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    Determination of mechanical properties of polymer matrix composites reinforced with electrospinning N66, PAN, PVA and PVC nanofibers: A comparative study
    (Elsevier, 2021) Uslu, Emin; Gavgali, Mehmet; Erdal, Mehmet Okan; Yazman, Sakir; Gemi, Lokman
    Fiber-reinforced polymer matrix composites are widely used in many structural applications thanks to their exceptional properties. In recent years, the use of electrospinning nanofibers with unique properties as reinforcement agents has attracted a great deal of attention in improving the performance of these composites. Although there are many promising studies on this subject in the literature, there are still many issues that need to be investigated. In this study, an experimental research reporting on the production and mechanical properties of two-phase polymer matrix composites reinforced with various types of thermoplastic nanofibers is presented. Nanofiber mats were produced from N66, PAN, PVA, and PVC polymers by electrospinning technique. Composites were obtained by embedding these nanofibers into epoxy resin by using vacuum infusion process. Mechanical properties of the composites were determined by performing tensile tests and the results were compared. The morphologies of nanofibers and the fracture surfaces of the composites were examined with SEM. Finally, statistical evaluations were carried out using mechanical data. According to tensile test results, the best ultimate tensile strength of 38.04 +/- 3.7 MPa, elongation of 2.46 +/- 0.4 % and toughness of 532 +/- 137 kJ/m(3) were obtained from N66 nanofiber composite, while PVA nanofiber composite was the most favorable in terms of Young's modulus (2.40 GPa). It was observed that the polymer type significantly affected the performance of the composite. In addition to the best mechanical properties, N66 composite was found to be more stable and reproducible than other specimens. Due to the good impregnation of nanofibers, it was conclusively determined that the use of vacuum infusion process is suitable for the production of these materials.
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    The effect of cooling plate, mechanical vibration, and grain refinement on the microstructure and hardness of A380 produced by sand mold
    (Taylor & Francis Ltd, 2024) Uslu, Emin; Tigli, Ahmet; Colak, Murat
    The mechanical properties of aluminium alloys can be increased by controlling the grain size and morphology of the alloy. In these studies, mechanical vibration, cooling slope plate (CSP), and grain refiner were applied on sand mould casting using A380 alloys. The hardness, and microstructure of the cast samples are investigated. These processes lead to the refinement of grain structures and a decrease in the tendency for dendritic structure formation. The Effect of the solidification time (modulus) on the microstructure is investigated. It was determined that the solidification time varies depending on the section thickness, which affects the SDAS values. It was observed that the lowest SDAS values were in CSP and the highest values were in grain refiners added casting. The lowest hardness value was recorded at CSP casting. Meanwhile, the grain refiner added vibration casting exhibits the highest hardness.
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    Evaluation of Fe Content on the Fluidity of A356 Aluminum Alloy by New Fluidity Index
    (Springer Int Publ Ag, 2024) Durmus, Melek; Dispinar, Derya; Gavgali, Mehmet; Uslu, Emin; Colak, Murat
    Elements that are deliberately added to aluminum alloys or are incorporated into the alloy later depending on the production process affect the final product properties. In addition, liquid metal cleaning is important in minimizing undesirable elements. Considering the production process, one of the most harmful impurities that is likely to pass into the alloy via diffusion for aluminum is the element, Fe. It is known that this is due to the fact that although Fe is highly soluble in liquid aluminum and its alloys, it has very little solubility in solids. Depending on the Fe content, mechanical properties, porosity and fluidity properties are affected in aluminum alloys. In this study, stainless and carbon steel rods were dipped into the melt at 700 degrees C and 750 degrees C for 1, 2 and 5 h. Castings were performed before and after degassing. Four-channel fluidity mold with different section thickness was used in the trials. Additionally, microstructure characterization was performed under varying casting conditions. Fluidity Index was proposed which is a single value measured from all fluidity values in different sections. When the results were examined, it was determined that the diffusion material, holding time, casting temperature and liquid metal cleanliness had an effect on the fluidity. Due to the increase in diffusion time, a decrease in fluidity was observed in both carbon steel and stainless steel. It was found that fluidity was significantly reduced when using stainless steel.
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    A new approach for high-quality production of UHMWPE by applying powder vibration densification before sintering
    (Elsevier, 2023) Yilmaz, Galip; Uslu, Emin
    Due 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.
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    A novel perspective for Lactobacillus reuteri: Nanoencapsulation to obtain functional fish fillets
    (Elsevier, 2019) Ceylan, Zafer; Uslu, Emin; Ispirli, Humeyra; Meral, Raciye; Gavgali, Mehmet; Yilmaz, Mustafa Tahsin; Dertli, Enes
    Enrichment of food products with beneficial Lactic Acid Bacteria (LAB) is an important methodology used to develop functional food products. Lactobacillus reuteri E81 was successfully nanoencapsulated into poly (vinyl alcohol)-based nanofibers for its application to the surface of fish fillets. The Scanning Electron Microscopy analysis confirmed the nanoencapsulation of L. reuteri E81 in electrospun nanofibers (LRNF) that had an average diameter of 381.83 +/- 130.69 nm. LAB growth in rainbow trout fillets and fatty fish (mackerel) and were found to be 2.92 and in the range of 3.27 and 2.66 log CFU/g, respectively. Importantly, the antioxidative characteristics of fish fillets significantly increased following their coating with LRNF. The results revealed a significant increase in the inhibition of free radicals in the samples treated with nanoencapsulated L. reuteri as compared to control group fish fillet samples. DPPH activity significantly increased to 40.24%, 44.96%, 44.97 in mackerel samples treated with nanoencapsulated L. reuteri (MLR) and increased to 19.76%, 20.87%, 21.46% in rainbow samples treated with nanoencapsulated L. reuteri (RLR). MLR samples exhibited the highest ABTS radical-scavenging activity (1631 mu mol TEAC/g). FRAP value of MLR samples was found to be 1.70 times higher than the control group samples.
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    Solidification analysis for variable thickness aluminum castings: simulation and chill design insights
    (Iop Publishing Ltd, 2023) Yilmaz, Galip; Colak, Murat; Uslu, Emin
    Manufacturing 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.