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Öğe Azo dye-functionalized magnetic Fe3O4/polyacrylic acid nanoadsorbent for removal of lead (II) ions(Elsevier B.V., 2020) Sadak, Omer; Hackney, Robert; Sundramoorthy, Ashok K.; Yilmaz, Galip; Gunasekaran, SundaramWe report the fabrication of a nanoadsorbent for the removal of heavy metals. The nanoadsorbent is comprised of ferric oxide (Fe3O4) magnetic nanoparticles (MNPs) covalently conjugated with polyacrylic acid (PAA) and further functionalized with an azo dye (Congo red, CR) using carbodiimide. This Fe3O4 core and PAA-CR shell system (MNP/PAA-CR) exhibited binding affinity towards various cations (Pb2+, Fe2+, Fe3+, Cd2+, and Cu2+) at room temperature. Using MNP/PAA-CR we studied its heavy metal removal effectiveness and kinetics targeting Pb2+ under various reactions conditions including time and pH. The Pb2+ removal efficiency and adsorption capacity were maximal at pH 6.5 and 45 min of reaction time, and the Pb2+ adsorption kinetics better fit a pseudo second-order model than a first-order model. The adsorption of Pb2+ by MNP/PAA-CR was also investigated by the so-called Langmuir and Freundlich isotherms, and the Langmuir isotherm predicted a maximum absorption of 195.3 mg.g-1. Our results further indicated that MNP/PAA-CR is potentially reusable after desorption of the adsorbed metal with only small decline in adsorption ability over five consecutive cycles of regeneration. © 2020 Elsevier B.V.Öğe Conventional and Microcellular Injection Molding of a Highly Filled Polycarbonate Composite with Glass Fibers and Carbon Black(Mdpi, 2022) Yilmaz, Galip; Devahastin, Apichart; Lih-Sheng TurngConventional solid injection molding (CIM) and microcellular injection molding (MIM) of a highly filled polycarbonate (PC) composite with glass fibers and carbon black were performed for molding ASTM tensile test bars and a box-shape part with variable wall thickness. A scanning electron microscope (SEM) was used to examine the microstructure at the fractured surface of the tensile test bar samples. The fine and uniform cellular structure suggests that the PC composite is a suitable material for foaming applications. Standard tensile tests showed that, while the ultimate strength and elongation at break were lower for the foamed test bars at 4.0-11.4% weight reduction, their specific Young's modulus was comparable to that of their solid counterparts. A melt flow and transition model was proposed to explain the unique, irregular tiger-stripes exhibited on the surface of solid test bars. Increasing the supercritical fluid (SCF) dosage and weight reduction of foamed samples resulted in swirl marks on the part surface, making the tiger-stripes less noticeable. Finally, it was found that an injection pressure reduction of 25.8% could be achieved with MIM for molding a complex box-shaped part in a consistent and reliable fashion.Öğe Design, Manufacturing, and Comparative Analysis of a Mini Extruder for Polymer Flow Characterization: A Case Study on HDPE and PMMA Polymers(2024) Uslu, Emın; Yilmaz, GalipPolymer extrusion is one of the most widely used polymer processing methods and the sole option for many standard products. The modern extrusion machine has a very sophisticated design; for example, the extrusion screw has different zones and complex geometry. Determining the proper processing settings is always a challenge for engineers. Additionally, complex rheological properties of the polymers in extrusion sometimes yield challenging and unpredictable problems to troubleshoot. For convenience, a small-scale extrusion machine can be used to troubleshoot and analyze the polymers rather than the large manufacturing machines that are hard to work with. This study has produced a small-scale extrusion machine that is easy to manufacture without deviating from the extrusion process's nature. The extruder, whose production details are given, was tested with two different polymers: HDPE and PMMA. The correct temperature and screw rotation speed were determined with the extruder for the proper process parameters. In addition, the temperature-viscosity relationship of the polymers' flow nature was also determined.Öğe Exploring alternative polymer materials for joint liners: a software-guided material selection(Iop Publishing Ltd, 2024) Yilmaz, Galip; Gerdan, Zeynep; Colak, MuratThis study explores the alternative polymer materials and selection process for joint implant liners, focusing on applying CES Selector software to identify suitable polymer materials. CES Selector provides an easy-to-use interface. It offers multiple selection methods, including boundary values and property constraints. Seven materials were excluded from the analysis, resulting in 19 potential candidates, including unconventional options like EVOH, PCTA, PESU, PI, PPA, PPC, PPSU, and PSU. The materials underwent evaluation based on key criteria, including tensile strength, Young's modulus, compressive strength, fatigue strength, and fracture toughness. Overall, TPU exhibited a remarkable combination of high mechanical strength and adaptable Young's modulus, making it a top contender. However, in other evaluation criteria, PI surpassed TPU, solidifying its potential as a superior choice. This systematic approach provides valuable insights for engineers and designers seeking innovative materials for joint implant liners. The study results broaden the range of materials used in implant manufacturing, providing potential alternatives that offer better long-term durability and performance.Öğe Foundational Engineering of Artificial Blood Vessels' Biomechanics: The Impact of Wavy Geometric Designs(Mdpi, 2024) Yilmaz, GalipThe design of wavy structures and their mechanical implications on artificial blood vessels (ABVs) have been insufficiently studied in the existing literature. This research aims to explore the influence of various wavy geometric designs on the mechanical properties of ABVs and to establish a foundational framework for advancing and applying these designs. Computer-aided design (CAD) and finite element method (FEM) simulations, in conjunction with physical sample testing, were utilized. A geometric model incorporating concave and convex curves was developed and analyzed with a symbolic mathematical tool. Subsequently, a total of ten CAD models were subjected to increasing internal pressures using a FEM simulation to evaluate the expansion of internal areas. Additionally, physical experiments were conducted further to investigate the expansion of ABV samples under pressure. The results demonstrated that increased wave numbers significantly enhance the flexibility of ABVs. Samples with 22 waves exhibited a 45% larger area under 24 kPa pressure than those with simple circles. However, the increased number of waves also led to undesirable high-pressure gradients at elevated pressures. Furthermore, a strong correlation was observed between the experimental outcomes and the simulation results, with a notably low error margin, ranging from 19.88% to 3.84%. Incorporating wavy designs into ABVs can effectively increase both vessel flexibility and the internal area under pressure. Finally, it was found that expansion depending on the wave number can be efficiently modeled with a simple linear equation, which could be utilized in future designs.Öğe Joule heating of carbon fiber in hybrid composites with glass fibers: Investigation of electro-thermal and vibration characteristics(Elsevier, 2025) Uslu, Emin; Yilmaz, Galip; Uyar, MehmetThis study explores the innovative dual-purpose use of carbon fiber, functioning both as a structural and a heating element, expanding its potential in hybrid composites. A prototype composite was fabricated using the vacuum infusion process, featuring a single carbon fiber layer at the core for dual-purpose and two outer layers of glass fiber. Electrical heating tests revealed a stable relationship between voltage, resistance, power, and temperature, demonstrating efficient heat generation as the voltage increased. Thermal imaging confirmed uniform heat distribution with minor variations. Free vibration tests evaluated the composite's dynamic behavior under various electro-thermal conditions. Results showed that increasing temperature reduced the natural frequencies, particularly in the second vibration mode. Changes in Rayleigh damping coefficients at higher temperatures highlighted the composite's sensitivity to thermal inputs. These findings underline the potential of hybrid composites for advanced applications like turbine blades and aerospace components, where multifunctionality, self-heating, and vibration control are critical.Öğe A new approach for high-quality production of UHMWPE by applying powder vibration densification before sintering(Elsevier, 2023) Yilmaz, Galip; Uslu, EminDue to its extreme viscosity, UHMWPE powder requires elevated pressure and temperature settings to ensure a fully solid structure. But a gentle process is vital for reliability in certain applications, such as prosthetic liners. A unique type of large gap, not mentioned in the literature, has been observed to resist closing more than regular gaps due to the number of particles forming a shield against pressure. As a solution, a mechanical vibration treatment of the particles before heating was used to eliminate these particular large gaps. Optimum vibration parameters were found, and the samples' final solid density and mechanical properties increased. The particles' dimensions and coefficient of friction were measured, and their vibration-dependent characteristics were discussed. A custom-made microscope apparatus was used to observe the vibration-induced densification of the particles and the gaps resisting closing.Öğe Pelletizing ultra-high molecular weight polyethylene (UHMWPE) powders with a novel tapered die and addition of high density polyethylene (HDPE): Processing, morphology, and properties(Elsevier Sci Ltd, 2022) Yang, Huaguang; Yilmaz, Galip; Jiang, Jing; Xie, Jun; Langstraat, Thomas; Chu, Raymond; van Es, MartinThe extremely high molecular weight and molecular entanglement have rendered ultra-high molecular weight polyethylene (UHMWPE) superior properties. However, poor inter-particle diffusion makes it difficult to pelletize UHMWPE powders for easy processing/handling. A novel tapered die with air cooling was proposed to pelletize UHMWPE and a UHMWPE blend with 5 wt% high-density polyethylene (HDPE) for compression molding and material characterization. The tensile strength of samples prepared with the tapered die outperformed those by the regular die or from virgin powders. The addition of HDPE further improved the tensile strength. Fourier transform infrared spectroscopy (FTIR) revealed little chain scission and the lowest amount of oxidation from the tapered die. Intrinsic viscosity (IV) measurements confirmed the negligible chain scission and showed an increment in IV for the UHMWPE/HDPE blend. Multi-angle light scattering with size-exclusion chromatography (SEC-MALS) indicated no change in the UHMWPE molecular weight distribution, but some crosslinking in the blend. Polarized optical microscopy (POM) showed that the HDPE and extrusion led to a finer UHMWPE domain size and better fusion between UHMWPE and HDPE. The combined effect of enhanced molecular chain diffusion, improved consolidation, and lower oxidation using the tapered die led to 40% improvement of tensile strength for the UHMWPE/HDPE blend.Öğe Solidification analysis for variable thickness aluminum castings: simulation and chill design insights(Iop Publishing Ltd, 2023) Yilmaz, Galip; Colak, Murat; Uslu, EminManufacturing high-quality casting parts with complex geometries requires high engineering skill and precision. One essential quality concern is isolated hot spots within the castings, often in thick sections. Each hot spot must be consistently fed or mitigated through directional solidification techniques. The impact of various mold sands and the geometry of chill parts on solidification direction was investigated using specialized casting and general-purpose simulation programs. A parametric optimization method was employed to analyze directional solidification to adjust the geometry of the chill parts. The results indicate that employing diverse mold sands to enhance cooling in the thick sections was a viable strategy for achieving directional solidification in parts where the feeding pathway is obstructed due to changes in cross-section. Furthermore, the study revealed that intricate details in the chill part's geometry are not critical; however, a minimum volume (or weight) was necessary for adequate directional solidification. Lastly, an easily applicable mathematical model has been developed to determine the required volume of chill parts to ensure successful directional solidification.Öğe Tek ve çift katmanlı yapay damar konfigürasyonlarının Holzapfel-Gasser-Ogden hiperelastik modeli ile mekanik uyumluluk analizi(2022) Yilmaz, Galip; Uslu, EmınYaygınlaşan kalp-damar hastalıkları, yapay damarların önemini artırmıştır. Üretim şartları gereği farklı tasarımlar içeren bu damarların, doğal bir mekanik davranış göstermesi gerekmektedir. Üretim öncesi ihtiyaç duyulan analizlerin yapılması için karmaşık ve hiperelastik bir özellik gösteren damar mekaniğini modelleyen birçok çalışma bulunmaktadır. Bunlar arasından yaygın kullanımı olan Holzapfel-Gasser-Ogden (HGO) hiperelastik modeli bu çalışmada kullanılmıştır. Bu çalışma kapsamında bir simülasyon ortamı HGO modeliyle hazırlanmış ve literatürdeki verilerle doğruluğu teyit edilmiştir. İlk numune iki katmanlı tipik bir yapıda oluşturulmuştur. Sonraki numunelerde üretimde karşılaşılan farklı yöntemlere dayanan katman konfigürasyonları denenmiştir. İkinci numune için dış katmanın normalden çok ince bir yapıda tasarlandığı durum incelenmiştir. Az bir uyumsuzluk olmasına rağmen kalınlığı azalan dış katmanın damarın mekanik özellikleri üzerinde güçlü bir etkisinin olmadığı gözlemlenmiştir. Üçüncü tip numunede ise dış katmanın geometrik ve malzeme özellikleri bakımından iç katman olarak tasarlandığı bir durum denenmiştir. Mekanik özelliklerinin karmaşık ve uyumsuz olduğu gözlemlenmiştir. Son numune olarak, tek katmanlı bir yapı tasarlanmıştır. Bir miktar uyumsuzluk gösterse de bu numune sadelik açısından avantajlı bulunmuştur. Ayrıca ikinci ve üçüncü numunelerin malzeme parametreleri değişimiyle uyum analizi yapılmıştır. Üçüncü numunenin aksine ikinci numune için dış katman içindeki liflerin malzeme özelliklerinin ayarlanmasıyla kolayca referans numunesinin özelliklerinin yakalanabileceği gösterilmiştir.Öğe Thermal, rheological, and mechanical characterization of compression and injection molded ultra-high molecular weight polyethylene, high density polyethylene, and their blends(Wiley, 2023) Yang, Huaguang; Yilmaz, Galip; Jiang, Jing; Langstraat, Thomas; Chu, Raymond; van Es, Martin; Garg, PriyaTensile and impact test samples of ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), and their blends at various UHMWPE/HDPE weight ratios were prepared via compression molding and injection molding for thermal, rheological, and mechanical characterization. A twin-screw extruder with either a tapered die with air-cooling or a regular die was used to compound and extrude the materials prior to pelletization and molding. To the best of our knowledge, there has been no publication on pelletizing neat UHMWPE using a regular extruder. The differential scanning calorimetry analysis suggested the occurrence of re-crystallization and co-crystallization for all the blends. The rheology test confirmed that all the blends exhibited a solid-like behavior and the degree of compatibility increased with increasing HDPE content in the blends. A strong synergistic effect was observed the blends possessed a higher tensile and impact strength than their neat UHMWPE and HDPE counterparts. The compression molded (95/5) UHMWPE/HDPE samples extruded using the tapered die yielded the highest tensile strength (50.1 MPa), which was about 40% higher than that of the neat UHMWPE samples. The best composition of these blends for compression and injection molded parts is 10% HD and 50% HD, respectively.Öğe Thermal, rheological, and mechanical characterization of compression and injection molded ultra-high molecular weight polyethylene, high density polyethylene, and their blends(John Wiley and Sons Inc, 2023) Yang, Huaguang; Yilmaz, Galip; Jiang, Jing; Langstraat, Thomas D.; Chu, Raymond; van Es, Martin A.; Turng, Lih ShengTensile and impact test samples of ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), and their blends at various UHMWPE/HDPE weight ratios were prepared via compression molding and injection molding for thermal, rheological, and mechanical characterization. A twin-screw extruder with either a tapered die with air-cooling or a regular die was used to compound and extrude the materials prior to pelletization and molding. To the best of our knowledge, there has been no publication on pelletizing neat UHMWPE using a regular extruder. The differential scanning calorimetry analysis suggested the occurrence of re-crystallization and co-crystallization for all the blends. The rheology test confirmed that all the blends exhibited a solid-like behavior and the degree of compatibility increased with increasing HDPE content in the blends. A strong synergistic effect was observed the blends possessed a higher tensile and impact strength than their neat UHMWPE and HDPE counterparts. The compression molded (95/5) UHMWPE/HDPE samples extruded using the tapered die yielded the highest tensile strength (50.1 MPa), which was about 40% higher than that of the neat UHMWPE samples. The best composition of these blends for compression and injection molded parts is 10% HD and 50% HD, respectively. © 2022 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals LLC.
