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All-solution-processed multilayer ZnO/Ag NWs/ZnO/PVP/PVA composite is introduced as a transparent conductive film (TCF) for optoelectronic applications. Unlike conventional film formation methods that impose high investment expenses, scalable spray coating is applied over the layers using a hand-made spray apparatus. The resulting TCF exhibits high transmittance (T, 86% at 550 nm) and low sheet resistance (Rs, 6 Ω/sq), which is comparable to the sputtered counterparts. The bending test demonstrates the flexibility of the multilayer TCF with no noticeable increase in Rs, even after 1500 bending iterations. Moreover, chemical stability test (exposure to a corrosive agent) and adhesion examination confirm the capability of the fabricated TCF. Furthermore, the electrode is also thermally stable in heat up to 280 °C and is resistant against oxidation, as Rs remains almost unchanged after keeping the electrode in normal atmospheric condition for 200 days. The all-solution-processed electrode demonstrates desirable performance as a transparent electrode and potential to be applied in different optoelectronic and photovoltaic devices.

In this paper, the stresses and buckling behaviors of a thick-walled micro sandwich panel with a flexible foam core and carbon nanotube reinforced composite (CNTRC) face sheets are considered based on the high-order shear deformation theory (HSDT) and the modified couple stress theory (MCST). The governing equations of equilibrium are obtained based on the total potential energy principle. The effects of various parameters such as the aspect ratio, elastic foundation, temperature changes, and volume fraction of the canbon nanotubes (CNTs) on the critical buckling loads, normal stress, shear stress, and deflection of the thick-walled micro cylindrical sandwich panel considering different distributions of CNTs are examined. The results are compared and validated with other studies, and showing an excellent compatibility. CNTs have become very useful and common candidates in sandwich structures, and they have been extensively used in many applications including nanotechnology, aerospace, and micro-structures. This paper also extends further applications of reinforced sandwich panels by providing the modified equations and formulae.

In recent years, thin silver nanowires (Ag NWs) with diameters smaller than 150 nm have been synthesized by implementation of NaCl or FeCl3 as reaction promoters and high molecular weight polyvinylpyrrolidone (PVP) as the capping agent. However, the yield of Ag NWs still remains low, mostly due to the insufficient aspect ratio (AR) of the synthesized nanostructures and the production of Ag nanoparticles, which is an undesirable by product. This study proposes a modified technique to alleviate the problem by using a mixture of FeCl3/CuCl2 as the reaction promoter and two different types of PVP with molecular weight of 360 k and 40 k as the capping agents. The appropriate mixtures of FeCl3/CuCl2 (molar ratio of 1.48:1.45) and PVP 360 k/40 k (molar ratio of 2:1) allow for the rapid synthesis of NWs with diameter of about 110 nm and length of up to 50 μm. It is revealed that the ARs of the synthesized NWs are much greater. The NWs are then used for the fabrication of transparent conductive films (TCFs). The obtained TCF prepared by a scalable, in-house, and cost-efficient spray apparatus possesses a transmittance of 91%, sheet resistance of 10 Ω/sq, and optical haze value of 6.6%. In fact, the AR of the NWs is increased as much as 1135%, and further the figure␣of merit of the TCFs is improved by as much as 2785%.

In this article, vibration behavior of a micro cylindrical sandwich panel with foam core and reinforced graphene platelet composite layers on the top and bottom resting on elastic foundation based on modified couple stress theory is investigated. Hamilton’s principle is used to determine the governing equations of motion. These equations are solved by Navier’s method to obtain the natural frequencies. The results are compared with the extracted results by the other literatures. The effects of different parameters such as temperature change, volume fraction of graphene platelet, length to radius ratio, and the elastic foundation on the natural frequencies have been carried out. Also, the effects of reinforced materials for layers is discussed and compared with unreinforced composites layers. Sandwich structures are wildly used in different applications such as spacecraft, aeronautical, pressurized gas tanks, boilers, aircraft fuselage, marines, and civil structures, and these cases need high strength and low weight. The present work is a theoretical background for more explorations and further experimental researchers in the field of cylindrical reinforced panels.

Purpose This paper aims to improve some properties of poly (methyl methacrylate) by copolymerization with butyl acrylate (BA) monomer along with the incorporation of the stable and economical synthesized silicone-containing monomer hexamethyldisilazanomethacryloxyphenyl ketone (HDMK) into the copolymer matrix. Design/methodology/approach For this target solution copolymerization of methyl methacrylate (MMA), BA and HDMK were carried out using a 250 mL four-necked round-bottom flask. Before solution polymerization start-up, the reaction vessel was first charged with 34.8 mL toluene and heated to 170 °C with stirring and reflux cooling. A monomer mixture of 25.86 g (260 mmol) MMA, 26.40 g (200 mmol) BA, 3.00 g (8.60 mmol) HDMK and 0.45 g (2.00 mmol) dibenzoyl peroxide was added continuously from the dropping funnel over a period of 4 h. Findings The HDMK was successfully synthesized and the water resistance of acrylic resins was improved because of the existence of HDMK. Research limitations/implications The materials that were used in this research paper had a reasonably low cost. Also, the procedures for synthesis of monomers and polymers were extremely easy because there was no need for high pressure or temperature and no dangerous solvents were used. Practical implications The acrylic resin that contained HDMK was used to synthesis a white architectural paint for exterior coating. Examining the paint characteristics has shown acceptable washing and abrasion resistance, good brushing, excellent storage stability and great surface coating. Originality/value HDMK was synthesized for the first time.

In the current study, a numerical method is used to investigate the thermal energy transfer and pressure drop augmentation in helically coiled tube heat exchanger with a coiled wire insert made from copper. The impact of geometrical parameters of the inserts like diameter and cross sectional form on the intensification of the Nusselt and the friction factor number is studied. The Transition SST model is used to simulate the impact of turbulence. The model validation is performed by comparing the results with the empirical equations of prior experimental works. Results indicate that, using a circular cross section coiled wire inserts will enhance the Nusselt number and friction factor by 340.9%, 536.1%, respectively. Furthermore, using inserts with concentric circular cross section with diameter of 0.008 m and two rectangular cross sections are recommended for the intensification of heat transfer at the inlet mass flow rate 0.05 kg/s while, all inserts are suggested at the inlet mass flow rate of 0.075 kg/s. As a part of the study, a correlation is proposed for estimating the Nusselt number of these heat exchangers.

Electrochemical exfoliation of graphite has recently attracted a big attention as a simple, fast and scalable method for the preparation of high quality graphene, but there are some drawbacks that hinder its application. Direct deposition is one of the most critical challenges that makes it difficult to deposit uniform, compact and large scale graphene thin films. This work develops a facile electrophoretic deposition route to fabricate exfoliated graphene (EG) film on Ag nanowires (NWs) networks with a controllable film thickness in nanometers scale. EG thin films are deposited with different applied potentials and times from an EG dispersion in N, N -dimethylformamide solvent. Since confirmed by light transmittance results, the increase in deposition time or applied potential lead to an increase in the number of deposited EG layers. The scanning electron microscopy results confirm the uniformity and compactness of EG films deposited on Ag NWs network. Furthermore, transparency and conductivity of Ag NWs films before and after the deposition of EG are investigated. It shows significant improvement in its performance, as a result, it leads to Ag NWs/EG hybrid films exhibiting a sheet resistance of R s = 30 Ω sq -1 , and 85% light transmittance, comparable to conventional transparent conductive oxide films.

Synthetic fibers such as glass, carbon, etc., are used as reinforcement in polymer composites due to their high strength and modulus. However, synthetic fibers contribute to high costs and have a significant environmental impact. To overcome this challenge, various natural fibers, including banana, kenaf, coir, bamboo, hemp, and sisal fiber, as reinforced in a polymer matrix are investigated for mechanical properties. In this study, biocomposites with natural fibers as reinforced are developed and characterized. Treated and untreated natural fibers such as flax, maple, and pine as reinforced in thermoplastic, in this study, polypropylene (PP), are investigated for the mechanical properties, including tensile, flexural, and impact test. Mechanical test results exhibited that adding the natural fibers enhanced the tensile, flexural, and impact properties. It can be inferred that these biocomposites can be used as potential materials for the automobile industry.

The mechanical properties of SMAs can be modified using temperature or stress changes. This specific characteristic allows building smart materials that can repair or improve themselves. Shape-memory alloys provide adjustable natural frequencies, using the mentioned character, which is highly practical in producing any component sensitive to vibrations. In this study, the vibration behaviors of a thick-walled micro-cylindrical sandwich panel with two types of reinforcements carbon nanotubes (CNTs), and graphene platelets (GPLs) for the SMA-based layers (shape-memory alloy face sheets) is investigated. Using two well-known core materials (porous, and foam cores) has covered various structures and components. The higher-order shear deformation theory is considered, and based on Hamilton's principle, the governing equations of motion are driven. Navier's method is used to obtain the natural frequencies. The effects of different parameters such as aspect ratios, the volume fraction of CNTs or GPLs, various porous patterns, and temperature changes on the natural frequency are studied. The natural frequencies usually decrease when the temperature rises, while the use of SMA materials as the matrix has led to a rise in the magnitudes of the natural frequencies. It is believed that shape-memory alloys can bring fundamental changes to the industry; therefore, this study is the base point for further numerical and more specific works in the future.

This paper presents the design, development, modeling and control of a biomimetic multi degree of freedom compliant locomotive mechanism that can follow a prescribed trajectory. The research objective of this study is the design of a high mobility and flexible planar locomotive mechanism incorporating large deflecting compliant hinges. The actuation is realized using servo motors. Mechanism is consisted of five sliding carts, rail, 3D-printed supplementary pieces to house motors and pins. Carts are connected by monolithically designed two arm links joined by a large deflecting flexure. Four servo motors are mounted on the driven carts. Since sliding carts are identical, forward motion is achieved by changing the friction of carts through the connecting pins. Dynamical model is created in Matlab Simulink using Euler’s laws of motion principle, pseudo rigid body modeling (PRBM), vector closure-loop equations and kinematic constraints. To robustly control the position of the mechanism, first its nonlinear dynamics replaced with a family of linear time invariant systems which have parameter uncertainty. Then a robust controller is designed based on the Quantitative Feedback Theory (QFT) for the desired robust tracking and stability bounds. QFT is one of the most powerful robust control techniques which can take into account both phase and magnitude information of the system and enables the designer to minimize the cost of feedback by clearly observing the design constraints through robust performance bounds. Finally, the performance of the designed controller is validated though nonlinear simulations using the nonlinear dynamics of the mechanism. It has been shown that the mechanism can consistently track the desired inputs both in frequency and time domains.

Hybridization of natural fiber with synthetic fiber to reinforce polymer matrix composites is an effective way of increasing fatigue strength of composites with substantial amount of bio-based content. Flax is the strongest type of bast natural fiber, possessing excellent mechanical and damping properties. Fatigue properties of flax fiber hybridized with synthetic carbon fiber reinforced polymer matrix composites were studied. Fatigue properties of inter-ply hybrid flax-carbon fiber reinforced composite were compared to intra-ply hybrid flax-carbon fiber reinforced composites through tensile fatigue testing at 70% load of ultimate tensile strength and with a loading frequency of 3 Hz. For similar amount (by mass) of flax and carbon fiber, intra-ply flax-carbon fiber hybrid reinforced composite exhibited a very large increase (>2000%) in fatigue life compared to inter-ply flax-carbon fiber hybrid reinforced composites. Suitable hybridization can produce hybrid composites that are as strong as synthetic fiber composites while containing a high bio-based content of natural fibers.

The main goal of the present work is to explore the three dimensional (3-D) atomic force microscopy (AFM) images of human teeth and investigating their micromorphology. For this purpose, 10 fresh and permanent canine teeth were selected from a group of 40-year-old men who were candidate for the experimental processes. Afterward, they were all applied for studying the morphology of their hard tissues. The tapping mode of AFM was used to characterize the surface micromorphology on the square areas of 1 μm × 1 μm (512 × 512 pts). AFM results and surface stereometric analysis indicate the relationships between the micromorphology of the surface and the structural properties of these tissues across the length scales. As can be seen, the surface of cementum has the most irregular topography (D = 2.87 ± 0.01) while the most regular topography (D = 2.43 ± 0.01) is found in dentin. Furthermore, the more and less regularity of the surface have been found in inner enamel (Sq = 26.26 nm) and dentin (Sq = 41.28 nm), respectively. Stereometric and fractal analyses give valuable information about human canine teeth via 3-D micromorphology.

Because of excellent physical properties and wide range of applications in electrodes, electrical connections, microelectronic packaging, and heating mineral, Tungsten–copper (W–Cu) composite powders have been significantly remarkable. The substantial differences in the density and lack of fusion of copper and tungsten in both solid and liquid phases, led to occur some problems in W–Cu composite powders. Among the various methods of preparing tungsten–copper composites, the electroless plating process is one of the conventional methods as it is easy to use, efficient, and inexpensive. In this paper, the copper electrolyte solution containing copper sulfate as the main salt, formaldehyde as the reducing agent, sodium ethylene diamine tetra-acetate as the sophisticated agent, has been employed in the electroless copper plating process of tungsten powder. The effects of main parameters of electroless copper plating including NaOH concentration, time and operating temperature, and pre-activation of tungsten powder on the amount of deposited copper layer were investigated. Then, the phase behavior, morphology, mechanical, and corrosion behavior were evaluated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy(EDS), Vickers hardness tester, and electrochemical impedance spectroscopy (EIS), respectively. Results demonstrated an improvement in the morphology and amount of the copper, which was deposited on the surface of the activated tungsten powder. Indeed, the defects formed on the surface of the tungsten powder increased the sites for nucleation and growth of copper particles. In agreement with the Fick's 2nd law, the maximum deposition rate of 7.9 vol% was obtained at 14 g/l NaOH, 100 °C and processing time of 90 min, with a (111) orientation on the activated tungsten powder surface. The higher capacitance and the charge transfer resistance along with the highest ndl at the 14 g/l NaOH concentration demonstrated the homogeneity and integrity of W–Cu composite, the lowest hardness of 149.0 ± 2.8 Hv and a compressive strength of 187 ± 11 MPa.

The finite volume method is employed to analyze the fluid flow, heat transfer and entropy generation within a fluid channel. The fluid channel is filled with CuO-water nanofluid. The KKL model is used to estimate the dynamic viscosity and consider the Brownian motion. On the other hand, the influence of nanoparticles' shapes on the thermal conductivity is considered. The fluid channel is included with hot and cold fluid injection pipes which are modeled as active bodies in 2D model. Three different governing parameters are utilized such as Rayleigh number in range of 103

In the present work, a numerical method is used for the simulation of the heat transfer and entropy generation for the non-premixed combustion of CH4-air. The standard K-e model is established for the simulation of turbulence. Furthermore, the PDF (Probability Density Function) approach is used for the simulation of the reaction between the species. Twenty species are considered in this simulation. The model is validated by comparing the values of the outlet species mass fraction between the present numerical work and the previous experimental works. The effect of the equivalence ratio, on the heat flux, heat transfer coefficient, wall temperature, entropy generation rate and the outlet species mass fraction is obtained. Based on the results, two correlations are proposed for the prediction of the maximum heat transfer coefficient. These correlations show that if the equivalence ratio is doubled the maximum heat transfer coefficient is doubled too for ∅ 1. Furthermore, it was found that in the first region of the tube the maximum values of the heat flux, wall temperature and heat transfer coefficient occur.

Application of additive manufacturing (AM) technology in production of ceramic parts is considered as a state-of-the-art technique which has been recently introduced to industry. In the current study the imperative microstructural characteristics of the alumina manufactured via laser stereolithography (SLA) has been investigated. The microstructural characteristics of the developed ceramic parts and components are still unknown and require detailed investigation. A combination of optical microscopy and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), image analysis, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and micro-computed tomography (micro-CT) scans was used to evaluate the microstructural features of the alumina samples after each step of the manufacturing process (i.e. printing, debinding and sintering). In addition, the apparent density of each sample was measured using water displacement method. Results indicated that the porosity of printed alumina samples was significantly reduced after sintering process. EDS analysis confirmed elimination of binder material after debinding and sintering processes. XRD analysis detected existence of α-Al 2 O 3 in initial printed samples which was not changed during debinding and sintering processes. Due to detection of identical peaks for all samples, only one set of lattice parameters ( a and c ) was calculated from XRD patterns of all samples which was close to the ones reported in literature for alumina. TEM micrographs and corresponding diffraction patterns confirmed polycrystalline structure from different layers of the samples. High resolution transmission electron microscopy (HRTEM) and diffraction patterns from single layers were used to calculate lattice parameters for each sample. A slight increase was noticed in unit cell and grain size after sintering process. The obtained results help for better understanding of the properties through microstructural characteristics of the 3D printed ceramic parts.

Due to copyright restrictions, the access to the full text of this article is only available via subscription. Limited research on biomineralization in cement-based systems suggested that self-healing of surface cracks could be obtained by triggering biogenic calcium carbonate (CaCO3) precipitation within the cracks. While this is encouraging, there is not enough information regarding the influence of admixtures on crack remediation and durability of the biogenic CaCO3 against weathering conditions. In this study, the microorganisms were introduced to mortar with their growth medium, which included corn steep liquor (CSL) and urea. With this approach, the cracks on mortar surface were sealed with the CaCO3 and the water absorption capacity of the so-called self-healed mortar decreased compared to its counterpart cracked mortar samples. The biogenic CaCO3 precipitate was found to be durable against freeze-thaw; however the precipitate was unstable under rain water and light. While the addition of air entraining agents (AEA) did not influence the self-healing ability of cells, use of superplasticizers improved the self-healing ability in terms of crack sealing, water absorption, and durability of the precipitate. TÜBİTAK

The heat transfer enhancement in a D-shaped heat exchanger using nanofluid is analyzed using a modern numerical method. The double-MRT lattice Boltzmann method is utilized to simulate the fluid flow and heat transfer. On the experimental phase, the thermal conductivity and viscosity of Al2O3-EG/W(60/40 vol%) are measured using experiments with modern devices. Some correlations based on experimental data are developed as a function of temperature for different nanoparticle concentrations. These temperature/nanoparticle concentration-based correlations are used in the numerical simulations to enhance the accuracy of results. In the present investigation, the impacts of Rayleigh number (103

The natural convection heat transfer and fluid flow is analyzed using lattice Boltzmann numerical method . The entropy generation analysis and heatline visualization are used to study the convective flow field comprehensively. The hollow L-shaped cavity is considered and filled with SiO2-TiO2/Water-EG (60:40) hybrid nanofluid . The thermal conductivity and dynamic viscosity of nanofluid are measured experimentally. To use the experimental data of thermal conductivity and dynamic viscosity, two sets of correlations based on temperature for six different solid volume fractions of 0.5, 1, 1.5, 2, 2.5 and 3 vol% are derived. The influences of different governing parameters such different aspect ratios, solid volume fractions of nanofluid and Rayleigh numbers on the fluid flow, temperature filed, average/local Nusselt number , total/local entropy generation and heatlines are presented.

Carbon fiber composite frames were first used in Tour de France in 1986. With recent growth in research and development of composite frames, carbon fiber composites have become more popular in bicy...

This protocol describes a method for rapid manufacturing of soft pneumatic actuators and robots with an ultrathin form factor using a heat press and a laser cutter machine. The method starts with the lamination of thermoplastic polyurethane (TPU) sheets using a heat press for 10 min at the temperature of ~93 °C. Next, the parameters of the laser cutter machine are optimized to produce a rectangular balloon with maximum burst pressure. Using the optimized parameters, the soft actuators are laser cut/welded three times sequentially. Next, a dispensing needle is attached to the actuator, allowing it to be inflated. The effect of geometrical parameters on the deflection of the actuator are studied systematically by varying the channel width and length. Finally, the performance of the actuator is characterized using an optical camera and a fluid dispenser. Conventional fabrication methods of soft pneumatic actuators based on silicone molding are time consuming (several hours). They also result in strong but bulky actuators, which limits the actuator's applications. Moreover, microfabrication of thin pneumatic actuators is both time-consuming and expensive. The proposed manufacturing method in the current work resolves these issues by introducing a fast, simple, and cost-effective fabrication method of ultrathin pneumatic actuators.

Density is a fundamental physical property of a reinforcement in composite materials. It appears widely in calculations, which are mostly used for engineering designs. The purpose of this research project is to establish a standard test method to measure the density of flax fiber using Archimedes (buoyancy) method. Different immersion fluids were considered in the density measurement of flax fiber with and without use of a vacuum oven. Results of gas pycnometry tests of the same flax sample were used as the reference for comparison. Variables such as, specimen size, vacuum pressure, vacuum time and type of immersion fluid were studied by the ruggedness test. Results of this study suggest that use of certified lab grade soybean oil as test fluid, and submerging flax specimens in test fluid under vacuum pressure of 90–100 kPa for 10 min yields the closest values of density to those acquired by gas pycnometry method.

Carbon fiber-reinforced polymers are being used in advanced structural applications such as aerospace, automotive, and naval industries. Therefore, there is a rising need for predicting their fatigue life and improving their fatigue behavior. In this study, the fatigue behavior and changes in flexural modulus of bidirectional carbon fiber-reinforced polymers due to cyclic fully reversed bending are investigated. A unique fixture is designed and manufactured to perform fully reversed four-point bending fatigue tests on (0 °/90 °)15 carbon/polyester specimens with a stress ratio of R = −1 and frequency of 5 Hz. The expected downward trend in fatigue life with increasing maximum applied stress was observed in the S–N curves of samples. Based on the decay in the flexural modulus of the specimens, a modified exponential model is proposed to predict the life of carbon fiber-reinforced polymers under fully reversed bending. The empirical constants in the model are calculated based on the results of experiments. The model is applied to predict the fatigue life of the samples that did not fail during the tests and cycle-to-failure of the specimens are found.

Composites having high bio-based content with properties and costs rivaling those consisting of synthetic constituents are a goal of much current research. The obvious material choices — vegetable oil based resins and natural fibers — present the challenges of poor resin properties and weak fiber/matrix bonding, respectively. Conventional methods of overcoming poor resin quality involve the incorporation of additives, which dilute the resulting composite's bio-content and increases cost. To overcome these limitations while maintaining high bio-content, in this study, a newly developed biobased resin, epoxidized sucrose soyate (ESS), is combined with surface-treated flax fiber to produce novel bio-composites. Properties of manufactured composites were compared against those using epoxy resin reinforced with flax fiber. In addition to mechanical property evaluation, accelerated weathering was performed on the manufactured composites to evaluate the mechanical properties after exposing to UV and moisture. The results of this study revealed the successful production of bio-composites having properties that meet or exceed those of conventional pultruded members while having 85% bio-content. Moreover, composites using treated flax fiber and ESS resin showed less degradation in properties and appearance after accelerated weathering exposure. Keywords: Biocomposites, Degrading, Natural fibers, Natural resins, Weathering

Flax fiber composites have been found to exhibit suitable mechanical properties for general applications. Natural fibers exhibit lower mechanical properties than their synthetic counterparts as well as have a high degree of fiber to fiber mechanical variability based on growing conditions and plant varieties which lowers their mechanical performance predictability. However, Thermoset resins reinforced with flax fibers exhibit nonlinear behavior when subjected to loading which results in energy loss. This is beneficial in applications where vibration damping is anticipated. One potential method for increasing performance and strength of flax fiber is to hybridize it with synthetic fibers with the goal of improving composite mechanical properties as well as reducing composite to composite mechanical variability. In this study carbon fiber and flax fiber were used to manufacture different hybridized composites with varying flax fiber volume fractions. Resulting composites were characterized using tensile, flexural, impact and vibration tests. Also, results of experiments were compared against predictions of rule of mixture's model and Halpin-Tsai model. Findings of this study provides valuable information for designers for hybridizing flax and carbon fibers and results suggest that hybridizing synthetic fibers with natural fibers is an effective method of improving the mechanical properties and controlling vibration damping. Keywords: Bio-composites, Carbon, Epoxy, Flax, Hybridization, Sports equipment

There has been a vast growth in manufacturing of fiber reinforced plastics by means of liquid composite molding such as resin transfer molding and vacuum-assisted resin transfer molding processes. In these processes, compression of the porous media and pressure of the injected resin result in in-mold forces that need to be determined. Limited information exists regarding the processing parameters and extent of reinforcing potential natural fibers have in polymer matrices. Current study investigates the effect of different variables such as fiber volume fraction, shive content, fiber size, wax content, and resin viscosity on permeability of five different natural fiber mats. Flax fiber with low-, medium-, and high-shive content as well as hemp and kenaf fiber mats was selected for this study and an original experimental device was setup to measure the permeability of the mentioned fiber mats based on different variables. It was found that increasing fiber volume fraction will result in reduction of permeability of all mats. The presence of shive and larger fiber size increased the permeability. Higher wax content lowered the permeability. These competing factors could be used by manufacturers to produce a mat which had optimum permeability while still maintaining acceptable strength.

The aim of this study was to investigate the effect of zein protein treatments on the mechanical performance of flax fiber/thermoset resin composites. Flax fibers treated with corn zein protein to improve compatibility with epoxy and vinyl ester resin were processed into composites and tested under tensile, flexural, and short beam shear loadings. Pure zein treatments were tested at 1, 2.5, and 5% concentrations. Zein was also introduced to flax fibers through treatments with Corn Gluten Meal (CGM) and Dried Distiller Grains with Solubles (DDGS). The addition of zein protein increased the strengths of the composite for all three tests. Results demonstrated that the 2.5% pure zein treatment produced the largest gains with an increase of tensile strength by 8%, flexural strength by 17%, and short beam shear strength by 30% compared to untreated samples. To further investigate the effectiveness of zein treatments, Fourier Transform Infrared Spectroscopy (FTIR), chemical analysis, and Scanning Electron Microscopy (SEM) techniques were used. Results showed promise of using zein protein as an all-natural, environmentally friendly, coupling agent for flax fiber composites.

In this study, a novel, bio-based polyol was used in the formulation of a polyurethane (PU) matrix for a composite material where fl ax fi ber was used as the reinforcement. The viscoelastic properties of the matrix and fl ax fi ber were determined by a linear viscoelastic model through experimentation and the results were used as input for the material properties in the computational model. A fi nite element micromechanical model of a representative volume element (RVE) in terms of repeating unit cells (RUC) was developed to predict the mechanical properties of composites. Six loading conditions were applied on the RUC to predict and defi ne the viscoelastic behavior of the composite unit cell. The time-history of averaged response was determined in terms of stress and strains. The results of this study suggest that applying the overall rate-dependent behavior of fl ax fi ber to the micromechanical model leads to a good agreement between the micromechanical modeling and experimental results. The modeling approach is effi cient and accurate as long as the periodicity in the composite rules. This modeling approach can be used as a powerful algorithm in determining linear and nonlinear properties in material mechanics analysis and characterization.

Natural fibers have great potential to be used as reinforcement in composite materials. Cellulose, being a critical constituent of natural fibers, provides unquestionable advantages over synthetically produced fibers. Increasing demand for use of bio-based composites in different engineering and structural applications requires proper test methods and models for predicting their long-term behavior. In the present work, the time-temperature superposition principle was successfully applied to characterize creep behavior of flax/vinyl ester composites. The creep compliance vs time curves were determined and shifted along the logarithmic time axis to generate a master compliance curve. The time-temperature superposition provided an accelerated method for evaluation of mechanical properties of bio-based composites, and the results suggest that the time-temperature superposition is a useful tool for accelerated testing of long-term behavior of bio-based composites.

Electroactive polymers have attracted considerable attention in recent years due to their sensing and actuating properties which make them a material of choice for a wide range of applications including sensors, biomimetic robots, and biomedical micro devices. This paper presents an effective modeling strategy for nonlinear large deformation (small strains and moderate rotations) dynamic analysis of polymer actuators. Considering that the complicated electro-chemo-mechanical dynamics of these actuators is a drawback for their application in functional devices, establishing a mathematical model which can effectively predict the actuator\'s dynamic behavior can be of paramount importance. To effectively predict the actuator\'s dynamic behavior, a comprehensive mathematical model is proposed correlating the input voltage and the output bending displacement of polymer actuators. The proposed model, which is based on the rigid finite element (RFE) method, consists of two parts, namely electrical and mechanical models. The former is comprised of a ladder network of discrete resistive-capacitive components similar to the network used to model transmission lines, while the latter describes the actuator as a system of rigid links connected by spring-damping elements (sdes). Both electrical and mechanical components are validated through experimental results.

Fiber-reinforced composites are widely used in advanced structural applications, including aerospace. The reinforcement in these composites is usually synthetic or mineral fibers, such as carbon or glass fibers. Due to the advantages of natural fibers over their synthetic or mineral counterparts, they have been the center of attention for the past couple of decades. However, there are challenges to overcome before natural composites become more widespread in the advanced structural industry. In this study, two newly developed bio-based resins, derived from soybean oil, are combined with surface-treated flax fiber to produce novel bio-composites. Mechanical properties such as tensile and flexural strength, tensile and flexural moduli, interlaminar shear strength, and color gloss of the composite specimens before and after exposure to accelerated weathering (UV and moisture) have been studied. The results of this study reveal that bio-based composites using vinyl ester resin or 100% vegetable oil-based resins have the potential to be used in structural applications such as aerospace applications. In this study, the mechanical properties of manufactured composites showed improvement when using alkaline-treated flax fiber as reinforcement. In addition, after being exposed to accelerated weathering, the mechanical properties of composites using treated flax fiber showed lower reductions, with the exception of flexural strength. In general, it has been shown that the bio-based composites manufactured in this study meet, and most of the time exceed, the target properties set, based on commercially available pultruded fiberglass composites.

Ionic polymers have attracted considerable attention due to their interesting sensing and actuating behavior which make them a proper choice for use in a wide range of applications including biomimetic robots and biomedical devices. The complicated electro-chemo-mechanical dynamics of ionic polymer actuators is a drawback for their applications in functional devices. Therefore, establishing a mathematical model which could effectively predict the actuators' dynamic behavior is of great interest. In this paper, a mathematical model, named equivalent dynamic thermoviscoelastic (EDT) model, based on thermal analogy and beam theory is proposed for dynamic analysis of bending-type ionic polymer actuators. Then, the developed model is extended for analyzing the performance of the actuator in finite element software. The finite element analysis of the actuator enables consideration of material and geometric nonlinearities and facilitates modeling of functional devices based on the ionic polymer actuators. The proposed modeling approach is validated using experimental data. Copyright © 2015 John Wiley & Sons, Ltd.

A series of near-infrared reflective nano-pigments based on Co 1− x Zn x Cr 2− y Al y O 4 ( x = 0–1 and y = 0–2) have been synthesized via Pechini-type sol–gel method. Comprehensive analyses were carried out to characterize the resulting powders including X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared analysis and UV–Vis–NIR spectrophotometry. The colors of spinel structures were directly related to the occupation of tetrahedral and octahedral positions by the chromophores. The results revealed that the substitution of Zn 2+ for Co 2+ ions in the tetrahedral positions, and Al 3+ for Cr 3+ ions in the octahedral positions of CoCr 2 O 4 not only reduce the cost but also increased near-infrared solar reflectance ( R * > 43%). Furthermore, the coatings colored with the optimum pigments possessed high near-infrared solar reflectance ( R * > 50%) with respect to the conventional coatings. These facts express the potential of the pigments to be employed in cool coatings.

Graphene oxide sheets suspended in ethanol interact with excited CdS nanoparticles and contributed to photocatalytic reduction by accepting electron from nanoparticle. The UV-Vis measurement showed that electrical absorbance of the CdS/graphene oxide sheets increased by decreasing the irradiation time and after 2 h it remained constant which indicates the optimum reduction time. Furthermore, the direct interaction between CdS nanoparticles and graphene sheets hinders the collapse of exfoliated sheets of graphene. The 4-point probe measurement of nanocomposite with different ratios of graphene oxide in CdS solution after irradiation shows that the conductivity of them increased by increasing the amount of GO, but further increasing causes incomplete photo reduction process due to exorbitance increasing GO sheets which contribute to decreasing the conductivity. The CdS/RGO composite material can be used as a gas sensor for CO2based on its electrocatalytic behavior. The low-cost and easy fabrication sensor shows rapid response and high sensitivity. By varying the amount of GO the optimum concentration which shows high sensitivity is found and its good performance compared with other is attributed to its higher conductivity due to complete reduction. Moreover, the effects of thermal annealing on the conductivity of CdS/RGO film and the performance of devices are researched.

We report an advanced method for the self-organization of an optomagnetic nanocomposite composed of both fluorescent clusters (ZnS quantum dots, QDs) and magnetic nanoparticles (CoFe2O4). ZnS nanocrystals were prepared via an aqueous method at different temperatures (25, 50, 75, and 100 degrees C). Their structural, optical and chemical properties were comprehensively characterized by X-ray diffraction (XRD), UV-vis, photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), transmission electron microscopy (TEM), and infrared spectroscopy (FT-IR). The highest PL intensity was observed for the cubic ZnS nanoparticles synthesized at 75 degrees C which were then stabilized electrosterically using thioglycolic acid. The photophysical analysis of the capped QDs with a particle size in the range 9-25 nm revealed that the emission intensity and the optical band gap increases compared to uncapped nanocrystals (3.88 to 4.02 eV). These band gaps are wider than that of bulk ZnS resulting from the quantum confinement effect. Magnetic nanoparticles were synthesized via a co-precipitation route and a sol-gel process was used to form the functionalized, silica-coated CoFe2O4. Finally, thiol coordination was used for binding the QDs to the surface of the magnetic nanoparticles. The fluorescence intensity and magnetic properties of the nanocomposites are related to the ratio of ZnS and CoFe2O4. An optomagnetic nanocomposite with small size (12-45 nm), acceptable saturation magnetization (about 6.7 emu g(-1)), and satisfactory luminescence characteristics was successfully synthesized. These systems are promising candidates for biological and photocatalytic applications.

Ionic polymer conductive network composite (IPCNC) actuators are a class of electroactive polymer composites that exhibit some interesting electromechanical characteristics such as low voltage actuation, large displacements, and benefit from low density and elastic modulus. Thus, these emerging materials have potential applications in biomimetic and biomedical devices. Whereas significant efforts have been directed toward the development of IPMC actuators, the establishment of a proper mathematical model that could effectively predict the actuators’ dynamic behavior is still a key challenge. This paper presents development of an effective modeling strategy for dynamic analysis of IPCNC actuators undergoing large bending deformations. The proposed model is composed of two parts, namely electrical and mechanical dynamic models. The electrical model describes the actuator as a resistive-capacitive (RC) transmission line, whereas the mechanical model describes the actuator as a system of rigid links connected by spring-damping elements. The proposed modeling approach is validated by experimental data, and the results are discussed.

There has been a substantial increase in the usage of natural fibers and biodegradable polymers in composite materials due to the recent focus on sustainability of materials. Flax fibers have exhibited higher mechanical properties compared to most other natural fibers available. However, one of the major challenges faced in the use of flax fiber is its hydrophilicity. In this study, the tensile behavior of flax fiber tows removed from commercially available woven fabrics were investigated at different moisture levels. The breaking tenacity of fiber tows was shown to increase with an increase in moisture content of up to 25%. After this point, additional absorption of moisture resulted in a decrease of fiber tenacity. In addition, the diffusion process through flax fiber mat with different areal densities was investigated and the diffusion coefficients were determined using the desorption curves. Diffusion rates were not found to significantly change with varying areal densities of 200 to 400 gsm, but were significantly different when exposed to temperatures of 55 &deg, C versus 80 &deg, C.

Polymer based microfabrication technologies are used extremely in Bio-MEMS, especially in Microfluidic devices in recent years. In this paper, a novel method for fabrication of microstructures on a polymeric material using hot embossing lithography process is presented. The proposed method involves usage of low cost materials and procedure with respect to previous methods and can be processed in a short time. The master is made from SU-8 on an inexpensive glass substrate which is patterned by standard lithography. The embossing pressure can be increased in our master as the glass substrate used in this paper is more robust than Silicon. Master robustness and SU-8 to glass adhesion is optimized by some substrate pretreatments and SU-8 baking time and temperatures. Microchannels are replicated on a Polymethylmetacrylate (PMMA) stamp which is a plexiglass sheet with thickness of 1 mm. Significant embossing parameters including temperature, pressure and time are discussed and optimum values are determined. Microchannels are imprinted by depth of 50 μm and minimum width of 15 μm and aspect ratio more than 3. The microchannels are sealed by a PMMA cap using thermal annealing bonding.

The applications of self-healing in cement-based materials via biomineralization processes are developing quickly. The main challenge is to find a microorganism that can tolerate the restricted environment of cement paste matrix (i.e. very high pH, lack of oxygen and nutrients, small pore size etc.). The focus of this work was to determine the possible use of an ammonium salt-based air-entraining admixture (AEA) as a protection method to improve the survival of incorporated Sporosarcina pasteurii cells in cement-based mortar. Bacterial cells were directly added to the mortar mix with and without nutrients. Nutrients should be provided to keep the microorganisms viable even at early ages (i.e. 7 days). Surface charge of the bacterial cells and in vitro biogenic calcium carbonate (CaCO3) precipitation were not affected by the incorporation of AEA. However, introducing AEA did not influence the viability in mortar samples, which might be attributed to the type and chemistry of AEA used.

Because of their structure, natural fibers exhibit nonlinear viscoelastic behavior. Thermoset resins also behave in a similar way. With the increase in structural applications of bio-based composites, the long-term creep behavior of these materials becomes a significant issue. Time-Temperature superposition (TTS) provides a useful tool to overcome the challenge of needing a long time to perform creep tests. TTS principle assumes that the effect of temperature and time are equivalent when considering the creep behavior. In this study, frequency scans of flax/VE composites were obtained at different temperatures and storage modulus, loss modulus and tan δ were recorded. Application of horizontal and vertical shift factors to all three viscoelastic functions were studied. In addition, short-term strain creeps at different temperatures were measured and curves were shifted both with only horizontal, and with both horizontal and vertical shift factors. Resulting master curves were compared with a 24-h creep test and two creep models. Findings revealed that use of both horizontal and vertical shift factors will result in a smoother master curve for viscoelastic functions, while use of only horizontal shift factors for creep data provides an acceptable creep strain master curve. Consequently flax/VE composites can be considered as thermorheologically complex materials.

In this article, analytical dynamic model derivation and robust position control of a microrobot based on fast trilayer polypyrrole-bending actuators employing quantitative feedback theory is presented. The conjugated polymer actuators based on polypyrrole can be employed to achieve microscale precision positioning, having a wide range of application including biomimetic robots and biomedical devices. There has been extensive research on modeling the electrochemical dynamics of polypyrrole bending actuators. However, the mechanical dynamics modeling of actuator remains to be unexplored. In this article, we first develop a proper mechanical dynamics model for the fast-conducting polymer actuators that matches well with the existing experimental results and then extend it to a microrobot. In the controlling part, the robust control quantitative feedback theory will be used to control the microrobot with variable tip loading. The numerical simulation results show that the quantitative feedback theory controller has consistent and robust-tracking performance.

Conjugated polymers are emerging materials which have a wide range of applications including biomimetic robots and biomedical devices. These novel materials attract considerable attention owing to their interesting sensing and actuating behavior. However, complicated electro-chemo-mechanical dynamics is a drawback for their application in functional devices. Although extensive research has been conducted on static modeling of conductive polymers, the dynamic modeling is not well understood. In this paper we focus on dynamic modeling and robust control of a fast trilayer polypyrrole actuator as a distributed parameter system. The Euler–Bernoulli beam model with inclusion of Kelvin–Voigt damping and tip loading is utilized for vibration analysis of the smart actuator. Considering the spatio-temporal dynamics of the actuator, a one-point feedback controller based on quantitative feedback theory is designed that can suppress arbitrary external disturbances and consistently track desired inputs.

CH3NH3SnIxCl3-x were synthesized at various synthesis temperatures. UV-Vis absorption portrays maximum absorption for the sample prepared at 120 ○C whose band gap (1.25 eV) is lower than Pb-based ones (1.55 eV).

In recent years there has been a resurgence of interest in the usage of natural fiber reinforced composites in more advanced structural applications. As a result, the need for improving their mechanical properties, as well as service life modeling and predictions have arisen. In this study effect of alkaline treatment of flax fiber as well as addition of 1% acrylic resin to vinyl ester on mechanical properties and long-term creep behavior of flax/vinyl ester composites was investigated. To perform the alkaline treatment, fibers were immersed into 1500 mL of 10 g/L sodium hydroxide/ethanol solution at 78 °C for 2 h. Findings revealed that alkaline treatment was successful in increasing interlaminar shear, tensile and flexural strength of the composite but decreased the tensile and flexural modulus by 10%. Addition of acrylic resin to the vinyl ester resin improved all mechanical properties except the flexural modulus which was decreased by 5%. In order to evaluate the long-term behavior, creep compliance master curves were generated using the time-temperature superposition principle. Results suggests that fiber and matrix treatments delay the creep response and slows the process of creep in flax/vinyl ester composites in the steady state region, respectively.

This paper presents an electrowetting-on-dielectric (EWOD)-based droplet mixing and splitting device. In the proposed method, the droplet is sandwiched between the bottom and top substrate plates of the EWOD device. A dielectric layer of Parylene C and a thin coating of a hydrophobic Teflon layer are used to create the EWOD device. The device actuates the droplets by applying an electric potential and thus increases the wettability of the droplet on the EWOD surface. The Finite Element Method (FEM) based Coventorware software is used to accomplish the simulations. The simulated result shows that a significant change in contact angle (120° to 80°) of the droplet is occurred during the operations of both mixing and splitting. The EWOD device with Parylene C layer of 2 μm thickness and Teflon layer of 50 nm thickness started both droplet mixing and splitting operations at a low actuation voltage of 30 V.

With the increase in structural applications of bio-based composites, the study of long-term creep behavior of these materials turns into a significant issue. Because of their bond type and structure, natural fibers and thermoset resins exhibit nonlinear viscoelastic behavior. Time-temperature superposition (TTS) provides a useful tool to overcome the challenge of the long time required to perform the tests. The TTS principle assumes that the effect of temperature and time are equivalent when considering the creep behavior, therefore creep tests performed at elevated temperatures may be converted to tests performed at longer times. In this study, flax fiber composites were processed with a novel liquid molding methacrylated epoxidized sucrose soyate (MESS) resin. Frequency scans of flax/MESS composites were obtained at different temperatures and storage modulus and loss modulus were recorded and the application of horizontal and vertical shift factors to these viscoelastic functions were studied. In addition, short-term strain creep at different temperatures was measured and curves were shifted with solely horizontal, and with both horizontal and vertical shift factors. The resulting master curves were compared with a 24-h creep test and two extrapolated creep models. The findings revealed that use of both horizontal and vertical shift factors will result in a smoother master curves for loss modulus and storage modulus, while use of only horizontal shift factors for creep data provides acceptable creep strain master curves. Based on the findings of this study, flax/MESS composites can be considered as thermorheologically complex materials.