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Volume 8, Number 1, March 2019

Roll bonding (RB) process of bi-metal laminates as a new noble method of bonding has been widely used in the production of bimetal laminates. In the present study, asymmetric roll bonding process as a new noble method has been presented to produce Al/Cu bimetallic laminates with the thickness reduction ratios 10%, 20% and 30% together with mismatch rolling diameter (R2/R1) ratio 1:1, 1:1.1 and 1:1.2. ABAQUS as a finite element simulation software was used to model the deformation of samples. The main attention in this study focuses on the bonding properties of Al/Cu samples. The effect of the R2/R1 ratios was investigated to improve the bond strength. During the simulation, for samples produced with R2/R1 = 1:1.2, the vertical plastic strain of samples was reach the maximum value with a high quality bond. Moreover, the peeling surface of samples after the peeling test was investigated by the scanning electron microscopy (SEM).

Key Words
asymmetric roll bonding; mismatch roll diameter; peeling test; bimetal laminates; numerical simulation

(1) Mohamad Heydari Vini:
Department of Mechanical Engineering, Mobarakeh Branch, Islamic Azad University, Mobarakeh, Isfahan, Iran;
(2) Saeed Daneshmand:
Department of Mechanical Engineering, Majlesi Branch, Islamic Azad University, Isfahan, Iran.

This paper presents a review study for energy-efficient gas turbines (GTs) with cycles which contributes significantly towards sustainable usage. Nonetheless, these progressive engines, operative at turbine inlet temperatures as high as 1600°C, require the employment of highly creep resistant materials for use in hotter section components of gas turbines like combustion chamber and blades. However, the gas turbine obtain its driving power by utilizing the energy of treated gases and air which is at piercing temperature and pushing by expanding through the several rings of steady and vibratory blades. Since the turbine blades works at very high temperature and pressure, high stress concentration are observed on the blades. With the increasing demand of service, to provide adequate efficiency and power within the optimized level, turbine blades are to be made of those materials which can withstand high thermal and working load condition for longer cycle time. This paper depicts the recent developments in the field of implementing the best suited materials for the GTs, selection of proper Thermal Barrier Coating (TBC), fracture analysis and experiments on failed or used turbine blades and several other designing and operating factors which are effecting the blade life and efficiency. It is revealed that Nickel based Superalloys were promising, Cast Iron with Zirconium and Pt-Al coatings are used as best TBC material, material defects are the foremost and prominent reason for blade failure.

Key Words
gas turbine blade; turbine inlet temperature; thermal barrier coating; finite element analysis; failure analysis; blade efficiency; metallurgical analysis

(1) Mohd Saif, Parth Mullick:
Department of Mechanical Engineering, Sam Higginbottom University of Agriculture Technology & Sciences, Allahabad, India;
(2) Ashhad Imam:
Department of Civil Engineering, Sam Higginbottom University of Agriculture Technology & Sciences, Allahabad, India.

The utilization of fibre in concrete production not only solves the problem of disposing this solid waste but helps conserve natural resources. This study investigated the effect of waste aluminum shavings on bond strength of laterized concrete. Laterized concrete spliced beams of 150×250×2150 mm and 175×275×2300 mm were prepared. Fifteen specimens with 16 mm and 20 mm were cast with the addition of aluminium shavings at varying percentages of 1vol%, 1.5vol% and 2vol%; another ten specimens with 16 mm and 20 mm diameter bars at 0% of aluminium shavings were cast as control. Concrete cubes of number were prepared, three taken for each set of various percentages of aluminium shavings were used to determine the concrete strength. It was observed from the analysis that the compressive strength decreased as the percentage of aluminium shavings increased, while the aluminium shavings increased the bond between concrete and steel. However, for normal concrete there was an increase in bond resistance with increase in aluminium shavings. The bond resistance of 16 mm was found to be higher than that of 20 mm in all the specimens tested.

Key Words
aluminum shavings; spliced beams; laterized concrete beams; reinforcing bar; bending; splice length

(1) Olatokunbo M. Ofuyatan, Oluwafemi John:
Department of Civil Engineering, Covenant University, Ota, Lagos, Nigeria;
(2) Anthony A. Ivoke:
Department of Civil Engineering, university of Lagos, Lagos State, Nigeria;
(3) Adeoye M. Olowofoyeku:
Department of Civil Engineering, Yaba College of Technology, Yaba, Lagos, Nigeria;
(4) Adeyemi Adesina:
Department of Civil Engineering, Covenant University, Ota, Lagos, Nigeria.

Electrochemical double layer capacitors (EDLCs) which are fabricated using carbon based electrodes have been emerging at an alarming rate to fulfill the energy demand in the present day world. Activated charcoal has been accepted as a very suitable candidate for electrodes but its cost is higher than natural graphite. Present study is about fabrication of EDLCs using composite electrodes with activated charcoal and Sri Lankan natural graphite as well as a gel polymer electrolyte which is identified as a suitable substitute for liquid electrolytes. Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and Galvanostatic Charge Discharge test were done to evaluate the performance of the fabricated EDLCs. Amount of activated charcoal and natural graphite plays a noticeable role on the capacity. 50 graphite : 40 AC : 10 PVdF showed the optimum single electrode specific capacity value of 15 F/g. Capacity is determined by the cycling rate as well as the potential window within which cycling is being done. Continuous cycling resulted an average single electrode specific capacity variation of 48 F/g - 16 F/g. Capacity fading was higher at the beginning. Later, it dropped noticeably. Initial discharge capacity drop under Galvanostatic Charge Discharge test was slightly fast but reached near stable upon continuous charge discharge process. It can be concluded that initially some agitation is required to reach the maturity. However, the results can be considered as encouraging to initiate studies on EDLCs using Sri Lankan natural graphite.

Key Words
electrochemical double layer capacitors; natural graphite; activated charcoal; gel polymer electrolytes; electrochemical impedance spectroscopy; cyclic voltammetry; galvanostatic charge discharge test

(1) P.A.D. Hansika:
Department of Physical Sciences, Faculty of Applied Sciences, South Eastern University of Sri Lanka, Sammanthurai, Sri Lanka;
(2) K.S. Perera, K.P. Vidanapathirana, U.L. Zainudeen:
Department of Electronics, Faculty of Applied Sciences, Wayamba University of Sri Lanka, Kuliyapitiya, Sri Lanka.

Joining of Mg/Ti hybrid structures by welding for automotive and aerospace applications has attracted great attention in recent years due mainly to its potential benefit of energy saving and emission reduction. However, joining them has been hampered with many difficulties due to their physical and metallurgical incompatibilities. Different joining processes have been employed to join Mg/Ti, and in most cases in order to get a metallurgical bonding between them was the use of an intermediate element at the interface or mutual diffusion of alloying elements from the base materials. The formation of a reaction product (in the form of solid solution or intermetallic compound) along the interface between the Mg and Ti is responsible for formation of a metallurgical bond. However, the interfacial bonding achieved and the joints performance depend significantly on the newly formed reaction product(s). Thus, a thorough understanding of the interaction between the selected intermediate elements with the base metals along with the influence of the associated welding parameters are essential. This review is timely as it presents on the current paradigm and progress in welding and joining of Mg/Ti alloys. The factors governing the welding of several important techniques are deliberated along with their joining mechanisms. Some opportunities to improve the welding of Mg/Ti for different welding techniques are also identified.

Key Words
Mg alloy; Ti alloy; Mg/Ti dissimilar welding; intermetallic compound (IMCs); properties

(1) S.T. Auwal:
Department of Mechanical Engineering, Faculty of Engineering, Kano University of Science and Technology, Wudil, 3244 Kano, Nigeria;
(2) S. Ramesh:
Center of Advanced Manufacturing and Materials Processing (AMMP), Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia;
(3) S. Ramesh:
Department of Mechanical Engineering, Faculty of Engineering, Universiti Teknologi Brunei, Bandar Seri Begawan BE1410, Brunei;
(4) Caiwang Tan, Zequn Zhang, Xiaoye Zhao:
Shandong Provincial Key Laboratory of Special Welding Technology, Harbin Institute of Technology at Weihai, Weihai 264209, China;
(5) S.M. Manladan:
Department of Mechanical Engineering, Faculty of Engineering, Bayero University, 3011 Kano, Nigeria.

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