Tech Science Press
Not a member yet
3972 research outputs found
Sort by
Renewable Polymers: Synthesis and Characterization of Poly(4-ketopimelic acid-glycerol)
Get PDFCondensation polymerization of renewable resources-based monomers, 4-ketopimelic acid and glycerol, were studied using two different catalysts; p-toluenesulfonic acid and Sb2O3. The highest polymer yield of 96% was achieved by using a 3:4 mole ratio mixture of 4-ketopimelic acid and glycerol, with Sb2O3 (0.5 mol% relative to 4-ketopimelic acid) as catalyst and heating at 23–210 °C, under N2 for 1 h; then 210 °C, vacuum, 12 h. The poly(4-ketopimelic acid-glycerol) formed is insoluble in all common organic solvents and is shown to contain a branched polymeric structure with ketal and ester links by using FT-IR, 1H and 13C NMR spectroscopy
Variation of Physical Properties of Rigid Polyurethane Foams Synthesized from Renewable Sources with Different Commercial Catalysts
Get PDFIn this work, rigid polyurethane foams were synthesized from renewable sources using different catalysts to study their effect on the mechanical, thermal, chemical and surface properties of the foams. A commercial foam pattern was used as the reference pattern to compare the aforementioned properties. Concentrations of the commercial catalysts were optimized to obtain foams with similar mechanical properties to the commercial foam. Morphological characterization of the foams was performed by scanning electron microscopy (SEM). Fourier transform infrared (FTIR) spectroscopy was employed to investigate the characteristic functional groups. Thermal characterization was performed by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Furthermore, mechanical properties were also determined by dynamic mechanical thermal analysis (DMTA). The optimum system of catalysts was composed of 33 Lv and triethanolamine, which achieved a foam with better performance than the commercial foam
Chitosan-g-PMMA/Kaolin Bionanocomposites for Use in Bioadhesive Bone-Cement Implants
Get PDFChitosan grafted with poly(methyl-methacrylate) (PMMA) and adsorbed with kaolin functionalized as bioadhesive was prepared via emulsion polymerization technique and physiochemically characterized as a bone-graft substitute. The so prepared grafted bioactive bone cement (BBC) bionanocomposites (BNCs), chitosan-g-PMMA/kaolin, was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA). The water uptake, retention ability and the nanosize particle arrangement in the polymeric BBC-BNCs were studied along with the mechanical and biodegradation properties. These preliminary investigations of the BNCs will open the door for their use in bioadhesive bone-cement implants in the future
Mixed Convection in a Lid-Driven Square Cavity With Heat Sources Using Nanofluids
Get PDFThis paper presents a numerical study of two-dimensional laminar mixed convection in a lid-driven square cavity filled with a nanofluid and heated simultaneously at a constant heat flux q” by two heat sources placed on the two vertical walls. The movable wall and the bottom wall of the cavity are maintained at a local cold temperature TC, respectively. The finite volume method was used to solve the equations of flow with heat transfer across the physical domain. Comparisons with previous results were performed and found to be in excellent agreement. Results were presented in terms of streamlines, isotherms, vertical velocity profile, and local and average Nusselt numbers for Rayleigh number in the range (Ra=103-106), Reynolds number (Re=1-500), solid volume fraction of nanoparticles (ϕ=0-0.10), heat sources locations, and type of nanofluids (Cu, Ag, Al2O3 and TiO2). The influence of the relevant parameters such as the Rayleigh number, the Reynolds number and the volume fraction of the nonofluid on the average Nusselt number was studied in detail. It was found that the average Nusselt number increases with the increase of Rayleigh number and solid volume fraction of nanofluids. The results show that the Cu-water nanofluid improves heat transfer, and that the heat sources position has an influence on the flow and thermal fields, and on the local and average Nusselt numbers
Comparison of CS, CGM and CS-CGM for Prediction of Pipe’s Inner Surface in FGMs
Get PDFThe cuckoo search algorithm (CS) is improved by using the conjugate gradient method(CGM), and the CS-CGM is proposed. The unknown inner boundary shapes are generated randomly and evolved by Lévy flights and elimination mechanism in the CS and CS-CGM. The CS, CGM and CS-CGM are examined for the prediction of a pipe’s inner surface. The direct problem is two-dimensional transient heat conduction in functionally graded materials (FGMs). Firstly, the radial integration boundary element method (RIBEM) is applied to solve the direct problem. Then the three methods are compared to identify the pipe’s inner surfacewith the information of measured temperatures. Finally, the influences of timepoints, measurement point number and random noise on the inverse results are investigated. It is found that the three algorithms are promising and can be used to identify the pipe’s inner surface. The CS-CGM has higher accuracy and faster convergencespeed than the CS and CGM. The CS and CS-CGMare insensitive to the initial values. The CGM and CS-CGM are more insensitive to the measurement noises compared with the CS. With the increase of timepointsand measurement points, and with the decrease of measurement noises, the inverse results are more accurate
Low Velocity Impact Response and Failure Assessment of Textile Reinforced Concrete Slabs
Get PDFPresent paper proposes a methodology by combining finite element method with smoothed particle hydrodynamics to simulate the response of textile reinforced concrete (TRC) slabs under low velocity impact loading. For the constitutive modelling in the finite element method, the concrete damaged plasticity model was employed to the cementitious binder of TRC and Von-Mises criterion was used for the textile reinforcement. Strain dependent smoothed particle hydrodynamics (SPH) was used to assess the damage and failure pattern of TRC slabs. Numerical simulation was carried out on TRC slabs with two different volume fraction of glass textile reinforcement to predict the energy absorption and damage by coupling finite element method with SPH. Parametric studies were also conducted for simulating the effect of number of textile layers in TRC under impact. It is concluded that the proposed methodology well predicts the damage in TRC slabs at various locations. The results were also analysed using two parameter Weibull distribution and the impact failure strength is presented in terms of reliability function. The results indicated that the Weibull distribution allows describing the failure in terms of reliability and safety limits
A Dimension-Reduction Interval Analysis Method for Uncertain Problems
Get PDFIn this paper, an efficient interval analysis method called dimension-reduction interval analysis (DRIA) method is proposed to calculate the bounds of response functions with interval variables, which provides a kind of solution method for uncertainty analysis problems of complex structures and systems. First, multi-dimensional function is transformed into multiple one-dimensional functions by extending dimension reduction method to the interval analysis problem. Second, all the one-dimensional functions are transformed to standard quadratic form by second order Taylor expansion method. As a result, the multi-dimensional function is approximately represented by the functions that each interval variable occurs once, and interval power arithmetic can be used to efficiently calculate the bounds of response functions in restricted overestimation. Finally, three numerical examples and an engineering application are investigated to demonstrate the validity of the proposed method
Numerical investigation of penetration in Ceramic/Aluminum targets using Smoothed particle hydrodynamics method and presenting a modified analytical model
Get PDFRadius of ceramic cone can largely contribute into final solution of analytic models of penetration into ceramic/metal targets. In the present research, a modified model based on radius of ceramic cone was presented for ceramic/aluminum targets. In order to investigate and evaluate accuracy of the presented analytic model, obtained results were compared against the results of the Florence’s analytic model and also against numerical modeling results. The phenomenon of impact onto ceramic/aluminum composites were modeled using smoothed particle hydrodynamics (SPH) implemented utilizing ABAQUS Software. Results indicated that, with increasing initial velocity and ceramic thickness and decreasing support layer thickness, the radius of ceramic cone decreases; this ends up increasing residual velocity of the projectile and penetration time and extending the area across which the pressure is distributed. These findings indicate enhanced levels of target energy absorption and the required energy for bending and tensioning the target. As such, it can be observed that, at the same thickness and areal density, the ceramic target has its efficiency enhanced with increasing ceramic thickness and decreasing the support layer thickness. Finally, the results revealed that the associated data with SPH confirm the modified analytic model at higher accuracy than the Florence’s analytic model
Synthesis and Characterization of Interpenetrating Polymer Networks (IPNs) from Acrylated Soybean Oil and a-Resorcylic Acid: Part 1. Kinetics of Network Formation
Get PDFInterpenetrating polymer networks (IPNs) using an epoxy phase synthesized from chemically modified α-resorcylic acid, and an acrylate phase employing acrylated soybean oil are the main focus of this study. Part 1 details the epoxidation of α-resorcylic acid with epichlorohydrin in alkaline medium, as well as the study of the polymerization and network formation of the generated epoxy-acrylate interpenetrated systems. The epoxy content of the epoxidized α-resorcylic acid was measured by means of a titration using HBr in acetic acid solution, and the functionalization was studied by FTIR. From the obtained results, mainly calorimetry and gel time determination, it was clear that each phase is affected by the presence of the other, altering the rate and extent at which each individual reaction takes place; and that the two noncompeting reactions (step and free radical polymerizations) occurred at very close temperatures, with a very small gap of around 10 °C between the onsets of the reactions. This evidence leads to the conclusion that the IPNs are formed by a simultaneous process in which both of the networks are formed at approximately the same temperature
Exact Solutions and Mode Transition for Out-of-Plane Vibrations of Nonuniform Beams with Variable Curvature
Get PDFThe two coupled governing differential equations for the out-of-plane vibrations of non-uniform beams with variable curvature are derived via the Hamilton's principle. These equations are expressed in terms of flexural and torsional displacements simultaneously. In this study, the analytical method is proposed. Firstly, two physical parameters are introduced to simplify the analysis. One derives the explicit relations between the flexural and the torsional displacements which can also be used to reduce the difficulty in experimental measurements. Based on the relation, the two governing characteristic differential equations with variable coefficients can be uncoupled into a sixth-order ordinary differential equation in terms of the flexural displacement only. When the material and geometric properties of the beam are in arbitrary polynomial forms, the exact solutions with regard to the outof- plane vibrations of non-uniform beams with variable curvature can be obtained by the recurrence formula. In addition, the mode transition mechanism is revealed and the influence of several parameters on the vibration of the non-uniform beam with variable curvature is explored