Liste des documents
Behaviour of the electric arc for different times and for different values of welding currents
Welding is a permanent joiningprocess used to join different materials like metals, alloysor plastics, togetherat their contacting surfacesby application of heat and or pressure. The study of welding processes currently appears as an area of research both open and complex because it requires to share of knowledge in different fields of physics and mechanics.Thus, the description of one of the most commonly used processes,the arc welding, involves physical phenomena as varied as the study of plasmas, magnetic and hydrodynamic interactions, the description and quantification of heat transfer, etc. The aim of our work is the treatment of the influence of welding time and welding current on the form of the arc, voltage and current density in the GTWA process. For this, we realize a numerical study to determine the arc forms, the voltage and the current density, in which we use the finite element method for the calculation, using Comsol software. The Main results obtained are: 1-The arc shape and evolution of isothermal change with increasing weld time.2-The distribution of the voltage and the current density between the torch and the plate weld obtained by simulation are the same with the results presented in the literature. Voir les détails
Mots clés : arc welding, GTAW process, welding current, modeling, Finite elements method, COMSOL Multiphysics
DIAGNOSIS OF THE AC CURRENT DENSITIES EFFECT ON THE CATHODIC PROTECTION PERFORMANCE OF THE STEEL X70 FOR A BURIED PIPELINE DUE TO ELECTROMAGNETIC INTERFERENCE CAUSED BY HVPTL
This paper diagnosis the effect of the AC current densities induced by the electromagnetic interference between high voltage power line and buried power line on the cathodic protection performance of the X70 steel in simulated soil. First, the induced AC voltage onto the pipeline was calculated for different power line configuration, separation distances between transmission line and pipeline and parallelism lengths. The induced AC current density was calculated function to the induced AC voltage, soil resistivity, and holiday diameter. Then, the electrochemical characters of the X70 steel at various AC current densities are measured using the potentiodynamic method. The electrochemical parameters obtained by the electrochemical tests are used as boundary conditions in the cathodic protection simulation model. The results indicate that, under influence of AC current densities, the X70 steel is more susceptible to corrosion, and the cathodic protection is unable to maintain the protection potential. Voir les détails
Mots clés : cathodic protection, electromagnetic interference, AC Corrosion
Low-profile U-shaped DRA for ultra-wideband applications
In this paper, a microstrip-fed U-shaped dielectric resonator antenna (DRA) is simulated, designed, and fabricated. This antenna, in its simple configuration, operates from 5.45 to 10.8 GHz. To enhance its impedance bandwidth, the ground plane is first modified, which leads to an extended bandwidth from 4 to 10.8 GHz. Then by inserting a rectangular metallic patch inside the U-shaped DRA, the bandwidth is increased more to achieve an operating band from 2.65 to 10.9 GHz. To validate these results, an experimental antenna prototype is fabricated and measured. The obtained measurement results show that the proposed antenna can provide an ultra-wide bandwidth and a symmetric bidirectional radiation patterns. With these features, the proposed antenna is suitable for ultra-wideband applications. Voir les détails
Mots clés : Ultra-wideband applications, Dielectric resonator antenna, Low-profile antenna, Measurements
A Hybrid Integrated Ultra-Wideband/Dual-Band Antenna with High Isolation
In this paper, we propose a novel integrated ultra-wideband (UWB) monopole antenna with dual-band antenna. The antenna consists of planar rectangular with semi-elliptical base and a rectangular dielectric resonator antenna (DRA) with dual-band operation. Both of them are excited via coplanar waveguide (CPW) lines. The experimental measurements show that the planar monopole provides an impedance bandwidth between 2.44 and 11.9 GHz which largely covers the entire UWB spectrum, and the rectangular DRA operates at two bands; 5.3–6.2 and 8.5–9.4 GHz. Additionally, the proposed structure ensures low mutual coupling between the two ports (with S21 less than 22 dB in the whole operating frequency band). Voir les détails
Mots clés : CPW-fed line, Dielectric resonator antenna, Dual-band antenna, Integrated antennas, isolation, UWB antenna
High/Low Gain Rectangular Dielectric Resonator Antenna for WLAN Applications
In this paper, a novel integrated dual-port rectangular dielectric resonator antenna (DRA) is presented for 802.11a WLAN system applications. The antenna structure is formed by integrating the concept of antenna array with a single DRA element to produce a radiation characteristic necessity. The array is composed of four identical rectangular DRA elements placed on a horizontal ground plane and separated by a distance of 0.54λ at design frequency of 5.97 GHz, excited through rectangular shaped aperture slots by a microstrip transmission line from port 1. The central element fed from port 2 by 50 Ohm microstrip line via a slot etched on the ground plane. The designed proposed antenna sized of 60×80×0.672 mm3 operates over the frequency band between 5 and 6 GHz for VSWR. Voir les détails
Mots clés : High/Low Gain antenna, dielectric resonator antenna (DRA)
Nonlinear predictive control of a mobile robot: asolution using metaheuristcs
The basic features of model-based predictive control (MBPC) make it an interesting candidate for the control of mobile robots. However, fast solution procedures remain a challenge for nonlinear MBPC problems such as the one arising in mobile robot control. Metaheuristics are general purpose heuristics which have been successful in solving difficult optimization problems in a reasonable computation time. In this work, we present a comparison between the uses of three different heuristics, namely particle swarm optimization (PSO), ant colony optimization, and gravitational search algorithm for the solution of the nonlinear MBPC for a mobile robot tracking trajectory with dynamic obstacle avoidance. The computation times obtained show that PSO is a feasible alternative for real-time applications. The MBPC based on the PSO is applied to controlling a LEGO mobile robot with encouraged results. Voir les détails
Mots clés : nonlinear predictive control, Metaheuristcis, mobile robots, optimization
IMPROVING WEAR PROPERTIES OF HIGH-CHROMIUM CAST IRON BY MANGANESEALLOYING
High-chromium cast irons are widely needed by severalindustrial areas where wear is the dominant environment.They are used in mining, cement- and steel-making plants,and many others. Their microstructure consists of nettedeutectic carbides embedded in an austenitic or martensiticmatrix. The wear behaviour is mainly controlled by thecarbides shape and also matrix type. Several scientificworks try to improve the wear behaviour and to optimizethe life service of this cast iron by using various techniques.In this work, we intend to study the effect of manganesecontent on the microstructure properties and wearbehaviour of a 15 % chromium white cast iron used forball mill production. The present work treats the wearbehaviour, after heat treatment, of a manganese-alloyedhigh-chromium cast iron. A set of specimens were melted inan induction oven by varying the manganese content in therange 0–3 %. Heat-treated samples were analysed byoptical microscopy, MEB (SEM) scanning electronmicroscopy, differential scanning calorimetry, and X-raydiffraction and were wear tested by abrasion and friction.Increasing the manganese addition gave a structural evolutionand a wear resistance improvement. The best wearbehaviour is obtained with samples containing 3 % Mn. Voir les détails
Mots clés : Chromium cast iron, carbide-forming elements, eutectic carbides, secondary precipitation, abrasion, friction
Microstructure and Mechanical Behavior in Dissimilar SAF2205/API X52 Welded Pipes
The welding of a duplex stainless steel SAF 2205 DSS (UNS 31803) and high strength low alloy steel API X52by shielded metal arc welding process was conducted using two different filler metals, the duplex E2209 and austeniticE309 grade. The microstructures of the dissimilar metal joints have been investigated by optical microscopy, scanningelectron microscopy, energy-dispersive spectroscopy (EDS) and X-ray diffraction. EDS analysis at the interface X52 weldmetal showed an evident gradient variation of Cr and Ni between boundaries of fusion and type II, where the highesthardness value was recorded. Tensile strength and toughness values of the weld metal produced by E309 electrode areslightly higher than those of the weld metal produced by E2209 electrode. Potentiodynamic polarization tests of differentregions of the welded joints evaluated in 3.5% NaCl solution exhibit a high corrosion resistance of both weld metals. Voir les détails
Mots clés : Dissimilar metals welding, 2205 Duplex stainless steel, API X52 HSLA steel, Heat affected zone, mechanical properties
Asymmetric Generalized Gaussian Mixturesfor Radiographic Image Segmentation
In this paper, a parametric histogram-based image segmentation methodis used where the gray level histogram is considered as a finite mixture of asymmetricgeneralized Gaussian distribution (AGGD). The choice of AGGD is motivated byits flexibility to adapt the shape of the data including the asymmetry. Here, themethod of moment estimation combined to the expectation–maximization algorithm(MME/EM) is originally used to estimate the mixture parameters. The proposedimage segmentation approach is achieved in radiographic imaging where the imageoften presents an histogram with a complex shape. The experimental results providedin terms of histogram fitting error and region uniformity measure are comparableto those of the maximum likelihood method (MLE/EM) with the advantage thatMME/EM method reveals to be more robust to the EM initialization than MLE/EM. Voir les détails
Mots clés : AGGD, radiography, MLE/EM, MME/EM, image segmentation
Mechanical and Metallurgical Characterization of HSLA X70Welded Pipeline Steel Subjected to Successive Repairs
The aim of this work is to study the influence of successive weld repairs on the microstructure and themechanical behavior of the heat-affected zone (HAZ) of an HSLA X70 steel. Detailed microstructural examinationcombined to grain size measurement showed that beyond the second weld repair, the microstructure of the HAZ undergoessignificant change in the grain morphology and grain growth. The results of the X-ray diffraction analyzed using MAUDsoftware indicated an increase in the crystallite size and a decrease in the dislocation density according to the number ofweld repair operations. Consequently, a loss of mechanical properties, namely the yield strength and the toughness with thenumber of weld repairs, was recorded. Beyond the second weld repair operation, the properties of the welded joint do notfulfill the standards applied in piping industry. Voir les détails
Mots clés : HSLA X70 steel; Successive weld repair; Heat affected zone; Dislocation density