An Analytical Model for the Effective Dielectric Constant of a 0-3-0 Composite

An analytical expression for prediction of the effective dielectric constant of a three phase 0-3-0 ferroelectric composite is presented. The analytical results are verified with the experimental results from Nan et al [1]. We extend the analytical model, so that the influence of the shape of the third phase inclusion, on the effective dielectric constant of the composite, can be investigated. The results indicate that the dielectric constant increases ∼7 times, when the aspect ratio of the conductive inclusion is increased from 1 (sphere) to 10 (spheroid). The analytical predictions compare favorably with the experimental values.

Tribological Performance Study of HVOF-Sprayed Microstructured and Nanostructured WC-17wt.%Co Coatings

Abrasive and erosive wear of components and machinery is an ongoing challenge in the oil sands industry in northern Alberta, Canada. To improve the wear resistance by increasing surface hardness of steels, heat treatments and deposition of hard layers of metal alloys (such as stellite) by fusion welding techniques are traditionally used. However, these deposition techniques are not applicable to all shapes and add considerable weight to the final component. Thermal spraying techniques such as the use of high velocity oxy-fuel (HVOF) composite coatings based on WC-Co cermet system offer better wear resistance and greater flexibility in applications. This study presents work on two feedstock powders, namely nanocrystalline and microcrystalline WC-Co cermets, with identical matrix phase content: WC-17wt.%Co. The novelty of the research is that an engineered duplex Co coated WC-17wt.%Co cermet particle designed to withstand coating spalling under elevated loads as well as to limit abrasive debridement during wear is introduced for the first time to produce a more homogeneously-dispersed coating microstructure. The engineered particle has 6wt.% of the ductile phase material mixed into the core to insure that the reinforcement WC phase is discontinuous to limit the debridement during wear, while remainder (11wt.%) of the Co is applied as a coating on the particle to improve the ductility. The mechanical properties of the overall particle are further improved by controlling the size of the reinforcing phase (WC) in the matrix (Co). This resulted in a WC-17wt.%Co particle containing a characteristic WC grain in the order of 350 nm in the core with the Co outer coating of 1–2 μm thick, making the powder particle as nanocrystalline. HVOF deposited coatings of the nanocrystalline and microcrystalline powders were examined for microhardness, fracture toughness, sliding abrasion (ASTM G133-05) and dry-sand rubber wheel abrasion (ASTM G65-04) wear performance. The wear rate under various loads and sliding distances was studied. In both the coatings, it was found that the wear rate increased with increasing applied loads, while it decreased with increasing sliding distances. 3D surface analysis of the wear tracks using atomic force microscopy (AFM) revealed two distinctive mechanisms associated with the two coatings after abrasive wear. The improved wear resistance was attributed to the higher hardness value of the nanostructured WC-17wt.%Co coating. It was also found that the nanostructured WC-17wt.%Co coating has about twice the toughness of the conventional microstructured coating counterpart. The extent of the WC decarburization and the dissolution of Co in the coatings were also studied.

Enhancement of Mechanical Properties by Reinforcing Magnesium With Ni-Coated Carbon Nanotubes

In this study, carbon nanotubes (CNTs) are coated with nickel (Ni) to improve the wettability of the CNT surface and metal matrix, and allow an effective load transfer from the matrix to nanotubes. Pure magnesium is used as the matrix material and different weight percentages of Ni-coated multi-walled CNTs are incorporated as the reinforcing material. The nanocomposite materials are synthesized using the powder metallurgy route followed by microwave assisted rapid sintering. Mechanical property characterizations reveal an improvement of 0.2% yield strength, ultimate tensile strength and ductility with the addition of Ni-CNTs. As such, Ni-coated CNTs can be used as a reinforcement in magnesium to improve the formability of the material for light-weight, strength-based applications.

Field Assisted Sintering Technology (FAST) Model for Prediction of Final Properties

Sintering is the process of making materials from powder form by heating the powder below its melting point until the particles fuse to each other. Field assisted sintering technology (FAST), also sometimes known as spark plasma sintering (SPS), uses a pulsed and/or continuous electric current along with the simultaneous application of compressive pressure which leads to extremely high heating rates and short processing durations. A high relative density and small grain size promote superior properties such as greater hardness and electrical breakdown. Hence, selection of the proper sintering parameters is of paramount importance and a predictive model would be extremely useful in narrowing the range of experimental parameters. This will drastically reduce the number of extra attempts at obtaining certain properties in a material and save experimentation time, effort and material to name a few. Four of the most important FAST parameters: target temperature, holding time, heating rate and initial particle size, have been reviewed to assess their effect on the densification, hardening and grain growth of Alumina, Copper, Silicon Carbide, Tungsten and Tungsten Carbide through extensive literature survey. The relationship between each has been incorporated in a Microsoft Excel program which acts as a predictive tool to determine an estimate of the final properties based on the initial parameters chosen. This is done by curve fitting a polynomial onto the existing data points as closely as possible and using the polynomial to obtain final properties as a function of the initial parameters. The model was verified against an existing paper which sought to obtain the optimum sintering parameters for Copper. While the actual experimentation range was 400°C to 800°C, the program would have suggested a much narrower range from 650°C to 800°C and hence saved unnecessary additional efforts.

Deposition of Polypyrrole Onto a Novel Polymer Electrode for Use in a Biomimetic Artificial Excitable Cell Membrane

A novel and inexpensive bucky gel electrode has been investigated for use as the electrode substrate for deposition of polypyrrole. The electroactive polymer membrane was successfully deposited and the surface morphology studied using scanning electron microscopy. Given the properties of the bucky gel electrode and its ability to conduct ions, this work establishes the first step towards a semi-solid ion-gating system to be used in further applications.

Dry Adhesion Based on Electrospun Polymer Nanofibers

Dry Adhesion exists between polymer nano/microfibers. An elaborate experiment was performed to directly measure the adhesion between electrospun poly(ε-caprolactone) (PCL) microfibers using a nano force tensile tester. Electrospun nano/microfibers with radius ranging from 0.2 to 1.1 μm were investigated. It was found that the adhesion force depended on the fiber radius following a linear relationship, which complied with the classical Johnson-Kendall-Roberts (JKR) contact mechanics model. The force increased with temperature and decreased with relative humidity between two fibers positioned in orthogonal directions. Our data suggested the van der Waals’ (vdW) interactions are primarily operative between the micro-/nano-fibers.

Behaviour of Vacuum Casting Plastic Composites Under Different Treatments of Banana Fibres

Nowadays, the natural fibres market is having an important growth due to the commitment of contemporary society with the sustainable development that leads the natural resources preservation and the environment protection. Fibres from banana food wastes provide high mechanical properties related to other natural fibers such as flax, sisal, hemp, etc. The aim of the present research work is to compare different banana fibres processing in order to improve the matrix fibre adhesion and behavior of fibre under processing conditions. Simple Anova analysis has been implemented on four different formulations: 1. No fibre processing, 2. Alkaline processing with Caustic Soda (NaOH), 3 Maleic Anhydride, 4. Combination of Soda and Maleic Anhydride. Several samples of MTT 8040 resin, under vacuum casting, with silicone moulds, conditions, have been done. Mechanical properties and efficiency factors of adhesion fibre-matrix have been determined and compared.

Effect of Interleaved Electrospun Nanofiber on Flexural Properties of Fiber Glass Composites

Electrospinning is regarded as one of the most efficient processes to generate one-dimensional nano structures. The electrospinning process is simple and provides consistent mass production of nanofibers. The scalability of the electrospinning process has an excellent potential to fulfill the high volume requirements of nanofibers in the infrastructure applications. The present work emphasizes the use of interleaved electrospun nanofibers in fiber glass composite beams. The Flexural behavior of a simply supported beam under a centrally concentrated loading is studied. Flexural properties of a fiber glass composite beam with interleaved electrospun nanofibers are compared with a fiber glass composite beam without electrospun nanofibers. The material configuration of the composite beams is: woven E-glass fabric prepregs with a low temperature molding resin. In addition, interleaved between the plies are TEOS (Tetra Ethyl Orthosilicate) electrospun nanofibers. The nanofibers were produced by developing optimized operating process parameters and a stabilized sintering temperature cycle to ensure consistency in the fiber morphology and pore structure. The successful integration of the electrospun nanofibers within the prepreg layers was obtained by pre-impregnation with a B-staged resin film and de-bulking to remove excessive resin prior to vacuum bagging. A series of mechanical Flexure tests were performed per the ASTM D7264 standard specification. Micrographs were obtained to study the progressive deformation and damage mechanics due to flexural loading in the specimens and clearly illustrate the differences in the failure mechanism with and without the electrospun interface layers.

Rapid Spray Method for Improving Cu-Epoxy Interface Strength

A simple spray method using a plain orifice atomizer has been developed for depositing γ-aminopropyltriethoxysilane (APS) from solutions in water and in methanol onto copper surfaces. The peel strengths between copper foil and epoxy resin were measured with and without APS deposition. In all cases, a higher concentration of APS gives higher peel strength. APS applied from 1 wt% solution in methanol resulted in higher peel strength than when applied from a 1 wt% aqueous solution; the opposite was true with 0.2 wt% APS solutions, indicating a trade-off between deposited APS film thickness and surface coverage. APS was very effective when chemisorption occurred at the surface but much less effective when there was only physisorption. A study of the fracture surfaces showed that the failure is cohesive, inside the epoxy layer, and that the deposited APS on the copper surfaces had a long-range effect which was seen deep in the epoxy layer, well away from the copper surface.