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Öğe The effect of carbon nanotubes modified polyurethane adhesive on the impact behavior of sandwich structures(Wiley, 2021) Cetin, Mehmet EminSandwich panels with aluminum honeycomb cores have emerged as an essential class of lightweight building materials in a wide variety of structural engineering areas, including marine, railway, aerospace, and automotive structures. Although sandwich structures offer remarkable mechanical properties, for instance, high specific strength and stiffness, these structures are open to the damage created by the low-velocity impact. This study investigates the dynamic behavior of aluminum honeycomb sandwich panels with different core cell sizes based on neat and multi-walled carbon nanotube (MWCNT) reinforced polyurethane (PU) adhesives that are aimed. The enhancement in impact performance of honeycomb sandwich structures obtained by the inclusion of MWCNTs in the PU adhesive is investigated. The effect of the MWCNT reinforcements on square sandwich panels at 50 J energy level is examined using an instrumented drop tower test setup. After acquiring load-time histories, the numerical integration method is implemented to obtain load-deflection and energy-time curves. Also, energy balance modeling (EBM) is utilized to characterize the effectualness of MWCNT reinforcement to PU adhesive on the impact behavior of sandwich panels. Theoretical EBM is confirmed that absorbed energy in the shear and bending deflections increased as the percentage of MWCNT-added PU adhesive increases. Understanding the damage event implicated in absorbing and dissipating the impact energy is determined and compared for panels with different cell sizes, including nanoparticles, using the macroscopic optical images and microscopic scanning electron microscopy images of sandwich panels.Öğe The effect of halloysite nanotube modification on wear behavior of carbon-aramid fiber reinforced hybrid nanocomposites(Wiley, 2022) Cetin, Mehmet Emin; Bastosun, Yusuf; Tatar, Ahmet Caner; Cetin, M. Huseyin; Demir, Okan; Onal, Gurol; Avci, AhmetIn this study, the carbon-aramid fiber reinforced hybrid composites are fabricated using a vacuum-assisted hand lay-up method using halloysite nanotubes (HNTs) modified epoxy matrix. Ball-on-disk wear tests are performed to analyze the tribological effect of neat and HNTs-added specimens at 10, 15, and 20 N loads and 1 m/s sliding speed. Additionally, the wear rate and friction coefficient results are obtained to investigate the effect of the HNTs on the tribological behavior of hybrid composites. The wear mechanism of neat and nanocomposite specimens is specified by scanning electron microscopy (SEM) images, and the elemental analysis of worn surfaces is performed using EDX. Finally, the surface morphology is evaluated with 3D topography images. Additionally, thermal camera images are used to identify the thermal conductivity effect of HNTs on wear. The wear test results show that HNTs-addition to composite decreased the friction coefficient by 9%, 10%, and 11% for 10 N, 15 N, and 20 N loadings, respectively. The wear rate is also decreased average by 75% for wear loadings. Surface form images acquired from 3D topography support the enhancement in the friction coefficient and wear rate values. Furthermore, thermal camera images show that thermal conductivity improvement on the contact region is attributed to well thermal properties of HNTs. Furthermore, the solid-lubricant characteristic of HNTs as forming tribofilm is determined as the main reason for the enhanced tribological performance of nanocomposites. Finally, a detailed wear mechanism is proposed to explain the wear behavior of HNTs-added carbon-aramid hybrid composites based on SEM images.Öğe Effects of cryogenic and warm temperatures on quasi-static penetration resistance of carbon-aramid hybrid nanocomposites reinforced using halloysite nanotubes(Elsevier, 2021) Cetin, Mehmet Emin; Tatar, Ahmet Caner; Demir, Okan; Onal, Gurol; Avci, AhmetThe quasi-static penetration test of a composite structure aims to measure impact behavior under the out-of plane loadings without dynamic and rate effects. In this study, carbon-aramid reinforced nanocomposites were manufactured by vacuum-assisted resin transfer molding and hand lay-up techniques and characterized by quasi-static penetration tests. Halloysite nanotubes (HNTs) were added to epoxy resin as nanofillers. Quasi-static punch shear test (QS-PST) was performed using a 12.7-mm cylindrical punch with a 50.8-mm support span. QSPSTs tests were carried out at-50 degrees C,-25 degrees C, 0 degrees C, 25 degrees C, and 50 degrees C to determine the effect of temperature on quasi-static penetration behavior of neat and HNT-reinforced carbon-aramid nanocomposites. Absorbed energy values and penetration force-displacement curves were acquired from QS-PSTs for each sample. Photographs of the front and rear sides of the samples were taken and analyzed. Moreover, the samples were cut from the middle, and the damage throughout the thickness of the composite samples were examined. It was observed that for all test samples, damages increased when the temperatures decreased. For the same temperature, nano particle addition to the samples resulted in higher penetration force and less damage. We confirmed the possibility of increasing penetration resistance and energy absorption capacity by adding HNT to carbon-aramid fibers at cryogenic and warm temperatures.Öğe Experimental Investigation on the Effects of Core/Facing Interface Performance on the Low-Velocity Impact Behavior of Honeycomb Sandwich Panels(Springer, 2020) Meram, Ahmet; Cetin, Mehmet EminThis paper gives an important contribution by investigating the effectiveness of core/facing interface performance of aluminum honeycomb sandwich panels under low-velocity impact energy. Low-velocity drop tests were conducted on five different panels under 50, 75, and 100 J impact energies (loads). The following procedure is followed to evaluate the impact response of panels: the force-time histories are acquired; the numerical integration method is applied, and force-displacement histories are obtained; and then the damage mechanism and theoretical energy balance modeling are used to analyze the effectiveness of core/facing interface performance on the impact behavior of the panels. Scanning electron microscopy is used to examine the microstructural and the morphology of the core/face sheet interface of the aluminum honeycomb sandwich panels. The effects of voids, interface, and cohesive cracks on the impact behavior of the panels are analyzed. Energy balance modeling proved that energy absorbed in the bending and shear deflections increased as the resistance at the core/facing interface is increased. In addition, changing the initial impact energy from 50 to 100 J produced more than 120% increase in the effectiveness of the panels in terms of energy absorbed in shear and bending deformations.Öğe Fabrication, characterization and mechanical testing of carbon fiber sandwich composites with nanoparticle included polyurethane adhesives(Sage Publications Ltd, 2022) Cetin, Mehmet EminIn honeycomb core and composite face sheet sandwich panels, it is essential to understand the bonding characteristics of adhesive in relevance with its properties to observe synergistic effects of reinforcing nanoparticles such as multi-walled carbon nanotubes (MWCNTs). This study investigates the effects of MWCNT inclusion on polyurethane (PU) adhesive, which directly affects sandwich structures' structural and mechanical performance. MWCNTs are added to PU adhesive up to 0.2%, and their RAMAN spectroscopic analysis, Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analyses (TGA) and differential-scanning calorimetry analyses (DSC) are evaluated. Aluminum honeycomb carbon-fiber-reinforced composite (CFRC) sandwich panels are fabricated using an out-of-autoclave manufacturing process. Carbon-fiber prepreg is used for top/bottom face sheets. Mechanical strength of face/core bonding evaluated as a function of MWCNT addition and core cell sizes. Manufactured sandwich composite structures are investigated for flat-wise tensile strength and three-point bending strength. Results show that MWCNT reinforcement to PU adhesive and lower cell size increases bending and flat-wise tensile resistances.Öğe Improvement of the structural, thermal, and mechanical properties of polyurethane adhesives with nanoparticles and their application to Al/Al honeycomb sandwich panels(Walter De Gruyter Gmbh, 2022) Cetin, Mehmet EminUnderstanding the relationship between core/face adhesive interface and performance of MWCNT added nanoadhesives are essential for better designing and fabrication of aluminum honeycomb sandwich panels. In this study, we used multi-walled carbon nanotubes (MWCNTs) to prepare enhanced interfacial adhesion between honeycomb core and aluminum facesheet. MWCNTs are first introduced to isocyanate, and then MWCNTs/isocyanate blend poured into polyol to produce MWCNTs reinforced polyurethane (PU) nanoadhesives. The relationship between core/face adhesive interface and performance of MWCNT added nanoadhesives are investigated in detail in terms of thermogravimetric analyses (TGA), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, edge-wise compression tests, flat-wise tensile tests and three-point bending tests The experimental results showed that the MWCNT addition to PU adhesive led to enhanced thermal stability, flat-wise tensile strength and edge-wise compression strength for sandwich structures. This study gives a significant reference indicator on the fabrication of an improved core/face interface for obtaining sandwich panels with desired mechanical properties.Öğe Improvement of the structural, thermal, and mechanical properties of polyurethane adhesives with nanoparticles and their application to Al/Al honeycomb sandwich panels(Walter De Gruyter Gmbh, 2022) Cetin, Mehmet EminUnderstanding the relationship between core/face adhesive interface and performance of MWCNT added nanoadhesives are essential for better designing and fabrication of aluminum honeycomb sandwich panels. In this study, we used multi-walled carbon nanotubes (MWCNTs) to prepare enhanced interfacial adhesion between honeycomb core and aluminum facesheet. MWCNTs are first introduced to isocyanate, and then MWCNTs/isocyanate blend poured into polyol to produce MWCNTs reinforced polyurethane (PU) nanoadhesives. The relationship between core/face adhesive interface and performance of MWCNT added nanoadhesives are investigated in detail in terms of thermogravimetric analyses (TGA), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, edge-wise compression tests, flat-wise tensile tests and three-point bending tests The experimental results showed that the MWCNT addition to PU adhesive led to enhanced thermal stability, flat-wise tensile strength and edge-wise compression strength for sandwich structures. This study gives a significant reference indicator on the fabrication of an improved core/face interface for obtaining sandwich panels with desired mechanical properties.Öğe Investigation of carbon nanotube reinforcement to polyurethane adhesive for improving impact performance of carbon fiber composite sandwich panels(Elsevier Sci Ltd, 2022) Cetin, Mehmet EminIn this study, the development of a polyurethane adhesive by using carbon nanotubes (CNT) to enhance the lowvelocity impact behavior of aluminum honeycomb sandwich composite structures was investigated. The interaction of CNT and polyurethane for the impact behavior of sandwich composite panels is the main originality of this paper. The fabrication of carbon fiber reinforced composite (CFRC) sandwich structures was conducted using different polyurethane (PU) adhesives and different honeycomb cell sizes. CFRC sandwich structures were fabricated with multi-walled carbon nanotube (MWCNT) added and neat PU adhesives, 6.78 and 10.39 mm honeycomb cell sizes, and carbon fiber prepregs. Neat and nanotube added PU adhesives with MWCNT at reinforcement of 0.1% and 0.2% by weight percent were prepared. Sandwich composite panels were manufactured using the hot pressing method. Specimens of 100 x 100 mm were cut from the sandwich panels, and low-velocity impact tests were conducted at 100 J initial impact energy according to ASTM D7136 standard. After experiments, load-deflection curves, load-time, and energy-time histories were acquired. The absorbed energy values at maximum load were evaluated as a function of MWCNT content and honeycomb cell size. Specimens were sectioned from the impacted region and scanned using scanning electron and optical microscopes to analyze the damaged area. Specimens with MWCNT reinforced adhesives carried higher maximum loads compared to neat ones. CFRC sandwich structures with MWCNT added PU adhesives exhibited a 6% higher impact resistance at 100 J energy levels. Experimental results demonstrated that an increase in MWCNT loading and a decrease in PU adhesive cell size increased the maximum load values in CFRC sandwich panels. Among the nanotube added adhesives, 0.1 wt percent showed the best impact performance.Öğe Investigation of Earth's Bow Shock Characteristic Using Data Retrieved from THEMIS C Spacecraft(IEEE, 2023) Peker, Muhammed Yasin; Cetin, Mehmet EminThis study investigates the properties of the bow shock that occurs in the outermost layer of the Earth's magnetosphere. The properties of this shock wave, whose main cause is the supersonic solar winds, were investigated by analyzing the data obtained from the THEMIS C spacecraft. The data from this spacecraft, which was specially sent to the magnetosphere region by NASA, were obtained from SSCWeb (Satellite Situation Center Web) and CDAWeb (Coordinated Data Analysis Web) platforms, which are also published by NASA. These data were analyzed in Microsoft Excel and exported as statistical tables and graphs. Based on these tables and graphs, it was determined that when the THEMIS C spacecraft entered the magnetosheath region following an inbound trajectory by overcoming the bow shock and entered the magnetosphere by passing the magnetopause. A comparison of the data before and after the bow shock showed that the bow shock at the inspected time interval was quite strong and reduced the speed of the solar wind by about one-third.Öğe Micro Deep Drawability of the Superplastic Zn-22Al Alloy at a High Strain Rate and Room Temperature(Asme, 2020) Cetin, Mehmet Emin; Cora, Omer Necati; Sofuoglu, HasanThis study aimed to investigate the micro deep drawability of the Zn-22Al alloy at room temperature in which it shows superplastic properties. To this goal, first the two-step equal channel angular extrusion (ECAE) process was carried out to obtain an ultra-finegrained structure (UFG). Upon achieving the grain size of 200 nm, the formability of the alloy at room temperature and at a high strain rate was investigated both experimentally and numerically. Micro deep drawing experiments were performed at different deep drawing ratios (1.66, 1.84, 2.0, and 2.25) and for different sheet thicknesses (0.2, 0.4, and 0.6 mm). The finite element model of the micro deep drawing was also established to assess and compare the thickness variation in deep drawn parts. Results showed that the superplastic Zn-22Al alloy has a great potential in microforming applications. It was also noted that the limiting drawing ratio can be obtained as high as 2.25 in the room temperature condition.Öğe Quasi-Static tensile loading performance of Bonded, Bolted, and hybrid Bonded-Bolted Carbon-to-Carbon composite Joints: Effect of recycled polystyrene nanofiber interleaving(Elsevier Sci Ltd, 2023) Tinastepe, Mehmet Talha; Kaybal, Halil Burak; Ulus, Hasan; Erdal, Mehmet Okan; Cetin, Mehmet Emin; Avci, AhmetAlthough hybrid bolted/bonded (HBB) joints possess each joint technique's benefits, the adhesive layer performance significantly affects the load-carrying capacity of hybrid joints. Nanofiber interleaving has become an efficient solution to improve the adhesion performance of bonded and HBB joints. This paper reveals the effectiveness of polystyrene (PS) nanofibers interleaving on the mechanical properties of adhesively bonded and HBB single lap joints (SLJs). For this purpose, PS nanofibers are produced via electrospinning from wasted polymers as a nature-friendly implementation. The PS nanofiber mats were interleaved between adherends as a reinforcement layer, and specimens were tested under quasi-static tensile loading. A significant improvement was seen in the peak load value of 10% for the HBB joint, and the fracture energy of the bonded joint increased by 15% with PS nanofiber modification. The failure modes of PS-reinforced specimens developed as more gradually progressive compared to neat specimens thanks to the compatibility of the recycled PS nanofiber with the epoxy and improved adhesive layer performance with PS modification. Furthermore, the morphological analyses of post-fracture specimens were monitored to realize the damage and nano-toughness mechanisms.Öğe A statistical approach to explore cemented total hip reconstruction performance(Springer, 2018) Cetin, Mehmet Emin; Sofuoglu, HasanThis study was carried out to determine mechanical behavior and bone adaptation of total hip arthroplasty (THA) subject to concentrated and distributed muscle loads and hip contact forces during activities of walking and stair climbing. Finite element modeling of THA with different prostheses, activity and loading types was developed by adopting a statistical method. Two levels of prostheses, activity, and loading types were selected for the study. 2(3) factorial method was then pursued to design input and output data of finite element analysis. Maximum von Mises stresses were chosen to be output data on which statistical investigation was performed to investigate contribution and interaction of main factors on mechanical failure of cemented THA reconstructions by utilizing analysis of variance method (ANOVA). This study illustrated that the maximum von Mises stresses of THA showed considerable variation for main factors and their two-factor interactions.
