ă©paisseur de lâordre de 10 ÎŒm, rĂ©sultant dâun traitement de post-galvanisation est constituĂ© dâune phase ĂȘta, dzĂȘta, delta et gamma (interface substrat/revĂȘtement)
A new method to fabricate Fe-TiC composite using conventional sintering and steam hammer
The aim of this research paper is to fabricate a Fe-TiC composite by a novel and simple manufacturing method. The latter is based on two cumulative processes; a conventional sintering (transient liquid phase sintering) and a hot forging with steam hammer respectively. The blinder phase of the studied simples is varied from carbon steel to high alloy steel using alloying additive powders. The obtained outcomes showed that after the sintering process, the relative density of the performed simples is improved from 86% to 95.8% without any densification process. Otherwise, in order to ensure maximum densification and enhance in addition the solubility of the alloying additives the hot forging process is then applied. Indeed, the final obtained composite product is a TiC-strengthened steel with a relative density around 99% (about 6.5 g/cm3 of density) wherein 30% (wt.) of spherical and semi-spherical TiC particles are homogeneously distributed in the metal matrix
AmĂ©lioration de lâintĂ©gritĂ© des surfaces plates usinĂ©e de lâalliage d'aluminium 2017A par l'application de six nouvelles stratĂ©gies de galetage Ă bille.
Le galetage Ă bille est un traitement mĂ©canique superficiel de finition et de parachĂšvement des surfaces mĂ©canique fonctionnelles [1]. Il est largement pratiquĂ© suite Ă lâusinage des surfaces de formes cylindriques [2-3-4], sphĂ©riques [5], concaves ou convexes [6], plates [7] ou de formes complexes [5] des piĂšces mĂ©caniques. GĂ©nĂ©ralement lâamĂ©lioration de la rĂ©sistance Ă lâusure est le rĂ©sultat de lâamĂ©lioration de lâintĂ©gritĂ© des surfaces traitĂ©es par la recherche, la maitrise et lâoptimisation des paramĂštres significatifs du procĂ©dĂ© du galetage Ă billes. Dans la prĂ©sente recherche nous rĂ©vĂ©lons lâinfluence de la variation de lâapplication des stratĂ©gies de galetage Ă bille sur lâamĂ©lioration de lâintĂ©gritĂ© des surfaces plates de lâalliage dâaluminium 2017A pour les valeurs optimum de lâavance latĂ©rale, la vitesse de galetage, la profondeur de pĂ©nĂ©tration. Le travail expĂ©rimental, menĂ© dans cette Ă©tude possĂšde comme objectif lâapplication de six stratĂ©gies de galetage Ă bille de la surface plate des Ă©chantillons en alliage dâaluminium 2017A. Lâusinage des surfaces Ă©chantillons et leurs traitement superficiel par galetage Ă bille ont Ă©tĂ© rĂ©alisĂ© sur le mĂȘme centre dâusinage Ă commande numĂ©rique SPINNER VC650 Ă trois axes
CaractĂ©risation mĂ©canique de revĂȘtements sol-gel hybrides
Nous avons dĂ©veloppĂ© une solution sol-gel hybride organique-inorganique qui, aprĂšs application par trempĂ© ou pulvĂ©risation et suivi dâune Ă©tape de cuisson, permet dâapporter une protection contre la corrosion. Cette solution a Ă©tĂ© mise au point afin de pouvoir remplacer un acier inox 316L par un couple « inox 430 + dĂ©pĂŽt sol-gel » tout en conservant les mĂȘmes propriĂ©tĂ©s Ă©lectrochimiques. En parallĂšle Ă lâĂ©tude des propriĂ©tĂ©s Ă©lectrochimiques, nous avons dĂ©veloppĂ© une mĂ©thodologie pour caractĂ©riser les propriĂ©tĂ©s mĂ©caniques du revĂȘtement (duretĂ©, module dâĂ©lasticitĂ©, tĂ©nacitĂ©) ainsi que son adhĂ©rence sur le substrat
Scale effect on tribo-mechanical behavior of vegetal fibers in reinforced bio-composite materials
The nature of friction of vegetal fiber and polymeric matrix in bio-composite materials is very important for many industrial applications. In order to design natural fiber composites for structural applications, the scientific understanding of tribo-mechanical phenomena inside the heterogeneous structure of natural fibers and also the overall heterogeneous structure of the bio-composite is required. This implies a special focus on the fundamental aspects of vegetal fiber friction at the macro-, meso-, and microscale. This research paper investigates the multiscale mechanical and friction properties of natural fibers. The mechanical properties of flax fibers, glass fibers (as a reference) and polypropylene matrix has been evaluated at microscale and mesoscale by Atomic Force Microscopy (AFM) and Nanoindenter XP (MTS Nano Instruments), respectively, using nanoindentation technique. At the macroscale, the mechanical behavior has been considered for the global composite structure. The micro-friction response of each composite component has been measured by instrumenting AFM for scratch test technique. The results show the scale dependence of mechanical behavior for flax fibers, unlike glass fibers and polypropylene matrix where their mechanical performances are independent of the analysis scale. Tribological results in terms of dynamic friction coefficient show that flax fibers induce more friction than glass fibers, while polypropylene matrix generates the highest friction. This is sign that vegetal fiber friction is scale dependent property as shown when referring to the contact mechanics theory. The arisen results are very important for many technical applications in PMCs surface engineering based on plant fibers
Application de lâindentation a lâetude de la tenacite apparente dâinterface dans un beton arme
La dĂ©termination de lâadhĂ©rence dâun bĂ©ton sur une armature en acier fait trĂšs souvent appel Ă des techniques difficiles Ă mettre en Ćuvre et nĂ©cessite la plupart du temps une prĂ©paration longue et complexe de lâĂ©chantillon. Dans cette Ă©tude nous proposons dâĂ©tudier la tĂ©nacitĂ© apparente dâinterface entre un bĂ©ton et son armature mĂ©tallique, par des essais de macroindentation instrumentĂ©e. Le principe, relativement simple, consiste Ă crĂ©er et Ă propager une fissure le long de lâinterface bĂ©ton/armature acier
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