Sciences des matériaux
Electronic Properties of Carbon Nanotubes
Theoretical calculations predicted that carbon nanotubes were to present a metal behavior or semiconductor following their diameter and their chirality, these properties of conduction have inherited the structure of a particular band of graphite. Consequently, a limited number of wave vectors are allowed in this direction, It depends on the diameter and the winding of the graphene sheet on itself. If the edge conditions include the corners of the Brillouin zone, the behavior of the nanotube is metallic, this is the case for all “chair” type nanotubes and a third of “chiral” and “zig-zag” nanotubes. In other cases, the band structure has a bandgap, as a first approximation, inversely proportional at the radius of the nanotube. In addition, STM makes it possible to image the atomic structure of nanotubes and therefore to determine their chirality and their diameter. The transport properties can thus be correlated with the structure of the nanotube, the nanotube would be thus a quantum prototype of wire to a dimension. The various measurements carried out by AFM and STM on nanotubes monofeuillets showed that they behave indeed like such. The possible applications of these properties come within the province of nanoelectronic, not only the use of the nanotube like a molecular discussion thread but also like an active electronic element. Voir les détails
Mots clés : Carbon Nanotubes;STM;AFM
Preparation and characteristics of synthesized hydroxyapatite from bovine bones and by co-precipitation method
Hydroxyapatite (HA, (Ca10(PO4)6(OH)2) is a widely studied bioceramic due to its biocompatibility, bioactivity, and chemical similarity to the mineral component of bone. Generally, hydroxyapatite can be made from several natural and synthetic sources.The objective of this study is to prepare hydroxyapatite powders from different precursors (natural or chemical). Hydroxyapatite was synthetized by Co-precipitation method, the chemical precursors of which are [Ca(NO3)2.4H2O, (NH4)2HPO4] and the natural source was bovine bone. Bovine hydroxyapatite (BHA) was extracted from the bovine bone bio-waste via thermal method and milling process. Synthesized HA (SHA) was prepared by co-precipitation method with the pH 10.0 of mother liquor. The prepared powders were characterized using various analytical techniques such as XRD, FTIR spectroscopy, thermogravimetry (ATG), and scanning electron microscope (SEM). These techniques provide information about the structural, chemical, morphological and physicochemical of each of the prepared powders. The use of co-precipitation method produced a low crystallinity of HA while the thermal method increased crystallinity. On the other hand, the results showed that the Ca / P ratio of synthetic hydroxyapatite (SHA) as well as that of bovine bone source (BHA) was also stoichiometric. Voir les détails
Mots clés : hydroxyapatite, Bovine bone, synthesis, Co-precipitation.
Synthesis and characterization of hydroxyapatite powder derived of eggshell by precipitation method
Hydroxyapatite is the inorganic material with formula Ca10(PO4)6(OH)2. It is one of bioceramic was used for one repairs, fixing defects of filing voids in biomedical fields. The use of chicken eggshell is one of the natural sources to obtain the calcium phosphate compounds. The main objective of this study is to synthesize the hydroxyapatite by precipitation method from eggshell. The raw eggshell was calcined at 850°C for 2 hours following by grinding for 16 hours. The HA powder was synthesized by wet chemical method, using eggshells and phosphoric acid (H3PO4). X-ray diffraction spectroscopy (XRD, Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR) were used to characterize the morphology, composition and distribution of the particles. The Thermos gravimetric analysis (TGA-DTA) was also carried out to evaluate the stability of the synthesized HA powder. The particle-size distribution (PSD) of the powder was determined by the laser scattering particle size distribution analyzer. The results showed that the sintered at 1000°C of HA powder resembles the feature of pure and single apatite phase having favorable Ca/P ratio. Voir les détails
Mots clés : hydroxyapatite, Bioceramics, synthesis, Eggshell, Precipitation
Numerical study of polymer coating by UV photopolymerization.
Polymer-based coatings are used to protect a structure or device against mechanical attacks such as scratches, abrasion and erosion or against chemical attacks such as humidity, temperature, UV rays. This work concerns the development by photopolymerization UV of new coating materials based on a polymer as (Polyurethane Acrylate, oligomers) deposited on heat-sensitive materials such as thermoplastics (PC; PMMA,). Now, the polymers, which are already used in thermal powder coating. They generally show very high melting temperatures (around 200 °C). They will not be suitable for depositing on supports sensitive to high temperatures without risk of damaging them. In this work, we proposed a numerical study of the effect of different synthesis parameters (energy and applied UV rays, exposure time, temperature, external medium, etc.) on the conversion rate to a 3D mesh (crosslinking rate) and model optimization of coating parameters on heat-sensitive substrates. Voir les détails
Mots clés : polymers, coatings polymer, photopolymerization UV
Effect of fatigue on Mechanical Behaviors of Weld Overlay ENiCrMo-3 on 25CD4 Steel Substrate Using SMAW Process
In the present study, we investigated the effect of fatigue on the mechanical behaviors of weld overlay ENiCrMo-3 on a 25CD4 steel substrate using the SMAW process. The microstructure of the ENiCrMo-3/25CD4 substrate interface primarily consisted of columnar Ni-γ. a diffusion gradient of Fe, Cr, and Ni elements from the melting limits towards the type II boundary near the interface. Based on the fatigue test results, the specimen, which was tested at the ultimate tensile strength, exhibited superior fatigue endurance compared to the first specimen tested at the ultimate tensile strength. elasticity limit. This suggests that the material had greater fatigue resistance when subjected to a percentage of the ultimate tensile strength, as it withstood a greater number of cycles over a longer duration. The electrochemical behavior of the ENiCrMo-3 overlay and the 25CD4 substrate in a NaCl 3.5% solution indicated the presence of galvanic corrosion. The Tafel curves demonstrated that the corrosion process could be divided into two parts, emphasizing the aggressiveness of Cl- ions. Electrochemical impedance spectroscopy (EIS) measurements showed that the resistance to charge transfer of the ENiCrMo-3 hardfacing was greater than that of the substrate/ENiCrMo-3 interface and the substrate itself Voir les détails
Mots clés : 25CD4 steel substrate, ENiCrMo-3 hardfacing, fatigue behavior
Finite element investigation of the elasto-plastic behavior of AA6005 using the Hansel-Spittel rheological model and the Cockcroft and Latham fracture model
Understanding the behavior of materials requires accurate and expensive mechanical tests at different temperatures and stresses. The current trend toward numerical simulation has become an essential engineering tool. Therefore, researchers have made efforts in this area by building mathematical models based on experimental data. These models include data regarding the actual physical behavior of the material, such as its temperature sensitivity, strain rate sensitivity, and strain sensitivity. The constitutive equations of Hensel and Spittel (H-S) [1] have been frequently used (FES), due to their ease of numerical implementation, the inclusion of stress and strain history, and the calibration of parameters from tests. The objective of this work is to determine the mechanical characteristics of the aluminum alloy (AA 6005), taking into account the effect of work hardening. This behavior is then tested using finite element analysis tools to model it. The experimental results showed that the work-hardening behavior of the alloy (AA 6005) at room temperature is similar to all quasi-static strain rates studied in this work. In addition, in the range of strain rates investigated in this study, the finite element results correlate well with the experimental results. The simulated results can be really reliable only when a good constitutive equation is employed. Voir les détails
Mots clés : tensile test, rheological behavior Hasel-Spittel, Ductile Damage Fracture criterion
Modeling Cracks Using Digital Images Correlation and Phase-Field FE Analysis Techniques
In this work, the recently developed phase field fracture along with digital images correlation DIC techniques are used to study mode I crack behavior, an elastic brittle phase field model which is well implemented in some finite elements codes is used, in this model the damage evolution is driven only by elastic strains and is governed by the classical brittle phase-field law, the opensource digital images correlation Ncorr code is used to extract full displacement and strain field from experiments, this open-source DIC code can treats cracks in structure by taking into account discontinuities through the sub-sets, the discontinuities in the displacement field are well captured and used in the out-puts to compute the size of crack by tracking and locating the position of the crack tip, the best results are obtained by finding the smallest DIC parameters (sub-sets size and radius) which gives results without noise. Results are expressed in term of plots of displacement vs reaction-force, contour plots of displacement and strain field components, crack tip opening displacement and fracture path tracking. Results from both approaches are presented and then a discussed is conducted to show the capabilities of both methods to study and track crack evolution in structures under mode I loading. Voir les détails
Mots clés : Cracks, Finite Element Analysis, Phase Field Fracture, Digital Images Correlation, Ncorr
Damage Analysis In Open Hole Composite Specimens By Acoustic Emission: Experimental Investigation
In the present work, an experimental study is carried out using acoustic emission and DIC techniques to analyze the damage of open hole woven composite carbon/epoxy under solicitations. Damage mechanisms were identified based on acoustic emission parameters such as amplitude, energy, and cumulative account and rise time. The findings of the AE measurement were successfully identified by digital image correlation (DIC) measurements. The evolution value of bolt angle inclination during tensile tests was studied and analyzed. Consequently, the relationship between the bolts inclinations angles during tensile tests associated with failure modes of composite materials fastened joints is determined. Moreover, there is an interaction between laminate pattern, laminate thickness, fastener size and type, surface strain concentrations, and out-of-plane displacement. Conclusions are supported by microscopic visualizations of the composite specimen. Voir les détails
Mots clés : damage analysis, composite specimens, acoustic emission
Fusion and heat affected zones damage during fatigue assessment assisted by digital image correlation
This work aims at following strain field expansion incurred in welded austenitic stainless steel during cyclic loading assisted by three dimensional Digital Image Correlation (3D DIC) method. The latter is an indicative device helping to distinguish the high stressed area from the low stressed one during fatigue test. 3D DIC monitoring of strain field and stress condensation in the studied area reveals the presence of simultaneous strain localization in two regions bordering between them an area with a reduced stress level. SEM-ECCI analysis of the hybrid zone supposes that the microstructural damage in the welded joint would be controlled by hardening and softening phenomena, caused by sub-grains formation and twins annihilation during loading Voir les détails
Mots clés : Cracks, Image processing, Strain mapping, Welded joint
VARIABLE TIME TRIBOLOGICAL BEHAVIOR OF A DEPOSIT METAL E316L-17
Wear and corrosion are the main problems of mechanical elements in mechanical contact, and this results in enormous economic losses. This work describes the tribological effects during the variation of the friction time (1h, 3h, 12h and 24h) and the electrochemical behavior of the substrate solder coating. E316L-17/25CD4 using electric arc welding process. The tribological tests studied such as resistance to wear and coefficient of friction were carried out by a ball test with a friction speed of 20mm/s. The polarization curves were used to evaluate the electrochemical behavior (corrosion resistance) of the upper part of the hard coating. It was found that the wear resistance of E316L-17 increased with hardness. The corrosion current density of the coatings was determined. Voir les détails
Mots clés : E 316L-17, 25CD4 steel substrate, Electrochemical behavior, Tribological properties