Stress Distribution in Single Lap Joints with a Cracked Composite Adherend—Part I: Single Lamina Adherends

The effect of a crack in the overlap region of a single step lap joint is studied on the shear distribution in the adhesive layer. Each adherend is considered to be a lamina with unidirectional fibers aligned in the direction of the applied load. Crack location is selected to be in the top adherend, in the form of cut fibers and matrix bays. The shear-lag model is used to derive the equilibrium equations which are then solved using eigenvector expansion. Additionally, a finite element model of the lap joint was prepared and solved using ANSYS. The results of the two methods perfectly match each other. The effects of crack location along the length of the overlap, crack size, edge cracks, adhesive thickness, and type of fibers were investigated on the shear distribution in the adhesive layer and its corresponding peak values. The effect of dissimilar adherends was also investigated on the adhesive shear stress distribution. According to the results, in the presence of a crack, the peak adhesive shear stress is very susceptible to adhesive thickness and type of fibers used in each adherend. Other factors also influence the peak shear stress to some degree.     

Numerical Study of Adhesive Single-Lap Joints with Composite Adherends Subjected to Combined Tension–Torsion Loads

The present investigation focuses on modifying the strength of single-lap adhesively bonded joints under tension–torsion loading with the use of three-dimensional finite element (FE) modeling. A single-lap adhesively bonded joint is reinforced by fibers and analyzed by means of ABAQUS-6.9.1 FE code. The adherends are considered to be made of orthotropic materials, while the adhesive is neat resin or reinforced by various types of fibers. The carbon and glass unidirectional fibers are used for adhesive reinforcement. In the FE modeling, the behavior of all the members is assumed to be linear elastic. The ultimate bond strength is increased as the fiber volume fraction in the adhesive is increased. By changing the properties and the behavior of the adhesive from neat resin (isotropic) to fiber composite adhesive (orthotropic) and with various fiber volume fractions and by changing the orientation of the fibers in the adhesive region with respect to the global axes, the bond strength in tension–torsion loadings are changed. Also, the excessive adhesive layer is modeled and its effect on the joint strength is investigated.     

Unipolar Field and Diffusion Charging in the Transition Regime—Part II: Charging Experiments

Unipolar charging of narrowly distributed 30–100 nm DEHS aerosols in air is investigated, in order to determine the influence of the external electric field (E ₀ ≤ 5 kV/cm) and high charging intensities (n·t ≤ 5 · 10 ¹⁴ s/m ³ ) on the charging efficiency. The results are compared with a combined diffusion and field charging model based on the limiting-sphere concept described in Part I.

The experiments were carried out in a wire corona charger under conditions of complete radial turbulent mixing, which makes the determination of charging history straightforward and very accurate. The state of mixing was verified on the basis of the Deutsch model, by separate measurements of particle losses.

For positive charging, the agreement between measured and predicted mean charge was generally better than 5% for particles larger than 45 nm, which typically carried more than 4 unit charges; for 30 nm particles and relatively low charge levels the uncertainties in the model lead to deviations up to 30%.

In case of negative charging, the observed charge levels progressively exceeded those predicted on the basis of mean ion mobilities by factors up to 2 as the charging intensity increased, and there was evidence of additional charging by free electrons.     

Chloride-induced corrosion of steel in cracked concrete—Part II: Corrosion rate prediction models

Chloride-induced corrosion rate (i_corr) prediction models for RC structures in the marine tidal zone that incorporate the influence of crack width (w_cr), cover (c) and concrete quality are proposed. Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in the tidal zone. Experimental variables were w_cr (0, incipient crack, 0.4, 0.7 mm), c (20, 40 mm), binder type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). The two proposed models (one each for accelerated and natural i_corr) can aid not only in quantifying the propagation phase, but also provide a novel way to select c, w_cr and concrete quality.     

Fouling Control in a Submerged Flat Sheet Membrane System: Part II—Two‐Phase Flow Characterization and CFD Simulations

Abstract

Gas‐liquid two‐phase flow has been shown to be very effective in reducing fouling for different membrane modules with different feeds, including submerged flat sheet membranes used in membrane bioreactors for treatment of wastewater. Although gas‐liquid two‐phase flow occurring on the lumen side of tubular or hollow‐fiber membranes has been very well characterized the two‐phase flow regime in submerged membrane processes is different to that inside external membranes. Characterization of two‐phase flow in submerged flat sheet membrane modules has not been previously reported and hence the use of two‐phase flow in these modules has not yet been optimized. This paper reports on characterization of two‐phase flow for a submerged flat sheet membrane module with the aim of identifying the most effective flow profiles for fouling minimization. In order to better understand the fouling control process by two‐phase flow, CFD simulations were also conducted. It was found experimentally that an increase in the bubble size leads to an increase in the cleaning effect, however, for bubbles larger than the channel gap between the submerged flat sheet membranes, any further increase in the bubble diameter had only a minor effect on the cleaning process. CFD simulations revealed that flux enhancement was primarily due to an increase in the overall shear stress on the membrane and to more turbulence generated by introduction of the gas phase.     

Ageing of Adhesive Bonds with Various Surface Treatments,Part 1: Aluminium–Dicyandiamide Cured Epoxy Joints

Ageing studies on adhesive-bonded aluminium–dicyandiamide cured epoxy joints prepared using a variety of different surface treatments were carried out using 100% humidity and cycling the joints between 42–48–42 °C every hour. The pretreatments include a chromic acid, silica/siloxane pretreatment, nonrinse chrome pretreatment, titanium/zirconium (Ti/Zr) pretreatment, and anodised substrate with no pretreatment. Dielectric spectroscopy measurements were used to characterise the rate of the water uptake and monitor the conversion of the surface oxide to hydroxide. These data were correlated with the changes that occurred in the mechanical strength of the bonds. The changes in the surface structure were observed using electron microscopy and elemental analysis conducted using X-ray photoelectron spectroscopy. The dielectric permittivity changes observed were similar for all the different pretreatments, indicating that the predominant process was water absorption. However, small differences were observed that reflect the different surface treatments used. Ageing at an elevated temperature of 70 °C provided definite evidence of hydration of the surface oxide layer. Electron microscopy of the fracture surface indicated oxide-to-hydroxide conversion and was reinforced by X-ray photoelectron spectroscopy. Predominantly, the changes in the mechanical strength observed at low temperature are consistent with the plasticization of the adhesive. However, at the elevated temperature of 70 °C, evidence for weakening of the interfacial layer by hydration becomes evident as a reduction in the mechanical strength. The dielectric measurements allowed the changes in the bond to be followed nondestructively. The mechanical strength of the etched-only pretreatment aged surprisingly well and at the lower temperature of ageing was comparable with the no-rinse chrome and titanium/zirconium pretreatments. The least durable was the PT2Cr-free treatment; however, all treatments showed a significant level of durability at low temperature.     

Composite–composite adhesion in dentistry: a systematic review and meta-analysis

Controversy exists in the literature regarding the most optimal repair procedure for improving the adhesion between the repair resin and the existing resin composite materials. This systematic review analyzed the adhesion potential of resin-based composites to similar and dissimilar composites. Original scientific papers on adhesion to composites published in MEDLINE (PubMed) database between 1 January 1955 and 1 June 2010 were included in this systematic review. Bond-strength data were evaluated for different factor levels, namely surface conditioning methods (control, physical, chemical, physicochemical), substrate–adherent type (being of the same kind or dissimilar), substrate aging (thermocycling or water storage), and test methods (macroshear, microshear, macrotensile, microtensile). The selection process resulted in the final sample of 41 studies. In total, 160 different surface conditioning methods, being mainly combinations of the use of etching agents, application of grinding or air-abrasion protocols, and adhesive promoters (silanes, adhesive resins), have been investigated. When substrate is aged with thermocycling, bond-strength results for composite–composite combinations of the same material were significantly influenced by the surface conditioning method (p = 0.010) and with the test method (p = 0.014), but for dissimilar composite–composite combinations, only test method (p = 0.000) showed a significant effect on the results. When substrate is aged with water storage, bond-strength results for composite–composite combinations of the same material were significantly influenced by the surface conditioning method (p = 0.000), but for dissimilar material combinations only test method showed a significant effect (p = 0.000) on the results. For the composite combinations of the same kind, the impact of surface conditioning type and the test method in thermocycled group was higher on the results.     

Extraction of Uranium Nitrate with 30% (v/v) Tributyl Phosphate in Kerosene in a Pilot Annular Pulsed Disc-and-Doughnut Column—Part II: Axial Mixing and Mass Transfer Performance

Mass transfer experiments were carried out in an annular pulsed disc-and-doughnut column (APDDC) using 30% (v/v) TBP-kerosene + uranium nitrate + nitric acid + water system (uranium nitrate system) for both extraction and stripping processes. Parameters in the axial dispersion model (ADM) and plug-flow model (PFM), namely, the axial dispersion coefficient of the continuous phase and the number of mass transfer units, were regressed by correlating the respective model with the experimental concentration profile. The mass transfer coef?cient is calculated, and new correlations are developed to predict the axial mixing coefficient of the continuous phase and the volumetric mass transfer coefficient. The height of a transfer unit is also calculated. The influence of axial mixing on mass transfer performance for the uranium nitrate system is discussed.     

Ageing of Adhesive Bonds with Various Surface Treatments,Part 3: Aluminium–Dicyandiamide Cured Aluminium Filled Epoxy Joints

Ageing of adhesive-bonded aluminium–dicyandiamide cured epoxy alumina-filled joints prepared using a variety of different surface treatments and exposed to elevated temperatures and high humidity are reported. The uptake of moisture was followed using broadband dielectric spectroscopy, and attempts are made to correlate these changes with observations of variations in the mechanical properties and surface structure monitored by electron microscopy. It was found that the absorption of moisture, as indicated by the dielectric measurements, is similar for all the joints. Small differences observed may be ascribed to the influence of the pretreatment on the absorption behaviour. There was no evidence of changes in the oxide layer of the substrate. Detailed electron microscopic examination of the surfaces did indicate, after prolonged exposure, that change in the pretreatment is consistent with small differences in the dielectric data. Predominantly, the changes that were observed in the mechanical strength of the joints are consistent with the plasticization of adhesive in the joint rather than failure at the substrate interface. Ageing at 70°C did, however, indicate that there were changes in the interfacial layer and these can be correlated with the change in the failure mechanism. It was also observed that the titanium/zirconium (Ti/Zr) pretreatment showed signs of being less durable than the others used in this study.     

Stability of rare earth oxides in a moist environment at elevated temperatures—Experimental and thermodynamic studies: Part II: Comparison of the rare earth oxides

Volatilisation tests enabled to quantify the stability of different rare earth sesquioxides, RE₂O₃ (where RE = Sc, Dy, Er, Yb) and to understand the corrosion process. These tests were carried out at temperatures ranging from 1000 to 1400 °C in moist air with 50 kPa of water at atmospheric pressure, under a flowing gas velocity of 5 cm s^?1. Besides the volatilisation rate, the nature of the volatile gaseous species was determined. The proposed experimental method allowed too to assess the Gibbs free energy of formation of these gaseous volatile species. Finally, the stability of each rare earth oxide under a moist environment at high temperature was compared.     

Demonstrating a New Valence-Bond Interpretation of Conjugation in Polycyclic Conjugated Hydrocarbons with a Single Kekulé Structure

For polyene molecules with a single classical structure, those with more double bonds and more rings have more Dewar resonance structures. The more Dewar resonance structures a polyene has the more it is conjugated and stable. These generalizations are illustrated by comparing sets of molecules with the same number of fixed double bonds. A step-by-step algorithm for rapidly determining the number of Dewar resonance structures in small typical conjugated polyenes is given. Some new analytical equations for the number of Dewar resonance structures (DS) for series of pyrene-related conjugated polyenes with a single classical structure are also presented. Some general qualitative rules for evaluating relative order of conjugation in polyenes are summarized.     

Erbium-Ion-Doped Tellurite Glass Fibers and Waveguides—Devices and Future Prospective: Part II

Following on from Part I of this review article that focuses on the suitability of Er³⁺-doped tellurium oxide glass for optical amplification in fiber, this Part II article describes how the fiber gain data were then employed to engineer amplification in waveguides, which can be integrated with semiconductor pump sources. The gain characteristics and bandwidth of a phosphate modified tellurite waveguide formed on a GaAs substrate are discussed. The limiting structural compatibility of Er³⁺-doped tellurite glass with polydimethylsiloxane polymer for active–passive integration is overcome by adopting a nanoscale super-lattice approach for waveguide engineering.     

Structural Basis for Intumescence—Part II: Synthesis and Characterization of Intumescent Polymers Containing Spirophosphorus Moiety in the Backbone

Taking the spirophosphorus compound 3,9-dichloro-2,4,8,10-tetraoxo-3,9-diphosphaspiro-[5,5]-undecane-3,9-dioxide as one of the reactive monomers, a family of aromatic spirophosphates was synthesized using dihydric phenols, viz., resorcinol, hydroquinone, 4,4′–dihydroxydiphenyl, bisphenol-A and fluorene dicarbinol as the other monomers. The polymers were synthesized employing melt condensation technique under vacuum and characterized using FT-IR, ¹H-, ¹³C- and ³¹P-NMR spectroscopic methods. The number average molecular weight of the polymers was determined using vapour phase osmometry. Thermal properties of the polymers were studied using differential scanning calorimetry and thermogravimetry techniques. These studies indicated that the polymers containing spirophosphato moiety undergo eruptive degradations in the temperature region 310°–380°C leading to the formation of dense carbonaceous foam. The present study confirmed the spirophosphate structure as an essential requirement to show intumescence.     

Extraction of Caprolactam with Toluene in a Pulsed Disc and Doughnut Column–Part III: Mass Transfer Characteristics

Abstract

The mass transfer characteristics of a pulsed disc and doughnut column with a 0.04 m internal diameter and 4.24 m active column length are investigated in order to evaluate its contacting efficiency for caprolactam extraction with toluene. Pilot plant experiments for both the forward and back‐extraction process were performed in order to determine the concentration profile along the column length in both the extract and raffinate phase as a function of the operating conditions. The experimental conditions covered the industrial operating range. Furthermore the dispersed phase hold‐up, average droplet diameter and operating regime were determined and compared with the results obtained for the equilibrium situation, as discussed in Part II.

In the forward extraction process a significant influence of operating conditions was observed, where an increase in the flux decreased the separation efficiency, but an increase in pulsation intensity, temperature, or the addition of ammonium sulphate increased the separation efficiency. In the back‐extraction all concentration profiles were comparable and all caprolactam was extracted after a column length of L/m=2. Compared to the equilibrium situation the drop diameter and pulsation intensity required for the transition of the mixer‐settler to the dispersion operating regime were found to increase under mass transfer conditions, while the hold‐up decreased. HETS values were determined for both the forward and back‐extraction. For the latter HETS=0.28 to 0.41, whereas in the forward extraction HETS=0.32 to 0.67.

The concentration profiles were described with the backflow model, using a constant backflow parameter for the continuous phase and a constant overall mass transfer coefficient. The interfacial area was correlated using drop diameter and hold‐up expressions derived for the equilibrium situation, taking into account the relative effect of mass transfer. Using these expressions the measured data could be correlated and described well.     

Composite Electrodeposition of Ultrafine γ-Alumina Particles in Nickel Matrices; Part I: Citrate and chloride electrolytes

Electrodeposition of nanocomposite -alumina–nickel was examined using citrate and chloride electrolytes with rotating cylinder electrodes. Ultrafine alumina was detected in the nickel matrices and was found to depend on the applied current density. The particle incorporation rate dependence on the applied d.c. current density varied for the different electrolytes. In the chloride baths, higher particle concentrations were found in the deposits plated at low current densities compared to higher values. However, the opposite trend was noted for the citrate electrolyte where an increase in particle deposit content was observed with an increase in applied current density. Additionally, the nickel anodic behaviour was examined in order to devise a pulse-reverse (PR) plating method. PR deposition lead to an enhancement in the -alumina deposit concentration compared to DC plating in chloride electrolytes.     

Generalized aged-adjusted effective modulus method for creep in composite beam structures. Part II — Application

The generalized age-adjusted effective modulus method for creep in composite beams is compared to the original age-adjusted effective modulus method, and various examples comparing the accuracy of the solution under the assumption of a linear aging creep law are given. It is shown that the use of the classical aging coefficient χ always leads to an underestimation of creep effects in a composite beam structure, as compared to the exact solution of the integral equations for creep in the cross section. The underestimation is sometimes very small, sometimes larger, depending on the type of the compliance function assumed. For the CEB compliance function the difference from the exact solution is larger than it is for the ACl compliance function. On the basis of the generalized age-adjsted effective modulus method, a new aging parameter χ_F is introduced, and it is shown that its use either slightly overestimates the creep effects or predicts them accurately in some special cases. Parameter χ_F depends not only the type of compliance functions of the materials interacting within the composite cross section, but also on the geometrical properties of the cross section.     

Binary periodic distillation scheme with enhanced energy conservation—II: Experiment

A laboratory-scale periodic distillation column using the idealized Cannon scheme which has been proposed in Part I was constructed and some basic experiments were carried out in order to examine its performance in view of energy conservation.A five-stage column was used. The system employed is the water-methanol mixture. The Murphree stage efficiency which was estimated on the basis of experimental results was 84.6%. The average vapor rate, which is roughly proportional to the energy consumption rate, is 50 and 20% lower than the vapor rate required for obtaining the same separation by use of a conventional continuous column with the same number of stages whose Murphree stage efficiency is 84.6 and 100%, respectively.