Liste des documents
Estimation of ultrasonic wave parameters in materials under bending force
this paper presents the use of prism technique todetermine the longitudinal and transversal wave parameters in materials under simple bending forces. The weak number of studies on acoustoelastic behavior and the evolution of measurement methods led us to propose a complete feasibility study on measurements of longitudinal and shear waves for different mediums subjected to uniaxial compressive stresses.The expectation maximization algorithm is employed for parameters estimation those are amplitude, phase, time of flight, frequency and bandwidth. These parameters allow the verification of the parameter values modification resulting from the effect of bending stresses. Voir les détails
Mots clés : Ultrasonic, prism technique, expectation maximization algorithm
Fast Finite Element Computation for 3D Eddy Current Testing Problems with T-Ω Formulation
The paper deals with T-Ω formulation modeling of eddy current problems. The method is applied to the analysis of 3D eddy current testing of metallic plate with cracks, and the usefulness of the method is investigated by comparing calculated results with measured ones. Voir les détails
Mots clés : nondestructive testing, Eddy Current, Cracks, T-Ω formulation, 3D finite element.
Study of the Effet of the Geometry Shape of defecton the Reliability of NDT Device
This work concerns the study the effect of random properties and defect geometry on the reliability analysis ofthe non-destructive testing inspection device. Two kinds ofdefects geometries are considered as rectangle and triangle shapes respectively. A stochastic finite element method (SFEM) was used to solve the 2D electromagnetic equation incylindrical structure. The results obtained for both rectangle and triangle random shapes are given. Voir les détails
Mots clés : random geometry, random propertie, nondestructive testing, reiability analysis, stochastic finite elements
The Effect of Laser Treatment on the Erosion Resistance of a Copper -Nickel Austempered Ductile Iron
The present work investigates the effect of laser surface hardening on the erosion resistance of alloyed austempered ductile iron contain 1.5% copper and 1.5% nickel austenitized for different austenitising times.Continuous wave of CO2 laser was used to heat by overlapping technique. The laser processing parameters used were; 1000 w, laser power, 1000 mm\min. Scanning speed and 40 L\min. Argon flow rate. After laser treatments erosion tests were carried out on the untreated and laser treated samples surfaces. The erodent particles used were pressurized silica +300 to 500 flows at speed of 50 m\sec. The erosion tests were performed at different angles 30°, 60° and 90°. Erosion tests showed significant reduction in the erosion rate after laser treatment at all impinging angles. Erosion resistance is improved depending on the impingement angle, (weight losses ingrams at 90° > weight losses in grams at 60° > weight losses ingrams at 30°). Increasing the impingement angle increases the erosion rate for both untreated and laser treated samples. This improvement in erosion resistance was attributed to the fine and homogenous structure, high hardness and the elimination of graph itenodules which were the source of notches. Voir les détails
Mots clés : laser treatment, erosion, ADI, austempering, hardness, austenitising
Acoustic Emission Monitoring of high risk installation in industrial environment
Acoustic Emission (AE) technology is widely used to control in service pressure vessel in a wide range of industry. Acoustic emission monitoring and its benefits have long been known and utilized by many industries to optimize the use of structures, increase operational safety, and to save money through effective condition assessment and maintenance. The application and acceptance of AE monitoring within the civil engineering industry has greatly expandedin the past few years [1]. Among the technological progress of AE it is possible to apply the technology in Atex environment with industrial process giving some genuine information on propagating defects even in refining and petrochemical plants.The monitoring of critical equipment allows an early detection of significant defects and the ability of following their severity in serviceto give an alarm to improve the safety of equipments and particularly piping systems. Some industrial examples are given in this paper to shed into thelight the return of experience on AE long term monitoring. AE technology is used: to give an in situ diagnostic, to prevent catastrophic ruptures, to help to reduce maintenance costs, and to avoid shutdown with assessing risk based inspection. Voir les détails
Mots clés : Accoustic Emission, Monitoring
Contribution to the minimization of vibration ofrotating machines
Rotating machines are used in areas as diverse as transport (trainsmotorized vehicles, etc.) Production industry, or appliances. Thevibrations from them may êtregênantes; they are the source of somenoise radiated by this machine and are therefore undesirable forusers, they can be transmitted to neighboring structures andaccelerate deterioration or aging, can also damage the rotatingmachines-they mêmes.il is therefore of interest to develop methodsto reduce the vibration level of the machines, as well as that of theirenvironment direct.Ces optimization methods (minimization) canminimize the natural vibrations using against vibration generatedby actuators requiring external power. The objective of this work isto develop a method of minimizing vibrations of a rotating machine,which aims to reduce the vibrational level of an area of its outercasing. This field can then be used for attachment of this machineand so help to minimize the amount of vibration it transmits to itsdirect environment. A new method also converge to the globaloptimum (minimum vibration value), and take into account possiblevariations of vibrational disturbances to eliminate. It allows asignificant reduction of vibrations, without changing thecharacteristics of the system. Voir les détails
Mots clés : Rotating machines, vibration sensors, optimization.
Study of structural and thermal properties of SiO2 and Al2O3 in the Diatomite
Diatomite is a light colored rock formed entirely or substantially of "backbones" of diatoms. These unicellular algae are surrounded by a "shell" in silica, frustule, the accumulation of the substance can lead to the formation of a rock.In this work we determine the structural and thermal properties of SiO2 and Al2O3 in the diatomite using the plane wave method and linearized augmented (LAPW) in the functional theory of density (DFT).The potential for exchange and correlation is calculated by the generalized gradient approximation (GGA).Regarding thermal properties, we calculated the free enthalpy G, S entropy, specific heat C, thermal conductivity λ ..... etc of SiO2 and Al2O3 component. The temperatures used in this work are 1400, 1450 and 1500 respectively;The results are in good agreement with some experimental data. Voir les détails
Mots clés : DFT1, diatomite, thermal proprieties
INFLUENCE OF MECHANICAL PARAMETERS ON THE TRIBOLOGICAL AND THERMAL BEHAVIORS OF STEEL-COMPOSITE CARBONE/CARBONE COUPLE
The tribological and thermal behavior of dry sliding contact steel composite carbone/carbone and steel-organic matrix composites are studied according to the parameters normal load, sliding speed, friction coefficient and test time. In the case of automotive braking, using a mathematical model, the surface temperature of contact was determined. Four normal forces, four sliding speeds and four friction coefficients were applied in this study. These parameters have a significant influence on the variation of average contact temperature. The results illustrate the evolution of the contact temperature according to the braking time. Voir les détails
Mots clés : Temperature, friction, steel, composite, Disc, Trim.
Fundamental properties of the rocksalt ZnO and MgO: an ab-initio prediction
The one of the most accurate first-principales methods is the Full Potential Linearized Augmented Plane Wave (FP-LAPW) formalism, based on Density Functional Theory (DFT), has been exploited to study theatrically, the fundamental properties of the both ZnO and MgO rocksalt binary compound using 16 atoms rocksalt supercell which corresponds to (1×1×2) conventional cell. The Local Density Approximation (LDA) was used only for the structural properties, to treat the exchange-correlation terms. In order to explore the wanted properties. The recently modified semi-local Becke-Johnson potential within LDA correlation in the form of (mBJ) was used to predict the optoelectronic properties of ZnO and MgO binary materials. As results, our computed lattices parameters equal to: 4.22 Å and 4.16 Å respectively, showed satisfactory agreements with experimental values (4.27 Å and 4.2 Å) for ZnO and MgO respectively again. in order to understand the changeability between relaxed and un-relaxed of the electronic structures, The calculated band structures reveal that ZnO posses indirect band gap (Г-M) while for MgO have an indirect band gap (Г-Г) which agree well with the experiment and other theoretical calculations. Optical dielectric function, refractive index, absorption coefficient and optical conductivity, are well described in a wide range of the incident photon energy. The acquired results are used to give an significant guideline to the material's design for optoelectronic applications. Voir les détails
Mots clés : ZnO, MgO, FP-LAPW, Electronic materials, Optical parameters, ab initio calculations.
Structural, Mechanical, Electronic, Elastic and Chemical Bonding Properties of the Complex K2PtCl6-Structure Hydrides Sr2RuH6 First-Principles Study
We report a systematic study of the structural, electronic and elastic properties of the ternary ruthenium-based hydrides Sr2RuH6 within two complementary first-principles approaches. We describe the properties of the Sr2RuH6 systems looking for trends on different properties. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gap is about 2.99eV. Calculated density of states spectra demonstrate that the topmost valence bands consist of d orbitals of the Ru atoms, classifying these materials as d-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time. Voir les détails
Mots clés : Ruthenium-based hydrides; first-principles calculations; elastic constants; electronic structure