Mode-I adhesive fracture energy measurement with modified single-lap joint test geometry

The adhesive fracture energy or fracture toughness of adhesively-bonded joints comprising carbon-fiber-reinforced polymer composite substrates and three different types of adhesives was detemined using a modified single-lap joint (MSLJ). This joint was made by implanting end pre-cracks in the adhesive layer at the center of the bondline of a conventional single-lap joint (SLJ). This modification ensured that the crack propagated from a sharp starter crack from both ends of the overlap during testing, reducing the effect of spew fillets on the measured adhesive fracture toughness scatter band. The MSLJ specimens were tested to failure and the adhesive fracture energy was calculated using the Kinloch–Osiyemi model. The values of the adhesive fracture energy obtained from the MSLJ tests were compared with those from SLJ and the double-cantilever beam (DCB) test geometries. The fracture energy values obtained from the MSLJ specimens were significantly lower than those from SLJ specimens and agreed well with those from DCB specimens. The three differenent types of aerospace grade film adhesives tested were Redux 322, Redux 335K and Redux 319A.     

An analytical approach for the adhesion of a semi-infinite elastic body in contact with a sinusoidal rigid surface under zero external pressure

An analytical approach for the adhesion of a semi-infinite elastic body in contact with a sinusoidal rigid surface under zero external pressure is presented. Although Johnson (Int. J. Solids Struct. 32, 423 (1995)) has proposed an analytical solution for a slightly wavy surface, while Zilberman and Persson (Solid State Commun. 123, 173 (2002); J. Chem. Phys. 118, 6473 (2003)) have given a numerical solution for a highly wavy surface by considering the curvature of the contact area in the calculation of the interfacial term of the total energy, our solution is not only for small amplitude of roughness (i.e., the slightly wavy surface as Johnson's) but also for large amplitude of roughness (i.e., the highly wavy surface as of Zilberman and Persson). Our solution considers the curvature of the contact area as do Zilberman and Persson. Our results which are obtained for the total energy and equilibrium condition of the system agree with both Johnson's and Zilberman and Persson's results. The effects of the material constants and the surface roughness on the adhesion are clearly expressed and discussed.     

Impedance spectroscopic studies of ferroelectric Pb2Sb3DyTi5O18 ceramic

Abstract

The electrical properties of polycrystalline Pb₂Sb₃DyTi₅O₁₈ were investigated by complex impedance spectroscopy. The dielectric relaxation was found to be of polydispersive non-Debye type, and relaxation frequency shifts to higher frequencies with increasing temperature. Evidence of temperature dependent electrical relaxation phenomena as well as the negative temperature coefficient of resistance (NTCR) character of the sample have also been observed. The ac conductivity obeys the universal power law and dispersion in conductivity was observed in the lower frequency region. Also, the frequency dependent ac conductivity at different temperatures indicated that the conduction process is thermally activated. The activation energy was estimated to be 0·62 eV from the temperature variation of dc conductivity.     

Analysis and surface energy estimation of various model polymeric surfaces using contact angle hysteresis

Wetting of hydrophobic polymer surfaces commonly employed in electronic coatings and their interaction with surfactant-laden liquids and aqueous polymer solutions are analyzed using a contact angle hysteresis (CAH) approach developed by Chibowski and co-workers. In addition, a number of low surface tension acrylic monomer liquids, as well as common probe liquids are used to estimate solid surface energy of the coatings in order to facilitate a thorough analysis of surfactant effects in adhesion. Extensive literature data on contact angle hysteresis of surfactant-laden liquids on polymeric surfaces are available and are used here to estimate solid surface energy for further understanding and comparisons with the present experimental data. In certain cases, adhesion tension plots are utilized to interpret wetting of surfaces by surfactant and polymer solutions. Wetting of an ultra-hydrophobic surface with surfactant-laden liquids is also analyzed using the contact angle hysteresis method. Finally, a detailed analysis of the effect of probe liquid molecular structure on contact angle hysteresis is given using the detailed experiments of Timmons and Zisman on a hydrophobic self-assembled monolayer (SAM) surface. Hydrophobic surfaces used in the present experiments include an acetal resin [poly(oxymethylene), POM] surface, and silane, siloxane and fluoro-acrylic coatings. Model surfaces relevant to the literature data include paraffin wax, poly(methyl methacrylate) and a nano-textured surface. Based on the results, it is suggested that for practical coating applications in which surfactant-laden and acrylic formulations are considered, a preliminary evaluation and analysis of solid surface energy can be made using surfactant-laden probe liquids to tailor and ascertain the quality of the final coating.     

Investigation into deoxidation during vacuum induction melting refining of nickel base superalloy using CaO crucible

Abstract

The influence of carbon and aluminium on deoxidation during vacuum induction melting (VIM) of a Ni-6Cr-2Mo-6W-5Co alloy using a CaO crucible has been studied. It has been found that carbon plays a dominant role in deoxidation during the melting stage, and about 50-70% of the initial oxygen can be removed. Thermodynamics calculations show that the C-O reaction is far from the equilibrium state, and experimental results for carbon and oxygen contents in the liquid alloy correspond with those when the CO partial pressure p _CO is 10³-10² Pa. Aluminium addition can further reduce the oxygen content to below 6 ppm. Thermodynamics calculations for the C-Al, Al-CaO and C-Al₂O₃ reactions demonstrate that they can all take place during the melting process. These reactions bring about reductions in the amounts of carbon and aluminium, respectively, of about 1.3-3.5 times and 20-50 times those required for deoxidation only.     

Piezoresistive effect in amorphous carbon thin films

Abstract

In this contribution amorphous carbon (a-C) films are integrated as strain gauges in micromachined silicon boss membranes. Sputter deposited a-C films have high hardness and <2 % hydrogen content in it. The tribological properties of the a-C films are comparable with diamond and can be used for hard coatings. The films have very low resistivity which decreases with the temperature. Current voltage characteristics of a-C/oxide Si shows Ohmic behaviour. Variable range hopping mechanism is dominant at low temperatures and is thermally activated at room temperature and at higher temperatures. Piezoresistive gauge factor are measured in the temperature range 23–50°C.     

Experimental determination of the Hamaker constants for solid–water–oil systems

The van der Waals interaction (vdW) is a fundamental interaction in colloid and interface science. Regardless of the methods used in deriving the vdW interaction between two bodies as a function of their separation distance, the Hamaker constant is always an essential parameter involved. In this paper, a simple experimental method is presented to determine the Hamaker constant. As an example, the Hamaker constant of a solid-water-oil system is related to its surface and interfacial energies, which can be measured accurately. Based on the proposed method, the effects of two typical solid surfaces and three kinds of aqueous solutions on the Hamaker constant and wettability of the solid-water-oil system are studied. It is found that hydrophilic and hydrophobic solid surfaces will lead to rather different Hamaker constants and wettability behaviour. The detailed experimental results also show that the ionic surfactant solutions have a strong influence, whereas the pH value of the aqueous phase has a limited effect on the Hamaker constant. In addition, the electrolyte solutions do not strongly affect the Hamaker constant for the oil phase interacting with the solid surface across an electrolyte solution. Such determined Hamaker constants are in reasonable agreement with the reported Hamaker constants for oils (dodecane and hexadecane), mica, and metals (Ag, Au, and Cu) interacting across a pure water phase.     

Superconducting Bi(2223) thick film on Ba2HoNbO6: a new perovskite ceramic substrate

Abstract

Barium holmium niobate Ba₂HoNbO₆ (BHNO) has been developed as a new substrate for (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (Bi(2223)) superconductor film. Ba₂HoNbO₆ has a cubic perovskite structure with lattice constant a = 8·26 Å. The dielectric constant and loss factor of this material are in a range suitable for its use as a substrate for microwave applications. The Bi(2223) superconductor shows no detectable chemical reaction with BHNO, even under extreme processing conditions. Dip coated Bi(2223) thick film on Ba₂HoNbO₆ substrate had T _c(0) of 109 K and current density of around 4 × 10³ A cm ^{- 2} at 77 K and in zero magnetic field.     

Analysis and spectroscopy of rare earth doped magnesium aluminate spinel

Abstract

Rare earth cation segregation in magnesium aluminate spinel has been imaged and analysed in an aberration corrected scanning transmission electron microscope. The SuperSTEM at Daresbury Laboratory provided evidence for monolayer segregation of europium ions along grain boundaries in spinel. EELS spectra confirmed the Eu to be within 0.5 nm of the grain boundary region. Spinel is a candidate material for hard window applications owing to its excellent transparency, intrinsic hardness, fracture toughness and resistance to thermal and chemical erosion. Rare earth cation doped spinel maintains good transparency throughout visible and near infrared wavelengths.     

Synthesis and characterisation of Si3N4p/Cu nanocomposite powders by high energy ball milling

Abstract

The present work reported the preparation of Cu–25 wt-%Si₃N₄ nanocomposite powders via high energy ball milling (HEBM). The phases and morphologies of as-milled powders with various milling times were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that with increasing the milling time, the irregularly shaped Cu powder became flattened, and, subsequently, refined and near spherical. After 12 h milling, the particle size of Cu–Si₃N₄ composite powders was in the range of 200–300 nm, while the grain size of Si₃N₄ particulates, 10–25 nm, was well within a nanometre scale. A uniform distribution of the nanosized Si₃N₄ reinforcing phase throughout the Cu matrix was successfully obtained. A reasonable mechanism for the formation of Cu–Si₃N₄ nanocomposite powders during HEBM was also proposed.