Optimization of material formulation and processing parameters in relation to mechanical properties of bioepoxy/clay nanocomposites using Taguchi design of experiments

This article aims to study the effects of material formulation and processing parameters on mechanical properties of bioepoxy/clay nanocomposites based on epoxidized soybean oil (ESO) via Taguchi design of experiments (DoEs). A mixed‐level DoE with an L₁₆ orthogonal array was constructed to achieve maximum levels of tensile strength, tensile modulus, and impact strength for corresponding bionanocomposites. Pareto analysis of variance (ANOVA) was used to identify significant factors and preferred formulations in the manufacture of bioepoxy/clay nanocomposites. The ESO content was found to have the most significant effect with regards to bionanocomposite mechanical properties with contribution percentages of 66.63, 72.96, and 40.14% for their tensile strength, tensile modulus, and impact strength, respectively. With regards to material processing parameters, mechanical mixing speed was identified as a critical factor to achieve optimal tensile and impact properties. Nonetheless, the results also indicated clay content to be a significant factor for tensile strength, whereas curing agent type was vital for the improvement of tensile modulus and impact strength. Clay type and sonication time were also found to be significant factors for impact strength. In contrast to this, manufacturing parameters such as mechanical mixing temperature, mixing time, and sonication frequency were considered to be non‐significant factors due to their low cumulative contribution percentages of <10%. Finally, experimental confirmation tests based on the preferred combination of factors demonstrated good agreement with statistically predicted results. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45769.     

Effects of linearly heated left wall on natural convection within a superposed cavity filled with composite nanofluid-porous layers

The effect of a linearly heated left sidewall on natural convection flows in a cavity filled with nanofluid-superposed porous layers is investigated numerically using the Galerkin finite element method. Two cases, which use the vertical and horizontal directions for the porous–nanofluid layers, are considered to investigate the natural convection in the flow inside a square enclosure. In both cases, the left wall is linearly heated, whereas the right wall is isothermally cooled. The horizontal walls are assumed to be thermally insulated. The Darcy–Brinkmann model is used to solve the governing equations in the porous layer. The results show that the nanofluid produces more enhancement of heat transfer compared to the base fluid. Increasing the Rayleigh number $(Ra)$ values caused the intensity of the streamlines in case 2 to be stronger than that in case 1. Lower values of the thermal conductivity ratio ($K_r)$ imply greater heat transfer enhancement than for the high thermal conductivity ratios. At the low values of the thermal conductivity ratio ($K_r<1)$ and Darcy number values $(Da$$<$${10}^{-3})$, the heat transfer is more enhanced for case 2 compared to case 1 while higher Darcy number produced case 1 overcome case 2.     

Failure Analysis of Laser Weld Joint of X2NiCoMo18-8-5 Steel

Laser welded T-shaped steel joints were received in debris form. The debris were recovered from the crashed component. Different metallurgical analysis was made on these debris to reach the root cause of the failure. In this regard, optical microscope and scanning electron microscope were utilized for the confirmation of different observations. Huge deposits of oxidation products were observed on the thick part (i.e., plate) of the T-shaped joint. For the confirmation of these products a set of simulated experiments were also performed.     

The effect of alkaline etching time on the anticorrosion performance of vanadia film formed on high strength AA2024 in chloride media

Corrosion performance, morphology, and electrochemical characteristics of vanadia-based conversion coatings on high strength aluminum AA2024-T3 alloy were examined as a function of alkaline etching time prior to vanadia treatment. Corrosion resistance and coating performance improved after etching in an alkaline solution for 10 min followed by vanadia treatment at room temperature. Electrochemical impedance spectroscopy and polarization testing correlated to macro- and microscopic surface examination and visual inspection. Proper etching of aluminum AA2024-T3 panels in alkaline solution prior to vanadia coating is a time dependent and considers a critical step for improved coating performance and materials durability. Results showed that the optimum alkaline etching time prior to vanadia treatment was 10 min which offers the best resistance to localized corrosion attack in NaCl solution. Alkaline etching for 10 min has an important role in increasing the number of OH groups on the aluminum surface, contributing to the adhesion of the vanadia-rich aluminum oxide layer by promoting covalent bonding. Based on these results, processes active during alkaline etching are kinetically dependent and strongly influenced by etching time.     

Corrosion Failure of a 30-Ton Tripod Jack

A failure investigation of the four most suspected members in the assembly of a 30 ton tripod jack was carried out. It was found that under the combined effect of corrosion and high stresses, crack(s) were generated in the weld region of the leg extension. The crack(s) propagated under the corrosion and repeated loading until it reached a threshold size and the tripod jack collapsed. The problem initiated due to corrosion. Failure of the other members of the tripod jack, that is, spacer, brace, and bolts were the result of subsequent damage after (during) failure of the leg extension.

Determination of the optical constants of As–Se–Ag chalcogenide thick films with high precision for optoelectronics applications

Thin films of (As₅₀Se₅₀)_100?xAg_x (with 0?≤?x?≤?25 s) metal-chalcogenide glasses were deposited onto glass substrates by thermal evaporation technique under high vacuum (10^?6 mbar). The optical constants as well as the average thickness of the studied films are determined by the Swanepoel envelope method which is based on the optical transmission spectra measured in the spectral range 300–2500 nm. This method enables the transformation of the optical-transmission spectrum of a thin film of wedge-shaped thickness into the spectrum of a uniform film, whose thickness is equal to the average thickness of the non-uniform layer. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single-oscillator model. The optical absorption edge is described using the non-direct transition model proposed by Tauc relation. Analysis of the optical data revealed that an addition of Ag in the range from 0 to 25 at.% to the (As₅₀Se₅₀)_100?x binary alloys affected the optical parameters of the investigated thin films. For instance, the optical band gap decreased from 1.661 to 1.441 eV with increasing the Ag content from 0 to 25 at.%. The results were discussed in terms of Mott and Davis model as well as chemical-bond approach.     

Inhibitor and Activator: Dual Role of Subsurface Sulfide Enables Selective and Efficient Electro-Oxidation of Methanol to Formate on CuS@CuO Core-Shell Nanosheet Arrays

Selective electro-oxidation of aliphatic alcohols into value-added carboxylates at lower potentials than that of the oxygen evolution reaction (OER) is an environmentally and economically desirable anode reaction for clean energy storage and conversion technologies. However, it is challenging to achieve both high selectivity and high activity of the catalysts for the electro-oxidation of alcohols, such as the methanol oxidation reaction (MOR). Herein, a monolithic CuS@CuO/copper-foam electrode for the MOR with superior catalytic activity and almost 100% selectivity for formate is reported. In the core-shell CuS@CuO nanosheet arrays, the surface CuO directly catalyzes MOR, while the subsurface sulfide not only serves as an inhibitor to attenuate the oxidative power of the surface CuO to achieve selective oxidation of methanol to formate and prevent over-oxidation of formate to CO₂ but also serves as an activator to form more surface O defects as active sites and enhances the methanol adsorption and charge transfer to achieve superior catalytic activity. CuS@CuO/copper-foam electrodes can be prepared on a large scale by electro-oxidation of copper-foam at ambient conditions and can be readily utilized in clean energy technologies.     

Concho-antropexy or total inferior turbinectomy for hypertrophy of the inferior turbinates? A prospective randomized study

Twenty-five patients with bilateral nasal obstruction due to hypertrophy of the inferior turbinates were entered into a prospective study to compare the efficacy and the associated complications of total inferior turbinectomy and concho-antropexy. We found no significant statistical difference in the efficacy of these procedures in relieving nasal obstruction and discharge (p > 0.5). Total inferior turbinectomy was associated with more post-operative pain (p < 0.05) and with long-term dryness and crusting (p < 0.05) which were statistically significant. This is the first trial where concho-antropexy and total inferior turbinectomy are compared.     

Modeling and simulation of photovoltaic (PV) system during partial shading based on a two-diode model

This paper proposes accurate partial shading modeling of photovoltaic (PV) system. The main contribution of this work is the utilization of the two-diode model to represent the PV cell. This model requires only four parameters and known to have better accuracy at low irradiance level, allowing for more accurate prediction of PV system performance during partial shading condition. The proposed model supports a large array simulation that can be interfaced with MPPT algorithms and power electronic converters. The accurateness of the modeling technique is validated by real time simulator data and compared with the three other types of modeling, namely Neural Network, P&O and single-diode model. It is envisaged that the proposed work is very useful for PV professionals who require simple, fast and accurate PV model to design their systems.     

Precision friction measurement between ultrathin wire and microprobe

In this study, using an experimental technique based on small-span bending, the friction behaviors of ultrathin Pt wires with the tungsten microprobes have been reported. In the technique, friction force for sliding of a simply supported wire under bending load applied by closely positioned two opposite probes is measured by a microforce sensor. The force sensor is a capacitive detection type double-beam passive cantilever. Specificity of the microforce sensor provides the technological advantage for precise measurement of friction and normal contact forces sequentially under the observation by a high-resolution digital microscope. Static and kinetic frictions due to externally applied force, internal adhesive force and relative motion are successfully determined. Furthermore, the measured friction in wire-probe contact is used in the determination of the mechanical properties of the wire material.