Non-Cyanide Electrodeposited Ag–PTFE Composite Coating Using Direct or Pulsed Current Deposition

The effects of FC-4 cationic surfactant on electrodeposited Ag–PTFE composite coating using direct or pulsed currents were studied using scanning electron microscope (SEM), energy dispersive X-ray (EDS), optical microscope, and a linear tribometer. FC-4:PTFE in various ratios were added to a non-cyanide succinimide silver complex bath. Direct or pulsed current method was used at a constant current density to enable comparison between both methods. A high incorporation rate of PTFE was successfully achieved, with pulsed current being highly useful in increasing the amount of PTFE in the composite coating. The study of coating wear under sliding showed that a large majority of the electrodeposited coatings still managed to adhere to the substrate, even after 10 wear cycles of sliding tests. Performance improvements were achieved on all the samples with a coefficient of friction (CoF) between 0.06 and 0.12

Micro/Nanostructure and tribological characteristics of pressureless sintered carbon nanotubes reinforced aluminium matrix composites

This study reports the manufacture, microstructure, and tribological behaviour of carbon nanotube reinforced aluminium composites against pure aluminium. The specimens were fabricated using powder metallurgy method. The nanotubes in weight percentages of 0.5, 1.0, 1.5, and 2.0 were homogeneously dispersed and mechanically alloyed using a high energy ball milling. The milled powders were cold compacted and then isothermally sintered in air. The density of all samples was measured using Archimedes method and all had a relative density between 92.22% and 97.74%. Vickers hardness increased with increasing CNT fraction up to 1.5 wt% and then reduced. The microstructures and surfaces were investigated using high resolution scanning electron microscope (SEM). The tribological tests showed that the CNT reinforced composites displayed lower wear rate and friction coefficient compared to the pure aluminium under mild wear conditions. However, for severe wear conditions, the CNT reinforced composites exhibited higher friction coefficient and wear rate compared to the pure aluminium. It was also found that the friction and wear behaviour of CNT reinforced composites is significantly dependent on the applied load and there is a critical load beyond which CNTs could have adverse impact on the wear resistance of aluminium

The effect of initial etching sites on the morphology of TiO2 nanotubes on Ti-6Al-4V alloy

10.1149/2.0011511jesAnodization was performed in phosphate and fluoride containing electrolytes at different pH and sweep rates with the aim of analyzing the variation in current density during the process continuously. The effect of pH and sweep rate on the morphology of titanium dioxide (TiO2) nanotubes, grown on Ti-6Al-4V alloy, has been explicitly examined in this study. At the same time a microscopic analysis of the different stages of the formation of the nanotubes was performed. A new perspective to the growth mechanisms of the nanotubes was brought about in this study. The morphology of the nanotubes was closely related to the density of initial etching sites

Tracing Magnetic Fields by Atomic Alignment in Extended Radiation Fields

Tracing magnetic fields is crucial as magnetic fields play an important role in many astrophysical processes. Earlier studies have demonstrated that Ground State Alignment (GSA) is a unique way to detect weak magnetic fields (1G> B> 1exp(-15)G) in diffuse media, they consider the situation when the pumping source is a point source, which applies when the star is very far away from the diffuse media. In this paper, we explore the GSA in the presence of extended radiation fields. For the radiation fields with a clear geometric structure, we consider the alignment in circumstellar medium, binary systems, disc, and Local Interstellar Medium (LISM). For the radiation fields with unidentified pumping sources, we apply the method of multipole expansion and discuss the GSA induced by each component. We demonstrate that for general radiation fields, it is adequate to consider the contribution from dipole and quadrupole radiation components. We find that in general polarization of absorption arizing from GSA coincides with the projection of magnetic field in the 2D sky with 90 degree degeneracy. We conclude that the GSA is a unique tool to detect the direction of weak magnetic field, and it can be applied to diffuse media in any radiation field.Comment: 17pages, 17 Figures, ApJ publishe

The effects of unequal compressive/tensile moduli of composites

Abstract This paper investigates the effects of unequal compressive and tensile moduli of carbon fibre reinforced plastic (CFRP) composites. The basic assumption is based on the statistics that the compressive modulus is a fraction lower than the tensile modulus. Data evaluated by Finite Element Analysis (FEA) model, Classical Laminate Theory (CLT) model, and experiment are used to investigate these effects. The terms of compressive modulus are successfully introduced into the Tsai–Wu failure criterion for the production of failure envelops, into the Classical Beam Theory (CBT) and CLT for the investigation of flexural behaviour as well as the fibre microbuckling model for the analysis of compressive failure. The study shows that the failure criteria shift from stress domain to strain domain when the compressive modulus is considered, and the strain dominated failure criteria could generally provide more accurate prediction in composite material. Therefore it is proposed to apply strain dominated failure criteria for composite design, testing and certificate.Abstract This paper investigates the effects of unequal compressive and tensile moduli of carbon fibre reinforced plastic (CFRP) composites. The basic assumption is based on the statistics that the compressive modulus is a fraction lower than the tensile modulus. Data evaluated by Finite Element Analysis (FEA) model, Classical Laminate Theory (CLT) model, and experiment are used to investigate these effects. The terms of compressive modulus are successfully introduced into the Tsai–Wu failure criterion for the production of failure envelops, into the Classical Beam Theory (CBT) and CLT for the investigation of flexural behaviour as well as the fibre microbuckling model for the analysis of compressive failure. The study shows that the failure criteria shift from stress domain to strain domain when the compressive modulus is considered, and the strain dominated failure criteria could generally provide more accurate prediction in composite material. Therefore it is proposed to apply strain dominated failure criteria for composite design, testing and certificate

Multi-scale modelling of moisture diffusion coupled with stress distribution in CFRP laminated composites

Laminated composite structures operating in a marine environment are subject to moisture ingress. Due to the slow diffusion process of moisture, the distribution of moisture is not uniform so that the laminates can develop hygrothermal stresses. An accurate prediction of the moisture concentration and the associated hygrothermal stress is vital to the understanding of the effect of marine environment on failure initiation. The present paper investigates the time-dependent moisture diffusion and the stress distribution in carbon fibre reinforced polymeric (CFRP) composites by means of experimental study and Finite Element Analysis (FEA). Samples were made from CFRP pre-preg autoclave-cured, and then immersed in fresh water and sea water at a constant 50 °C for accelerated moisture diffusion. Laminates with [0]16, [90]16, [±45]4s lay-up sequences were investigated. A multiscale 3D FEA model was developed to evaluate the interfacial stresses between polymer matrix and carbon fibre and the stress distribution in the composite laminates. The analysis revealed that both the stress distribution and stress level are time-dependent due to moisture diffusion, and the interphase between fibres and matrix plays an important role in both the process of moisture diffusion and the stress/strain transfer. The interlaminar shear stresses of the laminates induced by hygrothermal expansion exhibited a significant specimen edge effect. This is correlated with the experimental observations of the flexural failure of laminates

Effects of hygrothermal stress on the failure of CFRP composites

This paper investigates the hygrothermal effects on the failure mechanisms in bending of carbon fibre reinforced polymer (CFRP) composites. Accelerated diffusion testing was carried out by immersion at 50 °C constant temperature and 70 bar hydrostatic pressure to study the effects of fresh or sea water diffusion into pre-preg CFRP laminates. Consequently the composite laminates were tested in bending after 1 and 3 months’ immersion. A three-dimensional finite element analysis (FEA) model was developed to couple the moisture diffusion, hygrothermal expansion and bending. Optical and field emission scanning electronic microscope (SEM) were employed to analyse the failure mechanisms of CFRP composites in bending after immersion. The study showed that the mechanical properties are significantly reduced after short term immersion due to the edge effects, while the damage to the fibre/polymer interface becomes more significant to laminate degradation after longer-term immersion

Mechanics and materials in the design of a buckling diaphragm wave energy converter

Not sure what acceptance date was so just used publication date