Browsing by Author "Aslan, Özgür"

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Citation Count: 0
Analytical Solutions of Model Problems for Large-Deformation Micromorphic Approach to Gradient Plasticity
(Mdpi, 2021) Aslan, Ozgur; Bayraktar, Emin; Mechanical Engineering
The objective of this work is to present analytical solutions for several 2D model problems to demonstrate the unique plastic fields generated by the implementation of micromorphic approach for gradient plasticity. The approach is presented for finite deformations and several macroscopic and nonstandard microscopic boundary conditions are applied to a gliding plate to illustrate the capability to predict the size effects and inhomogeneous plastic fields promoted by the gradient terms. The constitutive behavior of the material undergoing plastic deformation is analyzed for softening, hardening and perfect plastic response and corresponding solutions are provided. The analytical solutions are also shown to match with the numerical results obtained by implementing a user element subroutine (UEL) to the commercial finite element software Abaqus/Standard.
Citation Count: 1
Assessing Cast Aluminum Alloys with Computed Tomography Defect Metrics: A Gurson Porous Plasticity Approach
(Mdpi, 2023) Gul, Armagan; Aslan, Ozgur; Kayali, Eyuep Sabri; Bayraktar, Emin; Mechanical Engineering
Aluminum alloys have inherent tendencies to produce casting defects caused by alloying or metal melt flow inside the mold. The traditional detection method for these defects includes reduced pressure tests, which assess metal quality in a destructive manner. This leaves a gap between metal quality assessments and tensile test correlations. Computed tomography (CT) scans offer crucial assistance in evaluating the internal quality of castings without damaging the structure. This provides a valuable opportunity to couple mechanical tests with numerical methods such as finite element analysis to predict the mechanical performance of the alloy. The present study aims to evaluate the internal quality of cast aluminum alloys using CT scans and to correlate the defect metrics obtained from CT scans with mechanical test results. The Gurson-type material model and finite element methodology have been used to validate the correlation studies. Therefore, we propose a more holistic approach to predicting the behavior of metals by coupling damage models with CT scans and mechanical tests. The study investigates several CT metrics such as the defect volume, total defect surface, biggest defect surface, and projected area of defects. The conclusion reveals that CT scans provide crucial assistance in evaluating the internal quality of castings, and CT defect metrics can be used to build correlations between mechanical tests and CT evaluations. The study also suggests that the concept of adjusted representative material yield parameter (ARMY) or computed representative material yield parameter (CRMY) can be used to correlate CT metrics with mechanical strength in cast materials and parts for a given aluminum alloy. Overall, the study proposes a more comprehensive methodology to assess the quality of cast aluminum alloys and couple the quality to mechanical performance.
Citation Count: 0
Assessment of Tensile Properties of Cast High Mg containing Al-Mg-Cu Aluminum Alloy with Correlation of Computed Tomography Scans and Optical Crack Surface Analysis
(Springer int Publ Ag, 2023) Gul, K. Armagan; Dispinar, Derya; Kayali, E. Sabri; Aslan, Ozgur; Mechanical Engineering
In the casting of aluminum alloys, melt cleanliness has been crucial to achieve desirable final properties. Alloying elements, casting method and degassing procedures have been applied to obtain an internal structure free from defects. Most common defects have been double oxide metal films called bifilms. These defects have been detrimental to mechanical properties. Efforts in industry and academia have focused on removing those defects. Reduced pressure test (RPT) and optical evaluation of cross section of specimens have been the most preferred method of bifilm index evaluation method to assess melt quality. As this method is 2D cross-section analysis, there has not been a direct method to correlate mechanical properties with 3D volume analysis of both RPT and tensile specimens. Computed tomography scanning/imaging has been a promising and emerging method for 3D internal structure evaluation to evaluate internal defects. Subsequent mechanical properties fluctuation in correlation with defect quantity and size may be built in this methodology. In the present study, casting of aluminum alloys with high magnesium content and different alloying elements has been done. Effect of melt quality and defect quantities on internal structures have been investigated via RPT tests and computed tomography scans (CTS). Correlation of CTS and tensile tests has been shown. Tensile test specimen surfaces have been investigated via optical imaging, and bifilm effects have been shown. Alloy quality correlations with tensile tests have been established.
Citation Count: 0
Classification of Different Recycled Rubber-Epoxy Composite Based on Their Hardness Using Laser-Induced Breakdown Spectroscopy (LIBS) with Comparison Machine Learning Algorithms
(Mdpi, 2023) Yilmaz, Vadi Su; Eseller, Kemal Efe; Aslan, Ozgur; Bayraktar, Emin; Electrical-Electronics Engineering; Mechanical Engineering; Department of Electrical & Electronics Engineering
This paper aims toward the successful detection of harmful materials in a substance by integrating machine learning (ML) into laser-induced breakdown spectroscopy (LIBS). LIBS is used to distinguish five different synthetic polymers where eight different heavy material contents are also detected by LIBS. Each material intensity-wavelength graph is obtained and the dataset is constructed for classification by a machine learning (ML) algorithm. Seven popular machine learning algorithms are applied to the dataset which include eight different substances with their wavelength-intensity value. Machine learning algorithms are used to train the dataset, results are discussed and which classification algorithm is appropriate for this dataset is determined.
Citation Count: 0
Design of Recycled Aluminium (AA 7075+AA1050 Fine Chips)-Based Composites Reinforced with Nano-SiC Whiskers, Fine Carbon Fiber for Aeronautical Applications
(CRC Press, 2023) Aslan,O.; Klinkova,O.; Katundi,D.; Miskioglu,I.; Bayraktar,E.; Department of Basic English (Prep School); Mechanical Engineering
In the frame of the research project that is going on, the mechanical properties of recycled gas atomized scrap aluminium (AA7075) based hybrid composites reinforced with nano SiC filler (whisker)+ Graphene Nano plateless (GNP) and fine carbon Fibers elements have been evaluated. Firstly, the mixture was homogenized by means of ball milling process during 4 hours. After hot compaction at 200°C compaction of the compositions the final specimens have been produced with the novel combined method called “SINTER+FORGING” at 650°C followed by relaxation treatment at 200°C during the 2 hours. This type of hybrid composite is used for aeronautical applications. Static and dynamic-Time dependent compression tests have been conducted. Interface and microstructure of these composites have also been evaluated by Scanning Electron Microscope (SEM). © 2024 selection and editorial matter, N. M. Nurazzi, E. Bayraktar, M. N. F. Norrrahim, H. A. Aisyah, N. Abdullah, and M. R. M. Asyraf; individual chapters, the contributors.
Citation Count: 0
Design of Recycled Aluminium (AA7075)-Based Composites Reinforced with Nano Filler NiAl Intermetallic and Nano Niobium Powder Produced with Vacuum Arc Melting for Aeronautical Applications
(CRC Press, 2023) Kasar,C.; Aslan,O.; Gatamorta,F.; Miskioglu,I.; Bayraktar,E.; Department of Basic English (Prep School); Mechanical Engineering
In the frame of the common research project, the mechanical properties of recycled gas atomized scrap aluminium (AA 7075)-based composites reinforced with nano filler NiAl intermetallic and niobium (Nb) elements have been evaluated. Firstly, the mixture was homogenized by means of a ball milling process for 4 hours. After cold compaction of the compositions, the final specimens have been produced with “vacuum arc melting” for aeronautical applications. Static and dynamic compression tests have been conducted. Additional tensile tests have also been carried out. Experimental results were compared with a finite element method. The interface and microstructure of these composites have also been evaluated by a scanning electron microscopy. © 2024 selection and editorial matter, N. M. Nurazzi, E. Bayraktar, M. N. F. Norrrahim, H. A. Aisyah, N. Abdullah, and M. R. M. Asyraf; individual chapters, the contributors.
Citation Count: 0
Development of Ni-Al-Based Composites Reinforced with Recycled AA7075+AA1050 and Ceramics Produced by the Sintering plus Forging Process
(Springer international Publishing Ag, 2024) Gatamorta, Fabio; Klinkova, Olga; Aslan, Ozgur; Miskioglu, Ibrahim; Bayraktar, Emin; Mechanical Engineering
In this study, the microstructural formation and static/cyclic compression behavior of "Ni-Al+AA7075 +AA1050"-based composites reinforced with ceramics (TiC-TiB2) have been evaluated. It is aimed at creating a new design to be an alternative to traditional alloys/composites used in the aeronautical industry. These composites are generally produced using a combined method that we call "sinter + forging processes". The static and dynamic properties and also the microstructure (including the distribution of reinforcement elements) are evaluated in detail.
Citation Count: 0
Impact Behaviour of Recycled Rubber-Based Composites Reinforced with Glass Bubbles and Alumina Fibers (γ-Al2O3)
(Springer, 2023) Çakır Kabakcı,G.; Aslan,Ö.; Bayraktar,E.; Mechanical Engineering
In this research, recycled rubber-based composites are considered with glass bubble (GB) and fine gamma alumina fiber (γ-Al2O3) reinforcements. The effect of the reinforcements with matrix, fracture characteristics of the composite are studied by impact-loading tests (i.e., drop-weight tests). These test results are simulated by finite element analysis (FEM) and the results are compared with the experimental results. Microstructural and fracture surface analysis are carried out by means of scanning electron microscopy (SEM). Mechanical test results show that the reinforcement with glass bubbles and aluminum oxide ceramic fibers generally increase the damping capacity and fracture toughness of the composites. © 2023, The Society for Experimental Mechanics, Inc.
Citation Count: 3
A Large-Deformation Gradient Damage Model for Single Crystals Based on Microdamage Theory
(Mdpi, 2020) Aslan, Ozgur; Bayraktar, Emin; Mechanical Engineering
This work aims at the unification of the thermodynamically consistent representation of the micromorphic theory and the microdamage approach for the purpose of modeling crack growth and damage regularization in crystalline solids. In contrast to the thermodynamical representation of the microdamage theory, micromorphic contribution to flow resistance is defined in a dual fashion as energetic and dissipative in character, in order to bring certain clarity and consistency to the modeling aspects. The approach is further extended for large deformations and numerically implemented in a commercial finite element software. Specific numerical model problems are presented in order to demonstrate the ability of the approach to regularize anisotropic damage fields for large deformations and eliminate mesh dependency.
Mikro invertorlü ve dizi invertörlü fotovoltaik sistemlerin modellenmesi ve karşılştırılması
(2019) Durmuş, Gizem Nur Bulanık; Aslan, Özgür; Mechanical Engineering
Fotovoltaik paneller, güneş enerjisini seri ve paralel bağlanmış fotovoltaik hücreler vasıtasıyla doğrudan elektrik enerjisine dönüştüren yapılardır. Fotovoltaik panel verimliliğini negatif yönde etkileyen birkaç neden vardır. Panelin üzerine düşen geçici veya sürekli gölgeleme, panel veriminin düşmesinin sebeplerinden bir tanesidir. Paneller, bulutlar, binalar, toz, kuş veya yaprak gibi engeller nedeniyle gölgelenmeye maruz kalabilir.Ek olarak, sürekli gölgeleme sıcak nokta etkisi yaratır. Bu durum uzun vadede panelde veya panel grubunda arızalara neden olmaktadır. Sistemlerde ortaya çıkan bir diğer problem, fotovoltaik panellerin birbirine bağlanması noktasında ortaya çıkar. Fotovoltaik paneller, özellikle büyük ölçekli fotovoltaik sistemlerde seri olarak bağlanır. Seri bağlı paneller çok yüksek gerilimlere ulaşır ve yüksek gerilime dayalı problemler ortaya çıkabilir. Dizi invertörün kullanıldığı fotovoltaik sistemlerde, fotovoltaik paneller sınırlı şekillerde yerleştirilebilir. Bunun karşısında, mikro invertörler panel tabanlı sistemlerdir ve kurulumu kolaydır. Panelleri invertöre göre yerleştirmeye gerek yoktur. Mikro invertörler, genellikle küçük ölçekli fotovoltaik sistemler için tercih edilse de, bazı durumlarda büyük ölçekli fotovoltaik sistemlerde de kullanılır. Her panel kendi AC gücünü ürettiğinden, yüksek voltaj sorunu ortadan kalkar. Fakat yüksek maliyetleri ve dizi invertörlere göre daha düşük olan verimleri nedeniyle büyük ölçekli tesislerde tercih edilmemektedir. Bu tez çalışmasında, bu problemler göz önüne alınarak, Ankara İlinde 24 kWp kurulu güce sahip fotovoltaik bir sistemin, üç farklı gölge yoğunluğunda hem dizi invertör hem de mikro invertör ile bir paket program yardımıyla simülasyonları yapılmıştır. Yapılan simülasyon raporları doğrultusunda sistemler karşılaştırılmıştır.
Citation Count: 14
Modeling and simulation of coupled phase transformation and stress evolution in thermal barrier coatings
(Pergamon-elsevier Science Ltd, 2020) Sait, Ferit; Gurses, Ercan; Aslan, Ozgur; Mechanical Engineering; Aerospace Engineering
The thermally grown oxide layer is known to be responsible for the failure of coating systems due to the generation of severely high stresses. In this work, oxidation induced stresses generated in thermal barrier coating (TBC) systems are investigated for high temperature isothermal oxidation. In that sense, a comprehensive model, where phase transformation is coupled with mechanics is developed for the life-time estimation of TBC systems and a modified version of the Allen-Cahn type phase field approach is adopted in order to model the generation of thermally grown oxide (TGO) in finite strain constitutive framework. The top-coat material behavior is modeled using a rate-dependent Gurson type plasticity for porous materials which also accounts for creep. The results for the isothermal phase transformation analysis and the model validation using experimental results are demonstrated. The capability of the model in predicting the local stresses which is the main variable in the analysis of possible delaminations and accurate lifetime estimation of TBC systems is shown.
Citation Count: 0
A Numerical Approach to Simulating Oxidation in Thermal Barrier Coatings
(Elsevier, 2020) Saeidi,F.; Gurses,E.; Aslan,O.; Department of Mechanical Engineering; Department of Basic English (Prep School); Mechanical Engineering
Computational analysis and simulation of multi-physics phenomena taking place in coating systems is still a challenging task. Specifically, for ceramic coatings used as a system of protection for base materials against elevated temperatures, known as thermal barrier coating (TBC) systems, construction of continuum level models which can express coupled nonlinear phenomena has attracted great attention. Thermal stresses, oxidation, creep and numerous other mechanisms and phenomena makes it even harder to model and simulate the behavior of TBCs. In this article, a new numerical model which allows simulation of oxidation and thermally grown oxide (TGO) of bond-coat is presented. Phase field theory is used with finite strain formulation and implemented using user element subroutine (UEL) in ABAQUS software for finite element method. Results are compared with experimental data available for TGO in the literature. © 2020 Elsevier Inc. All rights reserved
Citation Count: 0
Numerical Modeling of Recycled Rubber Based Composites Reinforced with Glass Fibers at High Strain Rates
(Springer, 2022) K-Cakir,G.; Aslan,O.; Bayraktar,E.; Department of Basic English (Prep School); Mechanical Engineering
Due to its high impact energy absorption properties, devulcanized recycled rubber based composites can be considered as a low cost candidate material for military applications which require lightweight protection against shock waves. This work aims at modeling of low cost devulcanized recycled rubber based composite behavior at high strain rates. In that framework, we established a continuum-based material model in order to capture the macroscopic behavior of the recycled rubber based composite material and numerically reproduce the results from the basic characterization tests. The model is implemented for Finite Element Analysis Software ABAQUS/Standard as a user subroutine UMAT for implicit nonlinear finite element calculations in order to simulate the behavior of several RVEs representing the microstructure of the composite and it is behavior at high strain rates. © 2022, The Society for Experimental Mechanics.
Citation Count: 0
Recycled Natural Rubber-Based Composites Reinforced with Nano Boron Nitride in Thermal Conductive and Electrical-Insulating Fields
(Springer, 2023) Çakır Kabakcı,G.; Sonar,M.; Aslan,Ö.; Bayraktar,E.; Mechanical Engineering
In this research, recycled natural rubber (NR) based composites reinforced with the doped nano boron nitride (NBN) with the high resolution in thermal conductive and electrical-insulating field were designed, and their properties were studied. Good distribution of doped NBN in the matrix has shown substantial increments of thermal conductivity and high electrical insulation depending on the quantity in the matrix. Additionally, the thermal analysis indicates that NR/NBN composites have excellent heat-transfer capacity during heating and cooling processes, which suggests great potential application in thermal conductive and electrical insulating fields. The procedure can find multiscale particle-matching ways to achieve the maximum effective thermal conductivity under a given filler load. It should be emphasized that the optimized effective thermal conductivity obviously can be improved with the increase in the volume fraction of the reinforcement. © 2023, The Society for Experimental Mechanics, Inc.
Citation Count: 1
A Review on Analysis of Reinforced Recycled Rubber Composites
(Mdpi, 2022) Kabakci, Gamze Cakir; Aslan, Ozgur; Bayraktar, Emin; Mechanical Engineering
Rubber recycling attracts considerable attention by a variety of industries around the world due to shrinking resources, increasing cost of raw materials, growing awareness of sustainable development, and environmental issues. Recycled rubber is commonly used in aeronautic, automotive, and transportation industries. In this study, recycled rubber composites designed with different reinforcements in the literature are scrutinized by means of toughening mechanisms, mechanical and physical properties, as well as microstructural and fracture surface analysis. Microscale reinforcements (glass bubbles, alumina fiber, etc.) and nanoscale reinforcements (nanosilica, graphene nanoplatelets, etc.) utilized as reinforcements in rubber composites are thoroughly reviewed. The general mechanical properties reported by previous studies, such as tensile, compressive, and flexural strength, are investigated with the main goal of optimizing the amount of reinforcement used. The majority of the studies on recycled rubber composites show that recycled rubber reinforced with microscale particles leads to the development of physical and mechanical properties of the structures and also provides low-cost and lightweight composites for several application areas. Moreover, recycled rubber containing composites can be suitable for applications where high toughness and high resistance to impact are desirable. The present review aims to demonstrate research on reinforced recycled rubber composites in the literature and prospective outcomes.
Citation Count: 0
Static and Fatigue Behaviour of Recycled ThinSheet "Ti-Al-Nb" Based Composites Produced by Hot Forging Diffusion Process
(Springer international Publishing Ag, 2024) Zambelis, Georges; Gatamorta, Fabio; Aslan, Ozgur; Miskioglu, Ibrahim; Bayraktar, Emin; Mechanical Engineering
Within the framework of the common research project, the mechanical properties and fatigue behaviour of recycled thin sheet Ti-Al-based composites reinforced with atomized scrap aluminium (AA7075) and Nb elements have been evaluated. All the thin sheet sandwich structures were produced by the hot forging process, which is a semi-solid-forming process similar to partial melting hot forging. The effect of the chemical bonds during the production of these multifunctional sandwich composite structures was analysed using 3-point bending tests under static and dynamic (fatigue) loading conditions. Additional tensile tests have been carried out to evaluate the mating effect. Interface and microstructure of these composites have also been evaluated using scanning electron microscopy.
Citation Count: 2
Toughening Mechanism Analysis of Recycled Rubber-Based Composites Reinforced with Glass Bubbles, Glass Fibers and Alumina Fibers
(Mdpi, 2021) Kabakci, Gamze Cakir; Aslan, Ozgur; Bayraktar, Emin; Mechanical Engineering
Recycling of materials attracts considerable attention around the world due to environmental and economic concerns. Recycled rubber is one of the most commonly used recyclable materials in a number of industries, including automotive and aeronautic because of their low weight and cost efficiency. In this research, devulcanized recycled rubber-based composites are designed with glass bubble microsphere, short glass fiber, aluminum chip and fine gamma alumina fiber (gamma-Al2O3) reinforcements. After the determination of the reinforcements with matrix, bending strength and fracture characteristics of the composite are investigated by three-point bending (3PB) tests. Halpin-Tsai homogenization model is adapted to the rubber-based composites to estimate the moduli of the composites. Furthermore, the relevant toughening mechanisms for the most suitable reinforcements are analyzed and stress intensity factor, K-Ic and critical energy release rate, G(Ic) in mode I are determined by 3PB test with single edge notch specimens. In addition, 3PB tests are simulated by finite element analysis and the results are compared with the experimental results. Microstructural and fracture surfaces analysis are carried out by means of scanning electron microscopy (SEM). Mechanical test results show that the reinforcement with glass bubbles, aluminum oxide ceramic fibers and aluminum chips generally increase the fracture toughness of the composites.
Citation Count: 0
Toughening Mechanism of Recycled Rubber Based Composites Reinforced with Glass Fibers + Alumina Fibers for Military Applications
(Springer, 2022) K-Çakır,G.; Aslan,Ö.; Bayraktar,E.; Mechanical Engineering
Military grade composites are used in many different applications for their low weight to protect the equipment from harm or destruction. In this research, low-cost devulcanized recycled rubber based composites were designed with short glass fibers + glass bubbles reinforcements. After determination (in wt% percentages) of the reinforcements with matrix, a special process was applied to complete successfully the manufacturing of these composites (silanization of the recycled rubber and devulcanization before blending it with epoxy resin and reinforcement). All of the details of these processes were given in former papers (Irez et al., Materials 12:2729, 2019; Irez et al., Polymers 12:448, 2020; Irez et al., Mechanics of composite and multi-functional materials, Springer, pp 59–70, 2017; Irez and Bayraktar, Mechanics of composite and multi-functional materials, Springer, pp 73–80, 2019). After that, the relevant toughening mechanisms for the most suitable reinforcements were analyzed in detail for front and rear parts in the military applications (such as military vehicles, boats, etc.). For this purpose, certain mechanical and physical properties (ISO 13586: 2000), (KIC—Fracture toughness stress intensity factor and GIc—Critical energy release rate in mode I) have been determined by fracture toughness tests (static 3P bending test with single edge notch specimens). Microstructural and fracture surfaces analyses have been carried out by means of scanning electron microscopy (SEM). © 2022, The Society for Experimental Mechanics.
Citation Count: 2
Toughening Mechanism of Silicon Whiskers and Alumina Fibres (γ-Al2O3) Reinforced Ni-Al-Cu Matrix Composites Through “Sintering + Forging”
(Springer, 2023) Miskioglu,I.; Zambelis,G.; Gatamorta,F.; Aslan,O.; Bayraktar,E.; Department of Basic English (Prep School); Mechanical Engineering
In this study, the microstructural formation and static/dynamic compression behaviour of recycled Ni-Al-Cu matrix hybrid composites reinforced with silicon whiskers and alumina (Al2O3) fibres will be studied. It is intended to be an alternative to traditional alloys/composites used in the aeronautical industry. These composites generally are produced using by combined “sintering + forging” processes. The static and dynamic properties will be evaluated in detail, considering the relevant scanning electron microscopy (SEM) microstructures (including the distribution of reinforcement elements). © 2023, The Society for Experimental Mechanics, Inc.
Yüksek darbeli yüklemelere karşı sandviç yapısal bileşenin topoloji optimizasyonu
(2021) Şenel, Barkın; Aslan, Özgür; Baranoğlu, Besim; Mechanical Engineering; Department of Mechanical Engineering
Sandviç¸ yapılar, hafif, ekonomik ve dayanıklı olmasından dolayı günümüzde bir çok alanda kullanılmaktadır. Zırhlı askeri araçlardaki uygulamalar da bu alanlardan biridir. Literatürde daha önceden yapılan çalışmalara göre, sandviç¸ yapılar, monolit yapılara karşı büyük avantaj sağlamaktadır. Günümüzde araştırmacılar, bu avantajı artırmak için malzeme veya topoloji optimizasyonu açısından sandviç¸ yapıları geliştirmek için çalışmaktadır. Deneysel çalışmalardan önce uygulanan nümerik analiz denemeleri ise bu geliştirmeye zaman ve maliyet açısından yardımcı olmaktadır. Bu tez çalışmasında, seçilen farklı çekirdek geometri tipleri SolidWorks paket programında modellenmiştir. Daha sonra ise ABAQUS/ Explicit sonlu elemanlar programında analizleri yapılmıştır. Başlangıçta, sadece değerlendirme ve karşılaştırma amacıyla sabit parametreler altında analizler gerçekleştirilmiştir. Çıkan sonuçlara göre malzeme parametreleri, üretimde kullanılacak malzeme parametrelerine göre belirlenip analizler yapılmıştır. Fakat bu çalışmada, malzeme optimizasyonu yapılmamış¸, sadece topolojiye odaklanılmıştır. Ayrıca geometriler modellenirken, seçilen geometri tiplerinin üretim açısından sorun çıkarmayacak şekilde belirlenmesi amaçlanmıştır. Belirlenen bu parametreler ve analiz sonuçları ile, üretim açısından da kolay olmak üzere optimum bir çekirdek geometrisi önerilmiştir.