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Volume 9, Number 1, March 2020

The hybrid method of three-dimensional ion implantation and electric arc is presented as a novel plasma-ion technique that allows by means of high voltage pulsed and electric arc discharges, the bombardment of non-metallic and metallic ions then implanting upon the surface of a solid surface, especially out of metallic nature. In this study AISI/SAE 4140 samples, a tool type steel broadly used in the industry due to its acceptable physicochemical properties, were metallographically prepared then surface modified by implanting titanium and simultaneously titanium and nitrogen particles during 5 min and 10 min. The effect of the ion implantation technique over the substrate surface was analysed by characterization and electrochemical techniques. From the results, the formation of Ti micro-droplets upon the surface after the implantation treatment were observed by micrographs obtained by scanning electron microscopy. The presence of doping particles on the implanted substrates were detected by elemental analysis. The linear polarization resistance, potentiodynamic polarization and total porosity analysis demonstrated that the samples whose implantation treatment with Ti ions for 10 min, offer a better protection against the corrosion compared with non-implanted substrates and implanted at the different conditions in this study.

Key Words
carbon steel; corrosion; physicochemical properties; plasma technology; polarization resistance; surface treatment

(1) E.D. Valbuena-Niño, F. Sanabria:
Foundation of Researchers in Science and Technology of Materials, Colombia;
(2) L. Gil, L. Hernández:
Universidad Nacional Experimental Politecnica, Puerto Ordaz, Venezuela.

In this article, an analytical solution is presented for the steady-state axisymmetric thermal stress distributions in a composite hollow cylinder. The cylinder is composed of two isotropic and anisotropic materials which is subjected to the thermal boundary conditions of convective as well as radiative heating and cooling on the inner and outer surfaces, respectively. The solution of the temperature is obtained by means of Bessel functions and the thermal stresses are developed using Potential functions of displacement. Numerical results are derived for a cylinder which is similar to a gas turbine combustor and showed that the maximum temperature and thermal stresses (radial, hoop, axial) occurred in the middle point of cylinder and the values of thermal stresses in anisotropic cylinder are more than the isotropic cylinder. It is worthy to note that the values of the thermal conditions which estimated in this research, not to be presented in any other papers but these values are very accurate in calculation.

Key Words
anisotropic and isotropic materials; hollow cylinder; thermal stresses; bessel functions; potential function displacements; steady-state

(1) Mohammad Javad Namayandeh, Mehdi Mohammadimehr, Mojtaba Mehrabi:
Department of Solid Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran;
(2) Abbas Sadeghzadeh-Attar:
Department of Metallurgy and Materials Engineering, University of Kashan, Kashan, Iran.

With the use of differential quadrature method (DQM), forced vibrations and resonance frequency analysis of functionally graded (FG) nano-size beams rested on elastic substrate have been studied utilizing a shear deformation refined beam theory which contains shear deformations influence needless of any correction coefficient. The nano-size beam is exposed to uniformly-type dynamical loads having partial length. The two parameters elastic substrate is consist of linear springs as well as shear coefficient. Gradation of each material property for nano-size beamhas been defined in the context of Mori-Tanaka scheme. Governing equations for embedded refined FG nanosize beams exposed to dynamical load have been achieved by utilizing Eringen's nonlocal differential law and Hamilton's rule. Derived equations have solved via DQM based on simply supported-simply supported edge condition. It will be shown that forced vibrations properties and resonance frequency of embedded FG nano-size beam are prominently affected by material gradation, nonlocal field, substrate coefficients and load factors.

Key Words
forced vibrations; DQM; FG nanobeam; dynamic load; elastic substrate; nonlocal elasticity theory

Al-Mustansiriah University, Engineering Collage P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq.

Fracture toughness of SiC on Si thin films of thicknesses of 150, 750, and 1500 nm were measured using Agilent XP nanoindenter equipped with a Dynamic Control Module (DCM) in Load Control (LC) and Continuous Stiffness Method (CSM) protocols. The fracture toughness of the Si substrate is also measured. Nanovision images implied that indentations into the films and well deep into the Si caused cracks to initiate at the Si substrate and propagate upward to the films. The composite fracture toughness of the SiC/Si was measured and the fracture toughness of the SiC films was determined based on models that estimate film properties from substrate properties. The composite hardness and modulus of the SiC films were measured as well. For the DCM, the hardness decreases from an average of 35 GPa to an average of 13 GPa as the film thick increases from 150 nm to 1500 nm. The hardness and moduli of the films depict the hardness and modulus of Si at deep indents of 12 and 200 GPa respectively, which correlate well with literature hardness and modulus values of Si. The fracture toughness values of the films were reported as 3.2 MPa√m.

Key Words
fracture toughness; KC; nanoindentation; hardness; x-ray diffraction (XRD)

(1) Department of Mechanical and Aerospace Engineering, Old Dominion University, 241 Kaufman Hall, Norfolk, VA, USA;
(2) Applied Research Center-Thomas Jefferson National Accelerator Facility, 12050 Jefferson Ave, Newport News, VA 23606, USA.

The novelty of this paper is the use of a simple higher order shear and normal deformation theory for bending and free vibration analysis of functionally graded material (FGM) beams on two-parameter elastic foundation. To this aim, a new shear strain shape function is considered. Moreover, the proposed theory considers a novel displacement field which includes undetermined integral terms and contains fewer unknowns with taking into account the effects of both transverse shear and thickness stretching. Different patterns of porosity distributions (including even and uneven distribution patterns, and the logarithmic-uneven pattern) are considered. In addition, the effect of different micromechanical models on the bending and free vibration response of these beams is studied. Various micromechanical models are used to evaluate the mechanical characteristics of the FG beams for which properties vary continuously across the thickness according to a simple power law. Hamilton's principle is used to derive the governing equations of motion. Navier type analytical solutions are obtained for the bending and vibration problems. Numerical results are obtained to investigate the effects of power-law index, length-to-thickness ratio, foundation parameter, the volume fraction of porosity and micromechanical models on the displacements, stresses, and frequencies.

Key Words
functionally graded material; elastic foundation; shear deformation theory; bending; free vibration; stretching effect

(1) Lazreg Hadji:
Laboratory of Geomatics and Sustainable Development, University of Tiaret,14000 Tiaret, Algeria;
(2) Lazreg Hadji:
Department of Mechanical Engineering, University of Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algeria;
(3) Fabrice Bernard:
University of Rennes, INSA Rennes, Laboratory of Civil Engineering and Mechanical Engineering, France.

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