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    Effects of geometrical and processing parameters on mechanical properties of auxetic polyurethane foams

    , Article SN Applied Sciences ; Volume 4, Issue 6 , 2022 ; 25233971 (ISSN) Abedini, N. H. Z ; Nourani, A ; Mohseni, M ; Hosseini, N ; Norouzi, S ; Bakhshayesh, P. R ; Sharif University of Technology
    Springer Nature  2022
    Abstract
    This study aimed to investigate the influence of processing parameters on the mechanical properties of auxetic polyurethane foams including Poisson’s ratio and Young’s modulus. 12 different processing scenarios were considered using the method of Plackett–Burman in the design of experiments with three replicates for each one. Eventually, 36 foams were prepared with different densities and initial thicknesses, heating temperatures and times, applied compression ratios, and the rest times between two heating steps. The microstructures of the conventional and auxetic samples were observed by scanning electron microscopy (SEM). All samples were subjected to tensile loading in one direction with... 

    Measurement modulus of elasticity related to the atomic density of planes in unit cell of crystal lattices

    , Article Materials ; Volume 13, Issue 19 , 2020 , Pages 1-17 Rabiei, M ; Palevicius, A ; Dashti, A ; Nasiri, S ; Monshi, A ; Vilkauskas, A ; Janusas, G ; Sharif University of Technology
    MDPI AG  2020
    Abstract
    Young’s modulus (E) is one of the most important parameters in the mechanical properties of solid materials. Young’s modulus is proportional to the stress and strain values. There are several experimental and theoretical methods for gaining Young’s modulus values, such as stress–strain curves in compression and tensile tests, electromagnetic-acoustic resonance, ultrasonic pulse echo and density functional theory (DFT) in different basis sets. Apparently, preparing specimens for measuring Young’s modulus through the experimental methods is not convenient and it is time-consuming. In addition, for calculating Young’s modulus values by software, presumptions of data and structures are needed.... 

    Proposing a new model to approximate the elasticity modulus of granite rock samples based on laboratory tests results

    , Article Bulletin of Engineering Geology and the Environment ; Volume 78, Issue 3 , 2019 , Pages 1527-1536 ; 14359529 (ISSN) Behzadafshar, K ; Esfandi Sarafraz, M ; Hasanipanah, M ; Mojtahedi, S. F. F ; Tahir, M. M ; Sharif University of Technology
    Springer Verlag  2019
    Abstract
    An accurate examination of deformability of rock samples in response to any change in stresses is deeply dependent on the reliable determination of properties of the rock as analysis inputs. Although Young’s modulus (E) can provide valuable characteristics of the rock material deformation, the direct determination of E is considered a time-consuming and complicated analysis. The present study is aimed to introduce a new hybrid intelligent model to predict the E of granitic rock samples. Hence, a series of granitic block samples were collected from the face of a water transfer tunnel excavated in Malaysia and transferred to laboratory to conduct rock index tests for E prediction. Rock index... 

    Mechanical differences between ATP and ADP actin states: A molecular dynamics study

    , Article Journal of Theoretical Biology ; Volume 448 , 2018 , Pages 94-103 ; 00225193 (ISSN) Mehrafrooz, B ; Shamloo, A ; Sharif University of Technology
    Academic Press  2018
    Abstract
    This paper aims to give a comprehensive atomistic modeling of the nanomechanical behavior of actin monomer. Actin is a ubiquitous and essential component of cytoskeleton which forms many different cellular structures. Despite for several years great effort has been devoted to the investigation of mechanical properties of the actin filament, studies on the nanomechanical behavior of actin monomer are still lacking. These scales are, however, important for a complete understanding of the role of actin as an important component in the cytoskeleton structure. Based on the accuracy of atomistic modeling methods such as molecular dynamics simulations, steered molecular dynamics method is performed... 

    Nanomechanical properties of MscL α helices: A steered molecular dynamics study

    , Article Channels ; Volume 11, Issue 3 , 2017 , Pages 209-223 ; 19336950 (ISSN) Bavi, N ; Bavi, O ; Vossoughi, M ; Naghdabadi, R ; Hill, A. P ; Martinac, B ; Jamali, Y ; Sharif University of Technology
    Taylor and Francis Inc  2017
    Abstract
    Gating of mechanosensitive (MS) channels is driven by a hierarchical cascade of movements and deformations of transmembrane helices in response to bilayer tension. Determining the intrinsic mechanical properties of the individual transmembrane helices is therefore central to understanding the intricacies of the gating mechanism of MS channels. We used a constant-force steered molecular dynamics (SMD) approach to perform unidirectional pulling tests on all the helices of MscL in M. tuberculosis and E. coli homologs. Using this method, we could overcome the issues encountered with the commonly used constant-velocity SMD simulations, such as low mechanical stability of the helix during... 

    Dynamic analysis of a functionally graded simply supported Euler-Bernoulli beam subjected to a moving oscillator

    , Article Acta Mechanica ; Volume 224, Issue 2 , 2013 , Pages 425-446 ; 00015970 (ISSN) Rajabi, K ; Kargarnovin, M. H ; Gharini, M ; Sharif University of Technology
    2013
    Abstract
    The dynamic behavior of a functionally graded (FG) simply supported Euler-Bernoulli beam subjected to a moving oscillator has been investigated in this paper. The Young's modulus and the mass density of the FG beam vary continuously in the thickness direction according to the power-law model. The system of equations of motion is derived by using Hamilton's principle. By employing Petrov-Galerkin method, the system of fourth-order partial differential equations of motion has been reduced to a system of second-order ordinary differential equations. The resulting equations are solved using Runge-Kutta numerical scheme. In this study, the effect of the various parameters such as power-law... 

    Ranking the sawability of ornamental stone using Fuzzy Delphi and multi-criteria decision-making techniques

    , Article International Journal of Rock Mechanics and Mining Sciences ; Volume 58 , 2013 , Pages 118-126 ; 13651609 (ISSN) Mikaeil, R ; Ozcelik, Y ; Yousefi, R ; Ataei, M ; Mehdi Hosseini, S ; Sharif University of Technology
    2013
    Abstract
    The main purpose of this study is to compare the many different rock properties in the rock sawability. The comparison was realized with the combination of the analytic hierarchy process (AHP) and Fuzzy Delphi method and also TOPSIS method. The analysis is one of the multi-criteria techniques providing useful support in selecting among several alternatives with different objectives and criteria. FDAHP method was used in determining the weights of the criteria by decision makers and then ranking the sawability of the rocks was determined by TOPSIS method. The study was supported by the results obtained from a questionnaire carried out to know the opinions of the experts in this subject.... 

    Mechanical properties of double-layered graphene sheets

    , Article Computational Materials Science ; Volume 69 , 2013 , Pages 335-343 ; 09270256 (ISSN) Hosseini Kordkheili, S. A ; Moshrefzadeh Sani, H ; Sharif University of Technology
    2013
    Abstract
    In this paper, the molecular structural mechanics method is employed to calculate the mechanical properties of a double-layered carbon graphene sheet more accurately. For this purpose, covalent bonds are modeled using nonlinear beam elements and van der Waals interactions are replaced by nonlinear truss elements. Morse potential and Lennard-Jones potential equations are used to simulate the covalent bonds and van der Waals interactions, respectively. For each atom, van der Waals forces are considered with respect to all the other atoms located in its cut-off radius. In addition to in-plane mechanical properties of single and double-layered graphene sheets some out-of-plane properties like... 

    Shell-like instability of large diameter single-walled carbon nanotubes conveying fluid

    , Article Journal of Mechanical Science and Technology ; Volume 26, Issue 11 , 2012 , Pages 3389-3397 ; 1738494X (ISSN) Ali-Akbari, H. R ; Firouz Abadi, R. D ; Haddadpour, H ; Noorian, M. A ; Sharif University of Technology
    2012
    Abstract
    The instability of large diameter single-walled carbon nanotubes (SWCNTs) conveying fluid is investigated based on the molecular mechanics. Using the modal expansion for structural displacements, the governing equations of coupled fluid-structural dynamics of SWCNTs are derived. The natural frequencies and mode shape of the SWCNTs are obtained based on the molecular structural mechanics to account for the effect of chirality and discrete nature of SWCNTs. The results show that the vibrational behavior of large diameter SWCNTs conveying fluid is size dependent, but the effect of chirality is negligible. The obtained results are compared with the equivalent continuum-based model in the... 

    Production and characterization of UHMWPE/fumed silica nanocomposites

    , Article Polymer Composites ; Volume 33, Issue 10 , 2012 , Pages 1858-1864 ; 02728397 (ISSN) Ramazani, A ; Saremi, M. G ; Amoli, B. N ; Izadi, H ; Sharif University of Technology
    Wiley  2012
    Abstract
    Ultrahigh-molecular-weight polyethylene (UHMWPE)/fumed silica nanocomposites were prepared via in situ polymerization using a bi-supported Ziegler-Natta catalytic system. Nanocomposites with different nanoparticle weight fractions were produced in order to investigate the effect of fumed silica on thermal and mechanical properties of UHMWPE/fumed silica nanocomposites. The viscosity average molecular weight (M) of all samples including pure UHMWPE as the reference sample and nanocomposites were measured. Scanning electron microscope (SEM) images showed the homogenous dispersion of nanoparticles throughout the UHMWPE matrix while no nanoparticle cluster has been formed. Crystallization... 

    Preparation of ultrahigh-molecular-weight polyethylene/carbon nanotube nanocomposites with a Ziegler-Natta catalytic system and investigation of their thermal and mechanical properties

    , Article Journal of Applied Polymer Science ; Volume 125, Issue SUPPL. 1 , 2012 , Pages E453-E461 ; 00218995 (ISSN) Amoli, B. M ; Ramazani, S. A. A ; Izadi, H ; Sharif University of Technology
    Wiley  2012
    Abstract
    In this research, ultrahigh-molecular-weight polyethylene (UHMWPE)/multiwalled carbon nanotube (MWCNT) nanocomposites with different nanotube concentrations (0.5, 1.5, 2.5, and 3.5 wt %) were prepared via in situ polymerization with a novel, bisupported Ziegler-Natta catalytic system. Magnesium ethoxide [Mg(OEt) 2] and surface-functionalized MWCNTs were used as the support of the catalyst. Titanium tetrachloride (TiCl 4) accompanied by triethylaluminum constituted the Ziegler-Natta catalytic system. Preparation of the catalyst and the polymerization were carried out in the slurry phase under an argon atmosphere. Support of the catalyst on the MWCNTs was investigated with Fourier transform... 

    A novel nonlinear constitutive relation for graphene and its consequence for developing closed-form expressions for Young's modulus and critical buckling strain of single-walled carbon nanotubes

    , Article Acta Mechanica ; Volume 222, Issue 1-2 , 2011 , Pages 91-101 ; 00015970 (ISSN) Shodja, H. M ; Delfani, M. R ; Sharif University of Technology
    2011
    Abstract
    Carbon nanotubes (CNTs) are viewed as rolled graphene. Thus, an appropriate formulation describing the behavior of CNTs must contain the key information about both their initial configuration as graphene and final configuration as CNT.On this note, to date, somemodels, in particular based on the Cauchy- Born rule, for the description of CNTs behavior exist. A simplifying assumption in some of these models is that the length and perimeter of the CNT equal the corresponding dimensions of the unrolled initial configuration, thus neglecting the induced hoop and longitudinal strains. On the other hand, the present work offers a purely nonlinear continuum model suitable for the description of the... 

    Incorporating multiscale micromechanical approach into PLSNs with different intercalated morphologies

    , Article Journal of Applied Polymer Science ; Volume 119, Issue 6 , September , 2011 , Pages 3347-3359 ; 00218995 (ISSN) Yazdi, A. Z ; Bagheri, R ; Kazeminezhad, M ; Heidarian, D ; Sharif University of Technology
    2011
    Abstract
    The objective of the present study is to predict Young's modulus of polymer-layered silicate nanocomposites (PLSNs) containing fully intercalated structures. The particular contribution of this article is to consider the changes in structural parameters of different intercalated morphologies in vicinity of each other. These parameters include aspect ratio of intercalated stacks, number of silicate layers per stack, d-spacing between the layers, modulus of the gallery phase, and volume fraction of each intercalated morphology. To do this, the effective particle concept has been employed and combined with the Mori-Tanaka micromechanical model. It has been shown that the simultaneous effects of... 

    Investigation of the gas barrier properties of PP/ciay nanocomposite films with EVA as a compatibiliser prepared by the melt intercalation method

    , Article Polymer - Plastics Technology and Engineering ; Volume 49, Issue 10 , 2010 , Pages 991-995 ; 03602559 (ISSN) Shafiee, M ; Ahmad Ramazani, S. A ; Danaei, M ; Sharif University of Technology
    2010
    Abstract
    In this research, polypropylene (PP) nanocomposite films were prepared by melt intercalation method and their properties have been evaluated. To facilitate the formation of either intercalated or exfoliated nanocomposites, ethylene vinyl acetate copolymer (EVA) was used as a compatibiliser. Morphology of composites was determined by X-ray Diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM analyses confirmed that increasing of EVA content leads to achievement of intercalated nanocomposites. Furthermore, differential scanning calorimetry (DSC) measurement indicated a decrease in crystallinity, melting point and crystallization temperature. Also, permeability tests showed... 

    Mechanical properties of graphene cantilever from atomic force microscopy and density functional theory

    , Article Nanotechnology ; Volume 21, Issue 18 , 2010 ; 09574484 (ISSN) Rasuli, R ; Iraji Zad, A ; Ahadian, M. M ; Sharif University of Technology
    2010
    Abstract
    We have studied the mechanical properties of a few-layer graphene cantilever (FLGC) using atomic force microscopy (AFM). The mechanical properties of the suspended FLGC over an open hole have been derived from the AFM data. Force displacement curves using the Derjaguin-Müller-Toporov (DMT) and the massless cantilever beam models yield a Young modulus of Ec ∼ 37, Ea ∼ 0.7TPa and a Hamakar constant of ∼ 3 × 10 -18J. The threshold force to shear the FLGC was determined from a breaking force and modeling. In addition, we studied a graphene nanoribbon (GNR), which is a system similar to the FLGC; using density functional theory (DFT). The in-plane Young's modulus for the GNRs were calculated from... 

    Micro resonator nonlinear dynamics considering intrinsic properties

    , Article Scientia Iranica ; Volume 16, Issue 2 B , 2009 , Pages 121-129 ; 10263098 (ISSN) Sayyaadi, H ; Tadayon, M. A ; Eftekharian, A. A ; Sharif University of Technology
    2009
    Abstract
    One of the most important phenomena to affect the motion behaviour of Micro Resonators is their thermal dependency. This has recently received the attention of researchers widely. A thermal phenomenon has two main effects, the first is damping, due to internal friction, and the second is softening, due to Young's modulus-temperature relationship. In this research work, some theoretical and experimental reported results are used to make a proper model, including thermal phenomena. Two Lorentzian functions are used to describe the restoring and damping forces caused by thermal phenomena. In order to emphasize the thermal effects, a nonlinear model of the MEMS, considering capacitor... 

    Investigation of properties of polyethylene/clay nanocomposites prepared by new in situ ziegler-natta catalyst

    , Article Materials and Design ; Volume 30, Issue 7 , 2009 , Pages 2309-2315 ; 02641275 (ISSN) Nikkhah, S. J ; Ramazani Saadat Abadi, A ; Baniasadi, H ; Tavakolzadeh, F ; Sharif University of Technology
    2009
    Abstract
    This paper is devoted to investigation of morphological and physical-mechanical properties of polyethylene (PE)/clay nanocomposites prepared via in situ polymerization method using bi-supported Ziegler-Natta catalyst. Bentonite type clay and MgCl2 (ethoxide type) were used as the support of TiCl4. Catalyst support and polymerization process have been done in slurry phase using Triisobutylaluminum as the co-catalyst. The microstructure of the nanocomposites was examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM indicated that almost fully exfoliated PE/clay nanocomposites were produced successfully using this method. According to permeability... 

    Mechanical properties of graphene cantilever from atomic force microscopy and density functional theory

    , Article Nanotechnology ; Volume 21, Issue 18, Article number 185503 , 2010 ; 09574484 Rasuli, R. (Reza) ; Iraji Zad, A. (Azam) ; Ahadian, M. M ; Sharif University of Technology
    Abstract
    We have studied the mechanical properties of a few-layer graphene cantilever (FLGC) using atomic force microscopy (AFM). The mechanical properties of the suspended FLGC over an open hole have been derived from the AFM data. Force displacement curves using the Derjaguin–Müller–Toporov (DMT) and the massless cantilever beam models yield a Young modulus of Ec ~ 37, Ea ~ 0.7 TPa and a Hamakar constant of ~ 3 × 10 − 18 J. The threshold force to shear the FLGC was determined from a breaking force and modeling. In addition, we studied a graphene nanoribbon (GNR), which is a system similar to the FLGC; using density functional theory (DFT). The in-plane Young's modulus for the GNRs were calculated... 

    Sintering characterizations of Ag-nano film on silicon substrate

    , Article Advanced Materials Research ; Volume 829 , 2014 , Pages 342-346 ; ISSN: 10226680 ; ISBN: 9783037859070 Keikhaie, M ; Akbari, J ; Movahhedi, M. R ; Alemohammad, H ; Sharif University of Technology
    Abstract
    Nowadays, thin films have many applications in every field. So, in order to improve the performance of thin film devices, it is necessary to characterize their mechanical as well as electrical properties. In this research work we focus on the development of a model for the analysis of the mechanical and electrical properties of silver nanoparticles deposited on silicon substrates. The model consists of inter-particle diffusion modeling and finite element analysis. In this study, through the simulation of the sintering process, it is shown that how the geometry, density, and electrical resistance of the thin film layer are changed with sintering conditions. The model is also used to... 

    Elastic properties of actin assemblies in different states of nucleotide binding

    , Article Cellular and Molecular Bioengineering ; Volume 5, Issue 1 , 2012 , Pages 1-13 ; 18655025 (ISSN) Ghodsi, H ; Kazemi, M. T ; Sharif University of Technology
    Abstract
    In this paper, the elastic properties of monomeric actin (G-actin) and the trimer nucleus (G-actin trimer) in different states of nucleotide binding are estimated using steered molecular dynamic (SMD) simulations. Three nucleotide binding states are considered: ADP- and ATP-bound actin and nucleotide-free actin assemblies. Our results show that nucleotide binding and the corresponding changes in structure have significant effects on the mechanical behaviors of actin assemblies. Simulations reveal that the deformation behavior of G-actin monomers is generally elastic up to engineering strains of 16 and 40% in the tension and shear tests, respectively. In addition, the G-actin trimers react...