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CONTENTS
Volume 5, Number 3, September 2016
 

Abstract
Copper/silicon nitride (Cu/Si3N4) composites are fabricated by powder technology process. Copper is used as metal matrix and very fine Si3N4 particles (less than 1 micron) as reinforcement material. The investigated powder were used to prepare homogenous (Cu/Si3N4) composite mixtures with different Si3N4 weight percentage (2, 4, 6, 8 and10). The produced mixtures were cold pressed and sintered at different temperatures (850, 950, 1000, 1050°ree;C). The microstructure and the chemical composition of the produced Cu/Si3N4 composites were investigated by (SEM) and XRD. It was observed that the Si3N4 particles were homogeneously distributed in the Cu matrix. The density, electrical conductivity and coefficient of thermal expansion of the produced Cu/Si3N4 composites were measured. The relative green density, sintered density, electrical conductivity as well as coefficient of thermal expansion were decreased by increasing the reinforcement phase (Si3N4) content in the copper matrix. It is also founded that the sintered density and electrical conductivity of the Cu/Si3N4 composites were increased by increase the sintering temperature.

Key Words
Copper; Silicon Nitrides; powder metallurgy; sintering; electrical conductivity; coefficient of thermal expansion

Address
Mahmoud A. Ahmed, Walid M. Daoush: Department of Production Technology, Faculty of Industrial Education, Helwan University, 30 El Sawah Street, Cairo, Egypt

Walid M. Daoush: Department of Chemistry, Faculty of Science, Al-Imam Muhammad Ibn Saud Islamic University, Al Riyadh, KSA

Ahmed E. El-Nikhaily: Mechanical Department, Faculty of Industrial Education, Suez University, Suez, Egypt

Abstract
In this paper, an efficient and simple refined theory is presented for buckling analysis of functionally graded plates. The theory, which has strong similarity with classical plate theory in many aspects, accounts for a quadratic variation of the transverse shear strains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. The mechanical properties of functionally graded material are assumed to vary according to a power law distribution of the volume fraction of the constituents. Governing equations are derived from the principle of minimum total potential energy. The closed-form solutions of rectangular plates are obtained. Comparison studies are performed to verify the validity of present results. The effects of loading conditions and variations of power of functionally graded material, modulus ratio, aspect ratio, and thickness ratio on the critical buckling load of functionally graded plates are investigated and discussed.

Key Words
closed-form solution; refined plate theory; buckling analysis; functionally graded plate

Address
Tahar Hassaine Daouadji and Belkacem Adim: Departement de genie civil, Universite Ibn Khaldoun Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algerie

Tahar Hassaine Daouadji and Belkacem Adim: Laboratoire de Geomatique et Developpement Durable, Universite Ibn Khaldoun Tiaret, Algerie

Abstract
Fusion and characterization of bisphenol-A diglycidyl ether based thermosetting polymer mortars containing an epoxy resin, Fly ash and Rock sand are presented here for the Experimental study. The specimens have been prepared by means of an innovative process, in mild conditions, of commercial epoxy resin, Fly ash and Rock sand based paste. In this way, thermosetting based hybrid mortars characterized by a different content of normalized Fly ash and Rock sand by a homogeneous dispersion of the resin have been obtained. Once hardened, these new composite materials show improved compressive strength and toughness in respect to both the Fly ash and the Rock sand pastes since the Resin provides a more cohesive microstructure, with a reduced amount of micro cracks. The micro structural characterization allows pointing out the presence of an Interfacial Transition Zone similar to that observed in cement based mortars. A correlation between micro-structural features and mechanical properties of the mortar has also been studied.

Key Words
fly-ash; quarry dust; epoxy resin; compressive strength

Address
P. Sudheer: Department of Civil Engineering, MVGR College of Engineering, Vizainagaram, Andhra Pradesh, India

M.G. Muni Reddy: Department of Civil Engineering, College of Engineering, Andhra University, Visakhapatnam, Andhra Pradesh, India
S. Adiseshu: Department of Civil Engineering, College of Engineering, Andhra University, Visakhapatnam, Andhra Pradesh, India

Abstract
In this work effect of high energy milling on the structural and electrical properties of Ba(Fe1/2Ta1/2)O3 (BFT) ceramic synthesized using standard solid-state reaction method were investigated. X-ray diffraction studies indicated that the unit cell structure for all the samples to be hexagonal (space group: P3m1). FTIR spectra also confirmed the formation of BFT without any new phase. The milled (10 h) BFT ceramic showed the formation of small grain sizes (<2 µm) which is beneficial for dielectric applications in high density integrated devices. Besides, the milled (10 h) BFT ceramic sample exhibited superior dielectric properties (enhancement in ε´-value and reduction in tgδ - value) compared to un-milled one. Impedance analysis indicated the negative temperature coefficient of resistance (NTCR) character. The correlated barrier hopping model (jump relaxation type) is found to successfully explain the mechanism of charge transport in present ceramic samples.

Key Words
Ba(Fe1/2Ta1/2)O3; lead-free; structure; perovskite; dielectric constant; FTIR spectroscopy; electroceramic

Address
Uttam K. Mahto, K. Prasad: Aryabhatta Centre for Nanoscience and Nanotechnology, Aryabhatta Knowledge University, Patna 800001, India

Sumit K. Roy, S. Chaudhuri: Department of Physics, St. Xavier´s College, Ranchi 834001, India

K. Prasad: University Department of Physics, T.M. Bhagalpur University, Bhagalpur 812 007, India

Abstract
Compared to metal-to-metal tribology, polymer tribology presents further complexity as it is more prone to be influenced by operating conditions. Over the past two decades, progress in the field of wear of polymers has led to the establishment of more refined wear mechanisms. The current paper establishes the link between different load parameters and the wear rate of polymers, based on experimental investigations. A pin-on-plate reciprocating tribometer was used to examine the wear behaviour of polyamide sliding against a steel counterface, under constant and fluctuating loads, in dry conditions. In addition, the influence of controlled imperfections in the polymer surface upon its wear rate were examined, under cyclic and steady loading, in order to better understand surface fatigue wear of polymers. The imposed imperfections consisted of vertical artificial deep crack (slit) perpendicular or parallel to the direction of sliding. The study concludes with the followings findings; in general, wear of polymers shows a significant tendency to the type of applied load. Under cyclic loads, polymers show an increase in wear rate compared to those tested under static loads. Such increase was found to increase with the increase in cyclic load frequency. It is also demonstrated that surface cracks results in higher wear rates, particularly under cyclic loads.

Key Words
tribology; wear; polymers; surface defects

Address
Department of Mechanical Engineering, Faculty of Engineering, Alexandria University, Egypt


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