Modeling and analysis of surface roughness of microchannels produced by µ-WEDM using an ANN and Taguchi method

Rahim Jafari,Müge Kahya,Samad Nadimi Bavil Oliaei,Hakkı Özgür Ünver,Tuba Okutucu Özyurt 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.11

Microchannel heat exchangers are used to remove the high heat fluxes generated in compact electronic devices. The roughness of the microchannels has a significant effect on the heat transfer characteristics, especially the nucleate boiling and pumping power. Therefore, development of predictive models of surface texture is of significant importance in controlling heat transfer characteristics of these devices. In this study, micro-Wire electrical discharge machining (µ-WEDM) was employed to fabricate metal-based microchannel heat sinks with different surface textures. First, experiments were conducted to achieve the desired surface roughness values. Oxygen-free copper is a common material in the cooling systems of electronic devices because of its high thermal conductivity and low cost. Design of experiment approach based on the Taguchi technique was used to find the optimum set of process parameters. An analysis of variance is also performed to determine the significance of process parameters on the surface texture. An artificial neural network model is utilized to assess the variation of the surface roughness with process parameters. The predictions are in very good agreement with results yielding a coefficient of determination of 99.5 %. The results enable to determine µ-WEDM parameters which can result in the desired surface roughness, to have a well-controlled flow and heat transfer characteristics for the microchannels.

Microstructures and mechanical properties of friction stir welded dissimilar steel-copper joints

M. Jafari,M. Abbasi,D. Poursina,A. Gheysarian,B. Bagheri 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.3

Welding dissimilar metals by fusion welding is challenging. It results in welding defects. Friction stir welding (FSW) as a solid-state joining method can overcome these problems. In this study, 304L stainless steel was joined to copper by FSW. The optimal values of the welding parameters traverse speed, rotational speed, and tilt angle were obtained through Response surface methodology (RSM). Under optimal welding conditions, the effects of welding pass number on the microstructures and mechanical properties of the welded joints were investigated. Results indicated that appropriate values of FSW parameters could be obtained by RSM and grain size refinement during FSW mainly affected the hardness in the weld regions. Furthermore, the heat from the FSW tool increased the grain size in the Heat-affected zones (HAZs), especially on the copper side. Therefore, the strength and ductility decreased as the welding pass number increased because of grain size enhancement in the HAZs as the welding pass number increased.

Influence of Nickel-Coated Nanostructured WC-Co Powders on Microstructural and Tribological Properties of HVOF Coatings

Jafari, M.,Enayati, M. H.,Salehi, M.,Nahvi, S. M.,Hosseini, S. N.,Park, C. G. Springer Science + Business Media 2014 Journal of thermal spray technology Vol.23 No.8

Study effects of conventional flotation reagents on bioleaching of zinc sulfide

M. Jafari,S. Chehreh Chelgani,S.Z. Shafaie,H. Abdollahi,E. Hadavandi 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.78 No.-

Althoughflotation and bio-extraction of metals from its products are extensively investigated, there arefew studied which evaluated the effects of reagents on bioleaching process. Both structure andconcentration offlotation reagents are effective factors on microorganism activities. In this study,Kendall’s tau (t) as a statistical method was used to statistically access the effect of typical sulfideflotation surfactants (collectors: potassium amyl-xanthate, potassium isobutyl-xanthate, sodium ethyl-xanthate, potassium isopropyl-xanthate, and Dithiophosphate), and frothers: pine oil and methylisobutyl carbinol) on the bioleaching of Zn sulfides in a mixed culture (Leptospirillum ferrooxidans,Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans). To consider both structure andconcentration of these reagents, their molarities were used for the statistical evaluations. The Kendallassessments indicated that by increasing in the molarity of reagents, the pH value (the most effectivefactors of bioleaching) was increased (t: 0.56) while the ORP value (t:0.54), Fe3þFe2þ ratio (t:0.51) andnumbers of oxidizing bacteria (t:0.38) in the solution were decreased. Therefore, as a result of thesemulti-interactions, by increasing the molarity of reagents, Zn recovery was decreased (t:0.45). Theseresults potentially can be used for selection offlotation reagents when bioleaching would be themetallurgical metal extraction method.

Effect of Solidification Mode on Microstructure and Mechanical Properties of AISI420 Steel to SAF2507 Steel Dissimilar Joint Produced by Transient Liquid Phase

M. Jafari,M. Rafiei,H. Mostaan 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.10

In this investigation, the microstructure and mechanical properties of AISI420/SAF2507 dissimilar joint produced by TLPprocess were investigated at different bonding times. For this purpose, TLP process was carried out in a vacuum furnace at1050 °C using BNi-2 interlayer. The microstructure of different areas of the joint was evaluated by optical microscopy, scanningelectron microscopy and energy dispersive spectroscopy. Also, the mechanical properties of the bonded samples werestudied using microhardness and shear-tensile tests. It was found that isothermal solidification was completed after 60 minof bonding time. The width of DAZ in SAF2507 steel side was greater than that of AISI420 steel side at all bonding timesowing to the easier volume diffusion of boron in to the fully austenitic structure of AISI420 steel as compared with dualcrystal structure of SAF2507 steel. At bonding time of 60 min, by regarding the more time for diffusion as compared with1 min, boride compounds dissolved in the base metals and were discontinued. Thus, the aggregation of boride compoundsdecreased and as a result the microhardness decreased. In fully isothermal solidification sample, due to the lack of eutecticand intermetallic compounds and creating a homogenous joint (γ-Ni phase), the strength increased. In fact, transformationof athermal solidification to isothermal solidification led to the increase of the joint strength.

The analytical solution of the buckling of composite truncated conical shells under combined external pressure and axial compression

M. A. Boorboor Ajdari,S. Jalili,M. Jafari,J. Zamani,M. Shariyat 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.9

The objective of this research is determining the buckling load of composite truncated conical shells under external loading by theoretical and numerical methods. The boundary conditions are assumed to be clamped. At first, basic equations and stability relations of conical shells were derived. The analysis is carried out using Donnel-type stability equations for thin cross-ply conical shells. By applying Galerkin’s method, these equations are converted to a system of ordinary time dependent differential equations. Ritz method is employed for finding the dynamic stability load. Finally, the critical static and dynamic buckling loads and the corresponding wave numbers have been found analytically. Then comparison of results is considered. Results of analytical calculations are compared with numerical results and with other researchers’ analytical results. The effects of geometric parameters, the cone semi-vertex angle, number of layers and material of fibers on buckling loads are discussed.

Free vibration analysis of functionally graded coupled circular plate with piezoelectric layers

S. Jafari Mehrabadi,M. H. Kargarnovin,M. M. Najafizadeh 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.8

Based on classical plate theory (CLPT), free vibration analysis of a circular plate composed of functionally graded material (FGM) with its upper and lower surfaces bounded by two piezoelectric layers was performed. Assuming that the material properties vary in a power law manner within the thickness of the plate the governing differential equations are derived. The distribution of electric potential along the thickness direction in piezoelectric layers is considered to vary quadratically such that the Maxwell static electricity equation is satisfied. Then these equations are solved analytically for two different boundary conditions, namely clamped and simply supported edges. The validity of our analytical solution was checked by comparing the obtained resonant frequencies with those of an isotropic host plate. Furthermore, for both FGM plate and FGM plate with piezoelectric layers, natural frequencies were obtained by finite element method. Very good agreement was observed between the results of finite element method and the method presented in this paper. Then for the two aforementioned types of boundary conditions, the values of power index were changed and its effect on the resonant frequencies was studied. Also, the effect of piezoelectric thickness layers on the natural frequencies of FGM piezoelectric plate was investigated.

Double fuzzy rarely continuous functions

S. Jafari,M. R. Farahani,M. Vanishree,N. Rajesh 원광대학교 기초자연과학연구소 2023 ANNALS OF FUZZY MATHEMATICS AND INFORMATICS Vol.26 No.1

In this paper, we define fuzzy rare set, fuzzy dense set and fuzzy rarely continuous functions in double fuzzy topological spaces. We will explore several interesting properties and characterizations of these newly defined notions.

Effect of Entrained Air Voids on Salt Scaling Resistance of Concrete Containing a New Composite Cement

A.A. Ramezanianpour,M. Jafari Nadooshan,M. Peydayesh,A. M. Ramezanianpour 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.1

Salt scaling is a major damage problem for concrete pavements in cold environments. Salt scaling is a type of superficial damage caused by freezing and thawing a saline solution on the surface of concrete. Effects of a new composite Portland cement and air void on deicer scaling resistance of concrete were investigated in this paper. Another objective is to investigate effects of compressive strength, tensile strength, abrasion resistance and water penetration on the freeze-thaw deicer salt scaling. Specimens were tested for freeze-thaw deicer salt scaling resistance in accordance with ASTM C672 test method. Surface strengths of concrete play an important role in salt scaling resistance. There is no appropriate relationship between compressive strength and salt scaling resistance,when concrete mixtures are made with various cementitious materials. Results reveal that the mixture containing composite Portland cement with entrained air bubbles has the best performance in salt scaling test.

Experimental and numerical investigation of composite conical shells’ stability subjected to dynamic loading

Sina Jalili,Jamal Zamani,M. Shariyat,N. Jalili,M.A.B. Ajdari,M. Jafari 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.5

In this article, stability of composite conical shells subjected to dynamic external pressure is investigated by numerical and experimental methods. In experimental tests, cross-ply glass woven fabrics were selected for manufacturing of specimens. Hand-layup method was employed for fabricating the glassepoxy composite shells. A test-setup that includes pressure vessel and data acquisition system was designed. Also, numerical analyses are performed. In these analyses, effect of actual geometrical imperfections of experimental specimens on the numerical results is investigated. For introducing the imperfections to the numerical models, linear eigen-value buckling analyses were employed. The buckling modes are multiplied by very small numbers that are derived from measurement of actual specimens. Finally, results are compared together while a good agreement between results of imperfect numerical analyses and experimental tests is observed.