Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Citation - WoS: 1Citation - Scopus: 1Analysis and Comparison of the Projectile Impact Response of an Electron Beam Melt-Ti64 Body Centered Cubic Lattice-Cored Sandwich Plate(Springer, 2025) Erten, H.İ.; Çimen, G.; Yıldıztekin, F.M.; Güden, M.Background: One potential application of additively fabricated lattice structures is in the blade containment rings of gas turbine engines. The blade containment rings are expected to be able to absorb the kinetic energy of a released blade (broken blade) in order to protect the engine parts from damaging. Metallic lattice-cored sandwich plates provide a gap (free space) between two face sheets, which helps to arrest the released blade and increases the energy absorption capability of containment rings. Objective: The objective was to investigate numerically the projectile impact response of Body-Centered-Cubic (BCC) Electron-Beam-Melt (EBM) lattice-cored/Ti64 face sheet sandwich plates as compared with that of an equal-mass monolithic EBM-Ti64 plate. Methods: The projectile impact simulations were implemented in LS-DYNA using the previously determined flow stress and damage models and a spherical steel impactor at the velocities ranging from 150 to 500 m s−1. The experimental projectile impact tests on the monolithic plate were performed at two different impact velocities and the results were used to confirm the validity of the used flow stress and damage models for the monolithic plate models. Results: Lower impact stresses were found numerically in the sandwich plate as compared with the monolithic plate at the same impact velocity. The bending and multi-cracking of the struts over a wide area in the sandwich plate increased the energy absorption and resulted in the arrest of the projectile at relatively high velocities. While monolithic plate exhibited a local bent area, resulting in the development of high tensile stresses and the projectile perforations at lower velocities. Conclusions: The numerical impact stresses in the sandwich plate were distributed over a wider area around the projectile, leading to the fracture and bending of many individual struts which significantly increased the resistance to the perforation. Hence, the investigated lattice cell topology and cell, strut, and face sheet sizes and the lattice-cored sandwich plate was shown potentially more successful in stopping the projectiles than the equal-mass monolithic plates. © The Author(s) 2025.Article Citation - WoS: 2Citation - Scopus: 3Design and Manufacturing of a Hip Joint Motion Simulator With a Novel Modular Design Approach(Springer, 2023) Torabnia, Shams; Mihçin, Şenay; Lazoğlu, İsmailThe study is aimed to develop a hip joint wear simulator using a modular design approach to help experimentally monitor and control critical wear parameters to validate in-silico wear models. The proper control and application of wear parameters such as the range of motion, and the applied force values while estimating the lost material due to wear are essential for thorough analysis of wear phenomena for artificial joints. The simulator's dynamics were first modeled, then dynamic loading data was used to calculate the forces, which were further used for topology optimization to reduce the forces acting on each joint. The reduction of the link weights, connected to the actuators, intends to improve the quality of motion transferred to the femoral head. The modular design approach enables topology-optimized geometry, associated gravitational and dynamic forces, resulting in a cost-effective, energy-efficient product. Moreover, this design allows integration of the subject specific data by allowing different boundary conditions following the requirements of industry 5.0. Overall, the in-vitro motion stimulations of the hip-joint prosthesis and the modular design approach used in the study might help improve the accuracy and the effectiveness of wear simulations, which could lead into the development of better and longer-lasting joint prostheses for all. The subject-specific and society-based daily life data implemented as boundary conditions enable inclusion of the personalized effects. Next, with the results of the simulator, CEN Workshop Agreement (CWA) application is intended to cover the personalized effects for previously excluded populations, providing solution to inclusive design for all.Article Citation - WoS: 7Citation - Scopus: 7Investigating the Effects of Pa66 Electrospun Nanofibers Layered Within an Adhesive Composite Joint Fabricated Under Autoclave Curing(American Chemical Society, 2023) Esenoğlu, Gözde; Tanoğlu, Metin; Barışık, Murat; İplikçi, Hande; Yeke, Melisa; Nuhoğlu, Kaan; Türkdoğan, Ceren; Martin, Seçkin; Aktaş, Engin; Dehneliler, Serkan; Gürbüz, Ahmet Ayberk; İriş, Mehmet ErdemEnhancing the performance of adhesively joined composite components is crucial for various industrial applications. In this study, polyamide 66 (PA66) nanofibers produced by electrospinning were coated on unidirectional carbon/epoxy prepregs to increase the bond strength of the composites. Carbon/epoxy prepregs with/without PA66 nanofiber coating on the bonding region were fabricated using the autoclave, which is often used in the aerospace industry. The single lap shear Charpy impact energy and Mode-I fracture toughness tests were employed to examine the effects of PA66 nanofibers on the mechanical properties of the joint region. Scanning electron microscopy (SEM) was used to investigate the nanofiber morphology and fracture modes. The thermal characteristics of Polyamide 66 nanofibers were explored by using differential scanning calorimetry (DSC). We observed that the electrospun PA66 nanofiber coating on the prepreg surfaces substantially improves the joint strength. Results revealed that the single lap shear and Charpy impact strength values of the composite joint are increased by about 79 and 24%, respectively, by coating PA66 nanofibers onto the joining region. The results also showed that by coating PA66 nanofibers, the Mode-I fracture toughness value was improved by about 107% while the glass transition temperature remained constant.Article Yüksek Derecede Kurum Üreten 2b Gazyağı/hava Difüzyon Alevleri Üzerinde Diferansiyel Yayılımın ve Basıncın Etkileri(Gazi Üniversitesi, 2024) Korucu, Ayşe; Miller, RichardBu çalısmada, dört farklı ortam basıncında kurum, oluşum ve yıkım süreçlerini incelemek amacıyla, yoğun kurum üreten Gazyağı/Hava alevleri, gerçek gaz (GG) ve ideal gaz (İG) hal denklemleri ve Lewis (Le) sayısının bir olarak kabul edildiği modeller ele alınmıştır. Yarı-genel kurum oluşum ve yıkım modelini içeren indirgenmiş Gazyağı/Hava mekanizması (29-adım, 10 çeşit gaz) 2 boyutlu (2B) Direk Sayısal Simülasyon (DNS) verilerini oluşturmak için MPI FORTRAN ile kodu yazılmış bir program kullanılmıştır. Le sayısının bire eşit kabul edildiği alev tahminlerinin, Le sayısının bire eşit olmadığı (genelleştirilmiş difüzyon) durumların sayısal sonuçlarından elde edilen alev yapısı ve kurum özelliklerinin istatiksel olarak benzerlik sağlayıp sağlamadığı araştırılmıştır. Bu bağlamda yapılan çalışmanın sonucunda, ortam basınçları 1, 5, 10 ve 35 atm olan Le sayısının bir olarak kabul edildiği GGLE ve İGLE modelleri ile üretilmiş 2B DNS alev tahminlerinin kurum özelliklerinin ve alev yapılarının yanlış hesaplanmasına yol açtığı belirlenmiştir.Article Citation - WoS: 13Citation - Scopus: 16Influence of Recycled Carbon Fiber Addition on the Microstructure and Creep Response of Extruded Az91 Magnesium Alloy(KeAi Communications Co., 2023) Kandemir, Sinan; Bohlen, Jan; Dieringa, HajoIn this study, the recycled short carbon fiber (CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion. The objective was to investigate the impact of CF content (2.5 and 5.0 wt.%) and fiber length (100 and 500 µm) on the microstructure, mechanical properties, and creep behavior of AZ91 alloy matrix. The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy. In comparison to the unreinforced AZ91 alloy, the composites with 2.5 wt.% CF exhibited an increase in hardness by 16–20% and yield strength by 5–15%, depending on the fiber length, while experiencing a reduction in ductility. When the reinforcement content was increased from 2.5 to 5.0 wt.%, strength values exhibited fluctuations and decline, accompanied by decreased ductility. These divergent outcomes were discussed in relation to fiber length, clustering tendency due to higher reinforcement content, and the presence of interfacial products with micro-cracks at the CF-matrix interface. Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy, suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep. © 2023Review Citation - WoS: 13Citation - Scopus: 13A Review on Battery Thermal Management Strategies in Lithium-Ion and Post-Lithium Batteries for Electric Vehicles(Yıldız Technical University, 2023) Güngör, Şahin; Göçmen, Sinan; Çetkin, ErdalElectrification on transportation and electricity generation via renewable sources play a vital role to diminish the effects of energy usage on the environment. Transition from the conven- tional fuels to renewables for transportation and electricity generation demands the storage of electricity in great capacities with desired power densities and relatively high C-rate values. Yet, thermal and electrical characteristics vary greatly depending on the chemistry and struc- ture of battery cells. At this point, lithium-ion (Li-ion) batteries are more suitable in most applications due to their superiorities such as long lifetime, high recyclability, and capacities. However, exothermic electrochemical reactions yield temperature to increase suddenly which affects the degradation in cells, ageing, and electrochemical reaction kinetics. Therefore, strict temperature control increases battery lifetime and eliminates undesired situations such as lay- er degradation and thermal runaway. In the literature, there are many distinct battery thermal management strategies to effectively control battery cell temperatures. These strategies vary based on the geometrical form, size, capacity, and chemistry of the battery cells. Here, we focus on proposed battery thermal management strategies and current applications in the electric vehicle (EV) industry. In this review, various battery thermal management strategies are doc- umented and compared in detail with respect to geometry, thermal uniformity, coolant type and heat transfer methodology for Li-ion and post-lithium batteries.Article Citation - WoS: 12Citation - Scopus: 12High Strain-Rate Deformation Analysis of Open-Cell Aluminium Foam(Elsevier, 2023) Mauko, Anja; Duarte, Isabel; Borovinšek, Matej; Vesenjak, Matej; Ren, Zoran; Sarıkaya, Mustafa; Güden, MustafaThis study investigated the high-strain rate mechanical properties of open-cell aluminium foam M-pore®. While previous research has examined the response of this type of foam under quasi-static and transitional dynamic loading conditions, there is a lack of knowledge about its behaviour under higher strain rates (transitional and shock loading regimes). To address this gap in understanding, cylindrical open-cell foam specimens were tested using a modified Direct Impact Hopkinson Bar (DIHB) apparatus over a wide range of strain rates, up to 93 m/s. The results showed a strong dependency of the foam's behaviour on the loading rate, with increased plateau stress and changes in deformation front formation and propagation at higher strain rates. The internal structure of the specimens was examined using X-ray micro-computed tomography (mCT). The mCT images were used to build simplified 3D numerical models of analysed aluminium foam specimens that were used in computational simulations of their behaviour under all experimentally tested loading regimes using LS-DYNA software. The overall agreement between the experimental and computational results was good enough to validate the built numerical models capable of correctly simulating the mechanical response of analysed aluminium foam at different loading rates. © 2023 The AuthorsArticle Citation - WoS: 3Boşluk İletim Tabakasız ve Esnek Organo Kurşun İyodür Perovskit Güneş Hücresinin Çevresel Etki Değerlendirmesi(Gazi Üniversitesi, 2022) Sarıaltın, HüseyinPerovskit güneş pilleri (PSC) esneklik ve düşük maliyetli rulodan ruloya üretim gibi avantajlarla birlikte son zamanlarda güç dönüşüm verimliliğinde de önemli bir ilerleme kat etmiştir. PSC'lerin ticarileştirilmesinden önce çevresel performansının yaşam döngüsü değerlendirme (LCA) yöntemi ile araştırılması önemlidir. Bu çalışmada, literatür verilerinden istifade edilerek, esnek Polietilen tereftalat (PET) alt tabaka ve boşluk iletim katmanı (HTL) eliminasyonunu içeren çözelti bazlı organo-kurşun iyodür perovskit güneş hücresinin beşikten kapıya yaşam döngüsü analizi (LCA) gerçekleştirilmiştir. 1 m2 hücre alanı üretiminden kaynaklanan çevresel etkiler altı Uluslararası Referans Yaşam Döngüsü Veri Sistemi (ILCD) kategorisinde belirlenmiştir. Analizin sonucunda, en fazla etki değerinin yüksek elektrik enerjisi tüketimine sahip vakum biriktirme işlemi gereksinimine sahip olan alüminyum metal elektrot tabakasının imalatından kaynaklandığı bulunmuştur. Ticari fotovoltaik teknolojilerle karşılaştırma yapabilmek için en yaygın kullanılan çevresel göstergelerden birisi olan küresel ısınma potansiyeli (GWP), birim kWh elektrik üretimi için hesaplanmıştır. Buna göre, bu çalışmada incelenen HTL'siz esnek (HFF) PSC'nin ticari PV'lerle rekabetçi GWP değerine ulaşmak için 15-20 yıl cihaz ömrüne ihtiyacı olduğu bulunmuştur.Review Citation - WoS: 103Citation - Scopus: 136Digital Twin of Electric Vehicle Battery Systems: Comprehensive Review of the Use Cases, Requirements, and Platforms(Elsevier, 2023) Naseri, Farshid; Gil, S.; Barbu, C.; Jensen, A. C.; Larsen, P. G.; Gomes, Claudio; Çetkin, Erdal; Yarımca, GülşahTransportation electrification has been fueled by recent advancements in the technology and manufacturing of battery systems, but the industry yet is facing serious challenges that could be addressed using cutting-edge digital technologies. One such novel technology is based on the digital twining of battery systems. Digital twins (DTs) of batteries utilize advanced multi-layer models, artificial intelligence, advanced sensing units, Internet-of-Things technologies, and cloud computing techniques to provide a virtual live representation of the real battery system (the physical twin) to improve the performance, safety, and cost-effectiveness. Furthermore, they orchestrate the operation of the entire battery value chain offering great advantages, such as improving the economy of manufacturing, re-purposing, and recycling processes. In this context, various studies have been carried out discussing the DT applications and use cases from cloud-enabled battery management systems to the digitalization of battery testing. This work provides a comprehensive review of different possible use cases, key enabling technologies, and requirements for battery DTs. The review inclusively discusses the use cases, development/integration platforms, as well as hardware and software requirements for implementation of the battery DTs, including electrical topics related to the modeling and algorithmic approaches, software architec-tures, and digital platforms for DT development and integration. The existing challenges are identified and circumstances that will create enough value to justify these challenges, such as the added costs, are discussed.Article Citation - WoS: 10Citation - Scopus: 10Stiffness Modeling of a 2-Dof Over-Constrained Planar Parallel Mechanism(Elsevier, 2023) Görgülü, İbrahimcan; Dede, Mehmet İsmet Can; Kiper, GökhanStiffness model acquisition of over-constrained parallel mechanisms is relatively difficult since they have more than necessary kinematic loops. In this study, a stiffness modeling solution for over-constrained parallel mechanisms is proposed while considering the computational cost efficiency. Three contributions of the paper are: (1) Presenting the stiffness modeling procedure for serially connected closed-loop structures by using the Virtual Joint Method (2) Considering the effect of dynamic auxiliary forces and dynamic external forces on the mobile platform's deflection and achieving a direct solution by using superposition principle (3) A model fitting procedure for modifying the stiffness coefficients to comply with the experimental data. A 2 degrees-of-freedom over-constrained parallel mechanism is investigated as a case study. However, the proposed stiffness model is 6-DoF since compliant deflections occur in any direction. A finite element analysis and an experimental study verify the model's results.