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Öğe Investigation of low velocity impact behaviors of honeycomb sandwich composites(SpringerLink, 2018-08-09) Topkaya, Tolga; Solmaz, Murat YavuzHoneycomb sandwich composites are used as significant structural members in advanced engineering applications. Thus, it is critical to determine how they behave under impact loading, in addition to other loads. In this study, low velocity impact loading behaviors of honeycomb sandwich composites were experimentally investigated. Almost all of the design parameters of honeycomb sandwich composites were investigated. The results indicated that the core thickness of honeycomb had no effect on the strength of the composite, and the parameter influencing the impact behavior of the specimen the most was the face sheet thickness. When the face sheet thickness of the specimen was increased, the most apparent strength increase was observed in the models using carbon fiber-reinforced composite face sheets. For all face sheet types subject to impact energy of 10 Joules, the upper face sheets of 0.5 mm-thick specimens were perforatedÖğe Finite element analysis of the stress distributions in peri-implant bone in modified and standard-threaded dental implants(Taylor & Francis, 2016-01) Topkaya, Tolga; Dündar, Serkan; Solmaz, Murat Yavuz; Yaman, Ferhan; Atalay, Yusuf; Saybak, Arif; Asutay, Fatih; Çakmak, ÖmerThe 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 FIII (300 N). The maximum stress values occurred in FIII (300 N) when the Nobel Replace implant is used, whereas the lowest ones, in the case of FI (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.Öğe Progressive failure analysis in adhesively, riveted, and hybrid bonded double-lap joints(Taylor & Francis, 2013-11) Topkaya, Tolga; Solmaz, Murat YavuzOne of the important processes in structural design is the joining technique. Failure of composite joints involves different failure mechanisms depending upon the joining technique. In this study, a progressive failure analysis was performed on adhesively, riveted, and hybrid bonded double-lap joints. In the joints, a woven-type fiberglass-reinforced composite material was used as the main material; AV 2015 was used as the adhesive, and steel as the rivet material. The analyses were performed using ANSYS 12.1 finite element package software via software written using parametric design language (APDL) codes. At the end of the progressive failure analysis, failure loads and failure modes were determined for 30-, 45-, and 60-mm overlap lengths in accordance with the Maximum Shear Stress Theory and Hashin Criteria. For 45-mm overlap lengths, the joint strength of hybrid joints proved to be 2.72 and 1.145 times higher, respectively, than adhesive and fastening joints. Results showed that the failure load of the joint increased when the overlap length increased. In riveted joints, the failure occurring in the composite plates began around the rivet hole and the catastrophic failure of these types of joints resulted from fiber tensile failure.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 The flexural fatigue behavior of honeycomb sandwich composites following low velocity impacts(MDPI, 2020-01-13) Topkaya, Tolga; Solmaz, Murat YavuzThis study experimentally investigated the flexural fatigue behaviors of honeycomb sandwich composites subjected to low velocity impact damage by considering the type and thickness of the face sheet material, the cell size and the core height parameters. Carbon-fiber reinforced composite and the aluminum alloy was used as the face sheet material. First, the static strength of undamaged and damaged specimens was determined by three-point bending loads. Secondly, the fatigue behaviors of the damaged and undamaged specimens were determined. Low velocity impact damage decreased the flexural strength and fatigue lives but increased the damping ratio for all specimens. Maximum damping ratio values were observed on specimens with a aluminum face sheet.Öğe Stress distribution in a femoral implant with and without bone cement and at different inclination angles(Materialpruefung/Materials Testing, 2018-04) Topkaya, Tolga; Solmaz, Murat Yavuz; Turgut, Aydın; Dündar, Serkan; Şanlıtürk, İsmail HakkıThe purpose of this study was to investigate numerically the effects of the inclination (collodiaphyseal) angle and bone cement (polymethylmethacrylate) filling on the stress distribution of human femurs and implants after the implementation of a partial endoprotez arthroplasty. Ti6Al4V, which is the most commonly used implant material, was choosen for this study. In the numerical study, solid models of implants and femurs were created using the SolidWorks 2010 package program, then stress analyses were carried out at five different inclination angles, 120°, 125°, 130°, 135° and 140°, with and without bone cement (polymethylmethacrylate), using the ANSYS Workbench 12.0 package program. The anteversion angle was assumed to be 12.5° for all models. As a result of the increase in the inclination angle and the addition of bone cement, it was determined that the stress values of the femurs and implants were reduced. Within the limitations of this study it has been shown that parameters like bone cement, anteversion angle, and an appropriate inclination angle should be tested previous to partial endoprosthesis arthroplasty surgery necessary as a result of damage to the human femur.Öğe 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 crack orientation on the propagation of cracks in graphene nanoplatelet carbon fiber-reinforced epoxy composites using digital ımage correlation(SpringerLink, 2021-03-27) Topkaya, TolgaThis study experimentally investigated the fracture behaviors of graphene nanoplatelet (GNP) carbon fiberreinforced polymer (CFRP) composites for varying amounts of GNP reinforcement, crack lengths and crack orientation angles. The specimens were subjected to tensile loading, and their fracture toughness values were determined with respect to maximum damage load and crack length. To compare the results obtained from experimental data, the fracture toughness values, strain distributions and crack tip opening displacements were determined by using a Digital Image Correlation (DIC) technique from images recorded during the tests. The results showed that increasing the amount of GNP increased the fracture toughness of specimens. On the other hand, increasing the crack orientation angle decreased the fracture toughness. Increasing the crack length increased the fracture toughness values for a crack orientation angle of 30 ° but decreased for a crack orientation angle of 90 °. DIC results were found to be compatible with the calculated results using crack length and damage stress value
