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Boron nitride-MWCNT/epoxy hybrid nanocomposites: Preparation and mechanical properties
(ELSEVIER SCIENCE BV, 2014) Ulus, Hasam; Ustun, Tugay; Eskizeybek, Volkan; Sahin, Omer Sinan; Avci, Ahmet; Ekrem, Mursel
In this study, production and mechanical properties of hybrid nanocomposites have been investigated. Hybrid nanocomposites are consisting of boron nitride nanoplatelets (BN) and multiwall carbon nanotubes (MWCNT) embedded in epoxy resin. The BN and MWCNT were mixed to epoxy resin in different weight fractions and mixtures were utilized for tensile test specimen production. The synthesized BN and produced hybrid nanocomposites were characterized by SEM, TEM, XRD, FT-IR and TGA analyses. The elasticity modulus and tensile strength values were obtained via tensile tests. The fracture morphologies were investigated after tensile test by means of scanning electron microscopy. (C) 2013 Elsevier B.V. All rights reserved.
Effect of Hardness upon Temperature Rise of Steel Specimens during Bending Fatigue by Using Infrared Thermography
(TRANS TECH PUBLICATIONS LTD, 2011) Selek, Murat; Sahin, Omer Sinan; Kahramanli, Sirzat
In this study, the effects of hardness on temperature increase of ST 37 steel during fatigue loading were investigated. Steel specimens are made of ST 37 steel and subjected to heat treatment to obtain different hardness. The specimens were subjected to reverse bending fatigue loading and the specimens were observed by using a infrared (IR) camera during the test. The obtained thermal images were recorded by FUR E45 IR camera and then transferred to the image processing program developed by using MATLAB. Thus after image processing, thermal values used to detect the temperature rise of the surface of the steel specimen under fatigue loading were obtained. During the fatigue, the material is subjected to strain energy input which result in plastic or/and elastic deformation. This event results in an increase of temperature within material. The energy conservation requires that the generated heat shows itself as heat transfer by conduction, convection and radiation and internal energy increase. Besides, if the material has undergone plastic deformation, an additional term which accounts this effect should be included within energy conservation equation. In order to observe the effect of plastic deformation upon temperature increase of material, the ability of plastic deformation has been changed through the change of hardness and the thermal variations during fatigue has been investigated.
Enhancement of Flexural and Shear Properties of Carbon Fiber/Epoxy Hybrid Nanocomposites by Boron Nitride Nano Particles and Carbon Nano Tube Modification
(KOREAN FIBER SOC, 2015) Ulus, Hasan; Sahin, Omer Sinan; Avci, Ahmet
In this study, the effect of boron nitride nano particle (BNNP) and/or carbon nanotube (CNT) adding for epoxy modification upon tensile, flexural and shear properties of epoxy resin and carbon fiber (CF) laminated nanocomposites were investigated. Epoxy based polymer nanocomposites were prepared by conventional casting in stainless steel mold and the CF/epoxy laminated nanocomposites were produced via vacuum assisted resin transfer molding (VARTM). Experimental results showed that the tensile, shear and flexural properties of epoxy nanocomposites and CF/epoxy laminated nanocomposites considerably increased by adding nanoparticle. Scanning electron microscopy (SEM) was utilized in order to determine damage formation of experimented nanocomposite samples. The results of laboratory tests showed that the highest values of mechanical properties were obtained for BNNP-CNT hybrid nanocomposite specimens. Bending stiffness increasement values of BNNP-CNT/Epoxy and BNNP-CNT-Epoxy/CF achieved by 27.5 %, and 38.5 %, respectively. Shear strength increasement for BNNP-CNT/Epoxy and BNNP-CNT-Epoxy/CF were determined by 23 %, and 90 %, respectively.
Enhancement of Wear and Friction Characteristics of Epoxy Resin by Multiwalled Carbon Nanotube and Boron Nitride Nanoparticles
(TAYLOR & FRANCIS INC, 2015) Duzcukoglu, Hayrettin; Ekinci, Serafettin; Sahin, Omer Sinan; Avci, Ahmet; Ekrem, Mursel; Unaldi, Mahmut
Epoxy resins are widely used in engineering applications. However, their low thermal stability limits their usage at high sliding velocities and loads. The mechanical properties and thermal stability of a machine element subjected to friction and wear are very important. In this study, friction and tribology behaviors of multiwalled carbon nanotubes (MWCNTs) and boron nitride (BN)-modified epoxy resin have been investigated. Epoxy resin modified by three different nanoparticle configurations, 0.3% MWCNT, 0.5% BN, and 0.5% MWCNT/0.3% BN, was investigated. The tribological characteristics of nanoparticle-modified epoxy resin were compared with properties of neat resin. The friction and tribological behavior of modified epoxy resin were tested using a ball-on-disc test stand at 1.2 and 1.5 ms(-1) sliding velocities under 10 N applied load. The tests were done under dry condition and 1,800 m distance. The friction coefficient, wear loss, and temperature increase during testing were recorded and compared with that obtained for neat epoxy. It is observed that nanoparticle modification resulted in enhanced wear resistance and a reduction in friction coefficient and working temperatures.
Experimental and statistical analysis of low velocity impact response of filament wound composite pipes
(ELSEVIER SCI LTD, 2018) Gemi, Lokman; Kayrici, Mehmet; Uludag, Muhammet; Gemi, Dilek Soylu; Sahin, Omer Sinan
Nowadays, filament wound composite pipes (GRP) are used as a structural element in many applications such as natural gas and oil transmission lines, and portable bridge constructions for military purposes. GRP pipes can expose to impact loading from various causes. This loading can cause an invisible level of damage. Thus, the detection and evaluation of such damages are of great importance. In this study, the low velocity impact response of (+/- 55 degrees)(3) filament wound E-glass/epoxy composite pipes has been studied. The pipes have been subjected to drop weight impact loading with various impact energies. The force-time and force-displacement relations have been examined. The impact damage formation was also evaluated. It is concluded that the damage development in the pipes is controlled by displacement trough radial direction. The obtained results were evaluated statistically by means of Weibull approach. Microscopy analysis of impacted region revealed that debonding, radial cracks, transfer cracks and delamination damage modes are the main observed damage modes.
Experimental investigation of fatigue damage formation of hybrid pipes subjected to impact loading under internal pre-stress
(ELSEVIER SCI LTD, 2017) Gemi, Lokman; Sahin, Omer Sinan; Akdemir, Ahmet
In this study, the effect of impact loading upon fatigue behavior of hybrid composite pipes has been investigated. The composite pipes were subjected to tangential pre-stress as 3-48 MPa according to ANSI/AWWA C950 standard than, subjected to low velocity impact at 20 J. The impact pre-damaged pipes then subjected to cyclic loading at 50% sigma ult in accordance with ASTM D 2992-06. It is also observed that increasing the tangential pre-stress decreases impact damage area and increases fatigue life of the pipe. It is also showed that impact pre-damage are not effective on the fatigue life of the pipe at the pre-stress level of 24 MPa. (C) 2017 Elsevier Ltd. All rights reserved.
Fatigue Behavior and Damage Assessment of Stainless Steel/Aluminum Composites
(ASME-AMER SOC MECHANICAL ENG, 2011) Eskizeybek, Volkan; Avci, Ahmet; Akdemir, Ahmet; Sahin, Omer Sinan
Fatigue crack growth and related damage mechanisms were investigated experimentally in a stainless steel/aluminum laminated composite with middle through thickness crack, and two different fracture mechanics approaches applied to the composite to reveal their differences under fatigue loading. The laminated composite material, which has a unidirectional continuous AISI 304 stainless steel as fibers and Al 1060 as matrix, was produced by using diffusion bonding. Fatigue tests were conducted in accordance with ASTM E 647. The relationships between fatigue crack growth rate (da/dN), stress intensity factor (Delta K), and strain energy release rate (Delta G) were determined; and damage behavior was discussed. Both linear elastic fracture mechanics (LEFM) and compliance method were used, and the results were compared with each other. It is found that as the crack propagates, the LEFM overestimates the Delta G values. Interlaminar and fiber/matrix interface damage were evaluated by fractographic examination. [DOI: 10.1115/1.4003490]
Fatigue behavior of surface cracked filament wound pipes with high tangential strength in corrosive environment
(ELSEVIER SCI LTD, 2007) Avci, Ahmet; Sahin, Omer Sinan; Tarakcioglu, Necmettin
The aim of this study is to examine the corrosion fatigue behavior of filament wound composite pipes with a surface crack under alternating internal pressure. The filament wound pipes are composed of multi-layered E-glass/epoxy composites with a [+/- 75 degrees](3) lay-up. The surface notches were formed on the outer surface of the pipe along the pipe axis. Dilute (0.6 M) HCl acid was applied to the surface crack region by a corrosion cell mounted on the outer surface of the pipe. The results of an experimental investigation into the corrosion fatigue tests are conducted to observe the oil leakage failure and the crack propagation of the composite pipe subjected internal pressure loading with an open ended condition in which the pipe can be deformed freely in the axial direction. The internal pressure was generated by conventional hydraulic oil for fatigue loading. The fatigue tests are performed at 0.42 Hz frequency and a stress ratio of R = 0.05 in accordance with ASTM D-2992 standard. The oil leakage from the crack tip was observed after the crack propagation reached to the critical stress intensity level. The fatigue crack propagation behavior with the environment exposure was strongly dependent on the crack parameters such as crack-depth ratio and crack-aspect ratio. The micro structure of the fracture surface with the effect of environment and the fatigue loading were also observed. (c) 2006 Elsevier Ltd. All rights reserved.
The Free Vibration Behaviors Of Hybrid Stacked Composite Plates With A Hole
(Selçuk Üniversitesi, 2014) Sahin, Omer Sinan; Gunes, Aydin
In this study, the free vibration characteristics of hybrid stacked fiber reinforced composite laminates with a hole was studied by using finite elements method. The hybrid composite laminates are composed of four layers with symmetrical and antisymmetrical sequences. The fiber reinforcement angles of plates are (15/-15)2, (30/-30)2, (45/-45)2 and (60/-60)2. The natural frequencies of hybrid composites were obtained for four different boundary conditions and different hole diameters and the results were presented in graphical form.
Friction and Wear Performance of Epoxy Resin Reinforced With Boron Nitride Nanoplatelets
(ASME, 2018) Ekrem, Mursel; Duzcukoglu, Hayrettin; Senyurt, Muhammet Ali; Sahin, Omer Sinan; Avci, Ahmet
In this study, the effects of addition of boron nitride nanoplatelets (BNNPs) upon friction and wear behavior of epoxy resin have been investigated by using pin-on-disk test. It has been reported in the literature that certain amounts of BNNP addition can be useful for enhancement of mechanical properties. Therefore, it is very important to obtain the effect of such addition upon friction and wear performance of epoxy resin. BNNPs have been incorporated at 0.3-0.5-0.7-1 wt %. It is shown that BNNP addition results in decrease in friction coefficient and wear. It is also shown that the best results are obtained with 0.5% nanoplatelet addition. It is also observed that heat conduction of epoxy resin is enhanced by the nanoplatelet addition.
Investigation of Bending Fatigue of Composite Plates by Using Infrared Thermography
(TRANS TECH PUBLICATIONS LTD, 2011) Sahin, Omer Sinan; Selek, Murat; Kahramanli, Sirzat
In this study, the temperature rise of composite plates with a hole during fatigue loading was investigated. Woven glass/epoxy composite plates with eight plies were subjected to bending fatigue loading and materials were observed by using a thermal camera during the test. Previous works showed that a heat generation can form due to internal friction and damage formation. Therefore, a thermographic infrared imaging system was used to detect the temperature rise of composite specimens. During the tests, the thermal images of the specimens have been recorded by a thermal camera and then transferred to the image processing program which has been developed by using MATLAB. By using these thermal images, the spot temperatures of the specimen were obtained by using artificial neural networks. The obtained temperatures show local increase at places where the heat generation localized. These regions considered being the probable damage initiation sites. It is shown in this study that most probable damage initiation zones in the woven glass/epoxy composite material can be detected by using infrared thermography (IRT) approach prior to failure.
Investigation of Wear Performance of Canola Oil Containing Boric Acid under Boundary Friction Condition
(TAYLOR & FRANCIS INC, 2011) Duzcukoglu, Hayrettin; Sahin, Omer Sinan
The aim of this study is to investigate the tribological behaviors of pure canola oil and 5% boric acid-added canola oil after unexpected oil drainage. Tests were performed under 0.6 m/s sliding velocity and 80 N contact force using a pin-on-disc test stand. Tests were started with full lubrication and continued for 800 m. After that the oil was drained from the oil tank and the system was run for 10,000 m without lubrication. The variation of friction coefficient, contact temperature, and wear was compared for pure and boric acid-added oil. It was observed that boric acid-added oil can continue lubricating even after oil was drained from the tank.
Low-velocity impact behavior of carbon fiber/epoxy multiscale hybrid nanocomposites reinforced with multiwalled carbon nanotubes and boron nitride nanoplates
(SAGE PUBLICATIONS LTD, 2016) Ulus, Hasan; Ustun, Tugay; Sahin, Omer Sinan; Karabulut, Salim Egemen; Eskizeybek, Volkan; Avci, Ahmet
In this article, the mechanical properties and dynamic response of hybrid filler-modified epoxy/carbon fiber multiscale composites were investigated. The hybrid fillers composed of multiwalled carbon nanotubes and boron nitride nanoplates were dispersed in epoxy resin and used as matrix material. The multiscale hybrid laminated composites were stacked symmetrically consisting of 10 plies of woven carbon fibers and fabricated by vacuum infusion technique. The mechanical properties of the hybrid composites were investigated by tensile tests. Impact response and energy absorption capacity were investigated by using weight drop test method and the tests were performed according to ASTM-D-7136 standard with impact energies of 5, 10, and 15J. The impact force and displacement versus interaction time were measured. The impulsive force, energy absorption capability, and damage formation were also investigated. It is observed that when the resin is modified by nanoparticles, both strength and the % strain at fracture increase considerably. However, it is shown in the subject manuscript that the enhancement of mechanical has not fully transferred to dynamic response and energy absorption capacities of nanocomposites.
Mechanical properties and microstructure of composites produced by recycling metal chips
(SPRINGER, 2018) Aslan, Abdullah; Gunes, Aydin; Salur, Emin; Sahin, Omer Sinan; Karadag, Hakan Burak; Akdemir, Ahmet
In this study, the processing and mechanical properties of porous metal matrix composites (MMCs) composed of spheroidal cast iron chips (GGG40) and bronze chips (CuSn10) and formed by hot isostatic pressing were investigated. Bronze chips (CuSn10) were used as a matrix component, and spheroidal cast iron (GGG40) chips were used as a reinforcement component. The MMCs were produced with different CuSn10 contents (90wt%, 80wt%, 70wt%, and 60wt%). The hot isostatic pressing process was performed under three different pressures and temperatures. The produced MMCs were characterized using density tests, Brinell hardness tests, and compression tests. In addition, the consolidation mechanism was investigated by X-ray diffraction (XRD) analysis and scanning electron microscopy. The test results were compared with those for bulk CuSn10 and bulk GGG40. Mechanical tests results revealed that the metallic chips can be recycled by using hot pressing and that the mechanical properties of the produced MMCs were similar to those of bulk CuSn10. XRD and microscopy studies showed that no intermetallic compounds formed between the metallic chips. The results showed that the CuSn10 and GGG40 chips were consolidated by mechanical interlocking.
Production and mechanical characterization of prismatic shape machine element by recycling of bronze and cast-iron chips
(GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2018) Aslan, Abdullah; Salur, Emin; Gunes, Aydin; Sahin, Omer Sinan; Karadag, Hakan Burak; Akdemir, Ahmet
In this study, the production and mechanical properties of porous metal matrix composites (MMC's) by recycling of spheroid cast iron chips (GGG-40) and bronze chips (CuSn10) by hot isostatic pressing was investigated. The metal matrix composites were produced with four different CuSn10 contents, three different pressures and temperatures and effects of production parameters on porosity, hardness, flexure properties were examined. Samples were produced in prismatic shape with specified porosity. The mechanical properties were determined by Brinell and Micro Vickers hardness tests and three-point bending test. The consolidation mechanism of metallic chips was also investigated with optic microscopy. It was examined whether any second phase occurred between metallic chips by the help of XRD test. As a result of porosity test, it is found that metal matrix composites can have porosity value of as much as 20%. It is also showed that owing to excessive plastic deformation of Cu Sn10, the hardness of MMC material can be higher than bulk CuSn10. Three-point bending test showed that the flexure properties of MMC materials are is lower than that of bulk CuSn10. As a consequence, it showed that metallic chips were recycled with hot pressing successfully.
Thermal buckling behavior of cross-ply hybrid composite laminates with inclined crack
(ELSEVIER SCI LTD, 2006) Avci, Ahmet; Sahin, Omer Sinan; Ataberk, Necati
Thermal buckling analysis of symmetric and antisymmetric cross-ply laminated hybrid composite plates with an inclined crack subjected to a uniform temperature rise are presented in this paper. The first-order shear deformation theory in conjunction with variational energy method is employed in the mathematical formulation. The eight-node Lagrangian finite element technique is used for obtaining the thermal buckling temperatures of hybrid composite laminates. The effects of crack size and lay-up sequences on the thermal buckling temperatures for symmetric and antisymmetric plates are investigated. The results are shown in graphical form for various boundary conditions. (c) 2006 Elsevier Ltd. All rights reserved.
Thermal stability and adhesive strength of boron nitride nano platelets and carbon nano tube modified adhesives
(SAGE PUBLICATIONS LTD, 2018) Ekrem, Muersel; Sahin, Omer Sinan; Karabulut, Salim Egemen; Avci, Ahmet
The effect of multi-walled carbon nanotube and/or boron nitride nano platelets usage on shear strength and thermal stability of epoxy based adhesives have been investigated. Commercially available diglycidyl ether of bisphenol A based epoxy was used as matrix and reinforced by using nanofillers. The resulting adhesive was tested for its shear-lap adhesion to aluminum alloy sheets (2024-T3). The nano particles modified epoxy adhesives were characterized by Fourier transform infrared, differential scanning calorimetry, and thermal gravity analyses analysis. These characterizations revealed that incorporation of nano particles can result in enhancement in chemical stability. Single lap strength joint testing was conducted in accordance with ASTM-D-1002-10 standard. Fracture morphologies and the effects of multi-walled carbon nanotubes and boron nitride nano platelets on epoxy adhesive were investigated after shear tests by means of scanning electron microscopy. Compared to neat epoxy, increases of 30% in shear strength and 57% in energy required to break joints have been obtained by multi-walled carbon nanotube/boron nitride nano platelet modification.
ZnO-TiO2 nanocomposites formed under submerged DC arc discharge: preparation, characterization and photocatalytic properties
(SPRINGER, 2014) Avci, Ahmet; Eskizeybek, Volkan; Gulce, Handan; Haspulat, Bircan; Sahin, Omer Sinan
A rutile TiO2 (alpha-TiO2) and hexagonal wurtzite ZnO nanocomposite was directly and synchronously synthesized via arc discharge method submerged in de-ionized water. In correlation with the detailed characterization of the morphology, and crystalline structure of the prepared ZnO-TiO2 nanocomposites, the UV-visible and photoluminescence properties were studied. X-ray diffraction and transmission electron microscopy investigations revealed the co-existence of alpha-TiO2 and hexagonal wurtzite ZnO phases with the ZnO and alpha-TiO2 nanoparticles are in nanorod and nanospheres morphologies, respectively. The diameters of the synthesized nanocomposite particles are in the range of 5-70 nm. Interestingly, the as-prepared ZnO-TiO2 nanocomposite shows better photocatalytic activity for photodegradation of the methylene blue dye than both of pure ZnO and TiO2 nanocatalyts. This work would explore feasible routes to synthesize efficient metal or/and metal oxide nanocomposites for degrading organic pollutants, gas sensing or other related applications.

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