Liste des documents
Study of the effect burnishing on superficial hardness and hardeningof S355JR steel using experimental planning
Surface hardness plays an important role in lifetime of a mechanical piece subjected to friction and wear. Indeed, thehardness can be improved by superficial plastic deformation processes (SDP), such as mechanical surface treatment"MST", in particular the ball burnishing. However, the treatment result of is conditioned by mastery of operationthus ensuring treated piece good mechanical and geometric properties. Experimental work was carried out byapplying the ball burnishing process on steel tensile specimens S355JR, in order to observe the influence oftreatment parameters regime on surface hardness 'Hv' and the effect of latter on tensile behavior of this steel. Twoparameters of regime were considered namely: burnishing force "Py" and number of passes "i". The relationshipbetween these parameters and microhardness measured at "Hv" surface has been highlighting using factorial plans22. Moreover a mathematical model has been obtained allowing prediction of response (Hv) as well as optimizationof parameters of treatment regime. The experimental results showed that for surface hardness Hv it is possible toreach a 45% improvement rate for a burnishing force py = 20 Kgf and a number of passages i = 3 for this material.Regarding behavior of material during tensile test, for a low burnishing force (py = 10N) and a number of passes (i= 5), the section further weakening (S = 4.14), proof than ductility of material has decreased. Voir les détails
Mots clés : Surface hardness, factorial designs, ball burnishing, Mathematical model, tensile behaviour
Effects of work hardening on mechanical metalproperties—experimental analysis and simulation by experiments
The aim of the present work is to improve the materials’ performances, particularly their elastic property based on an optimalexploitation of surface work-hardening phenomenon, using surface plastic deformation treatment (DPS). The surface of amechanical piece is considered as the most vulnerable zone that determines its mechanical performances. To improve thesurface physico-mechanical properties, the surface plastic deformation treatment (DPS) is often used. The (DPS) acts by acombined action of: surface hardening, structural modification, and the generation of the compression residual stresses, thefactors that will create a heterogeneous plastic deformation. Knowing that during operation the mechanical pieces have to besubjected to a stress smaller than the elastic limit (taking into account the safety margins), where the material behavior isreversible, and to reach the maximum allowable stresses, we have to increase the material’s elastic limits. This objective canbe realized through an optimal use of work hardening phenomenon for the treated surface by the DPS. The work hardening ischaracterized by the increase of the yield strength (Re), the surface hardness (Hv), and consequently the increase of thebrittleness. Depending on the considered metals, when the piece has a defect variation: cavity, inclusion (precipitate), orzones of different hardness, it can create a stress concentration which generates a local hardening. This phenomenon is one ofthe main causes of crack generation. In our study, we consider the influence of work hardening on the elastic behavior ofXC38 steel and aluminum alloy. Voir les détails
Mots clés : Work hardening . Hardening of materials . Mechanical surface treatment (TMS) . Burnishing
Microstructure and mechanical behavior of dissimilar AISI 304L/WC-Cocermet rotary friction welds
In this work, dissimilar rapid Rotary Friction Welding of WC-Co cermet to AISI 304 L austenitic stainless steel hasbeen conducted using different friction times. The microstructural examination showed that the increase infriction time from 4s to 12s increases the grain size in both the heat affected zone and the thermo-mechanicallyaffected zone and enlarges the extent of the fully dynamically recrystallized zone. EDS analysis revealed theexistence of a FeeCreW rich band along the WC-Co/AISI 304 L interface in the central region of the weld jointand its absence from the peripheral region. The formation of this band suggests the occurrence of a mutual inter-diffusion between the cermet and the steel which enhanced the metallurgical bonding of the interface. Themechanical behavior investigated by nano-indentation measurements and nano-scratch tests revealed that, re-gardless the friction time effect and considering the 304 L ASS side, the highest hardness (HIT) and the lowestYoung's modulus (EIT) values were recorded in the fully dynamically recrystallized zone. Besides, the increase offriction time resulted in an increase of hardness and Young's modulus of each zone in the AISI 304 L steel side. Voir les détails
Mots clés : Rotary friction welding, WC-Co cermet, AISI 304L ASS, microstructure, Intre-diffusion, Bonding strength
Microstructure and mechanical behavior of dissimilar AISI 304L/WC-Co cermet rotary friction welds
In this work, dissimilar rapid Rotary Friction Welding of WC-Co cermet to AISI 304L austenitic stainless steel has been conducted using different friction times. The microstructural examination showed that the increase in friction time from 4s to 12s increases the grain size inboth the heat affected zone and the thermo-mechanically affected zone and enlarges the extent of the fully dynamically recrystallized zone. EDS analysis revealed the existence of a Fe-Cr-W rich band along the WC-Co/AISI 304L interface in the central region of the weld joint and its absence from the peripheral region. The formation of this band suggests the occurrence of amutual inter-diffusion between the cermet and the steel which enhanced the metallurgical bonding of the interface. The mechanical behavior investigated by nano-indentation measurements and nano-scratch tests revealed that, regardless the friction time effect and considering the 304 L ASS side, the highest hardness (HIT) and the lowest Young’s modulus (EIT) values were recorded in the fully dynamically recrystallized zone. Besides, the increase of friction time resulted in an increase of hardness and Young’s modulus of each zone in the AISI 304L steel side. Voir les détails
Mots clés : Rotary friction welding, WC-Co cermet, AISI 304L ASS, microstructure, Intre-diffusion, Bonding strength.
Natural extract of Opuntia ficus indica as green inhibitor for corrosion ofXC52 steel in 1M H3PO4
The purpose of this study is to evaluate the anti-corrosive effect of natural extract of Opuntia Ficus Indica (O.F.I) for XC52steel in 1M H3PO4. Experimental work has been achieved by weight loss, potentiodynamic polarization and EISmeasurement, as well as SEM surface characterization. Among the results obtained, we can mention an inhibitory efficiencyof 90% by gravimetric method and 83.9% by electrochemical method at 10% (v/v) of O.F.I. Moreover, The O.F.I extract actsas a mixed inhibitor; however, adsorption free enthalpy indicates a physisorption. The adsorption obeys the Langmuirisotherm model. These results have been improved by SEM micrographs Voir les détails
Mots clés : corrosion, Opuntia ficus indica, EIS, green inhibitor, XC52 steel
Endurance and Damage in Fatigue of Symmetrical Configuration 2P-2V-2P Perlon-Glass-Acrylic Composite Laminates of Orthopaedic Use
In this paper, an experimental characterization of fatigue behaviour on prismatic specimens of a symmetrical laminated composite material perlon- glass- acrylique 2P-2V-2P for orthopaedic use is conducted. Cyclic repeated solicitation is employed corresponding to applied minimum stress σmin equal zero. The various loading levels imposed on the specimens are 80%, 70%, 60%, 55%, 45%, 35% and 25% of the value of the static failure strength measured in flexure. A significant scatter characterizes the results of material fatigue lifetime. That is the consequence of the heterogeneity of the material structure. The scattered phenomenon prevents any prediction of the lifetime with a good probability using Wohler equation. This enables defining a constant degradation rate by 10% cycle decade. The microstructure morphology study through microscopic observations is also discussed and analyzed. The damage state in fatigue is characterized by a combination of density and orientation of micro-cracks. This damage is mainly due to mechanisms complexity of matrix micro-cracking, inter facial exfoliation, debonding and delamination. The damage evolution stages in the case of cyclic loading have the same nature than those found in static loading but have different chronology and scale Voir les détails
Mots clés : perlon, acrylic, Orthopaedic, fatigue, Scatter
Study of the effect burnishing on superficial hardness and hardening of S355JR steel using experimental planning
Surface hardness plays an important role in lifetime of a mechanical piece subjected to friction and wear. Indeed, the hardness can be improved by superficial plastic deformation processes (SDP), such as mechanical surface treatment "MST", in particular the ball burnishing. However, the treatment result of is conditioned by mastery of operation thus ensuring treated piece good mechanical and geometric properties. Experimental work was carried out by applying the ball burnishing process on steel tensile specimens S355JR, in order to observe the influence of treatment parameters regime on surface hardness ‘Hv’ and the effect of latter on tensile behavior of this steel. Two parameters of regime were considered namely: burnishing force "Py" and number of passes "i". The relationship between these parameters and microhardness measured at "Hv" surface has been highlighting using factorial plans 22. Moreover a mathematical model has been obtained allowing prediction of response (Hv) as well as optimization of parameters of treatment regime. The experimental results showed that for surface hardness Hv it is possible to reach a 45% improvement rate for a burnishing force py = 20 Kgf and a number of passages i = 3 for this material. Regarding behavior of material during tensile test, for a low burnishing force (py = 10N) and a number of passes (i = 5), the section further weakening (S = 4.14), proof than ductility of material has decreased. Voir les détails
Mots clés : Surface hardness, factorial designs, ball burnishing, Mathematical model, tensile behaviour
Effect of microstructure and precipitation phenomena on the mechanical behavior of AA6061-T6 aluminum alloy weld.
In the present study, the effect of microstructure and precipitation phenomena on the micro hardness, tensile strength, impacttoughness, and electrochemical behavior of tungsten inert gas (TIG)-welded AA6061-T6 aluminum alloy are investigated. Themicrostructure features showed mainly the grains of aluminum solid solution with the presence of some precipitates at the grainboundaries. Scanning electron microscope micrographs exhibited the presence of Fe-based intermetallic and B-equilibriumprecipitates throughout a-Al grains. In the heat-affected zone (HAZ), the dissolution, over-aged, and coalescence of precipitatesare observed; their hardening effects disappear and a decrease in strength and hardness are noticed. The fracture toughness valuesof each zone at different temperatures using Charpy V-notch test remained constant where the HAZ presents the highest absorbedenergy. However, the temperature did not have a significant effect on the absorbed energy for each zone. In addition, the fracturedsurface of base metal (BM) and HAZ are characterized by dimple-like structure and they are larger in the HAZ. The electrochemicalbehavior of each zone of the weld evaluated in NaCl + H2O2 solution revealed that the corrosion current density of BMand HAZ is lower than that of molten zone (MZ), which displays high corrosion current density in this electrolyte and would befastest to corrode. Voir les détails
Mots clés : Aluminum alloys, TIG welding, precipitates, microstructure, Fractography, Electrochemical behavior
Quantitative and qualitative analyses of intermolecular interactions in neutral/deprotonated aspirin@β-CD inclusion complexes: QTAIM and NBO analyses
Most of the researches in supramolecular chemistry area are focused on the conventional hydrogen bonds without taking into account unconventional intermolecular interactions. The nature and strength of the conventional and unconventional interactions in inclusion complexes formed between neutral aspirin (ASA) and its deprotonated form (ASA−) with β-cyclodextrin (β-CD) have been studied. It was conducted through combining atoms in molecules (AIM) theoretical criteria suggested by Koch and Popelier and natural bond orbital (NBO) analyses by means of dispersion-corrected density functional theory (DFT-D3) with the functional B3LYP using cc-pvdz basis set in the gas phase. We have found fve intermolecular closedshell interaction groups responsible for neutral ASA:β-CD and deprotonated ASA−:β-CD inclusion complexes stability: One is conventional O–H···O bond group. The four C–H···O, C–H···C, O–H···H–C and C–H···H–C groups are nonconventional. Also, with respect to the Koch and Popelier criteria, some of them present the properties of a hydrogen bond, while others do not. The non-covalent interaction energies are calculated using Espinosa approach. Finally, according to the AIM and NBO analyses, the topological parameters (electron density ρband its Laplacian ∇2ρb), estimated interaction energies (Eint), and the stabilization energy E(2)of both complexes were correlated with the intermolecular bond lengths Voir les détails
Mots clés : β-Cyclodextrin, Aspirin, Inclusion complex, DFT-D3, QTAIM, NBO
Analytical Modeling of Dual-Junction Tandem Solar Cells Based on an InGaP/GaAs Heterojunction Stacked on a Ge Substrate
An analytical model is used to describe the electrical characteristics of a dual?junction tandem solar cell performing with a conversion efficiency of 32.56%under air mass 1.5 global (AM1.5G) spectrum. The tandem structure consistsof a thin heterojunction top cell made of indium gallium phosphide (InGaP) ongallium arsenide (GaAs), mechanically stacked on a relatively thick germa?nium (Ge) substrate, which acts as bottom cell. In order to obtain the bestperformance of such a structure, we simulate for both the upper and lowersub-cell the current density–voltage, power density–voltage, and spectral re?sponse behaviors, taking into account the doping-dependent transportparameters and a wide range of minority carrier surface recombinationvelocities. For the proposed tandem cell, our calculations predict optimalphotovoltaic parameters, namely the short-circuit current density (Jsc), open?circuit voltage (Voc), maximum power density (Pmax), and fill factor (FF) areJsc = 28.25 mA/cm2, Voc = 1.24 V, Pmax = 31.64 mW/cm2, and FF = 89.95%,respectively. The present study could prove useful in supporting the design ofhigh efficiency dual junction structures by investigating the role of differentmaterials and physical parameters. Voir les détails
Mots clés : Analytical modeling, tandem solar cell, Spectral response, conversion efficiency