Crushing modes of aluminium tubes under axial compression

A numerical study of the crushing of circular aluminium tubes with and without aluminium foam fillers has been carried out to investigate their buckling behaviours under axial compression. A crushing mode classification chart has been established for empty tubes. The influence of boundary conditions on crushing mode has also been investigated. The effect of foam filler on the crushing mode of tubes filled with foam was then examined. The predicted results would assist the design of crashworthy tube components with the preferred crushing mode with the maximum energy absorption.

Natural rubber nanocomposite reinforced with nano silica

Inorganic nano fillers have demonstrated great potential to enhance the properties of natural rubber (NR). The present article reports the successful development of a NR nanocomposite reinforced with nano silica (SiO2). Its dynamic mechanical properties, thermal aging resistance, and morphology are investigated. The results show that the SiO2 nanoparticles are homogenously distributed throughout the NR matrix in a form of spherical nano-cluster with an average size of 80 nm when the SiO2 content is 4 wt%. With the introduction of SiO2, the thermal resistance and the storage modulus of NR host significantly increase, and the activation energy of relaxation of the nanocomposite, compared to the raw NR, increases from 90.1 to 125.8 kJ/mol.

Preparation, characterization and dielectric properties of temperature stable SrTiO3/PEEK composites for microwave substrate applications

Poly(ether ether ketone) (PEEK) is a potential candidate for electronic applications due to its low permittivity, low loss, high melting point, better chemical resistance, excellent insulating properties and easy processibility. Present paper discusses the preparation and characterization of SrTiO3 filled PEEK composite for microwave substrate applications. The dielectric constant, dielectric loss and temperature variation of dielectric constant of the composites have been studied up to 1 MHz using an Impedance Analyzer. Different theoretical approaches have been employed to predict the effective permittivity of composite systems and the results are compared with that of the experimental data. The crystallinity of the bulk composite is studied by X-ray diffraction studies. Scanning electron microscopic technique has been employed to study the dispersion of the particulate filler in PEEK matrix. Vickers hardness of pure and filled PEEK composite has been measured using Microhardness Tester. The effect of particle size on the dielectric as well as mechanical properties of SrTiO3/PEEK composite system is also studied by incorporating micronsize and nanosize fillers. Present study shows that a temperature stable composite can be realized by judiciously selecting appropriate filler concentration in the PEEK matrix.

Enhancement of ion dynamics in PMMA-based gels with addition of TiO2 nano-particles

Solvent and ion dynamics in PMMA based gels have been investigated as a function of the loading of nanosized TiO₂ particles. The gels have a molar ratio of 46.5:19:4.5:30 of ethylene carbonate (EC), propylene carbonate (PC), lithium perchlorate and PMMA, respectively. A series of samples with 0, 4, 6 and 8 wt.% TiO₂ filler were investigated. The diffusion coefficients for the lithium ions and for the two solvents (EC and PC) were investigated by pfg-NMR. It was shown that the addition of filler to the gel electrolytes enhances the diffusion of the cations, while the diffusion of the solvents remains constant. Raman measurements show no significant changes in ion–ion interactions with the addition of fillers, while the ionic conductivity is seen to decrease. However, the sample with 8 wt.% TiO₂ had a conductivity close to that of the unfilled sample.

Microscopic interactions in nanocomposite electrolytes

Nanocomposite electrolytes of a fully amorphous trifunctional polyether (3PEG) and poly- (methylene ethylene oxide) (PMEO) have been complexed with two lithium salts and nanoparticulate (~20 nm) fillers of TiO2 and Al2O3. Addition of the fillers to the polymer salt complexes shows a significant change in the conformational modes of both polymers, especially the D-LAM region between 200 and 400 cm-1, indicating a reduced segmental flexibility of the chain. These changes are more pronounced with the use of TiO2 than Al2O3. Incorporation of the nanoparticulate fillers to the electrolytes fails to influence the degree of ion association, suggesting that the number of charge carriers available for conduction in both polymers using both LiClO4 and LiCF3SO3 is not the source of any conductivity increase. Addition of the fillers, which was seen to increase the conductivity in PEO-based systems, generally lowers the conductivity in the present PMEO systems, while the addition of TiO2 has little or no effect except in the cases of 3PEG 1.5 and 1.25 mol/kg LiClO4. In this case, 10 wt % TiO2 provides a conductivity increase of half an order of magnitude at approximately 60 °C. We also report for the first time a Raman spectroscopy investigation into the PEO-based nanocomposite electrolytes. The present results are discussed in terms of the electrostatic interactions involving dielectric properties of the fillers, of special interest being the interactions between the polymer and the fillers and between the ionic species and the fillers, when the effect of crystallization can be ignored.

Conductivity in amorphous polyether nanocomposite materials

Using a completely amorphous polyether we have investigated the effect of the inclusion of a nano-particulate filler on a polymer electrolyte. Nano-sized TiO₂ is shown not to significantly affect the conductivity of composite electrolytes containing 1.0 or 1.25 mol/kg LiClO₄ or 1.5 or 2.0 mol/kg LiTFSI. At 1.5 mol/kg LiClO₄ a significant increase in conductivity is observed. Raman spectroscopy experiments have been used to investigate the effect of filler on ion-aggregation. Only one new vibrational mode can be assigned to the composite which is not due to the polymer electrolyte or the filler. From this work, we believe the increased conductivity observed by previous researchers as a result of filler addition may be largely attributed to the effect on the degree of crystallinity along with some disruption of ion-aggregation by the fillers in PEO based electrolytes.

Conducting composite using an immiscible polymer blend matrix

Carbon black (CB) fillers were used to study the feasibility of achieving multiple percolation using an immiscible (polar) polymer blend matrix. By tailoring the morphology of the insulating dual phase matrix it has been shown that the percolation threshold (Ф_c) can be reduced over single-phase matrices. Cocontinuity in the polymer matrix is important in reducing Ф_c by either preferentially isolating the conducting filler at the interface of the two phases or within one particular continuous phase of the matrix thereby forming a continuous conducting network within a continuous network (multiple percolation). Actual melt processing time has been found to influence the dispersion of the fillers and hence Ф_c. Polarity of the matrix as well as the processing method has also been found to influence the dispersion of the filler within the host polymer.

Improved cathodic disbondment performance of polyethylene blends

Cathodic disbondment (CD) performance of a range of modified polyethylenes (PE) compression molded on to steel plates at 320[degrees]C is reported. Adhesion strength was measured by the 90[degrees] peel test and good dry adhesion strength was obtained for all modified polyethylene materials and blends, as well as for the neat polymer. It is shown that dry bond strength does not correlate with CD performance. Initial results of wet peel tests of samples in various concentrations of NaOH are presented where it is observed that for samples with improved wet adhesion strength, CD performance was also Improved. Surface polarity was determined from contact angle measurements, and it is shown that increased surface polarity of the coating was not the only determinant for improved CD performance. Inorganic fillers such as talc were also found to improve CD performance by changing the bulk properties, with little measurable change in polarity. Some mechanistic aspects of CD performance are also discussed.

Impact response and energy absorption of aluminium foam-filled tubes

The effect of foam fillers on the impact behaviour and energy absorption of an aluminium tube is investigated. Both experimental test and computational simulation are employed in current study. For comparison, hollow tubes and foams are also tested, respectively. Foam filler is found to be ineffective in increasing the crushing loads of the composite tubes over the simple superposition of the crushing loads of hollow tube and foam. Also, foam filler increases the tendency for the concertina mode of folding. The foam fillers of tubes additionally result in increasing the SAE values over those of hollow tubes.

Dielectric percolative composites with high dielectric constant and low dielectric loss based on sulfonated poly(aryl ether ketone) and a-MWCNTs coated with polyaniline

Acidified multi-walled carbon nanotubes (a-MWCNTs) coated with polyaniline (PANI) (a-MWCNTs@PANI) nanofiller were prepared by in situ polymerization. Novel dielectric percolative composites, sulfonated poly(aryl ether ketone) (SPAEK)/a-MWCNTs@PANI, with high dielectric constant and low dielectric loss were fabricated using simple solution blending technique. A SPAEK/a-MWCNTs@PANI composite prepared in this fashion exhibited a high dielectric constant above 800, a dielectric loss tangent less than 1.1 at 10 kHz and room temperature. The morphological study of composites by SEM suggested that the in situ polymerization method of preparing a-MWCNTs@PANI nanofillers was useful to achieve good dispersion of fillers in SPAEK matrix.

Improving thermal conductivity of cotton fabrics using composite coatings containing graphene, multiwall carbon nanotube or boron nitride fine particles

Graphene, multi-wall carbon nanotube (MWCNT) and fine boron nitride (BN) particles were separately applied with a resin onto a cotton fabric, and the effect of the thin composite coatings on the thermal conductive property, air permeability, wettability and color appearance of the cotton fabric was examined. The existence of the fillers within the coating layer increased the thermal conductivity of the coated cotton fabric. At the same coating content, the increase in fabric thermal conductivity was in the order of graphene > BN > MWCNT, ranging from 132 % to 842 % (based on pure cotton fabric). The coating led to 73 %, 69 % and 64 % reduction in air permeability when it respectively contained 50.0 wt% graphene, BN and MWCNTs. The graphene and MWCNT treated fabrics had a black appearance, but the coating had almost no influence on the fabric hydrophilicity. The BN coating made cotton fabric surface hydrophobic, with little change in fabric color.

Carbon nanotube based elastomer composites-an approach towards multifunctional materials

The current study focuses on giving a basic understanding of tubular graphene sheets or carbon nanotubes (CNTs) and points towards their role in fabricating elastomer composites. Since the properties and the performance of CNT reinforced elastomer composites predominantly depend on the rate of dispersion of fillers in the matrix, the physical and chemical interaction of polymer chains with the nanotubes, crosslinking chemistry of rubbers and the orientation of the tubes within the matrix, here, a thorough study of these topics is carried out. For this, various techniques of composite manufacturing such as pulverization, heterocoagulation, freeze drying, etc. are discussed by emphasizing the dispersion and alignment of CNTs in elastomers. The importance of the functionalization technique as well as the confinement effect of nanotubes in elastomer media is derived. In a word, this article is aimed exclusively at addressing the prevailing problems related to the CNT dispersion in various rubber matrices, the solutions to produce advanced high-performance elastomeric composites and various fields of applications of such composites, especially electronics. Special attention has also been given to the non-linear viscoelasticity effects of elastomers such as the Payne effect, Mullin's effect and hysteresis in regulating the composite properties. Moreover, the current challenges and opportunities for efficiently translating the extraordinary electrical properties of CNTs to rubbery matrices are also dealt with.

Synergistic effect of multi walled carbon nanotubes and reduced graphene oxides in natural rubber for sensing application

Utilizing the electrical properties of polymer nanocomposites is an important strategy to develop high performance solvent sensors. Here we report the synergistic effect of multi walled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) in regulating the sensitivity of the naturally occurring elastomer, natural rubber (NR). Composites were fabricated by dispersing CNTs alone and together with exfoliated RGO sheets (thermally reduced at temperatures of 200 and 600 °C) in NR by a solution blending method. RGO exfoliation and the uniform distribution of fillers in the composites were studied by atomic force microscopy, Fourier transformation infrared spectroscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. The solvent sensitivity of the composite samples was noted from the sudden variation in electrical conductivity which was due to the breakdown of the filler networks during swelling in different solvents. It was found that the synergy between CNTs and RGO exfoliated at 200 °C imparts maximum sensitivity to NR in recognizing the usually used aromatic laboratory solvents. Mechanical and dynamic mechanical studies reveal efficient filler reinforcement, depending strongly on the nature of filler-elastomer interactions and supports the sensing mechanism. Such interactions were quantitatively determined using the Maier and Göritz model from Payne effect experiments. It is concluded that the polarity induced by RGO addition reduces the interactions between CNTs and ultimately results in the solvent sensitivity. © 2013 The Royal Society of Chemistry.

Development of high performance materials based on smart elastomer nanocomposites

 The present thesis explores the fabrication of technologically relevant nanocomposites out of a few elastomers and conducting fillers like carbon nanotubes, graphene and polyaniline. The developed materials have good applications in sensors, shape memory devices and capacitors. Different characterization methods reveal the influence of filler-elastomer interactions on the various properties of the obtained nanocomposites as well.