Double Bend Research Articles

Application of the chemical vapor infiltration and reaction (CVI-R) technique for the preparation of highly porous biomorphic SiC ceramics derived from paper

Chemical vapor infiltration and reaction (CVI-R) is used to produce biomorphic high porous SiC ceramics based on biological structures such as paper. The paper fibers are first converted into a biocarbon (C b) template by a carbonization step. In a second step methyltrichlorosilane (MTS) in excess of hydrogen is infiltrated into the C b-template by CVI technique, depositing a Si/SiC layer around each fiber. The reaction (R) between biocarbon and excess silicon to form additional silicon carbide occurs during a subsequent thermal treatment as a third step of the ceramization process. Due to the mild infiltration conditions (850–900 °C) the initial micro- and macrostructure of the carbon preform is retained in the final ceramics. The applied characterization methods after every step of the ceramization process are X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, Thermal Gravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM). The bending strength of the resulting porous ceramics is measured by the double ring bending test. It is found that a slight excess of free Si in relation to the amount of carbon from the C b-template must be deposited in the Si/SiC layer to achieve a nearly complete conversion of the C b-templates into SiC ceramic. The weight gain after infiltration has to be at least 400 wt.%. Varying the infiltration conditions such as temperature, MTS concentration and infiltration time, ceramics in a wide range of porosity (55–80%) and mechanical properties (5–40 MPa) can be produced. A thermal treatment temperature of 1400 °C is found to be optimal for the reaction between the deposited Si and the biocarbon.

X-ray reflectivity, photoelectron and nanoindentation studies of tetrahedral amorphous carbon (ta-C) films synthesized by double bend cathodic arc

Tetrahedral amorphous carbon (ta-C) films have been prepared with floating potential (no substrate bias voltage) on Si substrates by an off-plane double bend filtered vacuum cathodic arc (FCVA) system. The influences of arc current on mass density, chemical bonding and nanomechanical response have been studied for coatings. Based on X-ray reflectivity spectra, the maximum density of FCVA films is 3.27 g/cm 3. The hardness measurements performed as a function of indentation depth for 75-nm-thick films have a maximum hardness of 37.5 GPa and stress values up to 13 GPa. The sp 3 content in the ta-C films as determined by analysis of the C 1s core level spectra had a value of approximately 80% with standard deviation value 1.2% on 6-cm diameter Si waver. Therefore, these coatings have both structural and thickness uniformity, which can be used for large area coating applications (i.e. flat panel display units).

Effects of upstream installations on the reading of an ultrasonic flowmeter

The downstream flow of two typical installations in piping systems, the 90° bend and the double bend, is experimentally identified by flow angle measurements at the pipe wall. The identified downstream flow patterns are stable when the installation inflow is stabilized. An ultrasonic flowmeter is exposed to the downstream flow at various positions and circumferential angles. At each position the error shift of the flowmeter is recorded. A unique assignment between flow pattern and error shift is found paving the way for an intelligent correction of flowmeters.

Bonding configurations in DBOP-FCVA nitrogenated tetrahedral amorphous carbon films studied by Raman and X-ray photoelectron spectroscopies

Nitrogenated tetrahedral amorphous carbon (ta-C:N) films having nitrogen content from 0 to 10.3 at.%, have been produced by a double bend off-plane filtered cathodic vacuum arc system. X-ray photoelectron and Raman spectroscopies have been applied to study the effect of nitrogen in the bonding structure in the films. Deconvolution of the XPS spectra revealed a decrease in the amount of sp 3-bonded carbon in the ta-C:N films. A comparative study between the Raman parameters at 514 and at 633 nm excitation wavelength was presented. Nitrogen (N) incorporation led to a lower G peak position and higher I D/ I G ratios, indicating the development of larger sp 2 domains. Q (−ve) parameter (which measures the skewness of G line) increased sharply with the increased of N content in the films. The hardness of the films was evaluated by nanoindentation.

Equivalent Uniform Moment Diagram Factor for Reinforced Concrete Columns

The ACI Building Code, ACI 318-02, permits use of the equivalent uniform moment diagram factor C-sub-m for computing the effect of moment gradient, along the column height, caused by unequal column end moments. The concept of equivalent uniform moment diagram was introduced into design practice to eliminate the need for extensive calculations based on a solution to a differential equation. The expression currently in use by the ACI code is a simplified equation based on the elastic behavior of columns and does not include the inelastic material behavior of reinforced concrete columns. This study was conducted to investigate the influence of different variables on C-sub-m of slender, tied, reinforced concrete columns and to examine existing expressions for C-sub-m. 17,000 square reinforced concrete columns, each with a different combination of specified variables, were simulated. The columns studied were subjected to short-term ultimate loads and unequal end moments causing moment gradient in single curvature and double curvature bending. Two C-sub-m expressions are proposed for use in slender reinforced column designs.

Steel Member Strength by Inelastic Lateral Buckling

This paper develops a simple advanced method of designing steel members against out-of-plane failure, in which reduced elastic moduli are used in an out-of-plane buckling analysis to model the effects of high moment, residual stresses and geometrical imperfections on yielding. The reduced moduli are derived from the basic beam and column strength curves of the Australian steel code AS4100 in 1998. The strengths predicted for simply supported beams in uniform bending are exactly the same as those of AS4100, while those for simply supported columns are extremely close. The strengths predicted for simply supported beam-columns with equal and opposite end moments are a little higher than the less conservative predictions of AS4100, and are very close to the basic beam and column strengths when these are plotted against a consistent generalized slenderness. The strengths predicted for simply supported beams under double curvature bending are somewhat less than those of the AS4100 method of design by buckling analysis, while those for beams with central concentrated loads acting at or away from the centroid are very close, and those for end restrained beams under uniform bending and for sway columns are generally a little higher. While the method has been developed from and compared with the Australian code AS4100, it may be modified for any other modern code for the design of steel structures. It may be more widely applied to two-dimensional frames with in-plane loading, as part of a simple method of advanced analysis in which separate assessments are made of the in-plane and out-of plane strengths.

Properties of amorphous ZrO x thin films deposited by filtered cathodic vacuum arc

The deposition of amorphous zirconium oxide thin films by off-plane double bend filtered cathodic vacuum arc (FCVA) is reported for the first time. The ZrO x growth is at room temperature and X-ray diffraction (XRD) showed an amorphous film was deposited. Atomic force microscopy (AFM) confirmed that the film morphology is very smooth. The surface microstructure and interface properties of ZrO x thin films were investigated using monochromatic high-resolution X-ray photoelectron spectroscopy (XPS). From depth profile, it was deduced that the bulk of the film was ∼ZrO 1.9 and at the interface, O–Zr–Si types of bonds were observed to be present. Such amorphous films were observed to have a high optical bandgap of 5.2 eV and high refractive index of ∼2.0.

Minimum electron beam size of a double bend lattice

It is well known that the electron beam emittance can be lowered by keeping positive dispersion in the insertion straight section of an otherwise double bend achromat lattice. But the fact that the beam size at the straight section is not simply determined by the emittance any more has made the scheme suspicious. There was even a claim that the minimum electron beam size in the straight section remains unchanged regardless of the dispersion. It is shown in this article that the electron beam size can really be decreased by the positive dispersion of the straight section. It is also shown that the minimum of σ2/β of the dispersive straight section is 0.64 of that of the minimum double bend achromat lattice.

Experimental Investigation of Seismic Repair and Retrofit of Bridge Columns by Composite Jackets

This paper summarizes the results of comprehensive experimental studies on half-scale bridge columns repaired and retrofitted with composite-material jackets. The experimental program was composed of two interrelated subprograms. Initially, a total of fourteen half-scale squat circular and rectangular reinforced concrete columns were tested under fully reversed cyclic shear in a double bending configuration. In order to provide a basis for comparison, a total of three as-built columns were tested. Another ten column samples were tested after being retrofitted with different composite-jacket systems. One circular as-built column was repaired after failure. The repair process involved both crack injection, as well as addition of carbon/epoxy composite jacket. The repaired column was then retested and evaluated. Experimental results showed that all as-built columns developed an unstable behavior and failed in brittle shear mode. The common failure mode for all retrofitted samples was due to flexure with significant improvement in the column ductility. The repaired column demonstrated ductility enhancement over the as-built sample. In the second subprogram, a total of thirteen half-scale circular and square column models were constructed with short lap-splice details at the base, and were tested in flexure under lateral cyclic loading. Three as-built columns were tested and a total of ten columns were tested after being retrofitted with different composite-jacket systems. In general, the common mode of failure for the as-built samples was a brittle failure due to bond deterioration of the lap-spliced longitudinal reinforcement. The jacketed circular columns demonstrated a significant improvement in their cyclic performance. However, tests conducted on square jacketed columns showed a very limited improvement in clamping on the lap splice region and for enhancing the ductility of the column.

Comprehensive study of ZnO films prepared by filtered cathodic vacuum arc at room temperature

Room temperature deposition of high crystal quality zinc oxide (ZnO) films was realized by the filtered cathodic vacuum arc (FCVA) technique. Detrimental macroparticles in the plasma as byproducts of arcing process are removed with an off-plane double bend magnetic filter. The influence of oxygen pressure on the structural, electrical and optical properties of ZnO films were investigated in detail. The crystal structure of ZnO is hexagonal with highly c-axis orientation. Intrinsic stress decreases with an increase of chamber pressure, and near stress-free film was obtained at 1×10−3 Torr. Films with optical transmittance above 90% in the visible range and resistivity as low as 4.1×10−3 Ω cm were prepared at pressure of 5×10−4 Torr. Energetic zinc particles in the cathodic plasma and low substrate temperature enhance the probability of formation of zinc interstitials in the ZnO films. The observation of strong ultraviolet photoluminescence and weak deep level emission at room temperature manifest the high crystal quality of the ZnO films prepared by FCVA. Enlargement of the band gap is observed in the absorption and photoluminescence spectra, the band gap shifts towards lower energy with an increase of oxygen pressure. This phenomenon is attributed to the Burstein–Moss effect.

Deposition pressure dependence of internal stress in TiN films deposited by filtered cathodic vacuum arc

TiN films were deposited by an off-plane double bend filtered cathodic vacuum arc technique. The composition, structure, and surface morphology of the films were characterized by x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy, respectively. Internal stress was determined by a substrate bending method. The influence of the deposition pressure on the composition, structure, and internal stress of the films was studied systematically. At a deposition pressure of 1×10−5 Torr, the films are composed of single α-TiN0.30 phase with fairly low internal stress, and the atomic ratio of N to Ti is 0.32. As the deposition pressure increases to 5×10−5 Torr, the N/Ti ratio increases to 0.56, and the films are composed of a mixture of hexagonal α-TiN0.30 and cubic TiN0.90. The formation of TiN0.90 phase and the mismatch of these two kinds of phases contribute to a dramatic increase of internal stress in the films. The increase of deposition pressure to 2×10−4 Torr results in the formation of stoichiometric TiN films with single TiN phase, which corresponds to slightly lower internal stress. However, a further increase of deposition pressure results in a continuous increase in the N/Ti ratio and the formation of overstoichiometric films. The incorporation of excess N atoms in the films accounts for the further increase of internal stress.

Finite element prediction of the influence of confinement on RC beam–columns under single or double curvature bending

The present study investigates the finite element prediction of the compressive strength of concrete near the flexural critical regions of reinforced concrete (RC) beam–column members under a single or a double curvature bending. For this reason, an analysis model of the three-dimensional hypoelasticity-based finite element predictions of RC structures has been presented. Using the developed program, three RC beam–column members subjected to axial forces combined with bending moments have been analyzed. From finite element predictions, it has been known that concrete in the vicinity of a beam–column joint reacts not only under a uniaxial compressive stress state but also under a multiaxial compressive stress state, and that a flexural critical cross-section is observed at a small distance away from the beam–column joint. This is because the concrete in that region is confined by the existence of a beam–column joint, and that region is commonly the flexural critical cross-section of the RC beam–columns in a frame. It is also observed that the confining effect on concrete in that region is larger under double curvature bending than under single curvature bending.

Velocity and turbulence measurements downstream of flow conditioners

The flow downstream of three conditioners, a tube bundle and two perforated plates, is investigated experimentally by means of particle image velocimetry and hot wire anemometry for Reynolds numbers of the order 10 5. The conditioners are exposed to the flow disturbed by two different installations: a 90° single bend and a 2×90° out-of-plane double bend. Velocity profiles, turbulent fluctuations and Reynolds‘ stress are measured. The jets issuing from the holes and tubes of the conditioners are visualised in the near field which extends up to approximately four pipe diameters downstream of the conditioners. The disturbance imposed on the flow by the conditioners disappears at this position, while the decay of the disturbance caused by the installations takes place in the far field. The decay rate in the far field depends on the specific installation. It is found that this decay is more rapid for the double bend. While the velocity profiles match the profile for fully developed flow approximately at a position of 25 diameters downstream of the conditioners, the turbulent equilibrium state is not even reached at 50 diameters. The results also show that the perforated plates have a higher efficiency than the tube bundle in conditioning the disturbed flow.

The Influence of Heteroatoms on the Extent of Double Bond Pyramidalization

AbstractThe origin of double bond pyramidalization in the series of norbornene and norbornadiene derivatives and the effect of heteroatoms on the magnitude of the double bond bending are reported. For this purpose, equilibrium geometries, vibrational frequencies, and NBO second‐order perturbation energies were calculated by use of B3LYP/6‐31G** level wave functions. The optimized geometric parameters calculated for norbornadiene are in good agreement with the available experimental results. NBO second‐order perturbation analysis has been used to evaluate the effect of hyperconjugative interactions on double bond pyramidalization. In the second part of this study, the interaction of singlet oxygen with 4,5‐dioxatetracyclo[6.6.1.02,7.09,14]pentadeca‐2(7),9,11,13‐tetraene (15) and 4,5,15‐trioxatetracyclo[6.6.1.02,7.09,14]pentadeca‐2(7),9,11,13‐tetraene (16) has been studied at the B3LYP/6‐31G** level. In the case of addition of singlet oxygen to 15, 4,5,16‐trioxapentacyclo[6.6.1.12,7.02,7.09,14]hexadeca‐9,11,13‐triene (17) is produced. It was found that the reaction of singlet oxygen addition to the double bond in 16 does not occur. The degree of pyramidalization in this molecule is similar to the analog 12 {4,5,11‐trioxatricyclo[6.2.1.02,7]undeca‐2(7),9‐diene}, in which singlet oxygen addition takes place. The reasons of the lack of chemical reactivity with singlet oxygen in 16 are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Development of texture in TiN films deposited by filtered cathodic vacuum arc

X-ray diffraction was used to characterize the texture in TiN films deposited by an off-plane double bend filtered cathodic vacuum arc technique. The influence of deposition pressure, substrate bias, and deposition temperature on the texture of the films was studied systematically. The texture develops from a random orientation to a mixed (1 1 1) and (2 2 0) preferred orientation with increasing deposition pressure. As substrate bias is increased, the texture evolves from a (2 0 0) preferred orientation to a mixed (1 1 1) and (2 2 0) preferred orientation at a substrate bias of −100 V. However, further increase of substrate bias changes the texture back to the (2 0 0) preferred orientation again. The deposition temperature has no significant effect on the development of the film texture. Comparing the texture with the internal stress and surface roughness, it is observed directly that the texture in the TiN films is controlled by the internal stress and surface roughness.

Structure and mechanical properties of tungsten carbide films deposited by off-plane double bend filtered cathodic vacuum arc

High quality nanocrystalline tungsten carbide films were deposited by a filtered cathodic vacuum arc technique at room temperatures. X-ray diffraction and atomic force microscopy were used to characterize the crystalline structure and surface morphology of the films. Substrate bending methods and nanoindenter were used to measure internal stress, hardness, and Young’s modulus of the films. The film structure evolves from a single hexagonal α-W2C phase to a mixture phase, which is composed of a hexagonal α-W2C, a cubic WC1−x, and a cubic W phase, as the substrate bias, which is always negative, is increased to 200 V. As the substrate bias is further increased, the film structure changes gradually to a single α-W2C phase again. The variation trends of internal stress, hardness, and Young’s modulus with the substrate bias are similar. They increase with substrate bias, reaching a maximum of 7.2, 26, and 270 GPa, respectively, at a substrate bias of 200 V, then decrease with further increase of substrate bias.

Structural characteristics and mechanical properties of aluminium oxide thin films prepared by off-plane filtered cathodic vacuum arc system

Transparent and smooth alumina thin films have been deposited on Si (1 0 0) and quartz substrates at low temperature by an off-plane double bend filtered cathodic vacuum arc (FCVA) system, which is slightly different from traditional vacuum arc system. The films were analysed using X-ray diffraction and X-ray photoemission spectroscopy to investigate the crystalline and chemical characteristics of these thin films. The films displayed a very smooth surface morphology, which were verified from AFM and SEM. The compressive stress, hardness and Young's modulus of aluminium oxide thin films deposited under varying oxygen partial pressure were investigated, and compared with that by other technologies. Friction coefficient of stoichiometric film against steel and DLC balls were analysed by tribometer (pin-on-disk), respectively. The deposited stoichiometric aluminium oxide thin films possess good optical properties. The results show that the alumina thin films prepared by FCVA technology have potential applications as wear-resistance coatings and optical coatings.

Microstructural and surface properties of cobalt containing amorphous carbon thin film deposited by a filtered cathodic vacuum arc

Cobalt containing tetrahedral amorphous carbon (ta-C:Co) films were deposited on silicon wafers at room temperature under various bias conditions by an off-plane double bend filtered cathodic vacuum arc technique. The microstructural and surface properties of the ta-C:Co films were systematically studied by XPS, Raman, and surface energy measurements via contact angle measurements. Incorporation of Co increases the contact angle sharply to 107.5° as compared to the value for pure ta-C of ∼80°. XPS measurements showed that an increase in negative substrate bias affects both the sp3 content as well as the Co oxidation state on the sample surface. Correlation between XPS and surface energy measurements showed that two different mechanisms might cause the overall decrease in surface free energy of the films.

First crystallographic signature of an acyclic peptide nanorod: molecular mechanism of nanorod formation by a self-assembled tetrapeptide.

A terminally protected acyclic tetrapeptide Boc-Aib-Val-Aib-beta-Ala-OMe 1 (Aib: alpha-aminoisobutyric acid, beta-Ala: beta-Alanine) self-assembles into a continuous hydrogen-bonded supramolecular helix with an average diameter of 10 A (1 nm) starting from a double bend molecular conformation in crystals and further self-assembly of this supramolecular architecture leads to the formation of polydisperse nanorods of diameters 10-40 nm.

On the properties of nanocomposite amorphous carbon films prepared by off-plane double bend filtered cathodic vacuum arc

It is known to deposit hard thin films, such as tetrahedral amorphous carbon (ta-C), using a filtered cathode vacuum arc (FCVA). These ta-C films have interesting and useful properties because of the high sp 3 fraction of carbon atoms (up to 87%) in the film. However, the high internal stress in the films can limit their applications as the film may flake away from the substrate. In order to reduce the internal stress of the ta-C films and in an attempt to improve adhesion of thick films of this type, growth modifications such as incorporating metal into the ta-C films have been carried out. Nanocomposite amorphous carbon films were deposited by FCVA technique using metal–carbon composite target. Atomic force microscopy, Raman, and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of the films. Nanoindenter and surface profilometer were used to determine the hardness, Young's modulus, and internal stress. The same metal composition targets for different elements results in different metal composition in the corresponding nanocomposite amorphous carbon films. We attribute this observation to the dynamic balance deposition effect of the FCVA deposition process. The influence of the type of metallic elements and its composition in the films on the structural, mechanical properties, surface energy and field emission (FE) performance was studied. The incorporation of metal into the films results in the decrease of sp 3 fraction, internal stress in the films, but the hardness and Young's modulus remains at high level. The surface energy of the films increases with incorporating Ni atoms, but decreases after incorporating Fe and Al atoms into the films. After heat-treatment, the incorporation of metal into ta-C films can greatly improve the FE performance.