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ÖgeInvestigation of fuel sloshing in an aircraft wing fuel tank using ANN and CFD(Graduate School, 2025-01-22)In civil and military aviation, it is crucial to develop designs that adhere to specific requirements based on their intended use. This process involves thoroughly completing and documenting flight tests, as well as securing airworthiness certificates for the relevant aerial domain. Thus, aircraft and their associated systems, comprising subsystems and equipment that operate in conjunction, undergo a variety of performance evaluations. This approach ensures that all systems function seamlessly and achieve optimal performance levels, as evidenced by numerical data and recognized international documentation. Fuel systems, essential for flight operations, encompass all stages, from refueling the tanks to supplying fuel to the engine that generates thrust for the aircraft. These systems comprise several components that interact with other systems, including hydraulic, avionics, structural, and landing gear systems, and must align with the specific requirements imposed by each of these interrelated systems. The applicable requirements dictate that considerations such as structural integrity, thermal dissipation limits, compatibility with electronic equipment, and overall equipment weight must be addressed concurrently. The primary subsystems within the aviation fuel system are categorized under several critical headings, including hydraulic cooling, engine feeding, indication, and storage. Among these subsystems, the storage component significantly influences flight mechanics and has a considerable impact on overall weight. Given the specified requirements for the flight range, the stored fuel must adhere to a maximum mass limit, which means that a substantial fluid mass must be integrated into the aircraft's flight mechanics. Since this mass is fluid, its response to maneuvers manifests as sloshing mechanics. Consequently, the aircraft's center of gravity tends to shift as sloshing persists. The movement of the fuel and its effects on the center of gravity can be managed through design considerations in the storage area. Tanks that result in variations of the center of gravity due to fuel sloshing are typically incorporated into the aircraft's wings, fuselage, and, in some cases, external fuel tanks. However, as general-purpose primary training aircraft are the focus of this thesis study, no fuselage or external tanks are considered; the research is thus limited to the fuel stored within the wings. The wing tanks of the aircraft are designed symmetrically, with their placement mirrored across both wings. Under ideal conditions, the engine supply is also maintained to be as symmetrical as possible. However, since ideal flight conditions are nearly never achieved in practice, this symmetry is frequently disrupted by external factors and flight maneuvers. As a result, the movement of fuel within the wing can cause the center of gravity to deviate from the intended position due to gravitational effects. Various design features are integrated into the structural components of the wing to mitigate this issue. These features serve two primary purposes: firstly, to minimize the rate at which fuel deviates from its original position during maneuvers, and secondly, to facilitate the rapid return of the fuel to its initial position once the maneuver is completed. The qualitative and quantitative aspects of these design features are subject to constraints related to manufacturing feasibility, weight requirements, and structural integrity. The design elements discussed in this thesis focus on practical applications in the industry rather than purely theoretical approaches, and they provide examples that can be implemented in many primary training aircraft. In this context, the design details studied are discussed in the structural parts of the rib, which form the structure inside the wing tank and divide the tank into subsections. These ribs, called baffles, contain cutout holes that allow the movement of fuel and air between the subsections in the tank, and the usage, number, diameter, and placement of these cutouts constitute the design parameters within the study. The qualitative diversity of these parameters is created by considering different values for each parameter. The name barrier is used for baffle structures that do not use cutouts, and in the situation where no barrier is used in the design, it is used on the first, third, and sixth ribs, as well as use on the second, fourth, and seventh ribs, are also considered. On the other hand, the diameters of the cutouts on these flanges are added to the designs with values ranging from 30 mm to 156 mm. In cutout placement, the centered cutout and 20 mm upward and downward placements are also considered. The use of single, twin, and triple cutouts on each baffle is also added to the study as another parameter. In addition, sloshing effects are examined by taking into account different fuel volume fractions, which are operational parameters, and these volume fractions are considered 30%, 45%, and 60%, which are the rates where the sloshing effect can be clearly observed. The study examines a flight maneuver known as bank-to-bank, in which the aircraft is tilted at a 45° angle for a duration of 10 seconds, serving as a measure of input acceleration. Additionally, the structural components that divide the wing tank into compartments and enhance structural integrity are regarded in this study as elements functioning as breakwaters. Their effectiveness in influencing the movement of fuel is analyzed. The thesis focuses on numerical modeling of fluid movements, utilizing numerical solver programs to conduct analyses. An analysis set is developed, comprising various combinations of design and operational parameters. Given the necessity for extensive calculations, one-dimensional analyses are initially performed under specific assumptions. The results are substantial, with all five input parameters interrelatedly influencing two output parameters. The complexity of this data network renders traditional analytical or numerical methods impractical for human examination. Consequently, big data analytics, aided by artificial intelligence, is employed to examine this complex data landscape. A DNN is constructed to further investigate the relationship between inputs and outputs, yielding quantitative insights into how inputs affect outputs. The data gathered indicates the dominance of input parameters expressed as a percentage. To investigate these parameters more thoroughly, three-dimensional CFD analyses are planned by selecting specific design combinations that exhibit a significant impact. CFD analyses have been performed by varying the relevant parameters while keeping others constant, allowing for comparative assessments. Following these studies, we have concluded by determining the sensitivity of one-dimensional analysis in relation to CFD, the accuracy of ANN calculations, and the effectiveness ranking of the parameters affecting fuel sloshing. The effects of fuel sloshing are examined not only from a theoretical standpoint but also in the context of specific maneuvers involving aircraft wing geometry. Additionally, the effectiveness of various design and operational parameters employed to mitigate these effects is demonstrated through real-world examples encountered in the aviation industry. Furthermore, the applicability of big data analytics processes in analyzing flow interactions with mechanical systems is validated using DNN, with results achieved at a level suitable for industry application.
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ÖgeAn explicit phase field modeling of brittle plates with nonlocal operator method under certain loading condition(Graduate School, 2023-02-01)Due to its complexities and challenges, fracture modeling still faces many pressing issues despite increasing research efforts. One common method is the finite element method, which is commonly utilized in this field. However, FEM has some disadvantages when it comes to predicting failures, because it relies on continuum mechanics, which is a mathematical model that is not valid when there are cracks or other discontinuities in the displacement field. To address this problem, a new approach developed, called peridynamics, which is a different way of formulating the equations of continuum mechanics that is better suited to predicting failure in structures. PD can overcome the limitation of FEM, which requires describing and tracking of the crack path during the growth. While peridynamics can be used to a broad range of materials and mechanical problems, they are most often used to study for brittle fracture. On the other hand, PD can suffer from hourglass modes, which causes instability and it requires a constant horizon which needs significant computational costs. The nonlocal operator method (NOM) is a method for developing nonlocal forms using the concept of dual-support, and it also allows for the creation of implicit formulations of nonlocal theory. It is notable for its ability to be used with both variational and weighted residual methods, and it is a generalized version of the DH-PD approach that extends the idea of nonlocality. In addition to this, NOM allows for the variation of the energy functional in nonlocal theories. Traditional integral equations are defined in a single integral domain, while NOM and other dual-support approaches are based on the use of two integral domains. In the nonlocal operator method (NOM), partial derivatives are calculated using nonlocal versions of gradient, curl and divergence operators. These operators are used to approximate the local operators in the limit as the internal length scale approaches zero. The nonlocal operator method does not need the use of shape functions like FEM. Instead, it directly obtains discrete equations through the use of nonlocal operators, which greatly simplifies the numerical implementation. The phase field method is a numerical technique used to model brittle fracture in materials. It is based on the use of a phase field parameter, which changes continuously as the structure evolves, to simulate the evolution of cracks. One of the main advantages of this approach is that it can simulate multiple cracks, regardless of their number or shape, in a continuous manner without the need to explicitly track their positions. In this thesis, a nonlocal operator method combined with an explicit phase field method was used to model the propagation of quasi-static fractures and compare the computational efficiency of this approach with numerical models based on implicit methods from the literature. The strong form of the governing equations was derived based on the energy form of the phase field model, and both the mechanical field and phase field were updated using an explicit time integration. Numerical benchmark problems, including an L-shaped panel, a three-point bending test, and a notched plate with holes, were analyzed and the results were found to be in good agreement with previous work. To develop the computational performance of the explicit model, a hybrid implicit/explicit model was also proposed. Additionally, a local damping technique was used to decrease the ratio of kinetic energy to internal energy in the explicit phase field model and apply mass scaling, which saved computational time in the cases studied.
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ÖgeGrafen oksit katkılı polimer nanokompozitlerin çeşitliözelliklerinin incelenmesi(Lisansüstü Eğitim Enstitüsü, 2024-01-12)GO veya diğer nano katkı malzemelerinin polimer matrisinde kullanılmasındaki en büyük zorluklardan biri homojen olmayan dağılım ve topaklanmadır. In situ polimerizayon vede eriyik ve solvent karıştırma yöntemlerinin kombinasyonu iyi dağılmış GO katkılı polimer nanokompozitlerin elde edilmesi açısından umut vericidir. Bu nedenle takdim edilen doktora tezi, GO'nun sahip olduğu özellikleri polimer nanokompozit elde ederken etkili bir şekilde aktarabilme hedefiyle iki çalışma etrafında şekillenmiştir. İlk çalışmada in situ polimerizayon ile imal edilen PA6/GO nanokompozitlerin karakterizasyon, termal, mekanik, viskoelastik ve tribolojik özellikleri incelenmiştir. İkinci çalışmada, eriyik ve solvent karıştırma yöntemlerinin kombinasyonuyla imal edilen PA6/HDPE+GO polimer karışım nanokompozitlerinin termal, mekanik, viskoelastik ve tribolojik özellikleri incelenmiştir. İlk çalışmada, PA6/GO nanokompozitleri 4 farklı karışım oranında in situ polimerizasyonla elde edilmiştir. PA6/GO nanokompozitlerinin karakterizsyon, termal, mekanik, viskoelastik ve tribolojik özellikleri şu şekilde incelenmiştir: XRD bulguları, GO'nun tipik kırınma pikinin ortadan kalktığını göstermiştir. Kristal tipinin değişmesi PA6 zincirlerinin GO üzerine etkili bir şekilde aşılandığını göstermektedir. XPS sonuçları, GO/PA6 elemental taramasından elde edilen güçlü N1s sinyali, C1s dekonvolüsyon pikleri ile birlikte değerlendirildiğinde, GO'in PA6 ile aşılandığını göstermiştir. GO/PA6 ve GO FT-IR spektrumları karşılaştırıldığında yeni pikler ortaya çıkmıştır. Elde edilen pikler, yeni ara moleküler bağlardan kaynaklanan GO'daki konformasyonel değişikliklerin, PA6 zincirlerinin GO üzerine aşılandığını ortaya koymaktadır. Raman spektrumu, PA6'nın GO'ya aşılanmasının GO/PA6'nın G modunu genişlettiğini göstermiştir. Ayrıca, artan kusur için kabul edilen gösterge olan ID/IG oranının, GO'ya kıyasla arttığını ortaya koymaktadır. AFM verilerine göre, karboksilik asit ve amino asit grupları arasındaki reaksiyon, 10,8 nm tarama yüksekliğinde görüldüğü gibi PA6'nın GO yüzeyine başarılı bir şekilde bağlandığını göstermektedir. PA6 ve PA6/GO nanokompozitlerinin DSC sonuçları karşılaştırılmıştır. GO ağırlık oranının artmasıyla genel kristalleşme derecesinin (%Xc) azaldığını göstermiştir Ayrıca, PA6 ve PA6/GO nanokompozitleri için soğutma DSC eğrileri, iyi dağılmış GO'nun çekirdeklenme ajanı olarak işlev gördüğünü ve PA6 ile etkileşime girerek daha yüksek bir kristalleşme sıcaklığına yol açtığını göstermiştir. TGA sonuçları, GO konsantrasyonunun bozunma sıcaklığı (Td) üzerinde önemsiz bir etkisi olduğunu ve termal kararlılıkta çok az bir iyileşme sağladığını göstermiştir. Bulgular, PA6'ya kıyasla PA6/GO nanokompozitlerin elastisite modülü ve maksimum çekme mukavemetinin GO ağırlık oranının artmasıyla arttığını göstermiştir. Kopma uzaması verileri değerlendirildiğinde, artan GO ağırlık oranı sonucunda sertlik artmakta, polimer hareketliliği sınırlanmakta ve kopma uzaması azalmaktadır. PA6/GO nanokompozit numunelerin çekme testi sonrasında kopma yüzeylerinin morfolojisi incelenmiştir. SEM sonuçları, gerilme özelliklerindeki iyileşmenin homojen dağılma ve kimyasal etkileşim sonucu meydana geldiğini göstermektedir. PA6'ya kıyasla, nanokompozitlerin eğilme gerilmesi ve modül değerleri GO içeriği arttıkça önemli ölçüde artmıştır. Bu iyileştirme yine rijit GO kullanılarak elde edilmiştir. Çentikli Charpy darbe testi sonuçlarına göre nanokompozitlerdeki her GO içeriğinin PA6'ya göre darbe mukavemetini arttığını göstermektedir. Kopma uzaması sonuçlarıyla uyumlu olarak fazla miktarda GO'nun PA6/GO nanokompozitlerinin darbe mukavemetini artırmadığı sonucuna varılabilir. DMA malzemelerin viskoelastik özelliklerini belirlemekte kullanılan en önemli deney yöntemlerinden biridir. Sıcaklığın depolama modülü üzerine etkisi çok net görülmüştür. Depolama modülleri sıcaklığın etkisi ile sürekli olarak azalmıştır. Buna karşın nanokompozitlerinin depolama modülü, PA6'ya göre tüm sıcaklıklarda GO içeriğinin artmasıyla artış göstermiştir. Maksimum Tan Delta değerinin azaldığını ve camsı geçiş sıcaklığının (Tg) PA6 matrisindeki homojen GO dağılımı ve etkileşimi sonucunda arttığı görülmüştür. PA6/GO nanokompozitleri sürtünme katsayısı eğrilerinin, sürekli sürtünme katsayısına geçiş mesafesi nanokompozitlerdeki GO miktarının artmasıyla azalmıştır. GO'nun PA6 ile birleştirilmesi, sürtünme katsayısında önemli bir azalmaya neden olmuştur. PA6'ya kıyasla PA6/GO nanokompozitlerinin termal iletkenliklerinin GO ağırlık yüzdesi arttıkça arttığı gösterilmiştir. GO'nun homojen dağılımı ve güçlü PA6 monomer zinciri etkileşimleri ile GO'nun üstün termal özelliklerinin etkili bir şekilde aktarılmasını sağlamıştır. Ayrıca, sürtünme testleri sırasında ölçülebilir noktadan ara yüzü gösteren termal görüntüleme kamera sonuçlarına göre GO'nun PA6 ile birleşmesi sürtünme sıcaklıklarının düşmesine katkı sağlamıştır. PA6'ya kıyasla PA6/GO nanokompozitlerinin istisnai derecede iyi aşınma direnci olduğu vurgulanmalıdır. Herhangi bir sürtünme mesafesindeki aşınma hacmi PA6'dan daha küçüktür. PA6'ya kıyasla, PA6/GO nanokompozitleri artan GO içeriği ile çelik karşı yüzeyde sürekli ve düz bir transfer filmi oluşturmuştur. PA6 için derin oyuklar şeklinde görülen abraziv aşınma mekanizmasının baskın aşınma mekanizması olduğu bulunmuştur. GO'nun ağırlıkça % 0,5'inden sonra elde edilen nispeten düz ve pürüzsüz aşınma yüzeyleri, aşınma şeklinin adaziv aşınmaya dönüştüğünü göstermektedir. PA6/GO nanokompozitlerinde GO içeriğinin artmasıyla aşınma hızları azalmış ve her yük için PA6'ya göre önemli ölçüde daha düşük aşınma hızları elde edilmiştir. PA6/GO nanokompozitlerin aşınma hızının, kayma hızı yükseldikçe arttığı görülmüştür. Aşınma hızları, kayma hızının azalmasıyla önemli ölçüde azalmamıştır. Çünkü transfer film oluşturma yeteneği sınırlı olan PA6, zaten belirgin şekilde metal pürüz tepelerine maruz kalmaktadır. Sürekli ve sabit bir transfer film oluşması aşınma hızını azalmasına neden olmuştur. İkinci çalışmada, polimer karışım nanokompozitleri, PA6, HDPE, MAPE ve GO kullanılarak 5 farklı formülasyonla hazırlanmıştır. PA6/HDPE+GO nanokompozitlerinin termal, mekanik, viskoelastik ve tribolojik özellikleri şu şekilde incelenmiştir: PA6/HDPE+GO nanokompozitlerin DSC sonuçları karşılaştırılmıştır. GO içeriğinin artması, erime sıcaklıkları üzerinde önemsiz bir etkiye sahiptir. GO ağırlık oranının artmasıyla nanokompozitlerin kristalliği azalmıştır. GO konsantrasyonunun bozunma sıcaklığı (Td) üzerinde hafif bir etkisi olduğunu ve termal kararlılıkta çok az bir iyileşme olduğunu göstermiştir. İmal edilen nanokompozitlerin istenilen ağırlık oranında GO içerip içermedikleri yüzde ağırlık azalmalarıyla tatmin edici bir şekilde gösterilmiştir. PA6/HDPE+GO nanokompozitlerinin çekme testi sonuçları, GO'nun PA6/HDPE nanokompozitlerine dahil edilmesinin PA6/HDPE'e göre hem elastisite modülünü hem de maksimum çekme mukavemetini artırdığını göstermektedir. Bu iyileştirme doğrudan GO ağırlık oranıyla ilgilidir. Kopma uzaması verileriyle birlikte değerlendirildiğinde, rijit GO'nun PA6/HDPE deformasyonunu sınırladığını PA6/HDPE'ye göre önemli ölçüde azalma ölçülmüştür. PA6/HDPE+GO nanokompozit numunelerin çekme testi sonrasında kopma yüzeylerinin morfolojisi incelenmiştir. GO ağırlık oranının artmasıyla ara yüzey adezyon mukavemetinin önemli ölçüde yükseldiği görülmüştür. Bu gözlemler, gerilme özelliklerindeki iyileşmenin GO'nun matris içerisindeki homojen dağılımın neden olduğunu göstermektedir. Nanokompozitlerin, GO içeriği arttıkça PA6/HDPE'ye göre artan eğilme gerilmesi ve modül değerleri sergilediği görülmektedir. Bu iyileştirme, çekme deneylerinde olduğu gibi rijit GO'nun kullanımıyla elde edilmiştir. Charpy darbe testi sonuçları, nanokompozitlerde her GO içeriği için darbe mukavemetinin PA6/HDPE'ye göre azaldığını göstermektedir. Darbe mukavemeti, çatlak ilerlemesini kolaylaştıran ve gerilme transfer yolunu kısıtlayan oldukça sert GO varlığı nedeniyle düşmüştür. GO içeriğinin artırılmasının, PA6/HDPE+GO nanokompozit enerji emme yeteneğini azalttığı sonucuna varılabilir. Nanokompozitlerin depolama modülü, PA6/HDPE göre tüm sıcaklıklarda GO içeriğinin artmasıyla artış göstermiştir. Depolama modülündeki bu artış, GO'nun PA6/HDPE matrisine eklenmesiyle elde edilen sertlikle ilişkilendirilmektedir. PA6/HDPE+GO nanokompozitlerin maksimum Tan Delta değerinin azaldığını; camsı geçiş sıcaklığının (Tg) ise GO'nun varlığı ve PA6/HDPE matrisindeki homojen dağılımı ile arttığı gözlenmiştir. Sürtünme katsayısı eğrilerinin sürekli sürtünme katsayısına geçiş mesafesi, nanokompozitlerdeki GO miktarının artmasıyla hızlanmıştır. Nanokompozitlerdeki GO konsantrasyonunun artması, sürtünme katsayılarının azalmasına neden olmuştur. PA6/HDPE'ye kıyasla GO ağırlık oranının artmasıyla PA6/HDPE+GO nanokompozitlerinin termal iletkenliklerinin yükseldiğini göstermektedir. Bu artış, GO'nun homojen dağılımı ve GO'nun olağanüstü termal özelliklerinin verimli bir şekilde aktarmasıyla sağlamıştır. Artan ısı iletim katsayısı, sürtünme ısısının hızlı bir şekilde dağılmasına katkıda bulunmuştur, bu da GO ağırlık oranının artışıyla sürtünme sıcaklıklarının azalmasına katkı sağlamıştır. PA6/HDPE'ye göre, GO'nun PA6/HDPE nanokompozitlerine eklenmesi, çelik karşı yüzeyler üzerinde son derece homojen ve sürekli bir transfer filmi oluşturmuştur ve GO konsantrasyonu arttıkça transfer film oluşumu iyileşmiştir. Aşınma yüzeylerinden elde edilen SEM mikrografları, GO içeriğinin artmasının nanokompozitlerin aşınma direncini önemli ölçüde artırdığı açıktır. %0.25 GO içeriğinden sonra aşınma biçimi abraziv aşınmadan adeziv aşınma yönünde değiştiğini göstermektedir. PA6/HDPE+GO nanokompozitleri için GO içeriğinin artmasıyla aşınma hızlarının düştüğü ve PA6/HDPE'nin aşınma hızlarına kıyasla daha düşük aşınma hızları elde edildiğini göstermektedir. Sürtünme katsayıları ve transfer film sonuçları ile uyumlu bir şekilde, iyi dağılmış rijit GO, ağırlık oranı arttıkça, rijitlik ve yük taşıma yeteneklerini artırarak aşınma hızlarını azaltmıştır. Ayrıca sürtünme tarafından üretilen ısının azalması nedeniyle PA6/HDPE+GO nanokompozitler, karşı yüzey üzerindeki sürekli ve kararlı bir transfer film oluşturmuştur. Bu, aşınma hızını azaltmaya yardımcı olmuştur.
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ÖgeImplementation of novel carbon-based nanomaterials for high-performance gas sensors(Graduate School, 2024-02-15)Environmental pollution has emerged as a critical dilemma due to the rapid escalation of industrial activities on a global scale. Toxic gas emissions stand out as a primary contributor to numerous climate issues, such as global warming and acid rain, posing a threat to both the environment and public health in the short and long term. The precise detection of such pollutants holds immense significance across various sectors, including environmental management, defense, healthcare, and industry. Substantial research efforts have been dedicated to advancing high-performance gas sensors that can accurately detect low gas concentrations while exhibiting robust sensing characteristics and durability Carbon nanomaterials have gained significant attention for numerous applications. Their outstanding physical and chemical properties. Extensive research has been conducted to assess the potential of various carbon-based nanomaterials, such as fullerenes, carbon onions, carbon quantum dots, nanodiamonds, carbon nanotubes, and graphene, as gas sensing materials. This thesis aims to explore the potential of novel carbon materials and their implementation in gas sensing applications. The thesis consists of five chapters and is organized as follows: The first chapter comprises a published comprehensive review of the literature discussing recent progress in the utilization of carbon nanomaterials and their composites in gas sensing devices. The chapter introduces the sensing mechanism, design, and preparation techniques of such sensors. It also discusses the modification of carbon-based nanostructures with other nanomaterials and their effects on sensing performance. The second, third, and fourth chapters consist of published and in-press articles presenting the research findings obtained in the thesis research. The research reported in these three chapters and the related findings are summarized in the following paragraphs. The final chapter provides a complementary conclusion, addresses existing challenges, and offers inspiring recommendations for future research. In the second chapter, the synthesis of a novel composite involving quantum dots enhanced carbon nanotubes (CNTs) and graphene nanoplates (GNPs) is reported, along with its application as a sensing material for detecting various concentrations of ethanol at room temperature. Carbon quantum dots (CQDs) employed in this study were synthesized via a solvothermal process and integrated with CNTs and GNPs to investigate their synergistic effects on the structure of the resulting composite and its sensing properties. Transmission electron microscopy (TEM) images provided evidence of the successful integration between CNTs and GNPs. CNTs were observed to interconnect with GNPs, forming a web-like three-dimensional hybrid structure that significantly enhanced the specific surface area (SSA) of the composite. The introduction of CQDs influenced the final hybrid structure by introducing zero-dimensional roughness, achieved through the attachment of CQDs to the surfaces of both CNTs and GNPs. The hybrid composite served as a sensitive film deposited onto the surface of a 5 MHz quartz crystal microbalance (QCM) sensor through drop-casting. The hybrid nanocomposite-based sensor exhibited significantly enhanced sensing sensitivity. At a concentration of 500 ppm, the CQD-enhanced CNT-GNP composite showed approximately 10- and 15-fold higher responses compared to CNT- and GNP-coated sensors, respectively. The response and recovery times of the CQD-enhanced CNT-GNP composite sensor were found to be approximately 2 minutes and 0.5 minutes, respectively. The sensor demonstrated reasonable repeatability and good recovery. The sensing mechanism was attributed to the adsorption and desorption processes via interactions between ethanol molecules and the composite surface functional groups. In the pursuit of cost-efficient alternative sensing materials, asphaltenes, a byproduct of the petroleum industry, have garnered attention as a potentially valuable waste material. The third chapter of the dissertation presents the initial utilization of asphaltenes as an affordable carbon-based material for gas sensing. Asphaltenes, derived from various oil sources, underwent facile cross-linking reactions to produce nanoporous carbon materials, where asphaltene molecules from different layers are interconnected via covalent bonds. Characterization results of these cross-linked asphaltenes revealed a substantial enhancement in their SSA and surface functionality. QCM sensors with sensing films derived from various asphaltene samples were prepared to detect different ethanol concentrations at room temperature. All cross-linked asphaltene samples exhibited a significant enhancement in the sensing response (up to 430%) compared to their respective raw parent samples. This response of the cross-linked asphaltene samples was comparable to that obtained from graphene oxide. The sensor based on cross-linked asphaltenes demonstrated good linearity, with a response time of approximately 2.4 minutes, a recovery time of around 8 minutes, and excellent response repeatability. After 30 days, the sensor based on cross-linked asphaltenes showed an approximate 40% reduction in its response, suggesting long-term aging. This decline is partially attributed to the observed swelling. This study opens the door to a deeper exploration of asphaltenes and highlights their potential as a promising carbon-based material for sensing applications. In the fourth chapter, the thesis research went far to an interesting unexplored form of carbon materials. Despite all carbon nanomaterials being composed of sp2 and sp3 hybridized carbons, the one-dimensional (1D) sp carbon, known as Carbyne, remains elusive, and the properties of this novel carbon form have not been fully discovered yet. However, the unique structure of carbyne suggests its potential possession of significant chemical, optical, and magnetic properties. In this chapter of the study, the synthesis and characterization of these carbyne nanostructures were investigated to gain a better understanding of their unique properties and potentials. Carbyne synthesis was achieved through two different processes: ion-assisted pulse-plasma deposition (IA-PPD) and laser ablation in liquid (LAL). Raman, XPS, and FTIR observations for the LA-PPD sample indicated the successful synthesis of sp carbon chains of carbyne. However, these chains existed at low concentrations in the obtained nanofilms, alongside a high concentration of sp2 and sp3 carbon. On the other hand, characterization results of the LAL sample showed higher carbyne content, as confirmed by Raman spectra measurements, along with high crystallinity observed from XRD results. The practical application of the synthesized carbyne as sensing materials was investigated on QCM sensors to detect various pollutants at room temperature. The LAL carbyne also exhibited higher sensitivity in gas experiments compared to IA-PPD carbyne. In detecting various analytes, LAL carbyne showed greater selectivity for ammonia gas. The sensor exhibited a moderate response time of 4.7 minutes with full recovery in approximately 9.3 minutes. However, compared to other available carbon materials, the sensitivity of carbyne was found to be relatively low, revealing the need for further research to optimize carbyne synthesis and the fabrication of its sensors.
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ÖgeDesign, methodology development and production of composite cryogenic liquid oxygen tank for space applications(Graduate School, 2024-02-16)The thesis focuses on the development of composite cryogenic liquid oxygen (LOX) tanks for sounding rocket propulsion systems, addressing challenges in aerospace engineering. Traditional composite materials used in these tanks are expensive and subject to various regulations in their supply chain. This thesis explores cost-effective alternatives, emphasizing affordable and sustainable aviation applications. This is the first study conducted in Turkey on cryogenic composite tank systems. Through this study, numerous infrastructures and laboratory systems were established, marking the first step towards indigenous development of these systems for research and development. All of these efforts will pave the way for structural advancements within Turkey's National Space Program. Cryogenic temperatures and LOX compatibility are the primary challenges for composite LOX tanks. To ensure the tank's operation in a cryogenic environment, various aspects need to be studied, including epoxy and fiber behavior in cryogenic conditions, thermal expansion coefficient compatibility between liner material and composite material, and LOX compatibility. Although properties of many materials under high and room temperatures are available in the literature, there is a lack of sufficient testing and information for cryogenic environments, especially for composite materials. For LOX compatibility, it's crucial that the composite structure doesn't trigger the combustive properties of liquid oxygen. The success in developing these innovative tanks relies on designing new materials specifically tailored to meet macro and micro-scale thermomechanical requirements. These materials must address long-term structural integrity, leakage due to microcracks, and contamination concerns in composite materials. The original contribution of this research is the detailed presentation of the entire process of developing a composite liquid oxygen fuel tank, including material screening, design, analysis methods, manufacturing processes, and quality controls. The thesis aims to deliver all phases of the reliable composite oxygen fuel tank development for use in sounding rockets. Although significant work on cryogenic composite tanks is currently underway, there is no consistent and comprehensive publication. This research aims to obtain conclusive results using numerical and experimental studies, demonstrating the advantages and disadvantages of using composite LOX tanks. The study focuses on the thermal and mechanical properties of different epoxy resins under cryogenic conditions and their compatibility with liquid oxygen. It also examines the fracture toughness of laminate-based testing under both room and cryogenic temperatures. Two types of tank structures were tested: tanks with a metal liner (Type-II) and linerless tanks (Type-V). A method that links micro and macro scales was developed to calculate real stresses on fiber and matrix components, providing insights into the composite structure's damage state. At the beginning of the study, the properties of epoxy resins were thoroughly examined to evaluate their mechanical performance and compatibility with liquid oxygen in cryogenic conditions. Collaboration with local manufacturers aimed to develop domestic formulations, promoting nationalization in aviation materials and supporting self-sufficiency. The study revealed that the Huntsman 1564-3474 epoxy system showed potential mechanical performance in a cryogenic environment and demonstrated compatibility with LOX. However, a Type-V tank system produced with this resin system suffered complete damage after a liquid nitrogen filling test, indicating its unsuitability for cryogenic environments. Fracture toughness tests on composite laminates produced by filament winding provided insights into mode-II damage types under room and cryogenic conditions, predicting and preventing critical information on damage. Fractographic analysis revealed differences in damage modes under room and cryogenic conditions. In particular, vacuum infusion and toughened resin systems exhibited similar mode-II fracture toughness values at room and cryogenic temperatures, while the behavior of the cold-curing resin system showed a significant decrease in cryogenic temperatures. Additionally, the study evaluated the negative effects of the wet filament winding method on production quality. These findings emphasized the importance of considering component interactions and production-related issues for cryogenic environment performance. During the study, a micro stress calculation tool was developed through literature assistance to predict actual stress values on components in composite structures. In this method, fiber and matrix components within the composite structure are modeled using a representative unit cell element, simulating the behavior of all components throughout the laminate with the help of periodic boundary conditions. This enables a connection between stress values on the composite layer modeled as an orthotropic material at the macro scale and stress values at the micro level. Python programming language, MATLAB, Abaqus, and ANSYS softwares were used to develop the calculation tool. The tool's added parameterization capability allowed evaluating the effect of temperature-dependent changes in material properties on micro-scale stress values. This provides foresight for determining the necessary material properties under cryogenic conditions. Additionally, the epoxy systems used in the tests were evaluated using this calculation tool. Considering Von Mises stress, Epotek 301-2 and 301-2FL emerged as a potential systems for cryogenic temperatures based on its temperature-dependent elastic modulus and thermal expansion coefficient. Similarly, the T7110 system stood out in minimizing maximum stress on the matrix but could not provide sufficient strength for pressurized tanks under room temperature conditions. Commercial epoxy systems and the proven cryogenic performance of the IM7-977-3 system were compared, evaluating their cryogenic performances. One of the main contributions of this study is revealing the effects of various tank geometries and epoxy materials on micro stresses, highlighting the emergence of constituent effects. Furthermore, the research emphasizes the importance of material selection and design parameters for cryogenic applications by revealing the limitations of specific tank systems. Design, production, and testing studies were carried out for Type-II and Type-V tank systems, and design evaluations were performed. It was determined that Type-II tank systems are unsuitable for cryogenic applications due to high thermal expansion differences between the metal liner and composite material in cryogenic temperatures. Under cryogenic conditions, the metal and composite shell experienced high delamination forces due to high thermal expansion differences. For the development of a low-cost cryogenic Type-V tank, innovative methods such as a liquefiable paraffin mandrel and wet filament winding were utilized. At the end of the studies, a successful prototype Type-V pressure tank was produced, capable of withstanding pressures up to 30 bars without any leaks. However, after a liquid nitrogen filling test, the same tank was observed to crack completely, losing its non-permeability. Throughout the thesis process, the aim was to work on each sub-problem, but due to the scale of the proposed study, some limitations were encountered. There are some recommendations to further expand the study, which include: Mechanical and thermal tests based on component and component interaction should be expanded to better assess material performance at different temperatures. The thermal and mechanical properties of each composite component should be determined as a function of temperature. Manufacturing using the wet filament winding method introduces uncertainties for composite materials. The production of such space systems is generally accomplished with prepreg materials and automated fiber placement systems. NDT measurement techniques for determining microcrack evolution on composite laminates could be researched and developed under cryogenic environments. Determining fiber/matrix interaction under cryogenic conditions is crucial for developing composite cryogenic pressure vessels. In conclusion, this thesis makes significant contributions to the development of cryogenic liquid oxygen tanks by exploring new materials, manufacturing techniques, and analytical methods. The findings not only extend the boundaries of cryogenic composite tank technology but also open doors to new possibilities for cost-effective and sustainable aviation applications. The results of the study are intended to provide a solid foundation for future advancements in this critical field.