Gabriel Jiga

Hydroxyapatite with environmental applications

The aim of this study was to synthetize new nanoparticles based on methyltrimethoxysilane coated hydroxyapatite (MTHAp) for lead removal in aqueous solutions. The morphological and compositional analysis of MTHAp was investigated by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). Removal experiments of Pb2+ ions were carried out in aqueous solutions with controlled concentration of Pb2+ and at fixed pH of 5. After the removal experiment of Pb2+ ions from solutions, porous hydroxyapatite nanoparticles were transformed into PbMTHAp_5 via the adsorption of Pb2+ ions followed by a cation exchange reaction. Our results demonstrate that the porous hydroxyapatite nanoparticles can be used as an adsorbent for removing Pb2+ ions from aqueous solution.

Analytical and numerical evaluation of honeycomb core compression elastic modulus

Honeycomb cores used in engineering applications are subjected to compressive and bending loads. One of the most important elastic properties allowing the accurate design of the structural components which contain honeycomb cores is the out-of-plane Young modulus. The present paper provides analytical and numerical analysis, allowing an accurate design of the structural components containing honeycomb cores.Honeycomb cores used in engineering applications are subjected to compressive and bending loads. One of the most important elastic properties allowing the accurate design of the structural components which contain honeycomb cores is the out-of-plane Young modulus. The present paper provides analytical and numerical analysis, allowing an accurate design of the structural components containing honeycomb cores.

Behavior of composite sandwich panels with several core designs at different impact velocities

A sandwich composite represents a special class of composite materials that is manufactured by bonding two thin but stiff faces to a low density and low strength but thick core. The distance between the skins given by the core increases the flexural modulus of the panel with a low mass increase, producing an efficient structure able to resist at flexural and buckling loads. The strength of sandwich panels depends on the size of the panel, skins material and number or density of the cells within it. Sandwich composites are used widely in several industries, such as aerospace, automotive, medical and leisure industries. The behavior of composite sandwich panels with different core designs under different impact velocities are analyzed in this paper by numerical simulations performed on sandwich panels. The modeling was done in ANSYS and the analysis was performed through LS-DYNA.A sandwich composite represents a special class of composite materials that is manufactured by bonding two thin but stiff faces to a low density and low strength but thick core. The distance between the skins given by the core increases the flexural modulus of the panel with a low mass increase, producing an efficient structure able to resist at flexural and buckling loads. The strength of sandwich panels depends on the size of the panel, skins material and number or density of the cells within it. Sandwich composites are used widely in several industries, such as aerospace, automotive, medical and leisure industries. The behavior of composite sandwich panels with different core designs under different impact velocities are analyzed in this paper by numerical simulations performed on sandwich panels. The modeling was done in ANSYS and the analysis was performed through LS-DYNA.

Application of biocompatible magnetite nanoparticles for the removal of arsenic and copper from water

The progress of nanotechnology made possible the use of nanomaterials as adsorbents and magnetic iron oxides represents one of the first generations of nanoscale materials used in environment technologies [1]. A systematic characterization of commercial magnetite (Fe3O4) is presented in this research. The commercial (Fe3O4) magnetic adsorbents were characterized by various characterizations methods such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDX). This study was also focused on the study of adsorption isotherms and the kinetics evaluation. X-ray studies indicated that As3+ and Cu2+ removed by Fe3O4 did not seem to alter the structure of Fe3O4 but they were highlighted in the EDX analysis. In addition, the SEM studies were consistent with the XRD results. The rate of adsorption of contaminants, in contaminated solutions decreases when the amount of contaminant increases in all experiments performed. The results revealed that Fe3O4 nanoparticles are promising candidates which could be used as sorbents for the removal of arsenic from the marine environment, for site remediation and groundwater treatment.The progress of nanotechnology made possible the use of nanomaterials as adsorbents and magnetic iron oxides represents one of the first generations of nanoscale materials used in environment technologies [1]. A systematic characterization of commercial magnetite (Fe3O4) is presented in this research. The commercial (Fe3O4) magnetic adsorbents were characterized by various characterizations methods such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDX). This study was also focused on the study of adsorption isotherms and the kinetics evaluation. X-ray studies indicated that As3+ and Cu2+ removed by Fe3O4 did not seem to alter the structure of Fe3O4 but they were highlighted in the EDX analysis. In addition, the SEM studies were consistent with the XRD results. The rate of adsorption of contaminants, in contaminated solutions decreases when the amount of contaminant increases in all experiments performed. The results revealed that Fe3O4 nanoparticles ...

Electrical characterization of TiO2 nanotubes synthesized through electrochemical anodizing method

In the present paper, the electrochemical anodizing method was used for the obtaining of TiO2 nanotube layers, developed on titanium surface. Self-organized titanium nanotubes were obtained when an aqueous solution of 49.5 wt % H2O – 49.5 wt % glycerol – 1 wt % HF was used as electrolyte, the anodizing time being equal to 8 hours and the applied voltage to 25 V. Scanning electron microscopy shows that the one-dimensional nanostructure has a tubular configuration with an inner diameter of approximately 60 nm and an outer diameter of approximately 100 nm. The electrical properties of these materials were analyzed through dielectric spectroscopy method.

Analysis of the External Magnetic Field Influences on the Measurements Realized with a Single Strip Tester (SST) Using Finite Element Modeling

In this article it was studied the magnetic influence of an electromagnetic coil on the measurements, realized with a single strip tester. One major difficulty in modeling of the magnetic materials is the magnetic hysteresis. As a consequence, it was used the Frohlich-Kennelly model for defining the hysteresis of the soft magnetic material, from which is manufactured the magnetic core of the electrotechnical devices. A numerical study, based on finite element analysis, is proposed in order to model a Single Strip Tester (SST). For this it was made a geometrical description based on technical data of a SST developed by Brockhaus Messtechnik, which measures magnetic properties of silicon iron strips with an area of 280 × 30 mm2.

Comparative Study to Determine the State of Tension Using FEM in a Premolar Restored with a Composite Inlay versus a Ceramic Inlay

The aesthetic composite inlay or ceramic ones are useful for restoring posterior teeth affected by decay processes. The choice of the inlay type can sometimes be a challenge for the dentist. The aim of this study is to identify the optimal type of an inlay used for second-class cavities that can assure a good long-term prognosis of dental restoration. In order to achieve this study, it was performed an 3D analysis of stresses recorded in a premolar restored with a composite inlay and a ceramic inlay, the simulation being done by finite elements method (FEM) using Ansys program. The study results showed that stresses registered in the tooth restored through ceramic inlay are more favorable than those recorded in the case of the tooth restored with composite inlay. The aesthetic composite inlays are preferred instead ceramic ones by many practitioners because of the advantages it presents: requires minimal preparations, technique is easier thanks to the easier handling of composite material, allow future adjustment of the occlusal surface, being easily adjusted and repaired, are radiopaque and, last but not least, have a lower cost. The question that arises frequently in medical practice is related to inlays behavior in case of functional requirements, depending on the material from which they are made. Configuration of preparation, the technique and the materials used for cementing, and restorative materials can influence the type of resistance to fracture of these restorations. The ability of restorative materials to support the masticatory forces and distribution of stresses in the vicinity of the adhesive interface constitutes a decisive factor in acquiring a restoration with a high degree of resistance to fracture.

Screw Ball Actuator Stress Behavior

The new perspectives with regard to early stage beginning vehicles development introduce the need for using driving simulators also. The objective of this study consists in investigating the stress behavior during driving simulator operation at maximum balance angle. The investigation during functioning of the mechanism (the stresses that occur in the system) starts with the static stress analysis, followed by the investigation for different angular positions from 0° to 10° that are mandatory. The analysis can predict the structural stress level that may become very high and generate deficiencies for the entire assembly while using different materials, including composite materials.

Analysis of the stress-strain state in single overlap joints using piezo-ceramic actuators

In this paper is presented a 2D approach to finite element modeling and an analytical calculus of a single lap bonded joint. As adherent material were selected a sheet of wood, aluminum and titanium. For adhesive part were selected Bison Super Wood D3 in case of the wood single lap joint and an epoxy resin type DGEBA-TETA for gluing together aluminum and titanium parts. In the article is described a combined method, which consists in the placement of the piezoelectric actuator inside of the adhesive part, in order to determine the tensile stress in the overlap joint. A comparison between the analytical and numerical results has been achieved through a multiphysics modeling - electrical and mechanical coupled problem. The technique used to calculate the mechanical parameters (First Principal Stress, displacements) was the three-point bending test, where different forces were applied in the mid-span of the structure, in order to maintain a constant displacement rate. The length of the overlap joint was modi...