Moderate speed impact damage to 2D-braided glass-carbon composites

Hybrid glass-carbon 2D braided composites with varying carbon contents are impacted using a gas gun by impactors of masses 12.5 and 44.5. g, at impact energies up to 50. J. The damage area detected by ultrasound C-scan is found to increase roughly linearly with impact energy, and is larger for the lighter impactor at the same impact energy. The area of whitening of the glass tows on the distal side corresponds with the measured C-scan damage area. X-ray imaging shows more intense damage, at the same impact energy, for a higher-mass impactor. Braids with more glass content have a modest increase in density, decrease in modulus, and reduction in the C-scan area and dent depth at the impact site, particularly at the higher impact energies. Impact damage is found to reduce significantly the compressive strength, giving up to a 26% reduction at the maximum impact energy. © 2012 Elsevier Ltd.

A comparison of the value of viscosity for several water models using Poiseuille flow in a nano-channel.

The viscosity-temperature relation is determined for the water models SPC/E, TIP4P, TIP4P/Ew, and TIP4P/2005 by considering Poiseuille flow inside a nano-channel using molecular dynamics. The viscosity is determined by fitting the resulting velocity profile (away from the walls) to the continuum solution for a Newtonian fluid and then compared to experimental values. The results show that the TIP4P/2005 model gives the best prediction of the viscosity for the complete range of temperatures for liquid water, and thus it is the preferred water model of these considered here for simulations where the magnitude of viscosity is crucial. On the other hand, with the TIP4P model, the viscosity is severely underpredicted, and overall the model performed worst, whereas the SPC/E and TIP4P/Ew models perform moderately.

Micromachining of glassy carbon toolsets for micro embossing applications

Laser micro machining is fast gaining popularity as a method of fabricating micro scale structures. Lasers have been utilised for micro structuring of metals, ceramics and glass composites and with advances in material science, new materials are being developed for micro/nano products used in medical, optical, and chemical industries. Due to its favourable strength to weight ratio and extreme resistance to chemical attack, glassy carbon is a new material that offers many unique properties for micro devices. The laser machining of SIGRADUR® G grade glassy carbon was characterised using a 1065 nm wavelength Ytterbium doped pulsed fiber laser. The laser system has a selection of 25 preset waveforms with optimised peak powers for different pulsing frequencies. The optics provide spot diameter of 40 μm at the focus. The effect of fluence, transverse overlap and pulsing frequency (as waveform) on glassy carbon was investigated. Depth of removal and surface roughness were measured as machining quality indicators. The damage threshold fluence was determined to be 0.29 J/cm2 using a pulsing frequency of 250 kHz and a pulse width of 18 ns (waveform 3). Ablation rates of 17 < V < 300 μm3/pulse were observed within a fluence range of 0.98 < F < 2.98 J/cm2. For the same fluence variation, 0.6 μm to 6.8 μm deep trenches were machined. Trench widths varied from 29 μm at lower fluence to 47 μm at the higher fluence. Square pockets, 1 mm wide, were machined to understand the surface machining or milling. The depth of removal using both waveform 3 and 5 showed positive correlation with fluence, with waveform 5 causing more removal than waveform 3 for the same fluence. Machined depths varied from less than 1 μm to nearly 40 μm. For transverse overlap variation using waveform 3, the best surface finish with Rz = 1.1 μm was obtained for fluence 0.792 J/cm2 for transverse overlap of 1 μm, 6 μm, and 9 μm at machined depths of 22.9 μm, 6.6 μm, and 4.6 μm respectively. For fluence of 1.426 J/cm2, the best surface finish with Rz = 1.2 μm was obtained for transverse overlap of 6 μm, and 9 μm at machined depths of 12.46 μm, and 8.6 μm respectively. The experimental data was compiled as machining charts and utilised for fabricating a micro-embossing glassy carbon master toolsets as a capability demonstration.

Graphene composites for ultrafast photonics

Ultrafast lasers play a key role in a variety of devices, from basic research to materials processing and medicine. Graphene has great potential as saturable absorber for ultrafast lasers. Here we present an overview of graphene-based ultrafast lasers, from solution processing of the raw materials, to their incorporation into polymers, device fabrication and testing. © 2011 The Japan Society of Applied Physics.

Device and circuit-level performance of carbon nanotube field-effect transistor with benchmarking against a nano-MOSFET

The performance of a semiconducting carbon nanotube (CNT) is assessed and tabulated for parameters against those of a metal-oxide-semiconductor field-effect transistor (MOSFET). Both CNT and MOSFET models considered agree well with the trends in the available experimental data. The results obtained show that nanotubes can significantly reduce the drain-induced barrier lowering effect and subthreshold swing in silicon channel replacement while sustaining smaller channel area at higher current density. Performance metrics of both devices such as current drive strength, current on-off ratio (Ion/Ioff), energy-delay product, and power-delay product for logic gates, namely NAND and NOR, are presented. Design rules used for carbon nanotube field-effect transistors (CNTFETs) are compatible with the 45-nm MOSFET technology. The parasitics associated with interconnects are also incorporated in the model. Interconnects can affect the propagation delay in a CNTFET. Smaller length interconnects result in higher cutoff frequency. © 2012 Tan et al.

Fabrication of excitonic luminescent inorganic-organic hybrid nano- and microcrystals

Inorganic-organic (IO) hybrid nano- and microcrystals are fabricated by a low-cost, environmentally friendly and easily scaled-up route. Lead(II) iodide (PbI 2) nano/microcrystals are obtained by solvothermal techniques and subsequent IO hybrid (C 12H 25NH 3) 2PbI 4 crystals are produced by intercalation of the organic moiety. The hexagonally shaped crystals obtained range in size from 20 nm to ∼7 μm. Sequential stacking of inorganic/organic layers in these IO hybrid crystals results in strong room-temperature exciton photoluminescence, wherein the excitons are confined within the inorganic sheets. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Application of gel-casting to the fabrication of 1-3 piezoelectric ceramic-polymer composites for high-frequency ultrasound devices

A modified gel-casting technique was used to fabricate a 1-3 piezoelectric ceramic/polymer composite substrate formed by irregular-shaped pillar arrays of small dimensions and kerfs. This technique involves the polymerization of aqueous piezoelectric (PZT) suspensions with added water-soluble epoxy resin and polyamine-based hardener that lead to high strength, high density and resilient ceramic bodies. Soft micromoulding was used to shape the ceramic segments, and micropillars with lateral features down to 4 m and height-to-width aspect ratios of ∼10 were achieved. The composite exhibited a clear thickness resonance mode at approximately 70 MHz and a k eff ∼ 0.51, demonstrating that the ceramic micropillars possess good electrical properties. Furthermore, gel-casting allows the fabrication of ceramic structures with non-conventional shapes; hence, device design is not limited by the standard fabrication methods. This is of particular benefit for high-frequency transducers where the critical design dimensions are reduced. © 2012 IOP Publishing Ltd.

Biomimetic calcium carbonate-gelatin composites as a model system for eggshell mineralization

The composite nature of mineralized natural materials is achieved through both the microstructural inclusion of an organic component and an overall microstructure that is controlled by templating onto organic macromolecules. A modification of an existing laboratory technique is developed for the codeposition of a CaCO3-gelatin composite with a controllable organic content. First, calibration curves are developed to determine the organic content of a CaCO3-gelatin composite from infrared spectra. Second, a CaCO3-gelatin composite is deposited on either glass coverslips or demineralized eggshell membranes using an automated alternating soaking process. Electron microscopy images and use of the infrared spectra calibration curves show that by altering the amount of gelatin in the ionic growth solutions, the final organic component of the mineral can be regulated over the range of 1-10%, similar to that of natural eggshell. © 2012 Materials Research Societ.

Characterization of impact induced damage modes in single lap joints of woven GFRP composites

Single lap joints of woven GFRP composites have been investigated for impact induced damage modes using C-scan, X-ray micro tomography, imaging and finite element (FE) modelling. This has allowed for damage modes to be observed in 3D from macro to micro level-resulting in much better understanding of damage mechanisms and realistic FE modelling.