Influence of Fabrication Residual Thermal Stresses on Rubber-toughened Adhesive Tubular Single Lap Steel-Steel Joints under Tensile Load

The tensile load bearing capability of adhesively-bonded tubular single lap joints which is calculated under the assumption of linear mechanical adhesive properties is usually much less than the experimentally-determined because the majority of the load transfer of adhesively-bonded joints is accomplished by the nonlinear behavior of rubber-toughened epoxy adhesives. Also, as the adhesive thickness increases, the calculated tensile load bearing capability with the linear mechanical adhesive properties increases, while, on the contrary, the experimentally-determined tensile load bearing capability decreases.

In this paper, the stress analysis of adhesively-bonded tubular single lap steel-steel joints under tensile load was performed taking into account the nonlinear mechanical properties and fabrication residual thermal stresses of the adhesive. The nonlinear tensile properties of the adhesive were approximated by an exponential equation which was represented by the initial tensile modulus and ultimate tensile strength of the adhesive.

Using the results of stress analysis, the failure criterion for the adhesively-bonded tubular single lap steel-steel joints under tensile load was developed, which can be used to predict the load-bearing capability of the joint. From the failure criterion, it was found that the fracture of the adhesively-bonded joint was much influenced by the fabrication residual thermal stresses.     

Study of dynamic effects by convective velocity in the membrane process: Operator theoretic approach

This paper studies the dynamic mass transfer effects of solute through fluid-solid interactions in a heterogeneous system. It is found that the convective velocity in internal pores of the membrane can be used to accelerate the speed of the solute by convective velocity at the fluid phase. The theoretical model for the membrane transport is studied in this paper by using the operator theoretic method. A typical example of this dynamic interaction problem is applied in a multi-layered composite membrane. Danckwerts Boundary conditions are analyzed in the inner and outer regions of membrane process. A spectral evaluation of the transport operator is performed by the operator properties in the system. The findings of this paper are useful in guiding the design of membrane separation devices as well as in proving useful to the synthetic performance of composite membrane.     

Barrier property by controlled laminar morphology of LLDPE/EVOH blends

Using the extrusion blown film process, we obtained linear low density polyethylene (LLDPE)/ethylenevinyl alcohol copolymer (EVOH) blends with an improved barrier property by generating a laminar structure of the dispersed phase in the matrix phase. This laminar morphology induced by drawing and blowing was found to result in a significant decrease in toluene permeability with only 10 wt% EVOH. Effects of compatibilizer content and processing parameters such as blending sequence, screw configuration, and stretch ratio on the toluene permeability and morphology of the blends were investigated. It was revealed that the optimum amount of compatibilizer, maleic anhydride grafted LLDPE, should be used to improve the barrier property of the LLDPE/EVOH blends with a well developed laminar structure. The blending sequence had a significant influence on the permeability of the blends. The blend films exhibited a more pronounced laminar structure when all blend components were simultaneously melt blended in a single screw extruder. In addition, the screw configuration designed to impart a low shear stress and the balanced stretching in the machine and transverse directions were more favorable processing conditions in obtaining high barrier blends.     

Molecular thermodynamics of binary polymer solutions using modified double lattice model: Chain length dependence of primary lattice

In a previous study we modified a double lattice model by introducing a new interaction parameter, which improved the mathematical approximation defect, and gave a new expression for the Helmholtz energy of mixing. In the model the universal constants C_β and C_γ in the primary lattice were determined by comparing them with literature Monte Carlo simulation data, which is the only case for r₁ = 1 and r₂ = 100 (case I). In this study we introduce new universal constants, C_β and C_γ, as a function of the chain length of a polymer in a solvent (case II) by comparing them with other literature simulation data for various polymer chain lengths. The proposed model is compared with polymer–solvent systems. In an upper critical solution temperature phase behavior the theoretical results of case II were improved over those of case I. However, in a lower critical solution temperature phase behavior those of case I were not very sensitive to C_β and C_γ. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2627–2633, 1999     

Soft and Hard Adhesion

The force needed to pull a cylindrical stud from a soft elastomeric film depends on their elastic and geometric properties. For a rigid stud and a thick elastomeric film, the pull-off stress (σ) depends on the elastic modulus (E) of the film and the radius (a) of the stud as σ ∼ (E/a)^1/2 (soft adhesion). However, when the film is very thin, the pull-off stress is significantly higher than the case with thick films, and its value depends on the elastic modulus and the thickness (h) of the film as σ ∼ (E/h)^1/2 (hard adhesion). Here, we study the pull-off behavior of a soft cylindrical stud, one flat end of which is coated with a high modulus thin baseplate. As the flexural rigidity of this baseplate is varied, we observe the transition between the two types of adhesion. We present a simple physical interpretation of the problem, which could be of value in understanding various biofouling and adhesive situations.     

Removal of inorganic pollutants in rainwater by a peat-derived porous material

Although roof-top runoff water has been considered as an alternative water resource, the harvested rainwater needs to be treated for further use because it usually contains various contaminants such as heavy metals and microbes. The degree of the harvested rainwater quality depends upon its end use such as drinking water and irrigation. Especially, when harvested rainwater is to be used as gray water, a cost effective treatment system is required. Accordingly, the main purpose of this study was to examine the adsorption characteristics of peat, cost-effective biosorbent, for various inorganic pollutants such as ammonium, copper, cadmium and lead from roof-top runoff water. As part of efforts to investigate the sorption properties of peat, batch isotherm tests were carried out under various pH conditions. The characterization of peat was carried out with powder X-ray diffraction, Brunauer–Emmett–Teller, and scanning electron microscope measurements. Both heat-treated peat and non-treated peat appeared to have high sorption capacity for all inorganic contaminants (NH₄ ⁺, Cu²⁺, Cd²⁺, and Pb²⁺). An interesting finding is that the amount of NH₄ ⁺ sorbed on the sorbents was slightly higher compared to the other cations. Also, the sorption capacity of the peat sorbents increased with an increase of pH. On the other hand, kinetic data were well described by pseudo-second kinetic model, indicating that removal mechanism of cations by peat-derived sorbents is likely due to chemisorptions. The results of this study suggested that peat-derived porous materials can be used as effective sorbents for removal of cationic inorganic contaminants from harvested rainwater.     

Preparation of Nanosized Rutile TiO2 from an Aqueous Peroxotitanate Solution

A new facile method for direct preparation of well-crystallized rutile TiO₂ nanoparticles without any ionic impurities was reported. The nanosized TiO₂ was prepared by aging a peroxotitanate solution at 100°C for 0–12 h, formed by reaction of H₂O₂ and titanium tetraisopropoxide (TTIP). The method involves hydrolysis of TTIP and simultaneous digestion of hydrolyzed precipitates, and hydrothermal treatment into crystalline phases. It was found that the TTIP/H₂O₂ molar ratio in the preparation of peroxotitanate as a precursor for TiO₂ was crucial in the formation of a rutile phase. Transmission electron microscope observation for sols showed rod-like shapes with average particle sizes of around 100 nm in the elongated direction.     

Enhanced surface morphologies of screen-printed carbon nanotube films by heat treatment and their field-emission properties

A heating process for obtaining free-standing carbon nanotube emitters is presented with the aim of improving field-emission properties from the screen-printed multiwalled carbon nanotube (MWCNT) films. Using an atmosphere with an optimum combination of nitrogen and air for heat treatment of CNT films, the CNT emitters can be made to protrude from the surface. This allows for a high emission current and the formation of very uniform emission sites without special surface treatment. The morphological change of the CNT film by this technique has eliminated additional processing steps, such as surface treatment which may result in secondary contamination and damage to the film. Despite its simplicity the process provides a high reproducibility in emission current density which makes the films suitable for practical applications.     

Effect of clay modifiers on the morphology and physical properties of thermoplastic polyurethane/clay nanocomposites

Thermoplastic polyurethanes (TPUs)/clay nanocomposites were prepared via melt processing using the ester type and the ether type TPUs and three differently modified organoclays (denoted as C30B, C25A and C15A) as well as pristine montmorillonite (PM). XRD and TEM results showed that the addition of C30B with hydroxyl group led to the nearly exfoliated structures in both TPUs. In the case of C25A and C15A clays, partially intercalated nanocomposites were obtained in both TPUs, where C25A showed better dispersion than C15A. Natural clay (PM) was not effectively dispersed in both TPUs. The tensile properties of nanocomposites with C30B were better than ones with the other clays. Higher tensile properties were obtained for ester type TPU than ether type TPU nanocomposites with all clays tested. Although the improvement in tensile properties decreased after the second extrusion of the nanocomposites, properties of the nanocomposite after first melt processing were still good enough for practical applications. Morphological changes induced by the addition of clays were analyzed using FTIR, DSC and rheological test results. Some clays were observed to cause demixing of hard and soft segments in the nanocomposites and location of clays in either soft segment or hard segment domains was also studied.     

Synthesis and luminescence properties of new blue‐light‐emitting polyconjugated poly{1,1′‐biphenyl‐4,4′‐diyl‐[1‐(4‐t‐butylphenyl)]vinylene} polymers and copolymers

Three new soluble polyconjugated polymers, all of which emitted blue light in photoluminescence and electroluminescence, were synthesized, and their luminescence properties were studied. The polymers were poly{1,1′‐biphenyl‐4,4′‐diyl‐[1‐(4‐t‐butylphenyl)]vinylene}, poly((9,9‐dioctylfluorene‐2,7‐diyl)‐alt‐{1,4‐phenylene‐[1‐(4‐t‐butylphenyl)vinylene‐1,4‐phenylene]}) [P(DOF‐PVP)], and poly([N‐(2‐ethyl) hexylcarbazole‐3,6‐diyl]‐alt‐{1,4‐phenylene‐[1‐(4‐t‐butylphenyl)]vinylene‐1,4‐phenylene}). The last two polymers had alternating sequences of the two structural units. Among the three polymers, P(DOF‐PVP) performed best in the light‐emitting diode devices of indium–tin oxide/poly(ethylenedioxythiophene) doped with poly(styrene sulfonate) (30 nm)/polymer (150 nm)/Li:Al (100 nm). This might have been correlated with the balance in and magnitude of the mobility of the charge carriers, that is, positive holes and electrons, and also the electronic structure, that is, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, of the polymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 307–317, 2006