Feasibility study of friction stir welding of wood–plastic composites

In this study, feasibility of friction stir welding of wood–plastic composites is investigated. For this purpose, a special welding tool including a fixed heated shoe called ‘hot shoe’ is designed. Furthermore, rotating and travelling speeds of the pin and shoe temperature are considered as the variable parameters and tensile strength as the mechanical property of welded samples. A 3³ full factorial design of experiment and an analysis of variance is performed in this study. Experimental results show that acceptable weld could be obtained using the designed welding tool. Results also reveal that the statistically significant effects of all parameters are at the confidence level of 95%. It is also concluded that the shoe temperature is the most effective parameter.     

Effect of different acids during the synthesis of urea-formaldehyde adhesives and the mechanical properties of medium-density fiberboards bonded with them

The characteristics of urea-formaldehyde (UF) adhesives condensed by catalysis with four different acids, namely formic (HCOOH), hydrochloric (HCl), phosphoric (H₃PO₄), and sulfuric (H₂SO₄) acids, under alkaline–acidic–alkaline conditions at a molar ratio F/U = 1.12 were studied. The thermal curing properties of UF adhesives catalyzed with acid were characterized by differential scanning calorimetry at 10 °C/min heating rate. The resin structure examined by ¹³C-NMR spectroscopy showed that the resin catalyzed with HCl had a lower proportion of methylol groups, resulting in a lower level of formaldehyde emission. It was interesting to note that HCOOH resulted in the best overall mechanical properties of the medium-density fiberboard (MDF) panels. The HCl catalyst resulted in the poorest performance, providing the lowest internal bond strength, modulus of elasticity, and thickness swelling, with the exception of the free formaldehyde content. The resin catalyzed with H₂SO₄ had the highest free formaldehyde and the highest formaldehyde emission. H₂SO₄ and H₃PO₄ resulted in MDF mechanical properties relatively lower than for HCOOH. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47256.     

A Taguchi analysis on structural properties of polypropylene microcellular nanocomposite foams containing Fe2O3 nanoparticles in batch process

Polypropylene (PP) as a thermoplastic polymer has been foamed using batch foaming process. CO₂ is used as the blowing agent of the foaming. Ferrous oxide nanoparticles (nano Fe₂O₃) are also added as reinforcement. Effect of different parameters including nanoparticle weight percentage, foaming temperature and time on the structural properties of PP/nano Fe₂O₃ nanocomposites is investigated using Taguchi approach. Scanning electron microscope results depict that an appropriate microcellular structure is obtained with the cell density of 10⁹ cells/cm³ and almost 1 μm of cell size. Analysis of variance results indicated that foaming temperature is the most significant parameter on the structural properties. Cell density and expansion ratio are decreased by increasing foaming temperature. This phenomenon could be due to the reducing melt strength of polymer/gas mixture. It was also inferred that adding 2 wt% of nanoparticles leads to 80% improvement in cell density while cell size and expansion ratio was decreased.     

Optimization of mechanical properties of in situ polymerized poly(methyl methacrylate)/alumina nanoparticles nanocomposites using Taguchi approach

Polymer Bulletin - Alumina nanoparticles are among important metal oxides with specific properties but chemically incompatible with an organic matrix such as poly(methyl methacrylate) (PMMA). In...     

Facile and regioselective synthesis of thiazolidin-4-one derivatives catalyzed by basic ionic liquid [bmim]OH under ultrasonic irradiation

2-Iminothiazolidin-4-one derivatives were synthesized regioselectively in good to high yields by condensation of N,N-disubstituted thioureas and ethyl chloroacetate in the presence of basic ionic liquid [bmim]OH as a catalyst under conventional and ultrasonic irradiation conditions. Under ultrasonic irradiation, the reaction furnished the desired 2-iminothiazolidinones in higher yields (76–87%) and lower reaction times (30–55 min).     

Size-dependent nonlinear vibration of an electrostatic nanobeam actuator considering surface effects and inter-molecular interactions

In this paper, the size-dependent nonlinear vibration of an electrostatic nanobeam actuator is investigated based on the nonlocal strain gradient theory, incorporating surface effects. A comprehensive model regarding the von Karman geometrical nonlinearity, inter-molecular forces and both components of the electrostatic excitation (AC and DC) is proposed to explore the system behavior near the primary resonance. Utilizing Hamilton’s principle, the nonlinear equation of motion of the system is derived. The natural frequency and dynamic response of the system, comprising frequency and force response diagrams, are obtained analytically via multiple scales technique in conjunction with the differential quadrature method and validated through a numerical approach. The roles of the nonlocal and strain gradient parameters, surface elasticity, inter-molecular forces and quality factor on the system oscillations are examined. The acquired results unveiled that the size-dependent parameters can significantly displace the multi-valued portions and instability thresholds of the dynamical response. Furthermore, it is deduced that the surface effects induce the stiffness hardening of the nanobeam, whereas the inter-molecular forces impose the stiffness softening effect.

     

The Effect of Direct and Cross-Rolling on Mechanical Properties and Microstructure of Severely Deformed Aluminum

Severely deformed commercial pure aluminum sheets by constrained groove pressing are direct and cross-rolled. The grain size evolution and dislocation density during rolling are studied using Williamson-Hall analysis on x-ray diffraction patterns of the deformed samples. These results and optical microscopy observations show that subsequent direct or cross-rolling of constrained groove pressed aluminum can produce elongated fine grains. The minimum crystallite size is achieved after cross rolling of constrained groove pressed samples. By direct rolling or cross-rolling of annealed sheet, the maximum intensity in x-ray diffraction patterns remains on (200) like annealed aluminum but direct rolling or cross-rolling of constrained groove pressed sheets changes the maximum intensity from (111) for constrained groove pressed sheets to (220). Also, mechanical properties are studied using tensile test and hardness measurement. The results show that cross rolling on constrained groove pressed samples is more effective than direct rolling in mechanical properties improvement.     

Can a multi-hop link relying on untrusted amplify-and-forward relays render security?

Wireless Networks - Cooperative relaying is utilized as an efficient method for data communication in wireless sensor networks and the Internet of Things. However, sometimes due to the necessity of...     

Characterization and corrosion behavior of electroless Ni–P/nano-SiC coating inside the CO2 containing media in the presence of acetic acid

In this research, Ni–P and Ni–P/nano-SiC coatings were applied on the X70 steel substrate successfully without any surfactant. Then, CO₂ corrosion in the presence of acetic acid (HAc) was investigated using electrochemical techniques. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were used for surface analyses of the coatings. The electrochemical behavior of corrosion was investigated using polarization test and electrochemical impedance spectroscopy (EIS). XRD pattern of Ni–P/nano-SiC coating was very similar to that of Ni–P coating. EDS results demonstrated the presence of SiC particles in the coating. SEM images confirmed the presence of SiC nano-particles with almost uniform distribution in the coating. The corrosion current density was less in the Ni–P and Ni–P/nano-SiC coated samples than uncoated X70 steel. Ni–P/nano-SiC coated sample had the most corrosion resistance because of less effective metallic area available for corrosive media. The overall protection mechanism of Ni–P and Ni–P/nano-SiC coatings was achieved by formation of a layer of adsorbed hypophosphite anions (H₂PO₂⁻).     

An improved cuckoo search optimization algorithm with genetic algorithm for community detection in complex networks

This paper improved Cuckoo Search Optimization (CSO) algorithm with a Genetic Algorithm (GA) for community detection in complex networks. CSO algorithm has problems such as premature convergence, delayed convergence, and getting trapped in the local trap. GA has been quite successful in terms of community detection in complex networks to increase exploration and exploitation. GA operators have been used dynamically in order to increase the speed and accuracy of the CSO. The number of populations is dynamically adjusted based on the amount of exploration and exploitation. Modularity objective function (Q) and Normalized Mutual Information (NMI) is used as an optimization function. It was carried out on six types of real complex networks. The proposed algorithm was tested with GA, Artificial Bee Colony (ABC), Grey Wolf Optimizer (GWO), and CSO, with different iterations in modularity and NMI criteria. The results show that in most comparisons, the proposed algorithm has been more successful than the basic comparative algorithms, and it has proven its superiority in terms of modularity and NMI. The proposed algorithm performed an average of 54% better in modularity and 88% in NMI than other algorithms. It performed on average in modularity criteria 84.3%, 58.8%, 33.7% and 38.8%, respectively, compared to CSO, ABS, GWO and GA algorithms, and in terms of NMI index, 188.7%, 39.1%, 52.3% and 73.8%, respectively in CSO, ABS, GWO and GA algorithms performed better.