Sharif Digital Repository

Through advanced computational analysis, this work demonstrates that metamaterial structures when made by shape-memory polymers (SMPs) can provide unique intelligent mechanical behavior. For the first time, geometrical effects, pertaining to low and ultra-low densities, on the thermomechanical behavior of SMP-based octet-truss lattice meta-structures are studied in this work. A reliable constitutive thermo-visco-hyperelastic model is applied to analyze the shape-memory behavior of several designed octet-truss lattices with ultra-low and low relative densities, ranging from 0.04 to 0.23. Different compressive strain values are tested to determine the effect of pre-straining. It is concluded... 

In the present research, the influence of nanodiamond (ND) and a physical hybrid of ND and fumed nano-SiO2 were investigated on the performance of a typical tire tread compound. The styrene-butadiene rubber (SBR) and cis-butadiene rubber (BR) blend filled with a commercial grade highly dispersive silica at 70 phr loading were used as typical tire tread compound. ND was substituted partially with silica at two different concentrations of 5 and 10phr. Meanwhile, 5 phr of ND/nano-SiO2 hybrids with the weight ratio of 2.5/2.5 and 1/4 were substituted with silica. ND-Filled compounds exhibit increased scorch and cure time compared to controls. Improvement in different characteristics of the... 

ABSTRACTs: The need for fully dense material with well-engineered microstructures has led to the promising emergence of innovative sintering technologies among which the Spark Plasma Sintering (SPS) is one of the most favorite. Unlike the conventional sintering processes, SPS takes advantage of a current flow passing through the sintering die and metallic powders by which fast densification with minimal grain growth and enhanced physicomechanical properties can be obtained. Albeit there is a growing interest in the exploitation of SPS in producing sufficiently consolidated metallic parts, no analytical review has been released over the effects of SPS parameters on the densification behavior,... 

Graphene nanoplatelets (GNPs) are ideal reinforcements for improving the mechanical properties of aluminum-based matrices due to their outstanding properties. However, it essentially depends on their uniform dispersion in the matrix. In this study, the challenge of uniform dispersion of graphene was performed by functionalizing the non-covalent surface and sonication of GNPs applying non-ionic polymeric ethyl cellulose (EC) surfactant, in which a colloidal mixture was provided with Al powder and graphene, followed by sintering at 620 °C and consolidation. The density and mechanical properties of nanocomposite specimens were investigated and compared with a non-surfactant-assisted Al/GNP... 

In the initial recovery stage, only 5 to 15% of hydrocarbons can be extracted from oil reservoirs, so it is necessary to supply energy from an external reservoir or to use advanced solutions to increase oil recovery. By using secondary recovery method and flooding, greater amount of oil can be extracted. In this study, a new procedure of flooding using nanofluid was simulated. The nanofluid and source rock were modeled as a single phase and heterogeneous porous media, respectively. The geometry was considered as a two-dimensional rectangular area. Two phase Darcy equations and mass transfer equations were utilized to simulate this process. Moreover, the effects of different volume fractions... 

A suction-controlled ring device has been developed to continuously measure the coefficient of lateral soil pressure in deformable unsaturated soil samples from the at-rest to the active condition under application of increasing vertical pressure and controlled matric suction. The device incorporates a thin aluminum specimen ring equipped with horizontal strain gages for recording the lateral soil strains. In addition, a sensor recording water volume changes is utilized to continuously monitor the degree of saturation of the soil sample during tests. The matric suction within the soil texture is controlled using the axis translation technique. In order to verify the performance of the ring... 

In the present study, a novel theoretical model is developed, based on classical laminate theory, to predict the equivalent mechanical properties of the re-entrant lattice structures, which composed of continuous fiber reinforced composite struts. Three main mechanism of stretching, flexing and hinging are considered and a general closed-form formulation is derived to estimate the auxetic honeycomb's elastic and shear modulus as well as Poisson's ratios. In spite of previous studies in which the response of honeycomb structures is modeled using beam theory, here, each strut of unit cell is expressed as a composite laminate with orthotropic mechanical properties and classical laminate theory... 

Reservoir fluid modelling is one of the most important steps in reservoir simulation and modelling of flow lines as well as surface facilities. One of the most uncertain parameters of the reservoir fluids is the plus fraction. An accurate and consistent splitting scheme can reduce this uncertainty and as a result, enhance the modelling of reservoir fluids. The existing schemes for splitting plus fractions are all based on assuming a specific mole fraction-molecular weight distribution with predefined constant values that may yield inaccurate and inconsistent results. In this study, an optimization-based algorithm was developed to determine the aforementioned controlling parameters of the... 

In order to investigate the evolution of microstructure and flow stress during non-isothermal annealing, aluminum samples were subjected to strain magnitudes of 1, 2 and 3 by performing 2, 4 and 6 passes of multi-directional forging. Then, the samples were non-isothermally annealed up to 150, 200, 250, 300 and 350 °C. The evolution of dislocation density and flow stress was studied via modeling of deformation and annealing stages. It was found that 2, 4 and 6 passes multi-directionally forged samples show thermal stability up to temperatures of 250, 250 and 300 °C, respectively. Modeling results and experimental data were compared and a reasonable agreement was observed. It was noticed that... 

A severe plastic deformation is widely used to improve the mechanical properties of non-heat-treatable alloys. Thus, the investigation and modeling of microstructural evolutions of materials during large straining are of great importance. In this research, substructural evolutions of four different kinds of Al alloys namely Al-1Mn, Al-1Mg, Al-2.77Mg and Al-5Mg, have been studied using a dislocation based model and the mechanical properties of these alloys have been compared considering all microstructural parameters such as dislocation density, subgrain size, cell wall misorientation and the effect of alloying element. As a result, a simplified general equation has been expressed in order to... 

Cartilage is an avascular tissue with limited self-repair ability. Since the methods for treatment of cartilage defects have not been effective, new therapies based on tissue engineering are considered over the recent years. In this study, human cartilage tissue was decellularized and porous injectable microcarriers (MCs) composed of acellular extracellular matrix (ECM) of cartilage tissue and chitosan (CS), with different ECM weight ratios, were fabricated by electrospraying technique to be used in the treatment of articular cartilage defects. Various properties of ECM/CS MCs such as microstructure, mechanical strength, water uptake behaviour, and biodegradability rate were investigated.... 

In this study, nanostructured biodegradable pure Zn, Zn-4 wt. % Mn and Zn-24 wt % Mn alloys were produced by 20 h mechanical alloying and consequent cold pressing and sintering. Structural evolutions were investigated using the X-ray diffraction technique. Also, the microstructure was characterized by scanning electron microscopy. The effects of alloy composition on density, mechanical properties, corrosion behavior in Hank's solution, cell viability and cell attachment were investigated. Crystallite size of the synthesized alloys after 20 h of milling reached to less than 40 nm and remained less than 80 nm after consolidation and sintering for 1 h. Alloys contain MnZn13 as second phase... 

Understanding the co-crystallization behavior of ternary polyethylene (PE) blends is a challenging task. Herein, in addition to co-crystallization behavior, the rheological and mechanical properties of melt compounded high density polyethylene (HDPE)/low density polyethylene (LDPE)/Zeigler − Natta linear low density polyethylene (ZN-LLDPE) blends have been studied in detail. The HDPE content of the blends was kept constant at 40 wt% and the LDPE/ZN-LLDPE ratio was varied from 0.5 to 2. Rheological measurements confirmed the melt miscibility of the entire blends. Study of the crystalline structure of the blends using DSC, wide angle X-ray scattering, small angle X-ray scattering and field... 

Mechanical alloying and hot extrusion techniques were employed to produce in-situ fully dens Al-Ti composites without applying any heat treatment. The focus of this study is the investigation of fracture toughness in produced composites in order to improve it and to explain the mechanisms responsible for the fracture. The morphology of milled powders was studied by Scanning Electron Microscopy (SEM). The microstructure of the extruded composites was examined by Optical Microscopy (OM) and Field Emission Scanning Electron Microscopy (FESEM). Moreover, the density and hardness of samples were investigated. Three point bending test of the single edge notched beam (SENB) samples was applied to... 

Accurate determination of natural gas viscosity is important for successful design of production, transportation, and gas storage systems. However, most of available models/correlations suffer from complexity, robustness, and inadequate accuracy especially when wide range of pressure and temperature is applied. Present study illustrates development of two novel models for predicting natural gas viscosity for pure natural gas (CH4) as well as natural gas containing impurities. For this purpose, 6484 data points have been gathered and analyzed from the open literature covering wide range of pressure, temperature, and specific gravity levels, temperature ranges from -262.39 to 620.33 °F (109.6... 

This work represents the efficiency of a solar desalination pond as a second stage of proposed zero discharge desalination processes to reach fresh water and also concentrated brine from the effluent wastewater of the desalination unit of Mobin petrochemical complex. So a solar desalination pond is constructed after a pretreatment unit to concentrate the softened wastewater to about 20wt%. The concentrated wastewater is as a suited feed for a forced circulation crystallizer. During one year, the effects of major parameters such as ambient temperature and solar insolation rate are investigated, experimentally. specific gravity in each layer of concentrated brine wastewater is evaluated. Also,... 

A new simple and explicit reduced temperature and reduced pressure function has been proposed in the present study for modifying Redlich-Kwong equation of state (EoS) to calculate the density of carbon dioxide in the supercritical region. The average absolute error of the model was found to be 1.63 and 2.07% in the comparison with the literature and NIST density data respectively, which demonstrates superiority of the model over other EoSs  

In this research, the effects of nano-sized MgO in Al2O 3-SiC composites were investigated. The overall changes in the density and mechanical properties of sintered samples (hardness, bending strength and toughness) were evaluated. After mixing, drying and uniaxial compaction of the powders, they were first heat-treated at low temperature in an electric furnace to remove any residuals. They were then heat-treated at high temperature (1700 °C) inside a graphite furnace in argon atmosphere for sintering (at normal and high pressure). The content of MgO in the Al 2O3-10 vol% SiC composite was 0, 500, 1000, and 1500 ppm. Thefracture toughness(KIC)of sintered composite with 10... 

In this study Al2O3-SiC micro/nanocomposites have been fabricated by mixing alumina nanopowders and silicon carbide micro/nanopowders, followed by hot pressing at 1550, 1600, 1650 and 1700°C. The density, mechanical properties and fracture mode of Al2O3-SiC composites containing different volume fractions (2.5%, 5%, 7.5%, 10% and 15%) of micro/nanoscale SiC particles were investigated and compared with those of alumina. The relative density of composites could reach values very close to theoretical density, especially after sintering at 1700°C. However, relative density declined by increasing the SiC fraction at the same sintering temperature. The flexural strength of composites was best for... 

The properties of W-15 wt.%Cu composites were investigated by preparing two distinct composites of micrometer and nanoscale structures. Micrometer composite was produced by mixing elemental W and Cu powders and nanometer one was synthesized through a mechanochemical reaction between WO3 and CuO powders. Subsequent compaction and sintering process was performed to ensure maximum possible densification at 1000-1200 °C temperatures. Finally, the behavior of produced samples including relative density, hardness, compressive strength, electrical conductivity, coefficient of thermal expansion (CTE) and room temperature corrosion resistance were examined. Among the composites, nano-structured...