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Item Predicting energy absorption parameters of aluminum lattice structures filled tubes via artificial neural networks(2019)In this paper, the energy absorption parameters of aluminum body centered cubic lattice structures filled thin-walled tubes under axial loading are predicted via artificial neural networks (ANNs). Different tube thickness, lattice member diameters and number of lattice unit cells are considered as design variables, the total amount of energy absorption (EA), the specific energy absorption (SEA), the mean crush force (MCF) and the peak crush force (PCF) are considered as design criteria (energy absorption parameters). The proposed approach is based on finite element simulations for construction of the sample design space and verification, ANNs for predicting the energy absorption parameters. The results showed that the proposed ANN approach is able to predict the energy absorption parameters with high accuracy.Item Kafes yapı dolgulu hibrit tüplerin enerji sönümleme performanslarının sonlu elemanlar yöntemi kullanılarak incelenmesi(2019)İnce cidarlı tüplerin enerji sönümleme performanslarının iyileştirmesine yönelik literatürde birçok farklı yaklaşım önerilmiştir. Bu bağlamda farklı tipte malzemeler, kesit geometrileri, desenler vb. önerilmiş ve bu yapıların enerji sönümleme performansları incelenmiştir [1,2]. İnce cidarlı tüplerin enerji sönümleme performanslarını arttırmanın en etkili yollarından birisi de tüplerin içerisine düşük ağırlıklı dolgu malzemelerinin yerleştirilmesidir [3–5]. Öte yandan, gelişen eklemeli imalat teknolojileri karmaşık şekilli parçaların oldukça kolay şekilde üretilebilmesini mümkün kılmakta ve bu özgün düşük yoğunluklu malzemelerinin üretilmesi konusunda araştırmacıların ilgisini çekmektedir. Bu noktada, literatürde birçok farklı tipte kafes yapılar önerilmekle birlikte tasarım kolaylığı ve umut vadeden enerji sönümleme performansları nedeniyle hacim merkezli kübik yapıların mekanik davranışları literatürde sıklıkla incelenmiştir. Benzer bir motivasyonla hazırlanan bu çalışmada, HMK kafes yapısı ince cidarlı kare kesitli tüpler için dolgu malzemesi olarak kabul edilmiş ve HMK kafes yapı dolgulu hibrit tüplerin eksenel ve farklı eğik yükler altındaki davranışları sonlu elemanlar yöntemi kullanılarak incelenmiştir. Bu kapsamda değişken kalınlıklı kafes yapılar ile bu yapılarla aynı ağırlığa sahip eşdeğer kalınlıklı kafes yapılar oluşturulmuş ve bu yapılar ince cidarlı tüplerin içerisine konularak hibrit tüpler elde edilmiştir. Analizler Abaqus sonlu elemanlar paket programı kullanılarak gerçekleştirilmiştir. Hareketli ve sabit rijit duvarlar arasına konumlandırılan hibrit tüplerin modellenmesinde tüp yapılar için kabuk eleman, kafes yapılar için ise hem kiriş hem de katı elemanlar kullanılarak sonuçlar karşılaştırılmıştır. Analizlerde geometrik kusurların (imperfection) etkisi de dikkate alınmış, çeşitli pekleşme ve hasar modelleri malzemelerin davranışının benzetilmesinde uygulanmıştır. Oluşturulan sonlu elemanlar modelleri deneysel verilerle karşılaştırılarak ayrıca doğrulanmıştır. Sonuçlar fonksiyonel derecelendirilmiş kafes yapı dolgulu hibrit tüplerin ezilme davranışlarının ve enerji sönümleme performanslarının sonlu elemanlar yöntemi ile oldukça yüksek doğrulukta doğru tahmin edebildiğini ve fonksiyonel derecelendirilmiş kafes yapı dolgulu hibrit tüplerin eksenel ve eğik yüklemeler altında oldukça umut vadeden enerji sönümleme performanslarına sahip olduklarını göstermiştir.Item Yönlendirilmiş enerji bırakımlı eklemeli imalat süreçlerinde meydana gelen metalurjik faz dönüşümlerinin sonlu elemanlar yöntemi kullanılarak benzetilmesi(2019)Son yıllarda popülerlik kazanmış olan eklemeli imalat teknolojileri kullanılarak önceden imalatı veya tamiri oldukça zor veya imkânsız olan yapısal parçalar metalik, seramik, polimer ve karma malzemeler kullanılarak imal edilebilmektedir [1]. Bu teknolojilerin en önemli öne çıkan avantajlarından biri tek aşamada oldukça karmaşık geometri ve topolojilere sahip objelerin imalatına olanak sağlamalarıdır. Özellikle metal katmanlı imalat süreçlerinde, lazer/elektron demeti ile eritme ve sonrası katılaşma çevrimleri sırasında meydana gelen kompleks termal gradyanlar, imal edilecek parçaların nihai geometrilerini, mekanik özelliklerini ve mikro yapılarını doğrudan etkilemektedir. Bu noktada, ısı kaynağının etkisi ve malzeme biriktirme süreci eklemeli imalat süreçlerinde prensipte değiştirilebileceği için parçaların nihai mekanik ve mikro yapısal özellikleri bu yöntemde kontrol edilebilir [2]. Öte yandan, metal katmanlı imalat süreçleri boyunca meydana gelen mekanik ve mikro yapısal değişimlerin deneysel olarak gözlemlenmesi zor ve parametre sayısı dikkate alındığında çok pahalı ve zaman alıcıdır. Bu yüzden, metal katmanlı imalat süreçlerinin sayısal benzetim modelleri mikro yapıların ve mekanik davranışın imalat süreci boyunca tahmin ve kontrol edilebilmesi için güzel bir alternatif sunmaktadır [3-5]. Benzer bir motivasyonla hazırlanan bu çalışmada, Ti–6Al–4V alaşımının kullanıldığı yönlendirilmiş enerji bırakımlı eklemeli imalat süreçlerinde [3,6] meydana gelen katı hal faz dönüşümlerinin sonlu elemanlar yöntemi kullanılarak tahmin edilmesine olanak sağlayan bir benzetim modeli geliştirilmiştir. Süreç-mikro yapı benzetim modeli Abaqus yazılımına Fortran ve Python programlama dilleriyle yazılarak entegre edilen alt programlar ile geliştirilmiştir. Python programlama dili kullanılarak geliştirilen kodlar Abaqus içine gömülerek dinamik sonlu elemanlar termal süreç modeli oluşturulmuştur. Lazer kaynağının hareketinin, metal ile etkileşiminin ve lazer model parametrelerin tanımlanması için DFLUX kullanıcı alt kodu Fortran programı ile Abaqus içinde tanımlanmıştır. Abaqus içinde kullanıcıların her bir zaman adımında, alan çıktılarını kullanarak (örneğin sıcaklık alanı) yeni alan çıktılarını (örneğin mikro yapısal faz oranları) üretmesine olanak sağlayan USDFLD kullanıcı alt kodu ile hem termal alan çıktıları hem de metalürjik alan çıktıları bağdaşık olarak elde edilmiştir. Benzetim sonuçları, geliştirilen modelin büyük ölçekli yapısal parçaların yönlendirilmiş enerji bırakımlı eklemeli imalatı süreçlerinde malzeme içinde oluşan faz dağılımının sonlu elemanlar yöntemi kullanılarak etkin şekilde tahmin edilebileceğini göstermiştir.Item Investigation of the effect of temperature on the mechanical properties of E-Glass fiber reinforced composites(The Composites and Advanced Materials Expo (CAMX), 2014)In this study, mechanical characterization of E-Glass fiber reinforced composite materials that are manufactured via Vacuum Infusion (VI) (a.k.a Vacuum Assisted Resin Transfer Molding (VARTM)) is investigated. The mechanical properties are analyzed at different temperatures (23 oC (room temperature), 40 °C, 60 °C, 80 °C, 100 °C) by using a universal tensile testing machine integrated with a heat chamber. The mechanical tests are performed for 3 different reinforcement types such as (i) plain woven, (ii) biaxial stiched and (iii) quadraxial stiched E-Glass fabrics. The result of this study provides a database for applications that use composite materials at different temperatures.Item Performance investigation of an eight cylinder gasoline engine(American Society of Mechanical Engineers (ASME), 2014)Performance investigation of a Chevrolet 5.7, eight cylinder gasoline engine is experimentally carried out at laboratuary conditions by means of the special softwares called "NetDyn" and "WinDyn". This experimental work is intended to make contribution to the researchers that experimentally analyze the parameters of gasoline engines with the engine speed in detail. During the experiments, the engine speed is changed from 2500 rpm to 5250 rpm with 250 rpm intervals and steptime for succesive speeds is kept constant as 10 s. Engine power, engine torque, fuel and air flowrates per kW, mechanical efficiency, oil temperature and pressure, break mean effective pressure and exhaust temperatures are measured as a function of engine speed. As the engine speed was increased, it was observed that the air mass flow rate, exhaust and oil temperatures increased while the break mean effective pressure, mechanical volumetric efficiency, and engine torque decreased. Engine power increased between the engine speeds of 2500 rpm and 3750, but it decreased between the speeds of 3750 rpm 5246 rpm. Copyright © 2014 by ASME.Item Design of sma based actuators used in robotics(2013)This work introduces to Shape Memory Alloy (SMA) using in Robotics as actuators. We investigated a quadruped platform actuated by SMAs which act with variable elasticity. SMAs ought to prove necessary forces for all gaits. The main purpose of this study; determine the necessary for all actuation region and specify the essential actuation. Copyright © 2013 by World Scientific Publishing Co. Pte. Ltd.Item Low velocity impact response of glass fiber reinforced aluminium foam sandwich(European Conference on Composite Materials, ECCM, 2012)The aim of this study was the analysis of the bending and the low - velocity impact response of aluminium foam sandwich reinforced by the outer skins made of glass fiber reinforced epoxy matrix and the results were compared with those obtained for aluminium foam sandwiches without glass fiber skins. Static bending tests were carried on panels with the same nominal size at different support span distances in order to analyze the collapse modes and their capacity of absorbing energy, while the energy amount absorbed under dynamic loading was evaluated by means of impact tests. The experimental investigation has particular importance for applications which require lightweight structures with a high capacity of energy dissipation, such as transport industries.Item Investigation of irreversibilities in the compression process for alternative refrigerants in a vapor compression refrigeration cycle(2008)Irreversibility analyses during compression process are presented for some refrigerants namely, R290, R134a, R12, R22, and R152a in a vapor compression refrigeration cycle. The effects of evaporator temperature, condenser temperature and isentropic efficiency on the irreversibility rates and exergetic efficiencies of the refrigerants under study are investigated By the means of a computer code that simulates a vapor compression cycle including subcooling and superheating. For all the refrigerants in this study, the irreversibility in the compression process decreased as the evaporator temperature and isentropic efficiency increased and it increased with the increasing values of the condenser temperatures. Exergetic efficiency of the compressor increased as the isentropic efficiency of the compressor increased while it decreased with the increasing values of evaporator temperatures. In the case of increasing evaporator and condenser temperatures, and isentropic efficiency values, R22 and R152a approximately show the same and lowest values of compressor irreversibility while R290 has the lowest values. The compressor irreversibilities and compressor exergetic efficiencies of R12 and R 134a placed in the moderate range in the case of increasing evaporator and condenser temperatures, and isentropic efficiency values. Copyright © 2007 by ASME.Item Elastoplastic stress analysis of functionally graded disc under internal pressure-complas XII(2013)The study deals with elastoplastic stress analysis of a hollow disk made of functionally graded materials (FGMs) subjected to an internal pressure. The material properties of disc are assumed to vary radially according to power law function, but Poisson's ratio is taken constant. Small deformations and a state of plane stress are presumed, and the analysis of disk is based on Von-Mises yield criterion. The materials are assumed to be linear strain hardening, isotropic and not be affected by temperature. Variation of stresses and displacements according to gradient parameters are investigated by using analytical and finite element method. The results show that gradient parameters have an important role in determining the elastoplastic stress of functionally graded disc.Item Investigation of experimental research on the low velocity impact damage behavior of NCF composite plates - Complas XII(2013)In this study an experimental investigation is performed on the impact response of non-crimp fabric composite plates at room temperature. Chopped strand mat combi is used as reinforcing material and two kinds of matrix; epoxy and polyester, are also used as resin material in the composite plates. All specimens used in experiments are manufactured by vacuum assisted resin infusion method at Atard Defence and Aerospace Advanced Technology Application Research and Development Inc. An instrumented drop weight impact testing machine Instron-Dynatup 9250 HV is used for impact testing. Impact tests are performed under various impact energies ranging from initiation of damage to final perforation. Damage processes of the samples are analyzed from cross-examining load-deflection curves, energy profiling method and damaged specimens.Item Determination of noise level of a gas-fired pulse combustor(2007)Experimental determination of noise level of a Helmholtz type gas-fired pulse combustor is presented. During the tests, the tail pipe length was varied from 1.9 m to 1.3 m by 10 cm intervals. Noise level measurements were obtained from the outlet (exhaust side ) and inlet (air flapper side) at a length of 1 m from both sides by means of a noise level meter. As the length of the tail pipe was decreased, the noise level increased. At the measurements performed at the outlet, the peak value of equivalent continuous noise level, LEQ was 96.6 dB as the tailpipe length of the fundamental frequency were 1.3 m and 63 Hz, respectively. Similar kinds of measurements were carried out at the inlet, but the LEQ value was stronger at the outlet than the one at the inlet. It was also investigated that the effect of the type of gaseous fuel on the acoustic efficiency of the pulse combustor can be neglected when the results of the acoustic efficiencies were compared to those in the literature.Item Monitoring and control of PLC based motion control systems via device-net(Institute of Electrical and Electronics Engineers Inc., 2014)The control of mechanical systems are generally applied by using electric motors which are useful for the control of velocity, position and torque. On the other hand, servo motors are preferred due to their characteristic properties for the systems that require more accurate operations. In this study, a mechanical prototype having a two degree of freedom motion capacity integrated with AC servo motors is generated. The control of those AC servo motors is achieved by using an Omron PLC (Programmable Logic Controller). A SCADA program is developed for user control and monitoring. The connection between SCADA and PLC is obtained by using Device-Net web protocol. The velocity and position of the motion control system are monitored with real time animation on the screen. It is observed after the testing of the designed system that the position and velocity values are convenient. © 2014 IEEE.Item Irreversibility analysis of a vapor compression cascade refrigeration cycle(2009)Hydrocarbon based energy sources such as coal, oil and natural gas have been diminishing in an increasing speed. Instead of finding alternative energy sources, we have to use the available sources more effectively. By means of the irreversibility analysis, we can determine the factors or conditions that cause the inefficiencies in any energy system. In this study, irreversibility analysis of a compression cascade refrigeration cycle that consists of a high and low temperature cycles is presented. In the high temperature cycle, the refrigerants from different classes, namely R12 (CFC), R22 (HCFC), R134a (HFC) and R404a (Azeotropic) are selected as working fluids. In the low temperature cycle, R13 is only used as a working fluid. Irreversibility analysis of refrigerant pairs, namely R12-R13, R22-R13, R134a-R13, and R404a-R13 are carried out in a compression cascade refrigeration cycle by a computer code developed. The effects of evaporator temperature, condenser temperature, and the temperature difference between the saturation temperatures of the lower and higher temperature cycles in the heat exchanger (?T) and the polytropic efficiency on irreversibility of the system are investigated. The irreversibility of the cascade refrigeration cycle decreases as the evaporator temperature and polytropic efficiency increase for all of the refrigerant couples considered while the irreversibility increases with the increasing values of the condenser temperature and ?T. In the whole ranges of evaporator temperature (?65°C / ?45°C), condenser temperature (30–50°C), ?T (2–16K) and polytropic efficiency (%50/%100), the refrigerant pair R12-R13 has the lowest values of irreversibilities while the pair R404a-R13 has the highest ones. At the lower condenser temperature (<30°C) and higher polytropic efficiencies (85%–95%), the refrigerant couples except for R404a-R13 have approximately the same values of irreversibility.Item Physical properties of LLDPE and PP filled with wood flours(American Society of Mechanical Engineers (ASME), 2015)In this study, composites of polypropylene (PP), as well as linear low density polyethylene (LLDPE) thermoplastics filled with wood flour have been investigated to study the effect of size and amount of wood flour on their mechanical, thermal and aging properties. PP and LLDPE were mixed with five different types of wood flour, i.e., cedar, maple, oak, poplar, and select pine, by adding different percentages of wood flour at 30, 40 and 50 weight percentages. Mixing was done using a mini compounder at 180-210ºC and dog-bone shape samples were produced by using a mini-injection molding machine. Two different sizes of wood flour labeled as thin (425 – 500 µm) and thick (600 – 710 µm) were compared for PP-wood and LLDPE-wood composites. Mechanical properties of blends were investigated by tensile testing and thermal behaviors of blends were characterized by using DSC analyses. Poplar and maple show better tensile results among other wood types with 543.7 MPa and 600.5 MPa Young’s modulus and 21.05 MPa and 24.53 MPa tensile strength for LLDPE when comparing thick and thin wood flour blends, respectively. In the case of PP; poplar and select pine gave higher Young’s modulus and tensile strength results. Samples were also aged in acid and water solution for 3 days, and their weight and dimensional changes were recorded and compared with neat polymer samples to show physical stabilityItem Energy and exergy analysis of an air conditioning system using the mixture of outdoor and return air(2012)Energy and exergy analysis of the air conditioning systems employing the mixture of outdoor and return air (ACOR) are presented. The equations of heat transfer rate and exergy destruction are developed for ACOR according to the system parameters of moist air and condensate water. The effects of the incoming air dry bulb temperature to the coil and relative humidity, and leaving air dry bulb temperature from the coil on the heat transfer and exergy destruction are investigated by means of a computer code developed. The heat transfer from the air to the coil increased as the incoming air dry bulb temperature and relative humidity increased while the heat transfer decreased with the increase in the leaving air dry bulb temperature. The exergy destruction of the moist air increased as the incoming air dry bulb temperature increased, but it decreased with the increasing values of incoming air relative humidity values. Copyright © 2012 by ASME.Item Stress analysis of a rotating FGM circular disc with exponentially-varying properties(2012)In this study, elastic stress analysis of a thin circular disc made of functionally graded materials (FGMs) subjected to a temperature load and an inertia force due to rotation of the disc is investigated. Based on the two dimensional thermoelastic theories, the axisymmetric problem is formulated in terms of a second order ordinary differential equation which is solved by finite difference method (FDM). The FGM disc is assumed to have exponential variation of material properties in radial direction only and Poisson's ratio is kept constant. The result also compared with semi-analytical solution (SAS) and their consistence has been shown. Some numerical results of thermoelastic field are presented and discussed for an Al2O3/ZrO2 FGM. Copyright © 2012 by ASME.Item The linear stability of the responses of axially moving beams supported by an intermediate spring(EDP Sciences, 2016)In the present paper, the stability investigation of the linear responses of axially travelling beams supported by an intermediate linear spring is performed numerically by means of searching linear complex eigenvalues. The boundary conditions and the dynamic equation of motion are obtained by means of the Extended Principle of Hamilton for the two-span Euler-Bernoulli beam. Assuming the harmonic solution of the governing differential equations of motion, the dispersion relation is derived. To have a nontrivial solution in conjunction with the dispersion relation, the frequency equation is obtained by letting the determinant of the matrix representing the coefficients of the equations of the boundary conditions be equal to zero. The aim of this contribution is to compute the complex values of the natural frequencies from the nonlinear frequency equation by means of numerical methods for the beam supported by an intermediate spring. The real and imaginary parts of the complex eigenvalues versus the constant axial transport speed curves are depicted in order to show the linear instability. Depending on the signs of the real and imaginary parts of the complex eigenvalues, the boundaries of the instability regions were observed. © The Authors, published by EDP Sciences, 2016.Item Heat transfer enhancement methods: Concave and convex shape fins(Avestia Publishing, 2016)The heat transfer coefficient is a common engineering concept and a significant number of researchers are focusing on improving the heat transfer performance of the system by increasing the heat transfer coefficient. Heat transfer enhancement techniques are broadly classified in three broad categories: passive, active and compound techniques. This study is concerned with the effect of fins placed inside a rectangular channel on heat transfer and pressure drop to be concave and convex against flow. The effect of some independent parameters such as Reynolds number, height, diameter, number and angle of the fins on Nusselt number, friction coefficient were experimentally studied. Turbulent flow experiments were performed for the range 2514-13111 of Reynolds number. The results showed that Reynolds number is the most effective parameter. Based on the Reynolds number, the heat transfer increased between 1.4-2.8 times, friction coefficient increased between 1.1-3.4 times according to smooth channel. © Avestia Publishing, 2017.Item Design of hybrid composites from scrap aluminum reinforced with (SiC+TiO2+Gr+Ti+B)(Springer New York LLC, 2017)Hybrid Metal Matrix Composites (HMMCs) have very light weight, high strength, and show better resistance to corrosion, oxidation, and wear. Impact resistance is an especially important property of these HMMCs which is essential for automotive applications. In this study, hybrid aluminum matrix composites were designed through the powder metallurgy route. As matrix, fresh scrap aluminium chips (AA2014), byproduct of machining, were used. Silicon carbide (SiC), boron, titanium, titanium oxide (TiO2) and graphite (Gr) particles were used as reinforcement elements for the present work. The hybrid MMCs were prepared with SiC (5, 10 and 15 % by weight) as a main reinforcement and also certain amounts of Ti, B, TiO2 and graphite powders were added in the matrix. Within the framework of the present study, an original idea of producing a hybrid composite has been developed by using scrap aluminum (AA2014) chips. This consist of the mixing, blending and compacting of aluminum chips through press moulding and sintering. The influence of the reinforcement particles on the mechanical behavior of these composites was evaluated. Microstructure of each composite was analyzed by Scanning Electron Microscope (SEM). © The Society for Experimental Mechanics, Inc. 2017.Item Numerical investigation of amounts of heat, power and temperature distribution in IT-SOFC(Electrochemical Society Inc., 2013)In this study, thermodynamic and heat transfer concepts were combined to understanding correlation of heat, power and temperature gradient on the cell. All of heat sources and amounts has been determined for electrolyte supported SOFC having 81 cm2 active area and thus temperature gradient due to each heat source can computed and total temperature distribution clearly has been shown. For this, electrochemical, ohmic, activation and concentration polarization heat sources have been computed by using the boundary conditions taken from the experimental data such as current-voltage-power and mol fraction. Then 80% of the heat generated at 0.7 V and 700°C was removed by the heat transfer and then the maximum temperature difference is found less than 6 °C. Also, it was found that the electrical and the heat generations are 25.41 and 23.03 W, respectively. © The Electrochemical Society.
