Makine Mühendisliği Bölümü Koleksiyonu

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https://hdl.handle.net/20.500.12846/480

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Production and mechanical characterization of polyethylene matrix composites with the addition of linen and cotton waste fabric filler materials
(2022) İpekoğlu, Mehmet; Gündüz, Hasan; Albayrak, Önder
In this study, linen and cotton fibers obtained from fabric waste were used as filler materials and polyethylene was used as matrix material to produce fiber reinforced polymer composites using injection molding. Use of fabric waste as filler material enables utilization of linen and cotton wastes while decreasing the amount of polyethylene used in the composites resulting in an environmentally friendly material. Prepared samples with varying content of linen and cotton wastes (5, 10 and 20 vol. %) were compared with each other and with polyethylene samples without any filler, based on their yield, tensile and fracture strengths, percent elongation and hardness values. Samples were also evaluated for their chip formation characteristics based on chip lengths at various machining speeds and examined for their visual appearance. Results indicated that linen waste fibers can be used to improve the strength of polyethylene based composites while cotton waste fibers can be utilized to enhance the elongation characteristics of the samples.
GWP değeri düşük soğutucu akışkanlı, iç ısı değiştiricili soğutma sisteminin modellenmesi
(2023) Şişman, Süleyman; İpekoğlu, Mehmet; Parmaksızoğlu, İsmail Cem
Soğutma hem gıdaların güvenliği hem de pandemi sürecindeki örnekleri ile hayatımızın her alanında kitlesel bir büyüklüktedir. Yaygın olarak kullanılan soğutma sistemlerinde kazanılacak ufak bir verim artışı, soğutma makinelerinin sayısı ile çarpıldığında çok ciddi değerlere ulaşmaktadır. Bu çalışmada, iç ısı değiştiricisinin soğutma sistemine etkisi, bu yolla sistemin performansının artışı, düşük Küresel Isınma Potansiyeli (Gobal Warming Potential, GWP) değeri farklı soğutucu akışkanlar için incelenmiştir. R404A gibi yaygın kullanılan soğutucu akışkanlar düşük GWP değerine sahip soğutucu akışkanların performansları ile kıyaslanmış alternatif düşük GWP’li soğutucu akışkanların performansları araştırılmıştır.
A Compressor model to determine cooling cycle efficiencies and performances without or with internal heat exchanger for specific refrigerant
(2023) Parmaksızoğlu, İsmail Cem; Şişman, Süleyman; İpekoğlu, Mehmet
Today, the importance of refrigeration has increased due to the shortage of food, food storage, health, and industrial cooling. Global warming is the most important environmental problem that the world has faced recently. Global Warming Potential (GWP) values of HFC type refrigerants are high. In order to contribute to this environmental problem, HFC type refrigerants are replaced with alternatives. In some cases, especially when flammability is critical, alternative refrigerants are rarely preferred yet. Therefore, it is very important to use appropriate charge values. Cooling systems are modeled in order to use them under necessary and sufficient minimum conditions. While cooling system modeling, the most important problem is to choose the compressor model according to the appropriate refrigerant. In this study, a cooling system modeling code was developed and integrated with CoolProp software in MATLAB environment. The purpose of this investigation is to develop a method comp simulation software for determining which compressor model to use for a selected fluid. The modeling of refrigeration cycle with and without Internal Heat Exchanger.
Cooling performance prediction of a metal foam internal heat exchanger: An artificial neural network approach
(2023) Parmaksızoğlu, İsmail Cem; İpekoğlu, Mehmet
Although HFC refrigerants have high global warming potential (GWP) values, they are preferred due to their satisfactory cooling performance and A1 fire protection classification. If possible, alternatives of HFC-type refrigerants should be used; if not, they should be used with the least charge value. In this study, the effect of metal foam heat exchanger was investigated to reduce the amount of refrigerant in the refrigeration system. The performance of the metal foam incorporated internal heat exchanger (IHX) was estimated by trained artificial neural networks (ANNs) using the correlations given in the literature, and the results were compared with the experimental data presented in the literature. For the same cooling capacity, a higher performance is achieved by using IHX with metal foam additives. Although the developed correlation has been extracted for IHX, it could be applied for all HE with gas flow.
Pull-out strength of screws in long bones at different insertion angles: finite element analysis and experimental investigations
(De Gruyter, 2024) Gepek, Engin; İyibilgin, Osman; Bayam, Levent; Drampalos, Efstathios; Shoaib, Amer
Different types of plates are available to allow insertion of screws for internal fixation of long bone fractures. The aim of the study was to determine the effect of the insertion of screws at different angles on a long bone to the pull-out strength. Using 3D printed bone models, we tested the pull-out strength of screws in long bones at insertion angles between 0 and 40° with both finite element analysis and on printed models experimentally and compared the results. Test samples and cortical screws used were modeled with SolidWorks software and analyzed with Ansys software. As the screw insertion angle increases, the pull-out forces on the test specimens increase from 61.14 ± 3.5 N at 0° to 273 ± 6.8 N at 40° with an exception of a small drop between 15 and 20° from 235.4 ± 6.2 to 233 ± 6.9 N. Both methods showed an increase in the pull-out strength of screws as the insertion angle increases. This might be applicable in the clinical practice of bone fixation. Further studies on plate and screw fixation are needed to complement the findings.
Morphological, microstructural and photocatalytic characterization of undoped and Ni, Co doped Fe2O3 particles synthesized by sonochemical method
(Scientific & Technical Research Council Turkey-TUBITAK, 2022) Kaya, Elif Emil; Evren, Burak; Erdöl, Zeynep; Ekinci, Duygu; İpekoğlu, Mehmet; Özenler, Sibel
In this study, an abundant and eco-friendly photocatalytic material, Fe2O3 particles were synthesized by sonochemical method. Morphological and microstructural investigations of synthesized undoped and Ni, Co-doped Fe2O3 particles were performed. The effect of particle morphology and microstructure on its photocatalytic performance was further investigated. Comparative studies for evaluating particle crystallite sizes were conducted by Williamson-Hall (W-H) method and modified Debye-Scherrer (MDS). Crystallite sizes and lattice strains of Fe2O3 induced by process parameters were calculated by W-H method based on uniform deformation model (UDM). The crystallite sizes of the synthesized powders were calculated in the range of 200 nm and 76 nm by Williamson-Hall analysis. In addition to structural investigation, dislocation density of the synthesized particles was calculated by Williamson-Smallman relation. Afterwards, photocatalytic performance of Fe2O3 particles was investigated in detail. The photodegradation of methylene blue solutions in the presence of light in 20 min with samples 3,4, and 5 in 20 min were 0.937, 0.896, and 0.855, respectively. Moreover, the photodegradation of methylene blue solution with sample 5 for 15, 30, and 45 min were 0.9, 0.828, and 0.757, respectively. A photocatalytic activity of 24.25% has been observed under optimum conditions for the time interval of 45 min.
Investigation of the effects of additives on the electrical and magnetic properties of polyester resin
(Istanbul University Cerrahpaşa, 2022) Nişancı, Salih; İpekoglu, Mehmet; Nişancı, Muhammet Hilmi; Karhan, Mustafa; Uğur, Mukden
Polymers are widely used as insulation materials in the electrical industry because their existing electrical and mechanical properties can be altered by adding different types of additives. Successful prediction of the service life of the insulators used in the electrical industry is important for the reliability of the system. For this purpose, insulating materials are subjected to tests according to various standards. In this study, unlike the literature, a polymeric insulator was produced by adding 3 wt.% zinc oxide (ZnO), magnetite (Fe 3O 4), and nickel (Ni) into the polyester. The produced samples were subjected to the inclined plane test in accordance with ASTM (American Society for Testing and Materials) D-2303 standards. In order to analyze the electric and magnetic field distributions formed on the samples during the inclined plane test, first, the current flowing on the samples during the test was measured. Following this, analyses were carried out by creating a simulation model of the samples. Studies found in the literature mainly focus on two-dimensional investigation of the electrical field distribution. This study concentrates on the three-dimensional examination of the electrical field also considering the magnetic field distribution. Results of this study showed that prior numerical analysis gives insight into information about the real-life behavior of the samples.
Characterization of CP-Titanium produced via binder jetting and conventional powder metallurgy
(CSIC-Consejo Superior Investigaciones Cientificas, 2022) İyibilgin, Osman; Gepek, Engin
Titanium (Ti) and its alloys are among the most commonly used materials in biomedical applications. In addition to being biocompatible, these materials have notable low density and high corrosion resistance and mechanical properties. It is difficult or impossible to produce parts with complex geometry using conventional powder metallurgy (PM) method since this method is based on shaping powders under uniaxial forces using molds. Binder Jetting is a kind of additive manufacturing technique that do not need molds to shape powders. This study focuses on comparing the properties of the porous CP-Ti parts produced using PM and Binder Jetting. The parts were sintered for 120 min under Argon atmosphere at 1200 degrees C. After sintering, approximately 94% and 92% relative density values were achieved in the specimens produced using the PM and the 3D printer, respectively. It was also observed that the sample produced using 25 MPa compacting pressure has a hardness of 317 +/- 10 HV0.05 and a compressive (yield) strength of 928 MPa while its counterpart produced using the 3D printer has a hardness of 238 +/- 8 HV0.05 and a compressive (yield) strength of 342 MPa. Although the hardness and strength of the specimens produced with the 3D printer were lower than PM ones, their properties are appropriate for producing implants to replace bone structures.
Additive manufacturing technologies and its future in industrial applications
(Universiti Tun Hussein Onn Malaysia, 2021) İyibilgin, Osman; Gepek, Engin
Additive manufacturing technologies have developed rapidly in the last ten years and have become a technology with significant advantages compared to traditional manufacturing. Depending on discovering new materials and techniques, additive manufacturing technologies also develop and become more economical and sustainable technology. The widespread use of this technology in industrial areas has accelerated development and contributed to increased product quality. However, to ensure the development and continuity of this technology, it is necessary to reduce the production costs, increase the quality and accelerate the production processes. These processes also trigger competition and accelerate the development of technology. The areas that additive manufacturing technologies are mostly applied can be grouped as aerospace, biomedical, smart technologies, and other industrial applications. The fact that these areas are popular research areas also accelerates the development of additive manufacturing technologies. In this review, additive manufacturing technologies from past to present, advantages and disadvantages of these technologies, aspects that need to be developed, and industrial applications are examined and explained. When the studies on additive manufacturing technologies and industrial applications are examined, it is seen that this technology has a wide usage area. With the use of additive manufacturing technologies, previously encountered in prototypes and special applications, in automotive, biomedical, and smart technologies, it is seen that they have begun to take place more in people's daily lives.
Üretim parametrelerinin hidroksiapatit tozlarının özellikleri ve kaplama kalitesi üzerindeki etkilerinin incelenmesi
(2019) Albayrak, Önder; İpekoğlu, Mehmet; Altıntaş, Sabri
Biyomedikal uygulamalarda yaygın olarak kullanılan metal implantlar, çevre dokularla hızlı ve sağlıklı entegrasyonun sağlanması amacıyla, biyouyumluluğu yüksek malzemeler ile kaplanmaktadır. Kaplama malzemeleri arasında, yüksek biyouyumluluğa sahip olması ve kemiğin anorganik fazına büyük ölçüde benzer özellikler taşıması nedeniyle, hidroksiapatit özellikle tercih edilmektedir. Gerçekleştirilen bu çalışmada, kaplama amacıyla kullanılmak üzere asit-temelli sentez yöntemiyle nano boyutta hidroksiapatit (HA) tozları üretilmiş, elde edilen HA tozları elektroforetik depozisyon yöntemi ile Ti6Al4V metal ana yapı üzerine kaplanmıştır. HA sentezi aşamasında uygulanan reaksiyon sıcaklığı ve yaşlandırma süresi parametrelerinin üretilen tozların parçacık boyutu, toz morfolojisi ve ısıl kararlılığı üzerindeki etkileri incelenmiş; kullanılan tozların özelliklerinin sinterleme aşaması öncesinde gerçekleştirilen kaplamalarda çatlak oluşumuna etkileri belirlenmiştir. Yapılan deneyler sonucunda reaksiyon sıcaklığı ve yaşlandırma parametrelerinin, HA fazı oluşumu ve HA’nin yüksek sıcaklıktaki kararlılığı üzerinde belirgin bir etkisi olmadığı görülmüştür. 1200 ?C’de gerçekleştirilen sinterleme işleminin, 1000 ?C’de gerçekleştirilen sinterleme işlemine kıyasla HA’nin ısıl dekompozisyonuna olumsuz bir etkisi olmadığı belirlenmiş, bu nedenle kaplama dayanımını arttırmak amacıyla sinterleme işleminin 1200 ?C’de gerçekleştirilmesinin mümkün olduğu sonucuna ulaşılmıştır. Üretilen HA tozlarının yaşlandırma süresinin artmasıyla, sinterleme öncesi çatlak oluşumunda belirgin bir azalma olduğu gözlemlenmiştir.
Experimental and computational investigation of disc brake squeal
(Institute of Noise Control Engineering, 2017) Tozkoparan, Ömer Anıl; Yenerer, Hakan; Şen, Osman Taha; Güneş, Sunay; Özmen, Başaran; Haack, Matthias; Walther, Frank; İpekoğlu, Mehmet
In this paper, the high frequency noise problem brake squeal observed in automotive disc brake systems is experimentally and computationally investigated. Firstly, modal testing on the components of the brake system (brake disc, brake pad, carrier, caliper) is performed and the corresponding natural frequencies and mode shapes are obtained. Secondly, computational models of the given components are built and normal mode analyses are executed. A good match between the experimental and computational results is obtained in terms of both frequencies and mode shapes. Thirdly, a computational model of the brake corner assembly is built with the validated component models. Squeal analysis is then performed for different speed and brake pressure levels by using complex eigenvalue analysis. Based on the results, speed and brake pressure values that have high squeal propensity are identified. Finally, a controlled laboratory experiment is designed and built for the squeal investigation. In the setup, only a single brake corner assembly excluding the suspension system is used. During the experiments, acceleration and sound pressure data are recorded. Experiments at different speed and hydraulic brake pressure levels are performed, and several squeals are successfully measured at the same levels as calculated with the computational model. In conclusion, a finite element method for brake squeal is developed and experimentally validated. © 2017 Institute of Noise Control Engineering. All rights reserved.
Investigation of flow patterns and heat transfer in gas-driven thin liquid films
(International Symposium on Turbulence and Shear Flow Phenomena, TSFP, 2019) Budaklı, Mete; Gambaryan-Roisman, Tatiana; Stephan, Peter
Gas-driven liquid films are a promising candidate for heat up and evaporation of liquids in an efficient way. Many industrial fields benefit of this type of treatment, because of an intensive heat transfer, such as upcoming modern combustion chambers, reboilers, condensers or cooling applications, while gas-driven films represent a complex interaction of two fluids. The state of the film flow and the complex transport mechanisms owing to the interaction at the liquid-gas interface can have significant influences on the overall heat transfer performance, film stability, rupture and wetting process. One advantage of gas-driven liquid films is the stability against film rupture, since close to the film rupture conditions the shear force at the liquid-gas interface guides the liquid along the flow direction and promotes the wetting of the solid wall. In this study, gas-driven thin liquid film flows on unstructured and structured heated walls are investigated experimentally. The effect of different inlet temperatures of both the fluids on the heat transfer rate and the flow pattern is determined. Another aim of the present study is to give insight to the complex flow mechanisms and wetting behaviour of gas-driven thin liquid films on undulated surfaces fabricated as microgrooves. The gas and liquid Reynolds number are varied between 0 to 84000 and 80 to 1900, respectively. Measurements on wall temperature distribution are performed and Nusselt numbers are calculated. By using a high-speed infrared camera, the flow pattern of the liquid is recorded for different experimental parameter configurations revealing the wetting behaviour, flow patterns and rupture of the thin liquid layer. The measured results disclose that using shear at the interface of a thin liquid governs the film stability and heat transfer. An increase of interfacial shear leads to a highly wavy film flow, which is characterized mostly by 3-dimensional surface structure (see Figures below). Another major finding is that at small liquid mass flow rates, the gas flow does not have significant influence on the heat transfer enhancement. The dominance of the gas flow comes more into account at elevated film flow rates. © 2019 International Symposium on Turbulence and Shear Flow Phenomena, TSFP. All rights reserved.
Effect of coating method on the surface characteristics of niti shape memory alloy
(Trans Tech Publications Ltd, 2020) Şimşek, Görkem Muttalip; İpekoğlu, Mehmet; Yapıcı, Güney Güven
Metallic materials including stainless steel, cobalt-chromium alloys, titanium and its alloys, and nickel-titanium (NiTi) shape memory alloys have been used in biomedical applications since the 1940s due to their favorable mechanical properties. Classified as a smart material, NiTi alloy has gained noticeable popularity in biomedical fields such as orthopedic, dental, and cardiovascular applications as it retains reasonable corrosion resistance and biocompatibility along with unique shape memory properties. However, several studies have shown their limits in medical applications due to the risk of Ni ions release from the NiTi implant surface. In order to prevent Ni release, ceramic-based surface coatings such as hydroxyapatite, alumina, and titanium dioxide have been proposed applied by various methods such as electrophoretic deposition, sol-gel, biomimetic and dip coating. In this work, HA coatings on NiTi wire samples were obtained by using biomimetic and dip-coating methods. The biomimetic coating consisted of immersing the NiTi wire samples into simulated body fluid for 24 and 48 h periods, whereas dip coating was accomplished by placing the NiTi wire samples into the HA suspension and retracting the sample with a controlled speed. The effects of the two coating methods on coating quality, surface characteristics and corrosion behavior of NiTi wire samples were investigated. Dip coating method was shown to be a more favorable technique for the NiTi wire samples used throughout this study. © 2020 Trans Tech Publications Ltd, Switzerland.
An experimental investigation into frost accumulation over vertical finned and unfinned surfaces during impinging air flow
(American Society of Mechanical Engineers, 2020) Öksüz, Enes Abdülhakim; Saygın, Alper; Başol, Altuğ M.; Budaklı, Mete; Arık, Mehmet
Frost formation on evaporators negatively affects the cooling performance of refrigerators. It increases the thermal resistance between the refrigerant and air leading to a reduction in the system cooling capacity. In this study, the effect of frost accumulation over a bare and finned surface on the convective thermal resistances has been experimentally investigated under impinging flow conditions. The surfaces are vertically positioned in a horizontal wind tunnel. The convective resistances have been measured with an in-house developed heat flux measurement system. Finally, the effectiveness of the finned surface was derived from the measurements for dry, condensing flow and as well as for frosting conditions. Under frosting conditions, the effectiveness of the finned surface is measured as 1.4 that is by a factor of 2X lower compared to the effectiveness of the same finned surface operating under dry conditions. It has been observed that the frost accumulation initially takes place at the tip of the fins and leads to a 45% drop in the heat transfer rate when the fin tips are completely covered with frost. Further frost accumulation on the fin base does not result in an additional drop in the heat transfer rate. In this regard, the study emphasizes the importance of the fin tip design for the heat sinks operating under frosting conditions. Copyright © 2020 ASME.
Rapid heating and cooling chamber for a photonics junction measurement system
(IEEE Computer Society, 2020) Tarçın, Gökberk; Saygın, Alper; Muslu, Mete; Budaklı, Mete; Arık, Mehmet
Since many industrial applications require heat treatment processes or validation tests under certain ambient temperatures, thermal design is a key issue to be considered in order to ensure fast heating and cooling capabilities. Although most industrial furnaces provide the required isothermal conditions for various test applications or calibrations, a number of them does not provide rapid heating and cooling inside a closed system and the thermal equilibrium over different regions of the system are not satisfied as intended. This brings a number of challenges for the performance test of most electronics, which are affected by ambient temperatures, such as LEDs, lasers and transistors. Particularly, a test environment that can quickly and accurately adjust a uniformly distributed isothermal domain can be useful for many electronic components in order to test their performance at preselected ambient temperatures. In such systems, the design parameters have to be adjusted depending on the desired conditions. In fact, the design of those systems has to be planned in detail to achieve a system working fast and accurate, which shall contribute to reduction in operating time. Therefore, this study focuses on proposing a new approach to the development of a high-performance and high-resolution heating and cooling chamber used in a junction temperature measurement of light emitting diodes (LEDs). The major objective thereby is to achieve high heating and cooling rates of a controlled chamber that satisfies thermal conditions at a user defined temperature interval between 20°C and 80°C. Therefore, material properties and geometrical dimensions, power requirements and cooling performances of the chamber are analyzed as major design parameters. Numerical models are created for various design options, and simulations are performed for various working conditions under certain design constraints. The relationships between design parameters are determined. A final design is proposed that is able to reduce measurement time of photonic components at a temperature uniformity of less than + 0.5 °C. © 2020 IEEE.
An experimental study on the heat transfer and wettability characteristics of micro-structured surfaces during water vapor condensation under different pressure conditions
(Elsevier Ltd, 2021) Budaklı, Mete; Salem, Thamer K.; Arık, Mehmet; Dönmez, Barca; Menceloğlu, Yusuf
In this study, condensation characteristics of water vapor on micro-structured surfaces at different pressures and subcooling temperature has been investigated experimentally. This work represents a basic study in order to design a secondary evaporator section in a refrigeration cycle. A set of surfaces has been manufactured over copper substrates with one sample used as unstructured (smooth) reference surface and two micro-structured surfaces with longitudinal grooves having V-shape and square cross-sections. As the second step, the surfaces have been modified by using a polymer coating to achieve stronger hydrophobicity at the surface and hence to influence wettability such that increased heat transfer rates should be reached. The polymer coating has been created with a dip coating process by applying a mixture of perfluoroalkyl triethoxysilane. Concerning the wettability, a high-speed flow visualization study has been performed for the interpretation of heat transfer results. Experimental results showed that an increase in the droplet contact angle by applying the polymer coating over surfaces, while the largest droplet contact angle was obtained (130.9°±2.0°) for the surface with V-shaped micro-structuring compared to other surfaces. The comparison of heat transfer performance reveals an enhancement in heat transfer coefficient for the coated version of unstructured, square-grooved and V-grooved surface by 34.5%, 61.8%, and 73.4%, respectively. © 2020 Elsevier Ltd
Effects of alumina (Al2O3) addition on the cell structure and mechanical properties of 6061 foams
(Cambridge Univ Press, 2013) Mahmutyazıcıoğlu, Nazım; Albayrak, Önder; İpekoğlu, Mehmet; Altıntaş, Sabri
In this study, a powder blend representing 6061 Al-alloy was first mixed with Al2O3 ceramic particles and then foamed by using the powder compact melting method. 6061-Al2O3 foams and control specimens 6061 foams (without ceramic reinforcement) were produced. The effects of both different ratios of Al2O3 particle addition and different kinds of heat treatment on hardenability, structure and mechanical behavior of the final foams were investigated. Foams that were fully heat treated had the highest hardness values, and they performed best with an increase in collapse strength up to 100% over the untreated samples. Improved cell structure and decreased drainage were obtained when the Al2O3 addition was not more than 5 vol%. The compression test results were interpreted in terms of the foam's microstructure, and correlations were made relating to the unloading modulus and compression strength of the foams to the relative density.
Preparation and characterization of porous hydroxyapatite pellets: effects of calcination and sintering on the porous structure and mechanical properties
(Sage Publications Ltd, 2016) Albayrak, Önder; İpekoğlu, Mehmet; Mahmutyazıcıoğlu, Nazım; Varmış, Mehmet; Kaya, Emrah; Altıntaş, Sabri
In this study, porous hydroxyapatite structures were produced by using urea particles of 600-850 mu m size. Samples with two different urea composition (25 and 50 wt%) were prepared along with samples without any urea content by adding urea to commercially available hydroxyapatite in its as purchased and calcined states. The produced pellets were sintered at 1100 degrees C and 1200 degrees C for 2 h. Compression tests and microhardness measurements were conducted and changes in density values were examined in order to determine the effect of the calcination state of the prior hydroxyapatite powder, the sintering temperature and the amount of urea added. Also X-ray diffraction, Fourier transform infrared, and scanning electron microscopy analyses were conducted to determine the phase stability, functional groups, and pore morphology, respectively. Calcination is found to negatively affect the densification and sinterability of the produced samples, resulting in a decrease of compressive strength and microhardness. With the control of the urea content and sintering temperature uncalcined hydroxyapatite can successfully be used to tailor the density and mechanical properties of the final porous structures.
Mechanical characterization of B4C reinforced aluminum matrix composites produced by squeeze casting
(Cambridge Univ Press, 2017) İpekoğlu, Mehmet; Nekouyan, Amin; Albayrak, Önder; Altıntaş, Sabri
Boron carbide (B4C) ceramic particles were used as reinforcement material to produce aluminum (Al) matrix composites by squeeze casting method. Four different B4C contents as 0, 3, 5, and 10 wt%, and three different squeeze pressures as 0, 75, and 150 MPa were used in which the samples consisted of pure Al without B4C and the samples obtained without applying pressure were used as control samples. To determine the effect of squeezing pressure and the amount of B4C added on machinability and mechanical properties, average chip length and surface roughness of the samples were evaluated and hardness measurements were accomplished, yield and ultimate tensile strengths were determined, respectively. Also, the changes in density and microstructure were investigated. B4C reinforcement was found to decrease the average chip length and density of the samples while increasing the hardness and surface roughness. On the other hand, application of squeeze pressure had a positive effect on the densification and mechanical properties of the samples.
Calibration-free extraction of constitutive parameters of magnetically coupled anisotropic metamaterials using waveguide measurements
(Amer Inst Physics, 2017) Hasar, Uğur Cem; Buldu, Gül; Bute, Musa; Muratoğlu, Abdurrahim
A calibration-free method for extraction of electromagnetic properties of magnetically coupled anisotropic biaxial metamaterial (MM) slabs from waveguide measurements is proposed. It relies on three measurement steps (thru, empty line, and the same line arbitrarily loaded by the MM slab) to extract electromagnetic properties. It is evaluated against another calibration-dependent method for retrieval of electromagnetic properties of a MM slab constructed by C-shaped resonators. From evaluation analysis, we note that our method, as compared to the calibration-dependent method, not only accurately extracts electromagnetic properties without requiring the use of expensive calibration standards but also is reference-invariant. Published by AIP Publishing.

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