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Öğe Mechanical properties of fiber/graphene epoxy hybrid composites(SpringerLink, 2020-11-18) Çelik, Yahya Hışman; Topkaya, Tolga; Kılıçkap, ErolThe 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 compositesÖğe Numerical analysis of the effect of implant geometry to stress distributions of the three different commercial dental implant system(Sivas Cumhuriyet Üniversitesi, 2015-02-11) Topkaya, Tolga; Solmaz, Murat Yavuz; Dündar, Serkan; Eltas, AbubekirObjectives: The success of dental implants is related to the quality, quantity of local bones, implant design and surgical technique. Implant diameter and length are accepted as key factors. Present work focuses to investigate the effect of titanium implant geometry to stress distributions in implant system. Materials and Methods: For this purpose three different implant models which are currently being used in clinical cases constructed by using ANSYS Workbench 12.1. The stress distributions on components of implant system under static loadings were analyzed for all models. Results: The maximum stress values that occurred in all components happen in the case of loading in which the Nucleoss T-4 (Nucleoss, Turkiye) implant is used, but the occurred lowest stress values happen in the case of Fı loading in which Nobel Active (Nobel Biocare, Zurich, Switzerland) implant is used. In all models, the maximum tensions have occurred in the neck region of the implants. Conclusions: The crestal bone loss in the neck region of the implants reduced the long-term survival rate of implants.The length and the size of the implant are the two important factors in the stress distribution.Öğe Characterization of hazelnut, pistachio, and apricot Kernel Shell particles and analysis of their composite properties(Taylor & Francis, 2021-05) Çelik, Yahya Hışman; Topkaya, Tolga; Kılıçkap, Erol; Başaran, Eyüp; Yalçın, RojinIn this study, hazelnut, pistachio, and apricot kernel shells were ground size of 0–300 µm, 300–600 µm, and 600–850 µm. 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.Öğe Fatigue behavior of honeycomb sandwich composites under flexural and buckling loading(INCDTP - Leather and Footwear Research Institute (ICPI), 2016) Topkaya, Tolga; Solmaz, Murat YavuzThis study experimentally investigated the fatigue behaviors of honeycomb-sandwich composites under buckling and three-point bending loads. The ASTM C 365 and ASTM C 393 standards were used as references to prepare test specimens and conduct experiments. The investigation looked at how the cell diameter, core thickness and thickness of the skin material affected the fatigue behavior. It was observed that the most significant parameter affecting fatigue under buckling loads was the cell diameter, and the least significant parameter affecting fatigue under three-point loads was the thickness of the skin material.Öğe The effect of implant number and position on the stress behavior of mandibular implant retained overdentures: A three-dimensional finite element analysis(Elsevier, 2015-07-16) Topkaya, Tolga; Solmaz, Murat YavuzThe present study evaluated the effects of ball anchor abutment attached to implants with a 4.30 mm diameter and 11 mm insert length on stress distribution in a patient without any remaining teeth in the lower jaw. In the study, the stress analysis was performed for five different configurations (2 with 4 implant-supported and 3 with 2 implant-supported) and three different loading types using ANSYS Workbench software. The stresses measured in the 4 implant-supported models were lower compared to the stresses measured in the 2 implant-supported models. The stresses on the implants intensified on the cervical region of the implants. When the effects of the loading sites on the stress were examined, the loading on the first molar tooth produced the highest stresses on the implants.
