Liste des publications
Novel and simplified model representing Current-Output Phase-Shift Full-Bridge DC-DC LCLC Resonant Converter in Arc Welding Application
In this paper, a novel and simplified model representing current-output phase-shift full-bridge DC-DC LCLC resonant converter in arc welding application is thoroughly presented. First, a switched model written in state space representation and featuring a bilinear form is proposed. The latter facilitates the derivation of both the reduced and full order averaged models in continuous conduction mode (ROAM and FOAM). Although the FOAM can be employed in linear or nonlinear control schemes and the derivation of steady state behavior, in this paper the ROAM is considered in designing both voltage mode control and current mode control by using the classical PID and the fractional order PID controllers. Simulation confirms that the switched model, ROAM and FOAM are quite accurate compared to the circuit simulation using SimPowerSystem toolbox of MATLAB/SIMULINK. Results clearly showed that depending on the switching frequency, the proposed topology can be applied either in constant voltage characteristic or dropped characteristic welding machines fulfilling either zero current Switching (ZCS) or zero voltage switching (ZVS). Besides, the fractional order PID controller seems to be more adapted for arc welding application than its traditional version. Voir les détails
Mots clés : LCLC resonant converter, switched model, reduced order averaged model, full order averaged model, arc welding, FOPID, IGWO
A new robust tilt-PID controller based upon an automatic selection of adjustable fractional weights for permanent magnet synchronous motor drive control
This paper focuses on achieving a good trade-off between performance and robustness for a class of uncertainty models including unstructured multiplicative uncertainties. In robust control, the simultaneous improvement of the two secure margins for nominal performances and robust stability using a standard controller structure represents two contradictory objectives and guaranteeing simultaneously of these goals represents therefore a major challenge for most researchers. In this context, a robust tilt-proportional integral derivative (T-PID) controller synthesized with an automatic selection of adjustable fractional weights (AFWs) is discussed in our work. Their parameters are optimized through solving a weighted-mixed sensitivity problem using an optimization tool which is based on the genetic algorithm. This problem is formulated from performance and robustness requirements where a fitness function is accordingly determined. Furthermore, thus its search space is built according to some guidelines for ensuring an automatic selection of adequate AFWs. The proposed constrained optimization problem is initialized by using arbitrary T-PID speed controller as well as through initial fixed integer weights (FIWs) which were chosen previously by the designer. To highlight the proposed control strategy, the synthesized robust T-PID speed controller is applied on the permanent magnet synchronous motor. Their performance and robustness are compared to those provided by an integer-order PID (IO-PID) and two conventional fractional-order PID (FO-PID) controllers. This comparison reveals superiority of the proposed robust T-PID controller over the remaining controllers in terms of robustness with reduced control energy. Voir les détails
Mots clés : Weighted-mixed sensitivity problem, Tilt-proportional integral derivative controller, Fractional-order FO-PID speed controller, Permanent magnet synchronous motor
Microstructural and Mechanical Properties of Welding and Thermal Spraying Coatings on Ductile Cast Iron
The subject of this work is to evaluate the influence and adhesion degree of different coating layers deposited on a ductile cast iron substrate by two different methods, thermal spraying and welding with and without use of an interlayer. Microstructures of different zones and interfaces of coated specimens are investigated using optical microscope and scanning electron microscope SEM. Also, the mechanical behavior was evaluated by tensile test. It is found that when stainless steel thermal spraying coating onto the ductile cast iron substrate, the use of the nickel-based interlayer Ni allowed us to mitigate the disadvantages of cracking at the interface. This is due to the mechanical effect of nickel plasticity. In the case of coating by welding, the use of nickel-based buttering ENi-CI allowed us to reduce the diffusion of graphite to stainless steel, resulting in a reduction in the formation of harder alloy carbides. Finally, the mechanicals tests in particular the tensile test shows that the coating by welding is effective but causes a structural hardening; on the other hand the coating realized by thermal spraying does not really present sufficient adhesion. Voir les détails
Mots clés : Ductile Cast Iron, mechanical properties, microstructure, Thermal Spraying, Welding Coating
On the evolution of microstructure, texture and corrosion behavior of ahot-rolled and annealed AZ31 alloy
The microstructure and texture evolution of an AZ31 alloy were investigated after hot rolling and subsequentannealing using electron backscatter diffraction (EBSD). First, the alloy was hot-rolled at 350 ? C up to low,medium and high strain (20, 50 and 85% of thickness reduction, respectively). The alloy samples where thenannealed at 350 ? C for 2, 10 and 60 min. The effect of strain level and annealing on corrosion behavior inseawater was also evaluated using electrochemical tests. At low strain, the microstructure was characterised bythe absence of twinning, mainly due to the prior thermo-mechanical history of the as-received alloy. However,various modes of twinning were observed at medium strain. At high strain, the dynamic recrystallization processresulted in a microstructure with a typical basal texture. The results demonstrate that twins are responsible forthe deviation of {0002} basal poles from normal towards the transversal direction. Annealing at 350 ? C for up to60 min led to normal grain growth in all the samples. In medium and highly strained samples, the deformationtexture was retained, while the low strain sample underwent noticeable changes due to the absence of dynamicrecrystallization. A synergetic effect of grain refinement and texture weakening was responsible for the alloy’senhanced corrosion resistance.AZ31 alloyCorrosionDynamic recrystallizationStatic recrystallizationRolling Voir les détails
Mots clés : AZ31 alloy, corrosion, Dynamic recrystallization, Static recrystallisation, rolling
Effect of WC-Co cermet positioning and NiCr interlayer on the microstructure and mechanical response of the dissimilar WC-Co / AISI 304 L rotary friction joint
In this work, incompatible properties of WC-Co cermet and AISI 304 steel were combined in the same component using rotary friction welding (RFW) process. The dissimilar joints were performed using a ductile NiCr interlayer with the change in the WC-Co cermet positioning i.e., fixed rotary side and feeding side. Similar microstructure across the weld joints was obtained of the different welding configurations that produced similar behavior in hardness and elastic modulus. A diffusion zone was formed at the weld interface as a result of the mutual inter-diffusion of both cermet (W and Co) and steel elements (Fe, Cr and Ni) that enhanced with the insertion of the interlayer when the cermet was fixed in rotary side. The introduction of the NiCr interlayer was beneficial to relax the residual stresses and improving the shear strength of the WC-Co cermet/AISI 304L steel joints, which is promising technology for drilling tools industries. Voir les détails
Mots clés : Rotary friction welding, WC-Co cermet, mechanical properties, NiCr interlayer, Interface
Influence of isothermal aging in LDX 2101 duplex stainless steel on the microstructure and local properties
In the present work, the interface morphology and the evolution of nitride precipitates in LDX 2101 stainless steel isothermally treated at 750 °C for various aging times were investigated. The microstructure results showed that the Cr2N nitrides precipitated along the δ/γ interface with 200 nm in length and continue to grow to 2 μm after 240 h of aging. However, only Cr2N nitrides were found at the δ/δ interface after long term of aging. Atomic force microscopy (AFM) analysis revealed that Cr2N nitrides andCr23C6 carbides started to precipitate after the first 10 min of aging with a small needle shape of the former and specific triangular morphology of the latter. The evolution of hardness and Young’s modulus of the interfaces, performed with nano-indentation measurements, showed that the δ/γ interface became harder (4.1 ± 0.2 GPa) with increasing aging times, whereas negligible changes in the hardness and elastic modulus were recorded at the δ/δ interface. 3D topographic analysis of the immersed surfaces revealed that the susceptibility of δ phase to preferential dissolution in 3.5% NaCl solution increased with aging time. This behavior was manifested by the important imperfections of δ phase, the high surface roughness (55.7 nm), and the deep corrosion pits (30 nm) along the δ/γ interface and around the Cr2N nitrides. Voir les détails
Mots clés : microstructure, Interface, precipitates, Nano-hardness, Surface degradation
Effect of WC-Co cermet positioning and Ni-Cr interlayer on the microstructure and mechanical response of the dissimilar WC-Co / AISI 304 L rotary friction joint
In this work, incompatible properties of WC-Co cermet and AISI 304 steel were combined in the same component using rotary friction welding (RFW) process. The dissimilar joints were performed using a ductile NiCr interlayer with the change in the WC-Co cermet positioning i.e., fixed rotary side and feeding side. Similar microstructure across the weld joints was obtained of the different welding configurations that produced similar behavior in hardness and elastic modulus. A diffusion zone was formed at the weld interface as a result of the mutual inter-diffusion of both cermet (W and Co) and steel elements (Fe, Cr and Ni) that enhanced with the insertion of the interlayer when the cermet was fixed in rotary side. The introduction of the NiCr interlayer was beneficial to relax the residual stresses and improving the shear strength of the WC-Co cermet/AISI 304 L steel joints, which is promising technology for drilling tools industries. Voir les détails
Mots clés : Rotary friction welding WC-Co cermet NiCr interlayer Interface Microstructure Mechanical properties
Dissimilar FSW of AA2024 and AA7075: Effect of materials positioning and tool deviation value on microstructure, global and local mechanical behavior
In this work, the effect of material location and tool deviation on the global and local mechanical behavior of dissimilar AA2024/AA7075 friction stir weld joints was investigated. The results showed that increasing the tool deviation value up to 1mm towards the AA2024, fixed in advancing side, improved the material mixing quality and enhanced the grain refinement in the stir zone. It was found that the highest ultimate tensile strength was obtained when the AA2024 alloy was fixed in the advancing side for 1mm tool deviation towards this material. Above this deviation value, a gradual decrease of the global mechanical properties of the weld joints was noticed. Digital image correlation (DIC) technique coupled to tensile testing revealed an improvement of local strain in the stir zone and the heat affected zones of the dissimilar joints when AA2024 alloy was positioned in the advancing side. Voir les détails
Mots clés : Dissimilar friction stir welding, tool deviation, DIC, mechanical properties, microstructure
Rotary friction welded C45 to 16NiCr6 steel rods: statistical optimization coupled to mechanical and microstructure approaches
In the present work, the dissimilar joints between C45 carbon steel and nickel-chromium 16NiCr6 steel rods were produced usingrotary friction welding process. Statistical analysis based on response surface methodology (RSM), microstructural examinationusing scanning electron microscopy with backscattered electron diffraction (EBSD) and mechanical tests were performed toinvestigate the friction weld joints. The results showed that friction time and rotation speed were the most effective parameters onthe weld joint quality with the highest t-ration of − 4.27, where the maximum bending strength of 1406.9 MPa was obtained at2000 rpm for 13 s friction time. Increasing friction time to 13 s resulted in remarkable decrease in grain size (about 35%) at theweld interface, which increased the hardness (350HV0.1) and elastic modulus (260 GPa). Voir les détails
Mots clés : Rotary friction welding . RSM methodology . Microstructure
Effect of heat treatment on microstructure and tribological behavior of friction stir processed Al2O3-reinforced AA2024-T351 matrix
In the present work, 2024-T351 Al alloy reinforced with alumina particulates (Al2O3p) was elaborated using friction stir processing (FSP). The effect of solution heat treatment followed by subsequent aging on microstructure, hardness, and tribological behavior is discussed. It was noticed that the hardness of the as-FSPed 2024-T351/Al2O3p was slightly enhanced in comparison to the as-received AA2024-T351 material, whereas the resulting wear resistance was remarkably improved. After heat treatment process, the composite volume increased, and swelling and pores were created at the processed area. The heat treatment caused a degradation in wear resistance compared to as-FSPed composites. The precipitation mechanism changed forAA2024/Al2O3p; reactions occurred at grain boundaries between Al2O3 and Cu or Mg, causing their depletion from the Al matrix. Intriguingly, the precipitation mode in heat-affected zone of the matrix also changed to grain boundary precipitation. Voir les détails
Mots clés : Friction stir processing, Metalmatrix composites, wear, friction