Microstructure and mechanical properties of as rolled high strength bainitic rail steels

Abstract

Bainitic steels are emerging with the potential to replace eutectoid steels to achieve longer rail life. Bainitic steels of two compositions were made and processed into rails 13 m in length. The properties of these rails were evaluated in the as rolled slow cooled condition. The results from bainitic rail steels were compared with those for 880 MPa grade pearlitic rail steel. It was found that in the as rolled slow cooled condition rail properties such as fracture toughness, Charpy impact energy, and endurance limit were superior to those of 880 MPa grade pearlitic rail steel.     

Surface oxidation of carbon fibre on tribological properties of PEEK composites

Abstract

In this work, ozone modification method and air oxidation were used for the surface treatment of polyacrylonitrile (PAN) based carbon fibre. The surface characteristics of carbon fibres were characterised by X-ray photoelectron spectroscopy. The interfacial properties of carbon fibre reinforced PEEK (CF/PEEK) composites were investigated by means of the single fibre pull-out tests. As a result, it was found that IFSS values of the composites with ozone treated carbon fibre are increased by 60% compared with that without treatment. X-ray photoelectron spectroscopy results show that ozone treatment increases the amount of carboxyl groups on carbon fibre surface, thus the interfacial adhesion between carbon fibre and PEEK matrix is effectively promoted. The effect of surface treatment of carbon fibres on the tribological properties of CF/PEEK composites was comparatively investigated. Experimental results revealed that surface treatment can effectively improve the interfacial adhesion between carbon fibre and PEEK matrix. Thus the wear resistance was significantly improved.     

Interfacial reaction and mechanical reliability of eutectic Sn–0·7Cu/immersion Ag-plated Cu solder joint

Abstract

In this study, the interfacial reaction and joint reliability of immersion Ag-plated Cu substrate with the Sn–0·7Cu (wt-%) ball–grid array (BGA) solder was investigated. During reflow, the Ag plating layer was dissolved completely into the molten Sn–Cu solder and some of the Cu layer was also dissolved into the molten solder. The dissolved Ag and Cu were precipitated as Ag₃Sn and Cu₆Sn₅ intermetallic compounds (IMCs) in the solder matrix. Upon reflow, the Sn–Cu solder exhibits an off-eutectic reaction to produce the eutectic phase and precipitate (Cu₆Sn₅ and Ag₃Sn). The Cu–Sn IMC layer was formed at the solder/Cu interface after reflow, and the IMC layer grew during aging treatment. During the shear tests, the failure mode switched from a bulk-related failure to an interface-related failure. After aging for 250 h, the joint failed partially at the solder/Cu₆Sn₅ interface. The brittle fracture was linked to the formation of thick Cu–Sn IMC layer.     

Effect of interfacial weight loss by silver migration on the pullout strength of a silver wire embedded in an adhesive matrix

In this study an effort is made to correlate interfacial weight loss, by migration, from the surface of a silver wire embedded in an adhesive matrix, to bond strength between the silver wire and the adhesive matrix. Comparative studies are also performed using an aluminum an wire in place of silver to accurately assess the effect of interfacial weight loss by silver migration. The results of the pullout tests on silver migrated specimens are compared with pullout tests on silver-wire specimens, which were immersed in water for 2 h but without silver migration. Pullout tests are performed in both wet, and dry conditions of the bonded specimens. It is determined that the pullout strength of bonded silver-wire specimens in wet condition decreases by as much as 86%, subsequent to silver migration. The loss of bond strength for silver-migrated specimens tested in dry condition varies between 23% and 4%, depending on the embedded length used.     

Transparent ultra-hydrophobic surfaces

Self-cleaning surfaces have received a great deal of attention, both in research studies and commercial applications. Both transparent and non-transparent self-cleaning surfaces are highly desired, as they offer many advantages and their potential applications are endless. As in many other cases, also in the case of self-cleaning surfaces, nature found a solution before man. The Lotus flower is a symbol of purity in Asian cultures, even when rising from muddy waters it stays clean and untouched by dirt, organisms and pollutants. The Lotus leaf "self-cleaning" surface is hydrophobic and rough, showing a two-layer morphology. While hydrophobicity produces a high contact angle, the two-layer morphology reduces the adhesion of dirt and water drops to the surface. Because of this low adhesion, water drops easily slide across the leaf surface carrying the dirt particles with them. In the present work the Lotus leaf morphology was mimicked using hydrophobic chemistry and a two-layer topography, with a base layer of silica and a top layer of intrinsically nanostructured polyhedral oligomeric silsesquioxanes (POSS) particles. Results have indicated that, thus, a transparent ultra-hydrophobic coating can be obtained. When these materials were mixed and used as a single layer the hydrophobicity deceased significantly. The contact angle and sliding angle measurements were supported by AFM micrographs.     

Interfacial adhesion in sisal fiber/SBR composites: an investigation by the restricted equilibrium swelling technique

Short sisal fiber-reinforced styrene butadiene rubber (SBR) composites were prepared and characterized by the restricted solvent swelling technique. The solvent swelling characteristics of SBR composites containing untreated and bonding agent-added mixes were investigated in a series of aromatic solvents, such as benzene, toluene, and xylene. The diffusion experiments were conducted by the sorption gravimetric method. The adhesion between the rubber and short sisal fibers was evaluated from the restricted equilibrium swelling measurements. The anisotropy of swelling of the composite was confirmed by this study. The effect of fiber orientation in controlling the anisotropy of restricted swelling was also demonstrated. As the fiber content increased, the solvent uptake decreased, due to the increased hindrance and good fiber-rubber interactions. Bonding agent-added mixes showed enhanced restriction to swelling, due to the strong interfacial adhesion. The bonding system containing hexa-resorcinol in the mix produces an in-situ resin, which binds the fiber and the rubber matrix firmly. In addition, as the penetrant size increases from benzene to xylene, the uptake decreases. The swelling index values of the composites support this observation. Due to the improved adhesion between the short sisal fiber and SBR, the ratio of the volume fraction of rubber in the dry composite sample to the swollen sample (V _T) decreases. The extent of fiber orientation of the composites was also analysed from the restricted swelling method. SEM studies of the composite revealed the orientation of short fibers. The sorption data support the Fickian diffusion trend, which is typical in the case of cross-linked rubbers.     

The use of UNIFAC for the estimation of adhesion enhancement between polymers and mineral surfaces treated with silane coupling agents

The group contribution method of UNIFAC is used to investigate the influence on adhesion of thermodynamic compatibility between the filler surface and the polymeric matrix in filled polymeric composites. Compatibility is enhanced between polymers and mineral surfaces through the use of silane coupling agents of varying chemistry. In this study, glass beads were treated with ten different organofunctional silanes intended to induce differences in interfacial strength. Interfacial strength measurements were obtained from tests in which single, silane-treated glass beads were embedded in rectangular poly(vinyl butyral) specimens subjected to uni-axial stress until interfacial failure occurred at one of the poles of the sphere. The UNIFAC method was used to estimate the Gibbs free energies of mixing using the chemical structure of the polymer repeat unit and each of the silane organofunctional groups, and these values were correlated with the measured interfacial strengths. The results indicate that enhanced interfacial strength corresponds to systems with more favorable thermodynamic mixing.     

20—PURPOSE-GROWN WOOLS. PART I: MODIFICATION OF THE FELTING PROPERTIES OF WOOL THROUGH THE SHEEP'S FEED

A method is described whereby the shrinking property of wool can be modified during growth by the administration of chemical additives to the sheep's diet so as to enter the character of the fibre half-way through the growth of the staple. Thus, hard-root-soft-tip fibres can be grown to enhance shrinkage and soft-root-hard-tip fibres to impart shrink-resistance. Methods of modifying the shrinkage of wool have so far been confined to chemical treatments of the shorn fibre, but this original approach to shrinkage control also presents an opportunity for the mass production of a large variety of other types of special-purpose wools.     

Low density polyethylene-polypropylene blends: Part 2 - Strengthening and toughening with copolymer

Abstract

The strengthening and toughening of low density polyethylene (LDPE)-polypropylene (PP) blends with a commercial ethylene/propylene block copolymer (CO) have been investigated. It is shown that the addition of the copolymer improved the ductility of the LDPE-PP blends without any loss of elastic modulus. Particularly for the PP rich LDPE-PP blends, the copolymer can improve the ductility, tensile strength and impact strength simultaneously. It was found that the copolymer has no obvious influence on the crystallisation behaviour of the LDPE and PP phases, whereas the interfacial adhesion was enhanced significantly. The results suggested that the ethylene/propylene block copolymer is a suitable compatibiliser for LDPE-PP blends, which can be used as an effective additive for the recycling of the polyalkene mixtures, especially the PP rich LDPE-PP mixtures.     

Effect of nitric acid surface treatment on tensile and tribological properties of thermoplastic polyimide composite filled with carbon fibre

Abstract

Polyacrylonitrile based carbon fibres were submitted to nitric acid oxidation treatments to improve the interfacial adhesion of the carbon fibre reinforced polyimide (CF/PI) composite. The carbon fibre surfaces were characterised by X-ray photoelectron spectroscopy. Nitric acid oxidation not only affects the oxygen concentration, but also produces an appreciable change in the nature of the chemical functions, namely the conversion of hydroxy type oxygen into carboxyl functions. Nitrogen concentration of nitric acid oxidation treated carbon fibre is ～1·2 times higher compared with untreated one. The mechanical and tribological properties of the CF/PI composites treated with nitric acid oxidation were investigated. Results showed that the tensile strength of the CF/PI composites improved remarkably due to nitric acid treatment along with enhancement in friction and wear performance.