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    Characterization of Hazelnut, Pistachio, and Apricot Kernel Shell Particles and Analysis of Their Composite Properties
    (Taylor & Francis Inc, 2021) Celik, Yahya Hisma; Yalcin, Rojin; Topkaya, Tolga; Basaran, Eyup; Kilickap, Erol
    In this study, hazelnut, pistachio, and apricot kernel shells were ground size of 0-300 mu m, 300-600 mu m, and 600-850 mu m. The cellulose, ash, humidity, and metal contents of these powder particles were chemically analyzed and structural properties were characterized using X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectrometer (FT-IR) analysis. Their composites were fabricated by adding 0%, 10%, 20%, and 30% by weight of these powder particles to the polyester matrix material. The effect of chemical and structural properties of the powder particles on the physical, thermal, and mechanical properties of the composites was analyzed. The XRD analysis revealed that cellulose structure observed in powder particles. The peaks observed in their surface functional structures with FT-IR were mainly caused by cellulose and hemicellulose structures. These structures effected humidity and ash ratios. Nitrogen, carbon, hydrogen, and oxygen elements were seen in the structure. In addition, heavy metals such as Sn, Ca, K, Na, Mg, Fe, Ni, Mn, Cu, Zn, and Si were found. Powder particles added to the polyester material adversely affected the tensile strength of the matrix material. However, powder particles added to the matrix material at low rates had a positive effect on bending and compressive strength.
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    EFFECT OF MACHINABILITY OF GNP-GFRP COMPOSITES ON TENSILE STRENGTH AND FATIGUE BEHAVIOR
    (World Scientific Publ Co Pte Ltd, 2024) Topkaya, Tolga; Celik, Yahya Hisman; Kilickap, Erol
    The paper focuses on the cutting behavior of Glass Fiber Reinforced Polymer (GFRP) composites and GNP-GFRP composites that contain varying amounts of Graphene Nano Platelets (GNP). GFRP composites are increasingly being used in a variety of industrial applications due to their excellent mechanical properties, such as high strength, stiffness, and low weight. However, their machining and cutting behavior can be challenging due to the presence of the reinforcing fibers. Therefore, the study aims to investigate the machining behavior of GFRP composites and the effect of adding GNP on their cutting behavior. The effect of different parameters such as cutting speed, feed rate and reinforcement rate on cutting forces and delamination factor is investigated. In addition, the tensile strength and fatigue behavior of the composite materials with the best and worst delamination factors were also determined. Addition of up to 0.2 wt.% of GNP to GFRP composites resulted in an increase in cutting forces and delamination factor when drilling GFRP composites. While the cutting force and delamination factor decreased with the increase in cutting speed, the cutting force and delamination factor increased with the increase in the feed rate. Analysis of variance (ANOVA) was performed to determine the effects of drilling parameters and reinforcement ratio on cutting force and delamination factor according to full factorial experimental design. The most efficient factor on the cutting forces is found to be feed rate (84.97%), followed by the reinforced rate (6.48%) and cutting speed (6.13%). The most efficient factor on the delamination factor is determined to be feed rate for (44.49%), followed by the reinforced rate (29.20%) and cutting speed (21.73%).
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    Öğe
    Finite element analysis of the stress distributions in peri-implant bone in modified and standard-threaded dental implants
    (Taylor & Francis Ltd, 2016) Dundar, Serkan; Topkaya, Tolga; Solmaz, Murat Yavuz; Yaman, Ferhan; Atalay, Yusuf; Saybak, Arif; Asutay, Fatih
    The aim of this study was to examine the stress distributions with three different loads in two different geometric and threaded types of dental implants by finite element analysis. For this purpose, two different implant models, Nobel Replace and Nobel Active (Nobel Biocare, Zurich, Switzerland), which are currently used in clinical cases, were constructed by using ANSYS Workbench 12.1. The stress distributions on components of the implant system under three different static loadings were analysed for the two models. The maximum stress values that occurred in all components were observed in F-III (300 N). The maximum stress values occurred in F-III (300 N) when the Nobel Replace implant is used, whereas the lowest ones, in the case of F-I (150 N) loading in the Nobel Active implant. In all models, the maximum tensions were observed to be in the neck region of the implants. Increasing the connection between the implant and the bone surface may allow more uniform distribution of the forces of the dental implant and may protect the bone around the implant. Thus, the implant could remain in the mouth for longer periods. Variable-thread tapered implants can increase the implant and bone contact.
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    Mechanical properties of fiber/graphene epoxy hybrid composites
    (Korean Soc Mechanical Engineers, 2020) Topkaya, Tolga; Celik, Yahya Hisman; Kilickap, Erol
    The aim of this study is to determine the effect of graphene nanoparticle (GNP) reinforcement on the mechanical properties of glass fiber reinforced polymer (GFRP), carbon fiber reinforced polymer (CFRP) and aramid fiber reinforced polymer (AFRP) composites commonly used in the space and defense industry. Accordingly, GFRP, CFRP and AFRP composites were produced by using hot pressing method. In addition, hybrid fiber composites were produced by adding 0.1 %, 0.2 % and 0.3 % GNP to these fiber reinforced composites. The tensile strength and modulus of elasticity of the composites were determined. The tensile damage fracture regions were analyzed by scanning electron microscopy (SEM) and energy distribution spectrum (EDS). It was observed that the addition of 0.2 wt. % GNP to GFRP and CFRP composites increased tensile strength and modulus of elasticity. However, the addition of 0.2 wt. % GNP to AFRP composites had no effect on the tensile strength; on the contrary, it partially reduced the tensile strength but increased the modulus of elasticity. On the fracture damage surfaces of the GFRP and CFRP composites and the GNP/GFRP and GNP/CFRP hybrid composites, the fibers were completely separated. On the damage surfaces of AFRP composite and GNP/AFRP hybrid composites, the fibers were deformed but these fibers were not separated from each other. From the EDS analysis, it was observed that the element C increased in the composites with the addition of GNP to the fiber reinforced composites.