Excellence in Research and Innovation for Humanity

International Science Index

Commenced in January 1999 Frequency: Monthly Edition: International Abstract Count: 48505

Materials and Metallurgical Engineering

1683
83783
Identification of Damage Mechanisms in Interlock Reinforced Composites Using a Pattern Recognition Approach of Acoustic Emission Data
Abstract:
The latest advances in the weaving industry, combined with increasingly sophisticated means of materials processing, have made it possible to produce complex 3D composite structures. Mainly used in aeronautics, composite materials with 3D architecture offer better mechanical properties than 2D reinforced composites, especially with multi-axial stresses. Nevertheless, these materials require a good understanding of their behavior. Because of the complexity of such materials, the damage mechanisms are multiple, and the scenario of their appearance and evolution depends on the nature of the exerted solicitations. In order to better understand the damage scenarios of interlock composite materials, a multi-instrumentation was set-up in this work for tracking damage initiation and development, especially in the vicinity of the first significant damage, called macro-damage. The deployed instrumentation includes video-microscopy, Digital Image Correlation, Acoustic Emission (AE) and micro-tomography. The AE is a tool for discriminating between these mechanisms by extracting relevant features from the recorded signals, followed by an analysis of the data using pattern recognition techniques. In this study, a multi-variable AE data analysis approach was developed for the discrimination between the different signal classes representing the different emission sources during testing. Unsupervised classification technique was employed, without prior knowledge, to perform AE data clustering. The multi-instrumentation and the clustered data serve to label the different signal families and build a learning database. This latter is useful to construct a supervised classifier that can be used for automatic recognition of the AE signals. Different materials with different ingredients were tested under various solicitations in order to feed and enrich the learning database. The methodology presented in this work was useful to refine the first damage threshold for the new generation materials. The damage mechanisms around this threshold were highlighted. Signal classes were assigned to the different mechanisms. The isolation of a 'noise' class makes it possible to discriminate between the signals emitted by damages without resorting to spatial filtering or increasing the AE detection threshold. The approach was validated on different material configurations. For the same material and the same type of solicitation, the identified classes are reproducible and little disturbed. The supervised classifier constructed based on the learning database was able to predict the labels of the classified signals.
Digital Article Identifier (DAI):
1682
83694
Single Process Production of Cost-Efficient Hybrid Tapes from Mechanical Spread Heavy Tows and Thermoplastic Yarns
Abstract:
The importance of producing lightweight high-tech products has grown in the last decades by a large quantity. Composites with fiber reinforcement play the leading role in this development. By offering high tensile properties while density is low, fiber-reinforced plastics allow to create new products and overcome the limitations of conventional materials. Not only aerospace, automotive, construction or maritime companies have seen its potential, but companies in sport, medicine, design and so on have brought products of fiber-reinforced plastics in all aspects of our daily life. Besides thermoset materials, thermoplastic materials are increasingly used in the automotive sector due to its recyclability potential and improved processing techniques. A widely used method for the production of thermoplastic composites like pipes and containers is the tape winding process. A tape contains uni-directional fibers spread out side by side in a narrow array, which are pre-consolidated in a thermoplastic matrix. For tape winding, these continuous tapes are automatically wound around a mandrel in multiple layers while being heated in order to form the composite. The processes involved have significant drawbacks, e.g. the high energy demand which is necessary to coat the filaments in a thermoplastic material. The highly viscous thermoplastic needs to cover long distances in order to fully cover the reinforcement filaments. This also prolongs cycle time significantly. This study introduces a process that avoids long flowing paths by incorporating thermoplastic yarns into the tape creation process while evenly distributing these filaments next to the reinforcement fibers. With this technology a new generation of tapes is formed out of cost-saving heavy tows combined with thermoplastic filaments. These filaments are spread thin over a variable width, reducing the overall area density. The created textile is only lightly thermally fixated to form an interconnected strong tape that still holds the textile character. This unique flexibility ensures a better drapability, opening the tape winding process for more complex geometries and other versatile products. In the second part of this study, these tapes are introduced into the non-crimp production process. A tape layer was designed to insert these flexible hybrid tapes into the multiaxial warp-knitting machine. The produced non-crimp fabrics have the advantage of containing multiple fiber layers in different direction. The present study contains a detailed description of the created process. Different material combinations and fiber-volume ratios are used in order to cover different application fields. This includes heavy tows of carbon combined with polyamide 6 and glass fibers with polypropylene. Properties of the produced tapes were directly controlled through machine parameters. The so created Pre-consolidated tapes and composites of uni-directional tapes and multidirectional non-crimp fabrics were tested. The involved tests range from grinding patterns for determining the homogeneity over determining the dimension stability to tensile tests. The findings show that hybridized tapes with a wide range of different dimensional properties and homogeneous fiber distribution can be produced in order to supplement the line of offered Tapes. In addition the process involved allows for a faster cycle time and reduced energy consumption, reducing the overall cost of the Tape production process.
Digital Article Identifier (DAI):
1681
83643
Induction Heating and Electromagnetic Stirring of Bi-Phasic Metal/Glass Molten Bath for Mixed Nuclear Waste Treatment
Abstract:
For nuclear waste treatment and confinement, a specific IN-CAN melting module based on low-frequency induction heating have been designed. The frequency of 50Hz has been chosen to improve penetration length through metal. In this design, the liquid metal, strongly stirred by electromagnetic effects, presents shape of a dome caused by strong Laplace forces developing in the bulk of bath. Because of a lower density, the glass phase is located above the metal phase and is heated and stirred by metal through interface. Electric parameters (Intensity, frequency) give precious information about metal load and composition (resistivity of alloy) through impedance modification. Then, power supply can be adapted to energy transfer efficiency for suitable process supervision. Modeling of this system allows prediction of metal dome shape (in agreement with experimental measurement with a specific device), glass and metal velocity, heat and motion transfer through interface. MHD modeling is achieved with COMSOL and Fluent. First, a simplified model is used to obtain the shape of the metal dome. Then the shape is fixed to calculate the fluid flow and the thermal part.
Digital Article Identifier (DAI):
1680
83495
UV Resistibility of a Carbon Nanofiber Reinforced Polymer Composite
Abstract:
Nowadays, a great concern is placed on the harmfulness of ultraviolet radiation (UVR) which attacks human bodies. Nanocarbon materials, such as carbon nanotubes (CNTs), carbon nanofibers (CNFs) and graphene, have been considered promising alternatives to shielding materials because of their excellent electrical conductivities, very high surface areas, and low densities. In the present work, carbon nanofibers have been synthesized from solutions of Polyacrylonitrile (PAN)/ N,N-dimethylformamide (DMF) by electrospinning method. The carbon nanofibers have been stabilized by oxidation at 250 °C for 2 h in air and carbonized at 750 °C for 1 h in H₂/N₂. We present the fabrication and characterization of transparent and ultraviolet (UV) shielding CNF/polymer composites. The content of CNF filler has been varied from 0.01 to 0.05 weight fraction. Ultraviolet-visible (UV–vis) Spectroscopy has been performed to study the effect of thickness and composition on the vis transmittance of polymer composites.
Digital Article Identifier (DAI):
1679
83481
Application of Genetic Programming for Evolution of Glass-Forming Ability Parameter
Abstract:
A few glass forming ability expressions in terms of characteristic temperatures have been proposed in the literature. Attempts have been made to correlate the expression with the critical diameter of the bulk metallic glass composition. However, with the advent of new alloys, many exceptions have been noted and reported. In the present approach, a genetic programming based code which generates an expression in terms of input variables, i.e., three characteristic temperatures viz. glass transition temperature (Tg), onset crystallization temperature (Tx) and offset temperature of melting (Tl) with maximum correlation with a critical diameter (Dmax). The expression evolved shows improved correlation with the critical diameter. In addition, the expression can be explained on the basis of time-temperature transformation curve.
Digital Article Identifier (DAI):
1678
83402
Post Coronary Artery Stenting Reflighting: Need for Change in Policy with Changing Antiplatelet Therapy
Abstract:
Background: Coronary artery Disease (CAD) is a common cause of morbidity, mortality and reason for unfitness amongst aircrew. Coronary angioplasty and stenting are the standard of care for CAD. Antiplatelet drugs like Aspirin and Clopidogrel(Dual Antiplatelet therapy) are routinely prescribed post-stenting which are permitted for flying. However, in the recent past, Ticagrelor is being used in place of Clopidogrel as per ACC AHA and ESC guidelines. However Ticagrelor is not permitted for flying. Case Presentation: A 55-year-old pilot suffered Anterior Wall Myocardial Infarction. Angiography showed blockages in Left Anterior Descending Artery(LAD) and Right coronary artery (RCA). He underwent primary angioplasty and stenting LAD and subsequent stenting to RCA. Recovery was uneventful. One year later he was asymptomatic with normal Left ventricular function and no reversible perfusion defect on stress MPI. He had patent stents and coronaries on check angiogram. However, he was not allowed to fly since he was on Ticagrelor. He had to be switched over to Clopidogrel from Ticagrelor one year after stenting to permit him for flying. Similarly, switching had to be done in a 45-year-old pilot. Ticagrelor has been proven to be more effective than clopidogrel and as safe as Clopidogrel in preventing stent thrombosis. If Clopidogrel is being permitted, there is no need to restrict Ticagrelor. Hence "Policy" needs to be changed. Conclusions: Dual Antiplatelet therapy is the standard of care post coronary stenting which has been proved safe and effective. Policy needs to be changed to permit flying with Ticagrelor which is more effective than Clopidogrel and equally safe.
Digital Article Identifier (DAI):
1677
83345
Fabrication of Profile-Coated Rhodium X-Ray Focusing Mirror
Abstract:
A pair of Kirkpatrick-Baez (KB) mirrors were designed and fabricated for experiments within a hard x-ray energy range lower than 20 kev at beamline 20-ID in a synchrotron radiation facility, Advanced Photon Source (APS). The KB mirrors were deposited with Rhodium thin films using a customized designed and self-built magnetron sputtering system. The purpose of these mirrors is to focus the x-ray beam down to 1 micron. This is the first pair of Rhodium-coated KB mirrors with elliptical shape that was fabricated using the profile coating technique. The profile coating technique is to coat the substrate with designed shape using masks during the deposition. The mirrors were equipped at the beamline and achieved the designed focusing requirement. The details of the mirror design, the fabrication process, and the customized magnetron sputtering deposition system will be discussed.
Digital Article Identifier (DAI):
1676
83228
Effect of Fibres-Chemical Treatment on the Thermal Properties of Natural Composites
Abstract:
In the last decade, investments in sustainable processes and products have gained space in several segments, such as in the civil, automobile, textile and other industries. In addition to increasing concern about the development of environmentally friendly materials that reduce, energy costs and reduces environmental impact in the production of these products, as well as reducing CO2 emissions. Natural fibers offer a great alternative to replace synthetic fibers, totally or partially, because of their low cost and their renewable source. The purpose of this research is to study the effect of surface chemical treatment on the thermal properties of hybrid fiber reinforced natural fibers (NFRC), jute + ramie, jute + sisal, jute + curauá, and jute fiber in polymer matrices. Two types of chemical treatment: alkalinization and silanization were employed, besides the condition without treatment. Differential scanning calorimetry (DSC), thermogravimetry (TG) and dynamic-mechanical analysis (DMA) were performed to explore the thermal stability and weight loss in the natural fiber reinforced composite as a function of chemical treatment.
Digital Article Identifier (DAI):
1675
83005
Effects of Sintering Temperature on Microstructure and Mechanical Properties of Nanostructured Ni-17Cr Alloy
Abstract:
Spark Plasma Sintering technique is a novel processing method that produces limited grain growth and highly dense variety of materials; alloys, superalloys, and carbides just to mention a few. However, initial particle size and spark plasma sintering parameters are factors which influence the grain growth and mechanical properties of sintered materials. Ni-Cr alloys are regarded as the most promising alloys for aerospace turbine blades, owing to the fact that they meet the basic requirements of desirable mechanical strength at high temperatures and good resistance to oxidation. The conventional method of producing this alloy often results in excessive grain growth and porosity levels that are detrimental to its mechanical properties. The effect of sintering temperature was evaluated on the microstructure and mechanical properties of the nanostructured Ni-17Cr alloy. Nickel and chromium powder were milled using high energy ball milling independently for 30 hours, milling speed of 400 revs/min and ball to powder ratio (BPR) of 10:1. The milled powders were mixed in the composition of Nickel having 83 wt % and chromium, 17 wt %. This was sintered at varied temperatures from 800°C, 900°C, 1000°C, 1100°C and 1200°C. The structural characteristics such as porosity, grain size, fracture surface and hardness were analyzed by scan electron microscopy and X-ray diffraction, Archimedes densitometry, micro-hardness tester. The corresponding results indicated an increase in the densification and hardness property of the alloy as the temperature increases. The residual porosity of the alloy reduces with respect to the sintering temperature and in contrast, the grain size was enhanced. The study of the mechanical properties, including hardness, densification shows that optimum properties were obtained for the sintering temperature of 1100°C. The advantages of high sinterability of Ni-17Cr alloy using milled powders and microstructural details were discussed.
Digital Article Identifier (DAI):
1674
82983
Vibration Reduction of Mechanical Presses by Use of an Adaptive Mass Balancing System
Abstract:
The inertial forces of presses with mechanical linkages tend to cause oscillations as a result of moving drive parts, especially at high stroke rates. Conventionally, mass balancing systems which are rigidly connected to the drive train are used to avoid these vibrations. Generally, during the design process of presses and its mass balancing system, an estimated tool weight and/or center of gravity are used. However, real tools in the manufacturing industry differ in some cases significantly from the estimated tool, which, as a result, generates continued mechanical oscillations within the presses. The presented paper introduces a new approach for a mass-balancing system based on four linear motors which are attached to the press frame. These motors create through movement of attached weights inertial forces which act in the opposite direction of the inertial forces and thus absorb the press oscillations. The control signals of the four motors are independently modified by an evolutionary optimization algorithm which operates on the base of the measured oscillations of the press frame. The usage of the optimization algorithm allows the mass balancing system to adapt itself to varying production conditions such as the tool weight, the center of gravity of the tool, the stroke height or the stroke rate of the press. The publication provides the results of the conceptual design, the virtual testing, and optimization of this approach, which has been mainly carried out through multiple-body simulations. Furthermore, this paper shows the experimental application of the approach, a comparison between the simulation results and practical experiment, as well as, a further consideration of how this approach can be implemented into practical use.
Digital Article Identifier (DAI):
1673
82971
An Analysis of Packaging Materials for an Energy-Efficient Wrapping System
Abstract:
Shrink wrapping is widely used as a method for secondary packaging to assemble individual items, such as cans or other consumer products, into single packages. This method involves conveying the packages into heated tunnels and so has the disadvantages that it is energy-intensive, and, in the case of aerosol products, potentially hazardous. We are developing an automated packaging system that uses stretch wrapping to address both these problems, by using a mechanical rather than a thermal process. In this study, we present a comparative study of shrink wrapping and stretch wrapping materials to assess the relative capability of candidate stretch wrap polymer film in terms of mechanical response. The stretch wrap materials are of oriented polymer and therefore elastically anisotropic. We are developing material constitutive models that include both anisotropy and nonlinearity. These material models are to be incorporated into computer simulations of the automated stretch wrapping system. We present results showing the validity of these models and the feasibility of applying them in the simulations.
Digital Article Identifier (DAI):
1672
82960
Design Study on a Contactless Material Feeding Device for Electro Conductive Workpieces
Abstract:
A growing demand on the production rate of modern presses leads to higher stroke rates. Commonly used material feeding devices for presses like grippers and roll-feeding systems can only achieve high stroke rates along with high gripper forces, to avoid stick-slip. These forces are limited by the sensibility of the surfaces of the workpieces. Stick-slip leads to scratches on the surface and false positioning of the workpiece. In this paper, a new contactless feeding device is presented, which develops higher feeding force without damaging the surface of the workpiece through gripping forces. It is based on the principle of the linear induction motor. A primary part creates a magnetic field and induces eddy currents in the electrically conductive material. A Lorentz-Force applies to the workpiece in feeding direction as a mutual reaction between the eddy-currents and the magnetic induction. In this study, the FEA model of this approach is shown. The calculation of this model was used to identify the influence of various design parameters on the performance of the feeder and thus showing the promising capabilities and limits of this technology. In order to validate the study, a prototype of the feeding device has been built. An experimental setup was used to measure pulling forces and placement accuracy of the experimental feeder in order to give an outlook of a potential industrial application of this approach.
Digital Article Identifier (DAI):
1671
82959
Monitoring the Production of Large Composite Structures Using Dielectric Tool Embedded Capacitors
Abstract:
With the rise of public awareness on climate change comes an increasing demand for renewable sources of energy. As a result, the wind power sector is striving to manufacture longer, more efficient and reliable wind turbine blades. Currently, one of the leading causes of blade failure in service is improper cure of the resin during manufacture. The infusion process creating the main part of the composite blade structure remains a critical step that is yet to be monitored in real time. This stage consists of a viscous resin being drawn into a mould under vacuum, then undergoing a curing reaction until solidification. Successful infusion assumes the resin fills all the voids and cures completely. Given that the electrical properties of the resin change significantly during its solidification, both the filling of the mould and the curing reaction are susceptible to be followed using dieletrometry. However, industrially available dielectrics sensors are currently too small to monitor the entire surface of a wind turbine blade. The aim of the present research project is to scale up the dielectric sensor technology and develop a device able to monitor the manufacturing process of large composite structures, assessing the conformity of the blade before it even comes out of the mould. An array of flat copper wires acting as electrodes are embedded in a polymer matrix fixed in an infusion mould. A multi-frequency analysis from 1 Hz to 10 kHz is performed during the filling of the mould with an epoxy resin and the hardening of the said resin. By following the variations of the complex admittance Y*, the filling of the mould and curing process are monitored. Results are compared to numerical simulations of the sensor in order to validate a virtual cure-monitoring system. The results obtained by drawing glycerol on top of the copper sensor displayed a linear relation between the wetted length of the sensor and the complex admittance measured. Drawing epoxy resin on top of the sensor and letting it cure at room temperature for 24 hours has provided characteristic curves obtained when conventional interdigitated sensor are used to follow the same reaction. The response from the developed sensor has shown the different stages of the polymerization of the resin, validating the geometry of the prototype. The model created and analysed using COMSOL has shown that the dielectric cure process can be simulated, so long as a sufficient time and temperature dependent material properties can be determined. The model can be used to help design larger sensors suitable for use with full-sized blades. The preliminary results obtained with the sensor prototype indicate that the infusion and curing process of an epoxy resin can be followed with the chosen configuration on a scale of several decimeters. Further work is to be devoted to studying the influence of the sensor geometry and the infusion parameters on the results obtained. Ultimately, the aim is to develop a larger scale sensor able to monitor the flow and cure of large composite panels industrially.
Digital Article Identifier (DAI):
1670
82950
Elastomeric Nanocomposites for Space Applications
Abstract:
Elastomeric composites have been known for a long time, but, to our knowledge, space and the aeronautic community has been directing a special attention to them only in the last decade. The required properties of advanced elastomeric materials used in space applications (such as O-rings) are sealing, abrasion, low-temperature flexibility, the long-term compression set properties, impact resistance and low-temperature thermal stability in different environments, such as ionized radiations. Basically, the elastomeric nanocomposites are composed of a rubber matrix and a wide and varied range of nanofillers, added with the aim of improving the physico-mechanical and elasticity modulus properties of the materials as well as their stability in different environments. The paper presents a partial synthesis of the research regarding the use of silicon carbide in nanometric form and/or organophylized montmorillonite as fillers in butyl rubber matrix. The need of composite materials arose from the fact that stand-alone polymers are ineffective in providing all the superior properties required by different applications. These drawbacks can be diminished or even eliminated by incorporating a new range of additives into the organic matrix, fillers that have important roles in modifying properties of various polymers. A composite material can provide superior and unique mechanical and physical properties because it combines the most desirable properties of its constituents while suppressing their least desirable properties. The commercial importance of polymers and the continuous increase of their use results in the continuous demand for improvement in their properties to meet the necessary conditions. To study the performance of the elastomeric nanocomposites were mechanically tested, it will be tested the qualities of tensile at low temperatures and RT and the behavior at the compression at cryogenic to room temperatures and under different environments. The morphology of specimens will be investigated by optical and scanning electronic microscopy.
Digital Article Identifier (DAI):
1669
82947
Elaboration and Characterization of Green Wood-Biopolymer Composites
Abstract:
In the past two decades, Wood-Plastic Composites (WPCs) became an unmissable material not only because of the growing market purposes but also the scientific challenges. Their low production cost and the potential valorization of woody residues (or wood by-products) contribute to their attractiveness thus allowing to replace some commonly used polymers (PE, PP, PVC) by WPCs in several industrial sectors like automobile, construction, and furniture. On the other hand, some properties of WPCs can be tailored by adjusting the wood and polymer parameters. This study is focused on the elaboration and characterization of green WPCs by blending a biopolymer (Bioplast GS2189 supplied by Biotec-Germany) and spruce sawdust. Bioplast is a plasticizer-free thermoplastic material highly enriched in biologically-sourced raw materials and entirely biodegradable in an industrial composting environment. The spruce is a local species and its sawdust is often considered as a waste product from the local sawmills. Thus, the elaborated WPCs through this study are new eco-friendly materials. The spruce sawdust used as filler was obtained by using a sieve with a mesh size of 400 µm. The WPCs with different amount of wood (10, 15, 20, 25, 30 w%) were elaborated by blending the melt polymer and wood particles in a twin screw Brabender blender at 180°C. Then the mixtures with different composition ratios were shaped in an injection mold. The obtained WPCs samples were characterized according to their mechanical, thermal, structural and rheological properties, as well as their resistance to fungi and termites exposures. The water absorption and color measurement experiments were also performed on WPCs and the results were compared with those obtained on the neat polymer. The addition of wood particles into the Bioplast increases the stiffness of WPCs as measured by tensile and three-point bending tests. The crystallization and melt temperatures of WPCs seem to increase compared to those of raw polymer. The water absorption kinetics of WPCs is also observed. The Melt Flow Index (MFI) is highly decreased with increasing amount of wood particles in polymer. The mass losses due to the termites and fungal degradations are measured, showing that an increase of mass losses with increasing amount of wood content in Bioplast. All the results show that the polymer properties are modified by the presence of wood particles in WPCs.
Digital Article Identifier (DAI):
1668
82926
Influence of Kneading Conditions on the Textural Properties of Alumina Catalysts Supports for Hydrotreating
Abstract:
Mesoporous alumina is commonly used as a catalyst support for the hydrotreating of heavy petroleum cuts. The process of fabrication usually involves: the synthesis of the boehmite AlOOH precursor, a kneading-extrusion step, and a calcination in order to obtain the final alumina extrudates. Alumina is described as a complex porous medium, generally agglomerates constituted of aggregated nanocrystallites. Its porous texture directly influences the active phase deposition and mass transfer, and the catalytic properties. Then, it is easy to figure out that each step of the fabrication of the supports has a role on the building of their porous network, and has to be well understood to optimize the process. The synthesis of boehmite by precipitation of aluminum salts was extensively studied in the literature and the effect of various parameters, such as temperature or pH, are known to influence the size and shape of the crystallites and the specific surface area of the support. The calcination step, through the topotactic transition from boehmite to alumina, determines the final properties of the support and can tune the surface area, pore volume and pore diameters from those of boehmite. However, the kneading extrusion step has been subject to a very few studies. It generally consists in two steps: an acid, then a basic kneading, where the boehmite powder is introduced in a mixer and successively added with an acid and a base solution to form an extrudable paste. During the acid kneading, the induced positive charges on the hydroxyl surface groups of boehmite create an electrostatic repulsion which tends to separate the aggregates and even, following the conditions, the crystallites. The basic kneading, by reducing the surface charges, leads to a flocculation phenomenon and can control the reforming of the overall structure. The separation and reassembling of the particles constituting the boehmite paste have a quite obvious influence on the textural properties of the material. In this work, we are focused on the influence of the kneading step on the alumina catalysts supports. Starting from an industrial boehmite, extrudates are prepared using various kneading conditions. The samples are studied by nitrogen physisorption in order to analyze the evolution of the textural properties, and by synchrotron small-angle X-ray scattering (SAXS), a more original method which brings information about agglomeration and aggregation of the samples. The coupling of physisorption and SAXS enables a precise description of the samples, as same as an accurate monitoring of their evolution as a function of the kneading conditions. These ones are found to have a strong influence of the pore volume and pore size distribution of the supports. A mechanism of evolution of the texture during the kneading step is proposed and could be attractive in order to optimize the texture of the supports and then, their catalytic performances.
Digital Article Identifier (DAI):
1667
82805
Effect of Ce Addition on Mechanical Properties and Shape Memory Effect of Cu-14%Al-4.5%Ni Shape Memory Alloy
Abstract:
This paper aims to study the effect of Ce addition on mechanical properties and shape memory effect of Cu-based SMA (Shape Memory Alloy) in which Ce was added in three different percentages (0.3%, 1.0% and 3%) to base alloy (Cu-14%Al-4.5%Ni). Many tests and inspections such as XRD, compression test, HV hardness, thermo-mechanical test were performed on the Ce-modified alloys. Also, Differential Scanning Calorimetry (DSC) test and microstructure observation by optical and SEM for all alloys were done. The results showed that an increase in hardness, yield strength and maximum strain (ε max%) with increasing Ce % in base SMA (except in case of 3% Ce). It was seen that the thermo-mechanical properties showed an increase in recovery strain up to 98.72% with decrease in martensite modulus of elasticity and increase in austenite modulus of elasticity. Also, the transformation temperatures shifted to beyond the domain of the base SMA (100-170 ºC) and the SMA modified with 3% Ce showed better results than other alloys.
Digital Article Identifier (DAI):
1666
82765
Experimental and Simulation Stress Strain Comparison of Hot Single Point Incremental Forming
Abstract:
Induction assisted single point incremental forming (IASPIF) is a flexible method and can be simply utilized to form high strength alloys. Due to the interaction between the mechanical and thermal properties during IASPIF an evaluation of the process is necessary to be performed analytically. Therefore, a numerical simulation was carried out in this paper. The numerical analysis was operated at both room and elevated temperatures, then compared with experimental results. Fully coupled dynamic temperature displacement explicit analysis was used to simulated the hot single point incremental forming. The numerical analysis was indicating that during hot single point incremental forming were a combination between complicated compression, tension, and shear stresses. As a result, the equivalent plastic strain was increased excessively by rising both the formed part depth and the heating temperature during forming. Whereas, the forming forces were decreased from 5 kN at room temperature to 0.95 kN at elevated temperature. The simulation shows that the maximum true strain occurred in the stretching zone which was the same as in experiment.
Digital Article Identifier (DAI):
1665
82761
Characterization of the Long-Term Viscoelastic Behavior of Polymeric Composites
Abstract:
Dynamic mechanical analysis (DMA) is one of the most used experimental techniques to investigate the temperature and frequency dependence of the mechanical behavior of viscoelastic materials. The measured data are generally shifted by the application of the principle of the time– temperature superposition (TTS) to obtain the viscoelastic system’s master curve. The aim of this work is to show the methodology to define the horizontal shift factor to be applied to the storage modulus measured in order to indicate the validity of (TTS) principle for this material system. This principle was successfully used to determine the long-term properties of the Sheet Moulding Compound (SMC) composites.
Digital Article Identifier (DAI):
1664
82722
Properties of Composite Materials Made from Surface Treated Particles from Annual Plants
Abstract:
Annual plants are becoming more and more popular source of lignin and cellulose. In those days a lot of research is carried out in order to evaluate the possibility of utilization of fibres and particles from these plants in composite materials production. These lingo-cellulosic materials seem to be a great alternative to wood, however, due to waxy and silica layers on the surface of these stalks, one additional technological step is needed–erosion of the layers for the purpose of achieving better adhesion between particle and adhesive. In this research, we used several kinds of particle pre-treatment, in order to modify surface properties of these particles. Further, an adhesive was applied to the particles using laboratory blender and board were produced using laboratory press. Both physical and mechanical properties of boards were observed. It was found out that the surface modification of particles had statistically significant effect on properties of produced boards.
Digital Article Identifier (DAI):
1663
82705
Characteristics of Silicon Integrated Vertical Carbon Nanotube Field-Effect Transistors
Authors:
Abstract:
A new vertical carbon nanotube field effect transistor (CNTFET) has been developed. The source, drain and gate are vertically stacked in this structure. The carbon nanotubes are put on the side wall of the vertical stack. Unique transfer characteristics which depend on both silicon type and the sign of drain voltage have been observed in silicon integrated CNTFETs. The significant advantage of this CNTFET is that the short channel of the transistor can be fabricated without using complicate lithography technique.
Digital Article Identifier (DAI):
1662
82683
Solvent extraction of Rb and Cs from Jarosite slag using t-BAMBP
Authors:
Abstract:
Lepidolite after extraction of Lithium by sulfate produced many jarosite slag which contains a lot of Rb and Cs.The separation and recovery of Rubidium(Rb) and Cesium(Cs) can make full of use of Lithium mica. XRF analysis showed that the slag mainly including K Rb Cs Al and etc. Fractional solvent extraction tests were carried out; the results show that using20% t-BAMBP plus 80% sulfonated kerosene, the separation of Rb and Cs can be achieved by adjusting the alkalinity. Extraction is the order of Cs Rb, ratio of Cs to Rb and ratio of Rb to K can reach above 1500 and 2500 respectively.
Digital Article Identifier (DAI):
1661
82651
Parameter Optimization and Thermal Simulation in Laser Joining of Coach Peel Panels of Dissimilar Materials
Abstract:
The quality of laser welded-brazed (LWB) joints were strongly depend on the main process parameters, therefore the effect of laser power (3.2–4 kW), welding speed (60–80 mm/s) and wire feed rate (70–90 mm/s) on mechanical strength and surface roughness were investigated in this study. The comprehensive optimization process by means of response surface methodology (RSM) and desirability function were used for multi-criteria optimization. The experiments were planned based on Box–Behnken design implementing linear and quadratic polynomial equations for predicting the desired output properties. Finally, validation experiments were conducted on an optimized process condition which exhibited good agreement between the predicted and experimental. AlSi3Mn1 was selected as the filler material for joining aluminum alloy 6022 and hot-dip galvanized steel in coach peel configuration. The high scanning speed could control the thickness of IMC as thin as 5 µm. The thermal simulations of joining process was conducted by the Finite Element Method (FEM), and results were validated through experimental data. The Fe/Al interfacial thermal history evidenced that the duration of critical temperature range (700–900 °C) in this high scanning speed process was less than 1 s. This short interaction time leads to the formation of reaction-control IMC layer instead of diffusion-control mechanisms.
Digital Article Identifier (DAI):
1660
82601
Shuffled Structure for 4.225 GHz Antireflective Plates: A Proposal Proven by Numerical Simulation
Abstract:
A newly proposed antireflective selector with shuffled structure is reported in this paper. The proposed idea is made of two different quarter wavelength (QW) slabs and numerically supported by the one-dimensional simulation results provided by the method of characteristics (MOC) to function as an antireflective selector. These two QW slabs are characterized by dielectric constants εᵣA and εᵣB, uniformly divided into N and N+1 pieces respectively which are then shuffled to form an antireflective plate with B(AB)N structure such that there is always one εᵣA piece between two εᵣB pieces. Another is A(BA)N structure where every εᵣB piece is sandwiched by two εᵣA pieces. Both proposed structures are numerically proved to function as QW plates. In order to allow maximum transmission through the proposed structures, the two dielectric constants are chosen to have the relation of (εᵣA)² = εᵣB > 1. The advantages of the proposed structures over the traditional anti-reflection coating techniques are two components with two thicknesses and to shuffle to form new QW structures. The design wavelength used to validate the proposed idea is 71 mm corresponding to a frequency about 4.225 GHz. The computational results are shown in both time and frequency domains revealing that the proposed structures produce minimum reflections around the frequency of interest.
Digital Article Identifier (DAI):
1659
82591
Characterization of Electrospun Carbon Nanofiber Doped Polymer Composites
Abstract:
Ceramic, polymer and composite nanofibers are nowadays begun to be utilized in many fields of nanotechnology. By the means of dimensions, these fibers are as small as nano scale but because of having large surface area and microstructural characteristics, they provide unique mechanic, optical, magnetic, electronic and chemical properties. In terms of nanofiber production, electrospinning has been the most widely used technique in recent years. In this study, carbon nanofibers have been synthesized from solutions of Polyacrylonitrile (PAN)/ N,N-dimethylformamide (DMF) by electrospinning method. The carbon nanofibers have been stabilized by oxidation at 250 °C for 2 h in air and carbonized at 750 °C for 1 h in H2/N2. Images of carbon nanofibers have been taken with scanning electron microscopy (SEM). The images have been analyzed to study the fiber morphology and to determine the distribution of the fiber diameter using FibraQuant 1.3 software. Then polymer composites have been produced from mixture of carbon nanofibers and silicone polymer. The final polymer composites have been characterized by X-ray diffraction method, four point probe technique (FPPT), and energy dispersive X-ray (EDX) measurements. These results have been reported and discussed. At result, homogeneous carbon nanofibers with 40-250 nm of diameter were obtained with optimized electrospinning conditions.
Digital Article Identifier (DAI):
1658
82518
Polycaprolactone/Thermally Exfoliated Graphene Oxide Biocomposite Films: A Promising Moisture Absorption Behavior
Abstract:
Biocomposite materials were fabricated using mixing biodegradable polymer polycaprolactone (PCL) and Thermally Exfoliated Graphene Oxide (TEGO) through solution casting. Various samples of biocomposite films were prepared by varying the TEGO wt% composition by 0.1%, 0.5%, 1% and 1.5%. Thereafter, the density and water absorption of the composites were investigated with respect to immersion time in water. The moisture absorption results show that with an increase in weight percentage (from 0.1 to wt 1.5%) of TEGO within the biopolymer films, the absorption value of bio-nanocomposite films reduced rapidly from 27.4% to 14.3%. The density of hybrid composites also increased with increase in weight percentage of TEGO. These results indicate that the optimized composition of constituents in composite membrane could effectively reduce the anhydrous conditions of bio-composite film.
Digital Article Identifier (DAI):
1657
82505
Mechanical Properties of High Yield-To-Tensile Ratio High Strength Steels under Service Loading and the Structural Implications
Abstract:
High strength structural steels with a nominal yield strength in excess of 500 MPa offer the potential of structural weight reduction through reduced material usage. Today they are increasingly used in a range of structures including bridges, buildings and offshore structures. Many offshore structures such as jackets, topsides, jack-up structure legs, rack, pinions, etc., have successfully been fabricated and installed in the North Sea using high strength structural steels with nominal yield strength between 400 MPa and 800 MPa. Modern production routes for high strength structural steels, such as Quench and Tempered (QT) and Thermomechanically Controlled Rolled (TMCR), deliver high yield strengths, but with relatively less effect on the ultimate tensile strength resulting in high yield-to-tensile ratio (a proportion of the yield strength against the ultimate tensile strength). Consequently, the high yield-to-tensile ratio ( > 0.90) results in relevant design codes lacking confidence regarding performance. The concern is that these steels obtain their strength at the expense of ductility and strain hardening capacity when compared to low strength structural steel grades with yield-to-tensile ratio < 0.85. This study presents understanding into the mechanical properties and behaviour of high strength structural steels with yield-to-tensile ratio > 0.90 from which confidence and requirements regarding structural performance can be developed and re-evaluated in relevant codes and standards for these materials. The materials studied are S690QL and S960QL, typical high strength structural steels used in offshore applications produced using the QT route. Tension tests at different structural loading rates and Charpy V-Notch (CVN) impact tests were carried out on these grades at varying temperature conditions in order to characterise and predict the possible in-service structural performance in terms of strength and impact resistance. The results from the experimental tensile tests show that S690QL and S960QL are relatively unaffected by the effect of loading rate from quasi-static up to 4s-1 strain rates (typical strain rate that offshore or marine structures may be subjected to) as a result of the strength level with the yield stress being amplified by only about 6% and 3% respectively. Moderate increase in ductility was observed and the strain at the beginning of strain hardening was observed as the most sensitive parameter to the effect of loading rate. The micrographs of S690QL and S960QL show that the degree of strength sensitivity were associated with the finer-grained size microstructure and chemical compositions achieved via the QT production route. In terms of impact resistance, the Charpy impact tests carried out on these structural grades provide good impact resistance/toughness with the transition temperature ranging between -68°C to -56°C for S690QL and S960QL respectively.
Digital Article Identifier (DAI):
1656
82394
Structural and Electrical Properties of VO₂/ZnO Nanostructures
Abstract:
We examined structural and electrical properties of uniformly-oriented VO₂/ZnO nanostructures. VO₂ was deposited on ZnO templates by using a direct current-sputtering deposition. Scanning electron microscope and transmission electron microscope measurements indicated that b-oriented VO₂ were uniformly crystallized on ZnO templates with different lengths. VO₂/ZnO formed nanorods on ZnO nanorods with length longer than 250 nm. X-ray absorption fine structure at V K edge of VO₂/ZnO showed M1 and R phases of VO₂ at 30 and 100 ℃, respectively, suggesting structural phase transition between temperatures. Temperature-dependent resistance measurements of VO₂/ZnO nanostructures revealed metal-to-insulator transition at 65 ℃ and 55 ℃ during heating and cooling, respectively, regardless of ZnO length. The bond lengths of V-O and V-V pairs in VO₂/ZnO nanorods were somewhat distorted, and a substantial amount of structural disorder existed in the atomic pairs, compared to those of VO₂ films without ZnO. Resistance from VO₂/ZnO nanorods revealed a sharp MIT near 65 ℃ during heating and a hysteresis behavior. The resistance results suggest that microchannel for charge carriers exist nearly room temperature during cooling. VO₂/ZnO nanorods are quite stable and reproducible so that they can be widely used for practical applications to electronic devices, gas sensors, and ultra-fast switches, as examples.
Digital Article Identifier (DAI):
1655
82373
Spin Resolved Electronic Behavior of Zno Nanoribbons
Abstract:
The aim of this study is to understand the spin-resolved properties of ZnO armchair and zigzag nanoribbons. The spin polarization can be induced by either geometry of the nanoribbons or ferromagnetic electrodes. Hence, spin-dependent behavior is revealed in these nanostructures in the absence of external magnetic field. Both electronic structure and magnetic properties of the nanoribbons are analyzed, employing first-principles calculations through Density Functional Theory. The relevant properties using the spin-dependent band structure, conductance, transmission, density of states and magnetic moment are elucidated. These results can be utilized to describe the nanoscale structures and stimulate the experimental works.
Digital Article Identifier (DAI):
1654
82325
The Impact of Initiators on Fast Drying Traffic Marking Paint
Abstract:
Fast drying traffic marking paint comprising a solvent-borne resin, a filler, a pigment and a solvent that is especially suitable for colder ambient (temperatures near freezing) applications, where waterborne traffic paint cannot be used. Acrylic resins based on methyl methacrylate, butyl acrylate, acrylic acid, and styrene were synthesized in different solvents using organic peroxide initiators such as peroxyester, peroxyketal, dialkylperoxide and azo. After polymerization, the molecular weight (Mw), polydispersity index= PDI (Mw/Mn), viscosity, total residual monomer and APHA color were evaluated and results of organic peroxide initiators (t- butyl and t-amyl derivatives) were also compared with the azo initiator. The Mw, PDI, viscosity, mass conversation and APHA color of resins with t-amyl derivatives of organic peroxide initiators are very proper. The results of the traffic marking paints test such as non-volatile matter, no- pick- up time, hiding power, resistance to wear and water resistance study that produced with these resins also confirm this.
Digital Article Identifier (DAI):