Browsing by Subject "Mechanical properties"

Now showing 1 - 20 of 33

Open Access
Atomic strings of group IV, III-V, and II-VI elements
(American Institute of Physics, 2004) Tongay, S.; Durgun, Engin; Çıracı, Salim
A systematic first-principles study of atomic strings made by group IV, III-V, and II-VI elements has revealed interesting mechanical, electronic, and transport properties. The double bond structure underlies their unusual properties. We found that linear chain of C, Si, Ge, SiGe, GaAs, InSb, and CdTe are stable and good conductor, although their parent diamond (zincblende) crystals are covalent (polar) semiconductors but, compounds SiC, BN, AlP, and ZnSe are semiconductors. First row elements do not form zigzag structures.
Open Access
Bio-based polymer nanocomposites based on layered silicates having a reactive and renewable intercalant
(Wiley, 2013) Albayrak, O.; Şen, S.; Çaylbox, G.; Ortaç, B.
Soybean oil-based polymer nanocomposites were synthesized from acrylated epoxidized soybean oil (AESO) combined with styrene monomer and montmorillonite (MMT) clay by using in situ free radical polymerization reaction. Special attention was paid to the modification of MMT clay, which was carried out by methacryl-functionalized and quaternized derivative of methyl oleate intercalant. It was synthesized from olive oil triglyceride, as a renewable intercalant. The resultant nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of increased nanofiller loading in thermal and mechanical properties of the nanocomposites was investigated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The nanocomposites exhibited improved thermal and dynamic mechanical properties compared with neat acrylated epoxidized soybean oil based polymer matrix. The desired exfoliated nanocomposite structure was achieved when the OrgMMT loading was 1 and 2 wt % whereas partially exfoliated nanocomposite was obtained in 3 wt % loading. It was found that about 400 and 500% increments in storage modulus at glass transition and rubbery regions, respectively were achieved at 2 wt % clay loading compared to neat polymer matrix while the lowest thermal degradation rate was gained by introducing 3 wt % clay loading. © 2013 Wiley Periodicals, Inc.
Open Access
Design and fabrication of auxetic PCL nanofiber membranes for biomedical applications
(Elsevier, 2017-12) Bhullar, S. K.; Rana, D.; Lekesiz, H.; Bedeloglu, A. C.; Ko, J.; Cho, Y.; Aytac Z.; Uyar, Tamer; Jun, M.; Ramalingam, M.
The main objective of this study was to fabricate poly (ε-caprolactone) (PCL)-based auxetic nanofiber membranes and characterize them for their mechanical and physicochemical properties. As a first step, the PCL nanofibers were fabricated by electrospinning with two different thicknesses of 40 μm (called PCL thin membrane) and 180 μm (called PCL thick membrane). In the second step, they were tailored into auxetic patterns using femtosecond laser cut technique. The physicochemical and mechanical properties of the auxetic nanofiber membranes were studied and compared with the conventional electrospun PCL nanofibers (non-auxetic nanofiber membranes) as a control. The results showed that there were no significant changes observed among them in terms of their chemical functionality and thermal property. However, there was a notable difference observed in the mechanical properties. For instance, the thin auxetic nanofiber membrane showed the magnitude of elongation almost ten times higher than the control, which clearly demonstrates the high flexibility of auxetic nanofiber membranes. This is because that the auxetic nanofiber membranes have lesser rigidity than the control nanofibers under the same load which could be due to the rotational motion of the auxetic structures. The major finding of this study is that the auxetic PCL nanofiber membranes are highly flexible (10-fold higher elongation capacity than the conventional PCL nanofibers) and have tunable mechanical properties. Therefore, the auxetic PCL nanofiber membranes may serve as a potent material in various biomedical applications, in particular, tissue engineering where scaffolds with mechanical cues play a major role.
Open Access
The effects of surface treatment on optical and vibrational properties of stain-etched silicon
(Pergamon Press, 1995) Kalem, Ş.; Göbelek, D.; Kurtar, R.; Mısırlı, Z.; Aydınlı, A.; Ellialtioǧlu, R.
The effects of surface treatment on optical and vibrational properties of porous silicon. (por-Si) layers grown on p-type Si wafers by electroless etching technique were studied by FTIR spectroscopy and photoluminescence (PL). The results indicate a correlatiora between the PL intensity and the strength of the absorption bands induced by mulltihydride complexes (SiHn, n ≥ 2). However, similar correlation was also established for monohydride species as evidenced from the layers containing no multihydrides. Furthermore, a new band is observed at 710 cm-1 and assigned to multihydrides suggesting a ne it, local bonding environment in these layers. © 1995.
Open Access
Elastic and optical properties of sillenites: First principle calculations
(Taylor & Francis, 2020-04) Koç, H.; Palaz, S.; Şimşek, Ş.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present paper, we have investigated the electronic structure of some sillenites - Bi12MO20 (M = Ti, Ge, and Si) compounds based on the density functional theory. The mechanical and optical properties of Bi12MO20 have also been computed. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work. The band gap trend in Bi12MO20 can be understood from the nature of their electronic structures. The obtained electronic band structure for all Bi12MO20 compounds is semiconductor in nature. Similar to other oxides, there is a pronounced hybridization of electronic states between M-site cations and anions in Bi12MO20. Based on the obtained electronic structures, we further calculate the frequency-dependent dielectric function and other optical functions.
Open Access
Electrically unbiased driven airborne capacitive micromachined ultrasonic transducer design
(IEEE, 2012) Ünlügedik, Aslı; Atalar, Abdullah; Kocabaş, Coşkun; Oğuz, H. Kağan; Köymen, Hayrettin
We present a design method for airborne capacitive micromachined ultrasonic transducers (CMUT). We use an equivalent lumped element circuit to model both electrical and mechanical properties of CMUT and analyze it in frequency domain using harmonic balance approach. We use this method to design CMUTs for large transmitted power generation at low drive voltage amplitude. We determine the dimensions of an airborne CMUT using the proposed method that works at 30 kHz with 5 mm radius, 240 μm membrane thickness and 11.8 μm effective gap height. The CMUT is designed such that an atmospheric depression of 70% of effective gap height is maintained. © 2012 IEEE.
Open Access
Electronic and elastic properties of the multiferroic crystals with the Kagome type lattices -Mn3V2O8 and Ni3V2O8: First principle calculations
(Taylor & Francis, 2019-08-16) Koç, H.; Palaz, S.; Mamedov, Amirullah M.; Özbay, Ekmel
The electronic, mechanical, and optical properties of the Kagome staircase compounds, Mn3V2O8 and Ni3V2O8, have been investigated using the VASP (Vienna ab-initio Simulation Program) that was developed within the density functional theory (DFT). The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. The electronic band structures for both compounds and total and partial density of states corresponding to these band structures have been calculated. Spin up (spin down) Eg values for Mn3V2O8 and Ni3V2O8 compounds are 0.77 eV indirect (3.18 direct) and 1.58 eV indirect (0.62 eV) direct, respectively. The band gaps of both compound is in the d-d character. Bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropic factors, sound velocity, and Debye temperature were calculated and interpreted.
Open Access
Electronic properties of spin excitation in multiferroics with a spinel structure: first principles calculation
(Taylor & Francis, 2019-06-04) Koç, H.; Palaz, S.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present work, the structural, electronic and mechanical properties of LiVCuO4 and LiCu2O4 spinel type multiferroics have been investigated by means of first principles calculations. The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. The structural optimization of these multiferroics compounds has been performed by using VASP-code, and the lattice parameters and magnetic moments have been calculated. From our calculation, it has been determined that the LiVCuO4 compound is a narrow band gap semiconductor, while the LiCu2O4 compound is metallic in nature. Considering the spin states from the electronic band structure and density of the state (DOS) of the LiVCuO4 compound, it has been identified that Eg=1.87 eV for spin up and Eg=0.37 eV for spin down. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work.
Open Access
Evaluate of braze joint strength and microstructure characterize of titanium-CP with Ag-based filler alloy
(2012) Ganjeh, E.; Sarkhosh H.; Khorsand H.; Sabet H.; Dehkordi, E.H.; Ghaffari, M.
This research investigates the influences of brazing parameters (temperature and time) on microstructures and the mechanical properties of commercially pure (CP) titanium sheet when it is brazed with CBS34 (Ag-20Cu-22Zn-24Cd) braze filler foil. Brazing was performed in a conventional atmosphere control furnace. The brazing temperatures and holding times employed in this study were 800-870°C and 10-20min, respectively. The qualities of the brazed joints were evaluated by ultrasonic test and the microstructure and phase constitution of the bonded joints were analyzed by means of metallography, scanning electron microscope (SEM) and X-ray diffraction (XRD). The mechanical properties of brazed joints were evaluated by microhardness and shear tests. The diffusion between Ti, Ag, Cu, Zn and Cd from substrate and braze alloy, developed a strong reaction between each other. A number of intermetallic phases, such as TiCu and Ti2Cu in the Ag-Zn solid solution matrix have been identified especially at 870°C - 20min. Both the brazing temperature and the holding time are critical factors for controlling the microstructure and hence the mechanical properties of the brazed joints. The optimum brazing parameters was achieved at 870°C - 20min. Based on the shear test result, all cracks propagate along the brittle intermetallic compounds like Ti2Cu in the reaction layer which typically are composed of quasi-cleavage (Ag-Zn matrix) and brittle appearance. © 2012 Elsevier Ltd.
Open Access
First principles prediction of the elastic, electronic, and optical properties of Sb 2S 3 and Sb 2Se 3 compounds
(2012) Koc H.; Mamedov, A.M.; Deligoz, E.; Ozisik H.
We have performed a first principles study of structural, mechanical, electronic, and optical properties of orthorhombic Sb 2S 3 and Sb 2Se 3 compounds using the density functional theory within the local density approximation. The lattice parameters, bulk modulus, and its pressure derivatives of these compounds have been obtained. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valence electrons and the effective optical dielectric constant are calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data. © 2012 Elsevier Masson SAS. All rights reserved.
Open Access
Genetically-tunable mechanical properties of bacterial functional amyloid nanofibers
(American Chemical Society, 2017) Abdelwahab, M. T.; Kalyoncu, E.; Onur, T.; Baykara, M. Z.; Seker U.O.S.
Bacterial biofilms are highly ordered, complex, dynamic material systems including cells, carbohydrates, and proteins. They are known to be resistant against chemical, physical, and biological disturbances. These superior properties make them promising candidates for next generation biomaterials. Here we investigated the morphological and mechanical properties (in terms of Young’s modulus) of genetically-engineered bacterial amyloid nanofibers of Escherichia coli (E. coli) by imaging and force spectroscopy conducted via atomic force microscopy (AFM). In particular, we tuned the expression and biochemical properties of the major and minor biofilm proteins of E. coli (CsgA and CsgB, respectively). Using appropriate mutants, amyloid nanofibers constituting biofilm backbones are formed with different combinations of CsgA and CsgB, as well as the optional addition of tagging sequences. AFM imaging and force spectroscopy are used to probe the morphology and measure the Young’s moduli of biofilm protein nanofibers as a function of protein composition. The obtained results reveal that genetically-controlled secretion of biofilm protein components may lead to the rational tuning of Young’s moduli of biofilms as promising candidates at the bionano interface.
Open Access
Heat-damage assessment of carbon-fiber-reinforced polymer composites by diffuse reflectance infrared spectroscopy
(John Wiley & Sons, Inc., 2005) Dara, I. H.; Ankara, A.; Akovali, G.; Süzer, Şefik
Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to assess the effects of heat damage on carbon-fiber-reinforced polymer composites. Moisture-saturated graphite-epoxy laminates with a quasi-isotropic lay-up were heat-damaged above their upper service temperatures. The loss of matrix-dominated mechanical properties due to heat exposure was investigated in the laboratory under environmental testing conditions with mechanical tests, ultrasonic C-scanning, and DRIFT spectroscopy. The reduction of the mechanical strength of the composite materials was accompanied by an increase in the carbonyl band integral and a decrease in the phenyl ratio and hydroxyl and hydrocarbon band integrals, as shown by the DRIFT spectra. DRIFT was confirmed to be more effective than ultrasonic inspection in evaluating the extent of heat damage, and a good correlation was found between the mechanical test results and DRIFT spectra. © 2005 Wiley Periodicals, Inc.
Open Access
Increasing Ti-6Al-4V brazed joint strength equal to the base metal by Ti and Zr amorphous filler alloys
(2012) Ganjeh, E.; Sarkhosh H.; Bajgholi, M.E.; Khorsand H.; Ghaffari, M.
Microstructural features developed along with mechanical properties in furnace brazing of Ti-6Al-4V alloy using STEMET 1228 (Ti-26.8Zr-13Ni-13.9Cu, wt.%) and STEMET 1406 (Zr-9.7Ti-12.4Ni-11.2Cu, wt.%) amorphous filler alloys. Brazing temperatures employed were 900-950 °C for the titanium-based filler and 900-990 °C for the zirconium-based filler alloys, respectively. The brazing time durations were 600, 1200 and 1800 s. The brazed joints were evaluated by ultrasonic test, and their microstructures and phase constitutions analyzed by metallography, scanning electron microscopy and X-ray diffraction analysis. Since microstructural evolution across the furnace brazed joints primarily depends on their alloying elements such as Cu, Ni and Zr along the joint. Accordingly, existence of Zr 2Cu, Ti 2Cu and (Ti,Zr) 2Ni intermetallic compounds was identified in the brazed joints. The chemical composition of segregation region in the center of brazed joints was identical to virgin filler alloy content which greatly deteriorated the shear strength of the joints. Adequate brazing time (1800 s) and/or temperature (950 °C for Ti-based and 990 °C for Zr-based) resulted in an acicular Widmanstätten microstructure throughout the entire joint section due to eutectoid reaction. This microstructure increased the shear strength of the brazed joints up to the Ti-6Al-4V tensile strength level. Consequently, Ti-6Al-4V can be furnace brazed by Ti and Zr base foils produced excellent joint strengths. © 2012 Elsevier Inc. All rights reserved.
Open Access
Intimate relationship between structural deformation and properties of single-walled carbon nanotubes
(Cambridge, 2002) Yıldırım, Taner; Gülseren, Oğuz; Çıracı, Salim
Carbon nanotubes continue to surprise scientists with their novel properties. Recently we have discovered many intimate relationships between structural deformation and the properties of single-walled nanotubes (SWNT), that could be important in technological applications. From first-principles we show that by using pressure, carbon nanotubes can be covalently joined to form one and two-dimensional networks of interlinked nanotubes. We also find that the band gap of an insulating nanotube can be engineered by elliptical distortion, which is found to be in the elastic range. This could allow the fine-tuning of the properties of SWNTs via reversible deformation and ultimately lead to variable quantum devices. Finally, we have very recently shown that the chemical reactivity of nanotubes can be tuned by elliptical deformation, which may provide a way to attach various atoms such as H and metals to a specific location on a nanotube.
Open Access
Investigation on braze joint strength and microstructure of Ti-CP with Ag and Ti base filler alloys
(American Welding Society, 2012) Ganjeh, E.; Khorsand H.; Sarkhosh H.; Ghaffari, M.; Sabet H.; Dehkordi, E.H.
This research investigates influences of brazing parameters (brazing alloy, temperature and time) on microstructures and mechanical properties of a commercially pure (CP) titanium sheet which is brazed with CBS 34 (Ag-based) and STEMET 1228 (Ti-based) braze-filler foils. Brazing was performed in a conventional inert furnace at temperature ranges of 800-870°C and 10-30 minutes for holding times. Qualities of the brazed joints were evaluated by ultrasonic testing, and then, microstructure and phase constitution of the bonded joints were analyzed by means of metallography, scanning electron microscope (SEM), and X-ray diffraction (XRD). Mechanical properties of brazed joints were evaluated by shear testing. Diffusion of titanium from substrate to filler alloy developed a strong reaction between them. A number of phases such as TiCu, Ti 2Cu, TiAg, Ag-Zn solid solution matrix (for Ag-based brazed samples) and Ti 2Cu, (Ti,Zr) 2Ni, Zr 2Cu (for Ti-based brazed samples) have been identified. The optimum brazing parameters were achieved at a temperature of 870 °C-20 min for CBS 34 and 870 °C-30 min for STEMET 1228. The specimen using STEMET 1228 braze alloy demonstrates best bonding strength (equal to Ti-CP tensile strength). Copyright 2012 ASM International® All rights reserved.
Open Access
Mechanical and chemical properties of nanoparticle-coated E-glass fibers for composites applications
(2023-07) Ahmed, Md Kawsar
Glass fibers are the most extensively employed reinforcement materials in the fiber-reinforced composites field owing to their superior mechanical properties with cost-effectiveness. The mechanical and chemical properties of the composites are greatly dependent upon the reinforcement materials. In order to enhance the performance of composites, it is necessary to improve the mechanical property of the reinforcement materials, i.e., glass fibers. In this thesis, the mechanical and chemical properties of E-glass fibers were investigated via the incorporation of metal oxide nanoparticles. As part of this process, E-glass fibers were dip-coated with nanoparticle solutions using titania (TiO2), silica (SiO2), and zirconia (ZrO2) nanoparticles. Microscopic and spectroscopic analysis proved the presence of nanoparticles on the surface of the fibers. Tensile tests were conducted on bare and nanoparticle-coated fibers to see the effect of coating and the concentration of nanoparticles over the fiber’s surface. Weibull statistical analysis was carried out on bare and coated fibers to see the effect of stress on the probability of failures of the E-glass fibers. A fractographic study was also carried out on E-glass fibers to see the effect of tensile strength on the mirror region of the fracture surface. Additionally, chemical analysis was also carried out to see the resistivity of the fibers in a highly alkaline environment. The results suggest that glass fibers coated with TiO2 nanoparticles improved the tensile strength of fibers up to 11.7% by providing a lower probability of failure. On the other hand, coating with SiO2 nanoparticles had a slightly negative impact on the strength of fibers due to the lower quality of coating, leading to a decrease in the tensile strength and an increase in the probability of failure. Moreover, ZrO2 nanoparticles were found effective in providing resistance against the corrosion to the glass fibers in an alkaline environment for up to 4 days of dwelling. Nanoparticle-coated E-glass fibers are expected to improve the mechanical and chemical properties of glass fiber-reinforced composites for various industrial applications in the future.
Open Access
The mechanical, electronic and optical properties of Sn2P2S6 compound in different phases
(Taylor & Francis, 2021-12-01) Koc, H.; Palaz, S.; Simsek, S.; Mamedov, Amirullah M.; Ozbay, Ekmel
In present paper, the structural, mechanical, and electronic properties of the Sn2P2S6 compound under different pressures by the density functional methods in the generalized gradient approximation have been examined in the ferroelectric (Pc) and paraelectric (P2_1/c) phases. The lattice parameters, mechanical properties, electronic bands structures and partial density of states for both phases are presented and analyzed. The nonlinear optical properties and electro-optic effects of Sn2P2S6-Pc have been studied by the density functional theory in the local density approximation. Our structural estimation and some other results are in agreement with the available experimental and theoretical data. We present calculations of the frequency-dependent complex dielectric function (ω) and the second harmonic generation response coefficient χ(2) (−2ω, ω, ω) over a large frequency range. The electronic linear electro-optic susceptibility χ(2) (−ω, ω, 0) is also evaluated below the band gap. These results are based on a series of the LDA calculation. The results for χ(2) (−ω, ω, 0) are in agreement with the experiment below the band gap and those for χ(2) (−ω, ω, 0) are compared with the experimental data where available.
Open Access
Mechanical, electronic, and optical properties of the A4B6 layered ferroelectrics: ab initio calculation
(Wiley, 2015) Koc, H.; Simsek S.; Palaz S.; Oltulu, O.; Mamedov, A. M.; Özbay, Ekmel
We have performed a first principles study of the structural, elastic and electronic properties of orthorhombic SnS and GeS compounds using the density functional theory within the local density approximation. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. All of the calculated modulus and Poisson's ratio for SnS were less than the same parameters for GeS. Our calculations have discovered the large anisotropy of elastic parameters in the (100) and (010)-planes for both compounds. The band structures of orthorhombic SnS and GeS have been calculated along high symmetry directions in the first Brillouin zone (BZ). The calculation results for the band gap of Sn(Ge)S gave Eg = 0.256 eV (0.852 eV) and has an indirect character for an interband transition. The real and imaginary parts of dielectric functions and (by using these results) the optical constant such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant were calculated. All of the principal features and singularities of the dielectric functions for both compounds were found in the energy region between 2 eV and 20 eV. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Mechanochemical activation and patterning of an adhesive surface toward nanoparticle deposition
(American Chemical Society, 2015) Baytekin, H. T.; Baytekin, B.; Huda, S.; Yavuz, Z.; Grzybowski, B. A.
Mechanical pulling of adhesive tape creates radicals on the tapes surface. These radicals are capable of reducing metal salts to the corresponding metal nanoparticles. In this way, the mechanically activated tape can be decorated with various types of nanoparticles, including Au, Ag, Pd, or Cu. While retaining their mechanical properties and remaining "sticky, " the tapes can exhibit new properties derived from the presence of metal nanoparticles (e.g., bacteriostaticity, increased electrical conductivity). They can also be patterned with nanoparticles only at selective locations of mechanical activation.
Open Access
Metal oxide nanoparticle coatings for enhanced mechanical and chemical properties of glass fibers
(2024-01) Kurucu, Arda
Glass fibers are one of the most used reinforcement fibers in composites. They have highly demanded properties such as good mechanical properties, impact resistance, high strength-to-weight ratio, and cost-efficiency. Glass fiber composites are utilized in many fields such as aerospace, automotive, and maritime. Glass fibers are one of the components in the composite structure aside from the resin matrix and their properties heavily affect the overall properties of the composite material. By improving the properties of glass fiber reinforcement, composite performance can also be improved. Industrial-scale fabrication of glass fiber re-quires the construction of a certain glass-type exclusive factory. This study aims to have an alternative solution to meet the strength demands of industry with a relatively simple modification to the production process of E-glass fibers. In this study, the mechanical, chemical, and dielectric properties of glass fibers are altered via metal oxide nanoparticle coating. A thin layer of ZnO coating is applied onto the E-glass fibers via the dip coating method. Through spectroscopic and SEM characterization, the presence of ZnO coating is confirmed, and the effect of this coating on mechanical properties is investigated through micromechanical analysis. ZnO coating proved to increase the tensile strength of E-glass fibers by 14.67%. In addition to mechanical improvements, the ZnO nanoparticles proved to be effective in corrosion resistance. Their corrosion-resistant properties are investigated using an acidic environment. Coated fibers are then used to manufacture a glass fiber felt composite to investigate the effect of nanoparticles on signal transmittance properties of glass fiber composites. In addition to the modification of common E-glass fibers, a novel pure silica fiber fabrication method for advanced aerospace composite applications is developed. Principles of optical fiber production are utilized to fabricate structural high-purity fiber with unconventional fuel gas heating sources. This study aims to obtain know-how and knowledge on the production of pure silica fiber. To fabricate the pure silica fiber, a novel custom fabrication setup is designed and manufactured. This setup includes a custom heating system, a custom capstan tractor, and a custom feeding system.