Milesa Srećković

Characterization of laser beam interaction with carbon materials

This paper presents simulation and experimental results for the exposure of some carbon-based materials to alexandrite and Nd3+:YAG (yttrium aluminum garnet) laser radiation. Simulation of the heating effects was carried out using the COMSOL Multiphysics 3.5 package for samples of carbon-based P7295-2 fiber irradiated using an alexandrite laser and carbon-based P4396-2 fiber irradiated using an Nd3+:YAG laser, as well as by applying finite element modeling for P7295-2 samples irradiated using an Nd3+:YAG laser. In the experimental part, P7295-2 samples were exposed to alexandrite laser radiation while samples of carbon-based composite 3D C/C were exposed to Nd3+:YAG laser radiation. Micrographs of the laser induced craters were obtained by light and scanning electron microscopy, and the images analyzed using the ImageJ software. The results obtained enable identification of the laser–material interaction spots, and characterization of the laser induced changes in the materials investigated.

Modification of Carbon Cloth by Interaction with Pulsed TEA CO2 Laser

The interaction of a Transversely Excited Atmospheric (TEA) CO2 laser (pulse duration less than 2 μs) with carbon and activated carbon cloth was investigated. The investigations have shown that carbon cloth had been physically modified by the TEA CO2 laser. The type of modification strongly depends on laser working regime, such as energy density of the laser beam, etc. The morphology transformations induced by interaction with TEA CO2 laser beams resulted in different specific surface area of activated carbon cloth. Also, laser interaction induced minor changes in crystallographic structure parameters.

Stress Field Analysis in Composite Laminates with Embedded Optical Fiber

A typical intensity-modulated optical fiber sensor system consists of a light source, a sensing device, within which the intensity of light is altered by the measurand in some way, a detector to measure the intensity of the transmitted signal and optical fibers to carry light between these components. The optical fiber coating interaction with the host material plays a major role in determining the proper transfer of load from the structure to the optical fiber. Three-dimensional (3D) finite element (FE) model of the structure was performed to study and predict the behaviour of the stress/strain fields in and around acrylate coated embedded optical fibers in flexural test coupons of carbon fiber composite. The modeling results and the fracture surface scanning electron micrographs suggest that the soft acrylate coating is debonding.

Composite Rods with Embedded Optical Fibre - Modeling and Evaluation

An experimental facility for composite rod manufacturing by vacuum molding technique with embedded optical fibres has been designed and built. A mathematical model for composite rods, with embedded optical fibres, formation process is presented. Numerical solution of the model is given and compared to the experimental results. A good agreement with the experimental values is observed. Kinetics of curing reaction and heat transfer during the processing of fibre reinforced epoxy resins were considered. The finite difference method was utilized to solve the mathematical equations. The use of embedded optical fibre to detect damage in glass reinforced polymer (GRP) composite rod is described by a simple signal attenuation measurement system.

Reduction of Nanometric Magnetite Powder

The investigated nanometric magnetite powders were synthesized electrochemically, and examined by XRD and SEM techniques. Their reduction was conducted through the isothermal heating in hydrogen in the temperature range from 600 to 860 K. Kinetics of the hydrogen recovery process during oxidation of freshly formed Fe powders in a water vapor stream was also studied. It was assumed that the solid-gas reaction is diffusion controlled, and Jander’s model was applied to describe it. The experimental data suggest that the reoxidation process proceeds in two stages, at various activation energies. By changing the conditions of the electrochemical (EC) process we were able to produce the iron oxide powders with optimal particle size and activity, for pure hydrogen production through appropriate reduction/oxidation processes.

Synthesis and Characterization of Al, Y, Co and Cr Substituted Ultrafine Powder of NiFe2O4

The ultrafine spinel NiFe1.9M0.1O4 powders (M=Al, Y, Cr, Fe) were synthesized by thermal decomposition of appropriate mixtures of complex compounds with acetylacetone - (2,4 pentadione) ligands ([M(AA)x]) at 500 °C. Samples were annealed in the temperature range 600-1000 °C and the crystallization process was followed by XRD. The largest crystallite size and the highest crystallization rate are observed for NiFe1.9Al0.1O4, while the opposite was found for NiFe1.9Y0.1O4. Strain value in NiFe1.9Y0.1O4 changes sign at temperatures between 700-800 °C, while for NiFe1.9M0.1O4 (M=Al, Cr) it has a positive sign and reaches the maximum value at 700 °C. The crystal structure of the samples annealed at 1000 °C was refined using the Rietveld profile method. Cation substitution in Ni-ferrite changes its structural and microstructural parameters, and can also significantly influence other physical properties.

Laser doppler velocimetry and confined flows

Finding the mode, in which two component laser Doppler velocimetry can be applied to flows confined in cylindrical tubes or vessels, was the aim of this study. We have identified principle issues that influence the propagation of laser beams in laser Doppler velocimetry system, applied to flow confined in cylindrical tube. Among them, the most important are influences of fluid and wall refractive indices, wall thickness and internal radius ratio and beam intersection angle. In analysis of the degrees of these influences, we have applied mathematical model, based on geometrical optics. The separation of measurement volumes, that measure different velocity components, has been recognized as the main drawback. To overcome this, we propose a lens with dual focal length – primary focal length for the measurement of one velocity component and secondary focal length for the measurement of the other velocity component. We present here the procedure for calculating the optimal value of secondary focal length, depending on experimental set-up parameters. The mathematical simulation of the application of the dual focal length lens, for chosen cases presented here, confirmed the accuracy of the proposed procedure.

Interaction of laser beams with carbon textile materials

Purpose – The purpose of this paper is to present the results of interaction occurring during the exposition of some specific carbon textile materials obtained in laboratory conditions to beams of various laser types. Design/methodology/approach – Carbon fabric materials – fiber, felt and cloth – obtained from different precursor materials and prepared at various process conditions (oxidized, partially carbonized, carbonized, graphitized), were exposed to pulses of various lasers (Nd3+: YAG, alexandrite, ruby). Findings – Depending on the laser power, plasma and destructive phenomena occurred. In the case of an interaction between a Nd3+: YAG laser beam and specimens of thickness in millimeter range, the authors have estimated the threshold of the energy density for drilling and discussed the possible models of the interaction. Research limitations/implications – The results have implications in the estimations of quality as well as in the improvement of material processing, giving some new light to the c...

Numerical modelling of thermal effects on biological tissue during laser-material interaction

Among numerous methods of the modelling of laser interaction with the material equivalent of biological tissue (including macroscopic and microscopic cell interaction), the case of pathogenic prostates is chosen to be studied. The principal difference between the inorganic and tissue equivalent material is the term which includes blood flow. Thermal modelling is chosen for interaction mechanisms, i.e. bio-heat equation. It was noticed that the principal problems are in selecting appropriate numerical methods, available mathematical program packages and finding all exact parameters for performing the needed calculations. As principal parameters, among them density, heat conduction, and specific heat, there are many other parameters which depend on the chosen approach (there could be up to 20 parameters, among them coefficient of time scaling, arterial blood temperature, metabolic heat source, etc). The laser type, including its wavelength which defines the quantity of absorbed energy and dynamic of irradiation, presents the term which could be modulated for the chosen problem. In this study, the program Comsol Multiphysics 3.5 is used in the simulation of prostate exposed to Nd3+:YAG laser in its fundamental mode.

The interpretation of the intensity of components of laser scattering by interaction with matter

The measurement of scattered light properties offers many optical, acoustic, dielectric, thermodynamic data about the scattering medium. Brillouin spectroscopy with various modifications and different laser types has been a measurement technique in acoustics for a long time, but it is still important as an autonomous technique. It enables more detailed and exhaustive knowledge of the acoustic and optical properties of matter. A series of Rayleigh–Brillouin spectra are recorded for a set of organic solvents and phytol. The equipment used in spectra recordings enables the measurement of four components of scattered laser intensity Ihh, Ihv, Ivv and Ivh. The ratios of the linewidth, as well as shifts, are determined for Rayleigh–Brillouin spectra. According to them, the hypersound velocity and absorption coefficients can be calculated. There is much software for data processing obtained in laser interaction with matter, with different programming tools. An analysis of spectra is performed, i.e. an examination of which distribution (Gaussian or Lorentzian) better explains the experimentally obtained diagrams.