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CONTENTS
Volume 7, Number 1, March 2018
 

Abstract
Thermal bifurcation buckling behavior of fully clamped Euler-Bernoulli nanobeam built of a through thickness functionally graded material is explored for the first time in the present paper. The variation of material properties of the FG nanobeam are graded along the thickness by a power-law form. Temperature dependency of the material constituents is also taken into consideration. Eringen\'s nonlocal elasticity model is employed to define the small-scale effects and long-range connections between the particles. The stability equations of the thermally induced FG nanobeam are derived via the principal of the minimum total potential energy and solved analytically for clamped boundary conditions, which lead for more accurate results. Moreover, the obtained buckling loads of FG nanobeam are validated with those existing works. Parametric studies are performed to examine the influences of various parameters such as power-law exponent, small scale effects and beam thickness on the critical thermal buckling load of the temperature-dependent FG nanobeams.

Key Words
nonlocal elasticity theory; thermal buckling bifurcation; FG nanobeam; thermal effect

Address
IS2M Laboratory, Faculty of Technology, Mechanical engineering Department, University Abou Beckr Belkaid (UABT), Tlemcen, Algeria

Abstract
Niobium is a candidate base for new alloys devoted to applications at especially elevated temperatures. Elaborating and shaping niobium-based alloys by conventional foundry may lead to mechanically interesting microstructures. In this work a series of charges constituted of pure elements were subjected to high frequency induction melting in cold crucible to try obtaining cast highly refractory Nb-xCr and Nb-xCr-0.4 wt.%C alloys (x=27, 34 and 37 wt.%). Melting and solidification were successfully achieved. The as-cast microstructures of the obtained alloys were characterized by electron microscopy and X-ray diffraction and their hardness were specified by Vickers macro-indentation. The obtained as-cast microstructures are composed of a body centered cubic (bcc) niobium dendritic matrix and of an interdendritic eutectic compound involving the bcc Nb phase and a NbCr2 Laves phase. The obtained alloys are hard to cut and particularly brittle at room temperature. Hardness is of a high level (higher than 600Hv) and is directly driven by the chromium content or the amount of {bcc Nb – NbCr2} eutectic compound. Adding 0.4 wt.% of carbon did not lead to carbides but tends to increase hardness.

Key Words
niobium-based alloys; chromium; carbon; foundry; as-cast microstructures; hardness

Address
Patrice Berthod:
1. Institut Jean Lamour (UMR CNRS 7198), Campus Artem, University of Lorraine,
Postal Box 50840, F-54011 Nancy Cedex, France
2. Faculty of Sciences and Technologies, Campus Victor Grignard, University of Lorraine,
Postal Box 70239, F-54506 Vandoeuvre-lès-Nancy Cedex, France

Mélissa Ritouet-Léglise:Institut Jean Lamour (UMR CNRS 7198), Campus Artem, University of Lorraine,
Postal Box 50840, F-54011 Nancy Cedex, France


Abstract
In this paper, a closed-form rigorous solution for interfacial shear stress in simply supported beams strengthened with bonded prestressed E-FGM plates and subjected to an arbitrarily positioned single point load, or two symmetric point loads is developed using linear elastic theory. This improved solution is intended for application to beams made of all kinds of materials bonded with a thin plate, while all existing solutions have been developed focusing on the strengthening of reinforced concrete beams, which allowed the omission of certain terms. The theoretical predictions are compared with other existing solutions. Finally, numerical results from the present analysis are presented to study the effects of various parameters of the beams on the distributions of the interfacial shear stresses. The results of this study indicated that the E-FGM plate strengthening systems are effective in enhancing flexural behavior of the strengthened RC beams.

Key Words
concrete beam; prestressed composite plate; interfacial stresses; strengthening; adherend shear deformation

Address
Benferhat Rabia, Rabahi Abderezak, Tahar Hassaine Daouadji, Adim Belkacem: Département de génie civil, Université Ibn Khaldoun Tiaret; BP 78 Zaaroura, Tiaret, Algérie

Benferhat Rabia, Rabahi Abderezak, Tahar Hassaine Daouadji: Laboratoire de Géomatique et Développement Durable, Université de Tiaret, Algérie

Boussad Abbes, Fazilay Abbes: Laboratoire GRESPI—Campus du Moulin de la Housse, Reims Cedex 2, France
Adim Belkacem: Département des sciences et technologies, Centre Universitaire Tissemsilt, Algérie


Abstract
In the present study, a special attention has been paid to the effects regarding the use of different superplasticizers in different dosages. To do so, 36 mixes of normal and self-compacting concrete with two water/binder ratios of 0.35 and 0.45, four different types of superplasticizer including melamine-formaldehyde, naphthalene-formaldehyde, carboxylic-ether and poly-carboxylate, four different superplasticizer/cement ratios of 0.4%, 0.8%, 1.2% and 1.6% and two silica fume/cement ratios of 0% and 10% have been cast. Moreover, the initial and final setting time of the pastes have been tested. For self-compacting mixes, flow time, slump flow, V-funnel, J-ring and L-box tests have been carried out as well as testing the compressive strength and rupture modulus. For normal concrete mixes, slump test has been conducted to assess the workability of the mix and then for each mix, the compressive strength and rupture modulus have been determined. The results indicate that in addition to the important role of superplasticizer type and dosage on fresh state properties of concrete, these parameters as well as the use of silica fume could affect the hardened state properties of the mixes. For instance, the mixes whose superplasticizer were poly-carboxylic-ether based showed better compressive and tensile strength than other mixes. Besides, the air contents showed robust dependency to the type of the superplasticizer. However, the use of silica fume decreased the air contents of the mixes.

Key Words
superplasticizer type; superplasticizer dosage; silica fume; self-compacting concrete, normal concrete

Address
Department of Civil Engineering, Shahid Rajaee Teacher Training University,
Lavizan, Tehran, Iran


Abstract
TiO2/CH3NH3Pb1-xSbxI3-3xBr3x-based photovoltaic devices were fabricated by a spin-coating method using mixture solutions with SbBr3. Effects of SbBr3, CsI or RbBr addition to CH3NH3PbI3 precursor solutions on the photovoltaic properties were investigated. The short-circuit current densities and photoconversion efficiencies were improved by adding a small amount of SbBr3, CsI or RbBr to the perovskite phase, which would be due to the doping effect of Sb, Br and Cs/Rb atom at the Pb, I and CH3NH3 sites, respectively.

Key Words
photovoltaic device; perovskite; SbBr3; microstructure; CsI; RbBr

Address
Department of Materials Science, The University of Shiga Prefecture,
2500 Hassaka, Hikone, Shiga 522-8533, Japan



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