Browsing by Subject "Composites"

Now showing 1 - 20 of 22

Open Access
A mechanistic approach to determine the relationship between film structure, electronic properties, and photocatalytic activity of ALD ZnO thin films on glass gibers
(Springer, 2024-06-04) Arat, A. B.; Akyıldız, Halil I.
Atomic layer deposition (ALD), a high-conformality thin-film deposition technique, offers the opportunity to immobilize photocatalytic materials on high surface area substrates. Textile substrates are inexpensive, easily accessible materials with a fibrous nature, making them high surface area scaffolds for photocatalytic applications. This study applied ZnO thin-film coatings to fabric structures with different numbers of ALD cycles. The effect of coating thickness on the surface and electronic properties of the films and their photocatalytic properties were investigated. SEM, XRD, PL, and UV-Vis were used to examine the surface morphology, crystal structure, defects, and optical properties of the ZnO thin films. As the film thickness increased, the crystal sizes and the number of defects in the structure increased. Contact angle and Hall Effect measurements revealed that these structural defects are present on the surface of the films. Optimum wettability, mobility, and photocatalytic efficiency values were observed in the 15-nm coated samples, resulting in the highest photocatalytic activity and a turning point.
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
Bounds on size effects in composites via homogenization accounting for general interfaces
(Springer, 2020-01) Firooz, Soheil; Javili, Ali; Chatzigeorgiou, G.
This manuscript provides novel bounds and estimates, for the first time, on size-dependent properties of composites accounting for generalized interfaces in their microstructure, via analytical homogenization verified by computational analysis. We extend both the composite cylinder assemblage and Mori–Tanaka approaches to account for the general interface model. Our proposed strategy does not only determine the overall response of composites, but also it provides information about the local fields for each phase of the medium including the interface. We present a comprehensive study on a broad range of interface parameters, stiffness ratios and sizes. Our analytical solutions are in excellent agreement with the computational results using the finite element method. Based on the observations throughout our investigations, two notions of size-dependent bounds and ultimate bounds on the effective response of composites are introduced which yield a significant insight into the size effects, particularly important for the design of nano-composites.
Open Access
Conducting polymer composites of polythiophene with natural and synthetic rubbers
(Elsevier, 1996) Yigit, S.; Hacaloglu, J.; Akbulut, U.; Toppare, L.
Electrochemical synthesis of conducting polymer composites of polythiophene was achieved. Synthetic and natural rubbers were used as the insulating polymer matrices. FT-IR, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and mass spectrometry (MS) were utilized to characterize the composite blends. The conductivity measurements were done by using a standard four-probe technique. The above-mentioned methods show that the resultant composites have different properties compared to polythiophene due to interaction of the rubbers with electrochemical polymerization of thiophene, whereas the same argument is not valid for the polypyrrole synthesis via the same procedure.
Open Access
Designing tunable composites with general interfaces
(Elsevier, 2019) Saeb, S.; Steinmann, P.; Javili, Ali
In this manuscript, we employ interface enhanced computational homogenization to explore and detail on a number of unfamiliar characteristics that composites can exhibit at different length scales. Here, the interface between the constituents is general in the sense that both displacement and traction jumps across the interface are admissible. We carry out numerous computational investigations using the finite element method for a broad range of various material parameters. Our numerical results reveal that the effective response of a microstructure embedding general interfaces is intuitively unpredictable and highly complex. In particular, for certain ranges of material parameters the overall response shows insensitivity with respect to either microstructure size or stiffness-ratio between inclusion and matrix. This unique behavior is observed likewise for two- and three-dimensional unit-cells. Our findings provide a valuable guideline to design tunable composites utilizing interfaces.
Open Access
Extended general interfaces: Mori–Tanaka homogenization and average fields
(Elsevier Ltd, 2022-08-24) Firooz, S.; Chatzigeorgiou, G.; Steinmann, P.; Javili, Ali
A well-established methodology to capture interphases in heterogeneous materials is to replace them by a zero-thickness interface model. Commonly accepted interface models intuitively assume that to satisfy the angular momentum balance, interfaces must coincide with the mid-layer of their corresponding interphases. Recently, via adopting weighted averages, an extended general interface model has been developed that allows for arbitrary interface positions while fulfilling the angular momentum balance. This manuscript incorporates this novel interface model into the Mori–Tanaka method within the framework of homogenization. Analytical solutions are developed to determine effective properties as well as average local fields for fiber-reinforced and particle-reinforced composites. Computational simulations using the finite element method (FEM) are carried out to compare with the analytical solutions. Through a set of numerical examples, the significance of the interface position on the overall response of heterogeneous materials is highlighted. Our extended framework clarifies various ambiguous observations originating from the trivial assumption of restricting the interface position to the mid-plane. One advantage of the current interface model is that it covers both the elastic and cohesive interface models at its limits and therefore the analytical solutions are widely applicable regardless of the interface type.
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
Homogenization of composites embedding general imperfect interfaces
(2019-06) Firooz, Soheil
The objective of this work is to present a systematic study on the overall behavior of composites embedding general interfaces between the constituents. The zero-thickness interface model represents a finite-thickness interphase between the constituents. The term general interface refers to an interface model that allows for both displacement and traction jumps, unlike cohesive or elastic interface models. To set the stage, a comprehensive study on homogenization is carried out to examine the effects of various representative volume elements (RVE) and boundary conditions on the overall response of composites. Next, we extend the homogenization framework to account for interfaces hence, capturing size effects in both particulate and fiber composites. Two new analytical approaches are developed to determine the overall size-dependent response of composites. The first approach extends the composite sphere assemblage (CSA), composite cylinder assemblage (CCA) and the generalized self-consistent method (GSCM) resulting in bounds and estimates on the macroscopic properties of composites. In the second approach, we generalize the Mori{Tanaka method that not only determines the effective properties but also provides the state of the stress and strain in each phase of the medium including the interface. The proposed analytical results are thoroughly verified via a series of numerical examples using the finite element method.
Open Access
Hydrogenated carbon monolayer in biphenylene network offers a potential paradigm for nanoelectronic devices
(American Chemical Society, 2022-09-15) Demirci, S.; Gorkan, T.; Çallıoǧlu, Şafak; Özçelik, V. O.; Barth, J.; Aktürk, E.; Çıracı, Salim
A metallic carbon monolayer in the biphenylene network (specified as C ohs) becomes an insulator upon hydrogenation (specified as CH ohs). Patterned dehydrogenation of this CH ohs can offer a variety of intriguing functionalities. Composite structures constituted by alternating stripes of C and CH ohs with different repeat periodicity and chirality display topological properties and can form heterostructures with a tunable band-lineup or Schottky barrier height. Alternating arrangements of these stripes of finite size enable one to also construct double barrier resonant tunneling structures and 2D, lateral nanocapacitors with high gravimetric capacitance for an efficient energy storage device. By controlled removal of H atom from a specific site or dehydrogenation of an extended zone, one can achieve antidoping or construct 0D quantum structures like antidots, antirings/loops, and supercrystals, the energy level spacing of which can be controlled with their geometry and size for optoelectronic applications. Conversely, all these device functions can be acquired also by controlled hydrogenation of a bare C ohs monolayer. Since all these processes are applied to a monolayer, the commensurability of electronically different materials is assured. These features pertain not only to CH ohs but also to fully hydrogenated Si ohs.
Open Access
Implementation of high-quality warm-white light-emitting diodes by a model-experimental feedback approach using quantum dot-salt mixed crystals
(American Chemical Society, 2015) Adam, M.; Erdem, T.; Stachowski, G.M.; Soran-Erdem Z.; Lox, J. F. L.; Bauer, C.; Poppe, J.; Demir, Hilmi Volkan; Gaponik N.; Eychmüller A.
In this work, a model-experimental feedback approach is developed and applied to fabricate high-quality, warm-white light-emitting diodes based on quantum dots (QDs) as color-conversion materials. Owing to their unique chemical and physical properties, QDs offer huge potential for lighting applications. Nevertheless, both emission stability and processability of the QDs are limited upon usage from solution. Incorporating them into a solid ionic matrix overcomes both of these drawbacks, while preserving the initial optical properties. Here borax (Na2B4O7·10H2O) is used as a host matrix because of its lower solubility and thereby reduced ionic strength in water in comparison with NaCl. This guarantees the stability of high-quality CdSe/ZnS QDs in the aqueous phase during crystallization and results in a 3.4 times higher loading amount of QDs within the borax crystals compared to NaCl. All steps from the synthesis via mixed crystal preparation to the warm-white LED preparation are verified by applying the model-experimental feedback, in which experimental data and numerical results provide feedback to each other recursively. These measures are taken to ensure a high luminous efficacy of optical radiation (LER) and a high color rendering index (CRI) of the final device as well as a correlated color temperature (CCT) comparable to an incandescent bulb. By doing so, a warm-white LED with a LER of 341 lm/Wopt, a CCT of 2720 K and a CRI of 91.1 is produced. Finally, we show that the emission stability of the QDs within the borax crystals on LEDs driven at high currents is significantly improved. These findings indicate that the proposed warm-white light-emitting diodes based on QDs-in-borax hold great promise for quality lighting. © 2015 American Chemical Society.
Open Access
The investigation of advanced thermoplastic composite materials in aerospace applications
(2023-05) Yavuz, Zelal
The development of load-carrier reinforced composites is crucial in terms of a wide range of applications, such as aerospace, automotive, sports industry and so on. When these fields are taken into consideration, reducing the excessive weight of structural materials without any sacrifice in the performance is required. Thus, using reinforcement materials (e.g. carbon fibers) for polymeric matrices in composites is the most convenient way to follow. In this study, carbon fiber (CF) was used as a reinforcement material for thermoplastic based composites. Since bare CFs are too fragile to process they must be coated / sized such that the brittleness of CFs can be avoided during industrial applications. Therefore, sizing of carbon fibers is crucial for guiding them into service by protecting the CF’s surface. Yet, the traditional sizing agent (i.e. epoxy) is not suitable for handling continuous CF reinforced thermoplastic composites (CFRTPs) with high processing temperatures above 300 ℃. In this study a novel sizing agent was developed for this purpose. The effects of this sizing on the CFs’ physicochemical as well as surface properties were investigated. As a result, the impact on fiber-matrix interphase behavior can be analyzed. Moreover, the main problem for thermoplastic based composites which is the delamination between the reinforced fiber and thermoplastic matrix can be solved throughout the development of novel coating material so that inert carbon fibers can be made compatible with the matrix. In this thesis, the activation of carbon fiber’s surface, then providing a functional sizing agent and method in order to expel the present voids because of incompatibility between CF and thermoplastic matrix (i.e. Polyetherether ketone) were carried out by enhancing the adhesion. Hence, the wettability of CF by polyetherether ketone (PEEK) matrix was enhanced by altering the surface free energy of CF resulting in optimized adhesion. Thus, the delamination problem in thermoplastic based composites was solved throughout the sizing of CFs. The first part of this work consists of the elimination of current epoxy coating on the aerospace grade commercial carbon fibers. Then, the application of surface activation method was performed by acidic modification to make CFs ready for sizing process. The formation of functional groups (-COOH, -OH) on CF’s surface was achieved after degrading of present epoxy coating throughout CFs. As a result, the developed sizing agents could be binded easily onto CF’s activated surface through the hydrogen bonding. In the second part, four different polymeric sizing agents were prepared by taking the chemical compatibility with the matrix into consideration. The sizing process was performed via dip-coating method for the surface-activated CFs. The chemical and physical analyses for neat and treated CFs were carried out via microscopic and spectroscopic techniques. As a result of sizing process, the enhanced compatibility between the matrix and reinforcement material was proved by the Contact Angle Analysis and surface free energy calculations according to Young’s equation.
Open Access
Low-Temperature Deposition of Hexagonal Boron Nitride via Sequential Injection of Triethylboron and N2/H2 Plasma
(Wiley-Blackwell Publishing, Inc., 2014) Haider A.; Ozgit Akgun, C.; Goldenberg, E.; Okyay, Ali Kemal; Bıyıklı, Necmi
Hexagonal boron nitride (hBN) thin films were deposited on silicon and quartz substrates using sequential exposures of triethylboron and N 2 /H 2 plasma in a hollow-cathode plasma- assisted atomic layer deposition reactor at low temperatures ( ≤ 450 ° C). A non-saturating film deposition rate was observed for substrate temperatures above 250 ° C. BN films were charac- terized for their chemical composition, crystallinity, surface morphology, and optical properties. X-ray photoelectron spec- troscopy (XPS) depicted the peaks of boron, nitrogen, carbon, and oxygen at the film surface. B 1s and N 1s high-resolution XPS spectra confirmed the presence of BN with peaks located at 190.8 and 398.3 eV, respectively. As deposited films were polycrystalline, single-phase hBN irrespective of the deposition temperature. Absorption spectra exhibited an optical band edge at ~ 5.25 eV and an optical transmittance greater than 90% in the visible region of the spectrum. Refractive index of the hBN film deposited at 450 ° C was 1.60 at 550 nm, which increased to 1.64 after postdeposition annealing at 800 ° C for 30 min. These results represent the first demonstration of hBN deposi- tion using low-temperature hollow-cathode plasma-assisted sequential deposition technique. © 2014 The American Ceramic Society.
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
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.
Open Access
Non-covalent interactions between carbon nanotubes and conjugated polymers
(Royal Society of Chemistry, 2011) Tuncel, D.
Carbon nanotubes (CNTs) are interest to many different disciplines including chemistry, physics, biology, material science and engineering because of their unique properties and potential applications in various areas spanning from optoelectronics to biotechnology. However, one of the drawbacks associated with these materials is their insolubility which limits their wide accessibility for many applications. Various approaches have been adopted to circumvent this problem including modification of carbon nanotube surfaces by non-covalent and covalent attachments of solubilizing groups. Covalent approach modification may alter the intrinsic properties of carbon nanotubes and, in turn make them undesirable for many applications. On the other hand, a non-covalent approach helps to improve the solubility of CNTs while preserving their intrinsic properties. Among many noncovalent modifiers of CNTs, conjugated polymers are receiving increasing attention and highly appealing because of a number of reasons. To this end, the aim of this feature article is to review the recent results on the conjugated polymer-based non-covalent functionalization of CNTs with an emphasis on the effect of conjugated polymers in the dispersibility/solubility, optical, thermal and mechanical properties of carbon nanotubes as well as their usage in the purification and isolation of a specific single-walled nanotube from the mixture of the various tubes.
Open Access
Organic charge transfer cocrystals as additives for dissipation of contact charges on polymers
(American Chemical Society, 2022-12-06) Ekim, Sunay Dilara; Kaya, Görkem Eylül; Daştemir, M.; Yildirim, E.; Baytekin, H. T.; Baytekin, Bilge
Common polymers can accumulate surface charges through contact, a phenomenon known since ancient times. This charge accumulation can have detrimental consequences in industry. It causes accidents and yields enormous economic losses. Many empirical methods have been developed to prevent the problems caused by charge accumulation. However, a general chemical approach is still missing in the literature since the charge accumulation and discharging mechanisms have not been completely clarified. The current practice to achieve charge mitigation is to increase materials conductivity by high doping of conductive additives. A recent study showed that using photoexcitation of some organic dyes, charge decay can be started remotely, and the minute amount of additive does not change the material's conductivity. Here, we show the contact charging and charge decay behavior of polydimethylsiloxane doped with a series of organic charge transfer cocrystals (CTC) of TCNQ acceptor and substituted pyrene donors (CTC-PDMS). The results show that the CTC-PDMS are antistatic, and the discharging propensity of the composites follows the calculated charge transfer degree of the complexes. On the other hand, the CTC-PDMS are still insulators, as shown by their high surface resistivities. Kelvin probe force microscopy images of the contact-charged and discharged samples show a quick potential decay in CTC domains upon illumination. Combined with the fast overall decay observed, the antistatic behavior in these insulators can be attributed to an electron transfer between the mechanoions in the polymer and the CTC frontier orbitals. We believe our results will help with the general understanding of the molecular mechanism of contact charging and discharging and help develop insulator antistatics.
Open Access
Peridynamic modeling of nonlocal degrading interfaces in composites
(Elsevier B.V., 2022-09-19) Laurien, M.; Javili, Ali; Steinmann, P.
When modeling composite materials at small scales, the consideration of nonlocal effects is fundamental. In addition, the overall response of matrix-inclusion composites is strongly affected by the behavior of the interface between inclusion and matrix. This can be attributed to a possible detachment of the constituents as well as the high interface-to-volume ratio especially for nano-sized inclusions. Peridynamics is a nonlocal theory that is suitable to introduce a length-scale into a continuum description and take into account nonlocal interactions. Complex interface models within a peridynamic framework are, however, rarely studied. The objective of this work is to present a modeling approach to nonlocal interfaces accounting for opening and degradation within the framework of continuum-kinematics-inspired peridynamics (CPD). The proposed method is employed to study nonlocal effects in matrix-inclusion composites with focus on the effect of nonlocal interfaces. In our approach, the nonlocal interface is modeled as a finite thickness interface, i.e. a region where the subdomains overlap. Within this region, the constituents are pair-wise connected through interface bonding forces that follow a characteristic force-opening law. In computational experiments, our model captures the influence of the strength and size of the interface as well as the inclusion volume fraction on the overall response. In particular, non locality manifests itself through a “smaller–stiffer” material behavior and an increased influence of the interface, which highlights the importance of an appropriate nonlocal interface model.
Open Access
Property enhancement in unsaturated polyester nanocomposites by using a reactive intercalant for clay modification
(Wiley, 2013) Şen, S.; Gündem, H. B.; Ortaç, B.
Polymeric nanocomposites were synthesized from unsaturated polyester (UPE) matrix and montmorillonite (MMT) clay using an in situ free radical polymerization reaction. Organophilic MMT was obtained using a quaternary salt of coco amine as intercalant having a styryl group making it a reactive intercalant. The resultant nanocomposites were characterized via X-ray diffraction and transmission electron microscopy. The effect of increased nanofiller loading on the thermal and mechanical properties of the nanocomposites was investigated. All the nanocomposites were found to have improved thermal and mechanical properties as compared with neat UPE matrix, resulting from the contribution of nanolayer connected intercalant-to- crosslinker which allows a crosslinking reaction. It was found that the partially exfoliated nanocomposite structure with an exfoliation dominant morphology was achieved when the MMT loading was 1 wt %. This nanocomposite exhibited the highest thermal stability, the best dynamic mechanical performance and the highest crosslinking density, most probably due to more homogeneous dispersion and optimum amount of styrene monomer molecules inside and outside the MMT layers at 1 wt % loading. Copyright © 2013 Wiley Periodicals, Inc.
Open Access
Smart composites with tunable stress–strain curves
(Springer, 2020) Özcan, Mert; Çakmakçı, Melih; Temizer, İlker
Smart composites with tunable stress–strain curves are explored in a numerical setting. The macroscopic response of the composite is endowed with tunable characteristics through microscopic constituents which respond to external stimuli by varying their elastic response in a continuous and controllable manner. This dynamic constitutive behavior enables the composite to display characteristics that cannot be attained by any combination of traditional materials. Microscopic adaptation is driven through a repetitive controller which naturally suits the class of applications sought for such composites where loading is cyclic. Performance demonstrations are presented for the overall numerical framework over complex paths in macroscopic stress–strain space. Finally, representative two- and three-dimensional tunable microstructures are addressed by integrating the control approach within a computational environment that is based on the finite element method, thereby demonstrating the viability of designing and analyzing smart composites for realistic applications.
Open Access
Synthesis, characterization, and wear and friction properties of variably structured SiC/Si elements made from wood by molten Si impregnation
(2012) Dhiman, R.; Rana, K.; Bengu, E.; Morgen P.
We have synthesized pre-shaped SiC/Si ceramic material elements from charcoal (obtained from wood) by impregnation with molten silicon, which takes place in a two-stage process. In the first process, a porous structure of connected micro-crystals of β-SiC is formed, while, in the second process, molten Si totally or partly infiltrates the remaining open regions. This process forms a dense material with cubic (β-)SiC crystallites, of which the majority is imbedded in amorphous Si. The synthesis of preshaped "sprocket" elements demonstrates that desired shapes of such a dense SiC/Si composite ceramic material can be achieved, thus suggesting new industrial applications. The structure and composition of numerous as-synthesized samples were characterized in detail by using a wide range of techniques. Wear and friction properties were also investigated, with polished samples. The properties found for the present samples are very promising for abrasive applications and for new generation brake systems. © 2011 Elsevier Ltd.