Thermal and frictional properties of modified sisal fibre/phenolic resin composites

Abstract

In order to enhance the bonding force of sisal fibres (SF) and polymer matrix, different surface modifiers (alkali, coupling agent and borax) were used to treat the fibres. The SF/phenol formaldehyde (PF) resin composites were prepared through compression moulding. Thermal properties of the treated SFs and fibre composites were studied by thermogravimetric analysis and thermal expansion analysis. The effect of SF modification on the friction and wear properties of composites was investigated using wear tester under dry condition. The treated fibre surface and the worn surfaces of SF/PF composites were observed by SEM. The results showed that the surface of SF became rough after borax treatment, and the initial decomposition temperature increased by 13·6°C, compared to untreated SF. Thermal stability and wear properties of the PF composites with treated fibre were obviously increased due to the fibre modification. For example, wear volume of the composites with sisal treated by borax decreased by 73·3%. Scanning electron microscopy photos showed that the wear mechanism changed from fatigue wear to slight plough wear.     

SOLUTION OF DIFFERENT HOLES SHAPE BORDERS OF FIBRE REINFORCED COMPOSITE PLATES BY INTEGRAL EQUATIONS

Accurate boundary conditions of composite material plates with different holes are founded to settle boundary condition problems of complex holes by conformal mapping method upon the nonhomogeneous anisotropic elastic and complex function theory. And then the two stress functions required were founded on Cauchy integral by boundary conditions. The final stress distributions of opening structure and the analytical solution on composite material plate with rectangle hole and wing manholes were achieved. The influences on hole-edge stress concentration factors are discussed under different loads and fiber direction cases, and then contrast calculates are carried through FEM.     

Effect of variable electrode force on weld quality in resistance spot welding

Abstract

Resistance spot weldability is defined as the acceptable welding current ranges as determined by the weld lobe in resistance spot welding. Nowadays many studies have focused on the effect of welding current and welding time under constant electrode force on the weld quality and weldability. There is little research on the influence of variable electrode force on the weld quality and weldability because of the difficulty in controlling variable electrode force using pneumatic gun. In the present study, first, the influence of three stages of electrode force, including squeeze force, welding force and forging force, on the quality of welds is analysed. Then a design of experiment approach is applied to analyse the influence of the three stages of electrode force on welding quality and thus to obtain optimum parameter of variable electrode force by controlling the electrode force with servo gun. The comparisons of tensile shear strength, nugget size, weld lobe width and wear rate of electrode tip between variable force and constant force are carried out. The results show that the weld quality and weldability can be increased evidently using optimum parameter of variable electrode force without accelerating the electrode wear rate.     

Nano encoders based on vertical arrays of individual carbon nanotubes

Linear encoders for nanoscale position sensing based on vertical arrays of individual carbon nanotubes are presented. Vertical arrays of single multi-walled carbon nanotubes (MWNTs) are realized using a combination of electron beam lithography (EBL) and plasma-enhanced chemical vapour deposition growth. EBL is used to define 50- to 150-nm nickel catalyst dots at precise locations on a silicon chip. Precise control of the position, density and alignment of the tubes has been achieved. Aligned nanotube arrays with spacing varying from 250 nm to 25 μm are realized. Field emission properties of the array are investigated inside a scanning electron microscope equipped with a 3-d.o.f. nanorobotic manipulator with nanometer resolution functioning as a scanning anode. With this scanning anode and the single MWNT array, a nano encoder is investigated experimentally. Vertical position is detected by the change in emission current, whereas the horizontal position of the scanning anode is sensed from the emission distribution. A resolution of 98.3 nm in the vertical direction and 38.0 nm (best: 12.9 nm) in the lateral direction has been achieved.     

Microstructure and impact behaviour of ASTM A105/AISI 304L friction weldments

Abstract

Instrumented impact testing has been used to investigate the influence of the microstructure of the heat affected zone (HAZ) on the impact fracture behaviour of ASTM A105/AISI 304L friction weldments. The friction layer in the HAZ has been found to consist of two different parts. In the A105 side, a mechanically mixed layer made of bainite containing 304L 'protrusions' is present. The hardness of the bainite was found to increase as the friction pressure was decreased. In the 304L side, the friction layer was made of a thick shear band, formed by thermoplastic instability during welding. The impact fracture toughness was found to depend on both the crack nucleation and propagation stages, whose characteristics were related to the dynamic fracture toughness of the friction layers.     

Microstructural characterisation and corrosion behaviour of laser cladded Al–12Si alloy onto magnesium AS41/carbon fibre composite

Abstract

The quality and properties of laser clad layers are dependent on the microstructure and properties of the interfaces with the substrate. The present paper reports, in details, on the characterisation of microstructure of the coating and interfacial layers evolved as a result of the CO₂ laser remelting of previously plasma sprayed Al–12Si alloy onto C short fibres reinforced AS41–Mg composite. Scanning electron microscopy (SEM), wavelength dispersive X-ray (WDX) analysis and X-ray diffraction (XRD) were employed to identify the phases arising in the interfacial layers. The latter are composed mainly of Mg₁₇Al₁₂ and Mg₂Si phases. XRD was conducted on the clad layers at different distances from the interface. At the same layers, the potentiodynamic polarisation in sodium chloride solution was measured and it was found that as the Mg content increases in the clad coating, the corrosion resistance decreases. However, the corrosion current of the clad coating is around two orders of magnitude lower than that of the C/Mg composite.     

15—A STUDY OF NEEDLED FABRICS. PART V: THE APPROACH TO THEORETICAL UNDERSTANDING

Needled fabrics are complicated structures, and an exact analysis of their mechanics is not yet possible. Understanding is approached through three routes. Firstly, the behaviour of a fully bonded web is used to predict the effects of orientation, and to estimate the upper limits of strength. These estimates may be reasonable if the network that actually exists at the breaking point is used in calculations. Needled fabrics can give a fairly high utilization of fibre strength. Secondly, the effects of slippage are discussed qualitatively, by analogy with the behaviour of spun yams. The influences of entanglement, fibre length, fibre fineness, and fibre friction are discussed. Thirdly, a quantitative analysis, with many approximations, of a much-simplified model is made. Despite the unsatisfactory nature of some of the assumptions, the predictions are in general accord with experimental results.     

Adhesion Characteristics of Carbon Black Embedded Glass/Epoxy Composite

The surface of glass/epoxy composite material was embedded with carbon black which was dispersed in methyl ethyl ketone (MEK) during the curing process to enhance the adhesion strength of the glass/epoxy composite structure. The morphological effect of the carbon black on the surface of composite was observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Quantitative chemical bonding analysis with X-ray photoelectron spectroscopy (XPS) was also performed to observe chemical bonding states on the surface. The lap shear strength of the glass/epoxy composite adhesive joints where composite adherends were embedded with carbon black was investigated with respect to the type and amount of embedment. Also, the tensile properties of the carbon black embedded glass/epoxy composites were measured to observe the mechanical degradation of the composite due to the MEK. The surface free energies of carbon black embedded composites were determined from the van Oss–Chaudhury–Good equation to correlate the lap shear strength of the adhesive joints with the surface free energies of composite adherends. From the experimental results, it was found that the carbon black embedment of the composite adherend improved much the bond strength due to the increased surface roughness on nano-scale as well as increased surface free energy.     

Effect of Atmospheric Plasma Treatment on Carbon Fiber/Epoxy Interfacial Adhesion

In this work the effect of atmospheric plasma treatment on carbon fiber has been studied. The carbon fibers were treated for 1, 3 and 5 min with a He/O₂ dielectric barrier discharge atmospheric pressure plasma. The fiber surface morphology, surface chemical composition and interfacial shear strength between the carbon fiber and epoxy resin were investigated using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and the single fiber composite fragmentation test. Compared to untreated carbon fibers, the plasma treated fiber surfaces exhibited surface morphological and surface composition changes. The fiber surfaces were found to be roughened, the oxygen content on the fiber surfaces increased, and the interfacial shear strength (IFSS) improved after the atmospheric pressure plasma treatment. The fiber strength showed no significant changes after the plasma treatment.     

In vitro comparison of biocompatibility of CN x7 and DLC coatings

Carbon nitride (CN ^x7 and diamond-like carbon (DLC) coatings were prepared using dc magnetron sputtering at room temperature. The morphology, chemical composition and bonding state of the coatings were characterized by atomic force microscopy (AFM), Auger electron spectroscopy (AES) and Raman spectroscopy. Compared to DLC, CN ^x7 coating exhibited a slight improvement in hardness, coefficient of friction, roughness, and corrosion. The effects of CN ^x7 and DLC coatings on cultures of mouse fibroblasts and human endothelial cells were determined by scanning electron microscopy. The results showed that the coatings caused no adverse effects on the cells. CN ^x7 coating provided a comparable or better surface for the normal cellular attachment, growth, and morphology as compared to DLC. These results support the biocompatibility of both CN ^x7 and DLC and should initiate an interest in the biomedical applications of CN ^x7 coating.