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.     

Time–cost optimization: using GA and fuzzy sets theory for uncertainties in cost

Uncertainties should be considered in any time–cost trade‐off problems when minimizing project cost and duration, which leads to the so‐called stochastic time–cost trade‐off problem. A new approach to investigate stochastic time–cost trade‐off problems employing fuzzy logic theory is presented. The proposed approach fully embeds the fuzzy structure of the uncertainties in total direct cost into the model. An appropriate GA is used to develop a solution to the multi‐objective fuzzy time cost model. The accepted risk level of the project manager is defined through α cut approach for which a separate Pareto front with set of non‐dominated solutions has been developed. To compare the alternative set of options for any assumed project duration, associated fuzzy costs for different values of α cut are ranked employing two appropriate approaches for fuzzy costs comparison. The proposed models are applied to solve two benchmark test problems. It is shown that the models facilitate the decision‐making process by selecting specified risk levels and employing the associated Pareto front.     

Investigation of β phase formation in piezoelectric response of electrospun polyvinylidene fluoride nanofibers: LiCl additive and increasing fibers tension

As a piezoelectric polymer, poly (vinylidene fluoride) (PVDF) is attractive in energy conversion applications between electrical and mechanical forms because of its low cost, high flexibility, and biocompatibility. The piezoelectricity of electrospun PVDF polymer is due to changes in the crystalline structure (e.g., creating the β‐phase) during the electrospinning process. This research focuses on two approaches for investigation of β Phase formation: (1) addition of LiCl in different concentrations (0.001, 0.00133, 0.002, 0.004 wt%) as inorganic salt to the polymer solution, (2) increasing tension along the fiber axis by increasing the collector drum speed during the aligning process. Performances of these structures were evaluated by using X‐ray diffraction (XRD), Fourier Transform Infrared (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). A one‐step nano‐generator and cost‐effective package based on electrospun nanofibers was presented to measure output voltages as a performance factor. Results show that the addition of LiCl leads to β Phase formation in the crystalline structure, decreasing fiber diameter to 65 nm, and increment in the work of rupture and piezoelectric output. Moreover, the results show that increasing collector drum speed causes the alignment of β‐crystallites along the fiber axis and subsequently no considerable effect on the formation of β‐phases and output voltage. POLYM. ENG. SCI., 56:61–70, 2016. © 2015 Society of Plastics Engineers     

Cement take estimation using neural networks and statistical analysis in Bakhtiari and Karun 4 dam sites,in south west of Iran

Bulletin of Engineering Geology and the Environment - Water seepage from dam foundations causes reservoir water loss and raises the risk of dam instability. One method of remediation for...     

Zinc Oxide/Graphene Oxide as a Robust Active Catalyst for Direct Oxidative Synthesis of Nitriles from Alcohols in Water

Catalysis Letters - In this work, without using any linker or chemical modification of graphene oxide, a zinc oxide immobilized graphene oxide-based catalyst was used for the direct aerobic...     

Chemical vapor deposition of poly(3‐alkylthiophene) nanoparticles on fabric: Chemical and electrochemical characterization

Chemical vapor deposition of poly(3‐methylthiophene) and poly (3‐hexylthiophene) as conductive polymers on the surface of polyester fabrics was successfully obtained. Fourier transform infrared spectroscopy confirmed the formation of polymers on surface of fabrics (the fingerprint of polythiophenes, υ 600–1500 cm^?1). The uniformity of deposition and nanoparticles (average size of 60 nm) were proved with scanning electron microscopy. Electrochemical impedance spectroscopy showed that P3HT‐coated samples offer higher conductivity in compared to P3MT‐coated samples. The impedance modulus of P3HT‐coated samples was lowered nine times to that of row materials and reached to c8000 Ω. The samples have also shown electrochromic properties under electrical current, changing its color from yellowish green at 0 V to dark green at +12 V for poly (3‐hexylthiophene) samples and from brown at 0 V to red at +12 V for poly(3‐methylthiophene)‐coated fabrics (V = 0 V, λ = 450 nm; V = 12 V, λ = 650 nm). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40673.     

Ternary gas permeation through synthesized pdms membranes: Experimental and CFD simulation basedon sorption‐dependent system using neural network model

In this study, a predictive model for the separation of gases via a polydimethylsiloxane (PDMS) membrane has been developed. This model takes into account the effects of gas composition and pressure at the membrane surfaces on the gas sorption and diffusion coefficients in the membrane. Computational fluid dynamics (CFD) modeling has been employed in order to predict the behavior of a gas mixture containing C₃H₈, CH₄, and H₂ at various operating conditions and three zones (upstream, downstream, and membrane body). Artificial neural network (ANN) modeling has been applied to predict sorption and diffusion coefficients of each component of the gas mixture in the membrane. A procedure of calculation has been applied to combine the CFD modeling and the ANN modeling in order to predict sorption, diffusion, and composition of each component at various sites of the membrane. The results determined using the developed prediction model have been found to be in agreement with those determined using experimental investigations with an average error of 10.21%. POLYM. ENG. SCI., 54:215–226, 2014. © 2013 Society of Plastics Engineers     

Synthesis and characteristics of fly ash and bottom ash based geopolymers–A comparative study

The research was carried out to develop geopolymers mortars and concrete from fly ash and bottom ash and compare the characteristics deriving from either of these products. The mortars were produced by mixing the ashes with sodium silicate and sodium hydroxide as activator solution. After curing and drying, the bulk density, apparent density and porosity, of geopolymer samples were evaluated. The microstructure, phase composition and thermal behavior of geopolymer samples were characterized by scanning electron microscopy, XRD and TGA-DTA analysis respectively. FTIR analysis revealed higher degree of reaction in bottom ash based geopolymer. Mechanical characterization shows, geopolymer processed from fly ash having a compressive strength 61.4 MPa and Young's modulus of 2.9 GPa, whereas bottom ash geopolymer shows a compressive strength up to 55.2 MPa and Young's modulus of 2.8 GPa. The mechanical characterization depicts that bottom ash geopolymers are almost equally viable as fly ash geopolymer. Thermal conductivity analysis reveals that fly ash geopolymer shows lower thermal conductivity of 0.58 W/mK compared to bottom ash geopolymer 0.85 W/mK.     

Microstructural and mechanical assessment of transient liquid phase bonded commercially pure titanium

Diffusion joining of commercially pure titanium was successfully prepared via transient liquid phase bonding in vacuum environment. The process was carried out using AMS 4772 silver-based filler alloy at 900–1000°C for various holding time under the vacuum of 6?×?10^?7?Torr. Optical and scanning electron microscopy equipped with an EDS analyzer was conducted for microstructural evaluations. Mechanical properties were also investigated by shear test, fractographic assessment and X-ray diffraction analyses. The tendency to achieve isothermally solidified joint increased by increasing bonding time. No sign of athermal solidification was detected of sample bonded at 1000°C for 90?min. Consequently, the bonding condition of a high quality joint was obtained. Elemental analyses revealed that filler alloy’s elements (Ag, Cu) distributed more uniformly in fully isothermal solidified bond, whereas the aggregation of these elements is considerable in athermally solidified bond. Shear test results represented that the highest shear strength attributed to the sample bonded in isothermal solidified condition (bonded at 1000°C for 90?min).