Sharif Digital Repository

Design and operation of an optical fiber device for temperature sensing and thermal expansion measurement are reported. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. In this design, the light intensity modulation is based on the relative motion of the optical fibers and a reflective coated lens. By using displacement calibration data for this sensor, the linear thermal expansion of the aluminum rod is determined. This sensor shows an average sensitivity of about 11.3 mV/°C for temperature detection and 7 μm/°C for thermal expansion detection. Device resolution for a linear expansion measurement... 

Due to the growing applications of silicon in nano-scale systems, a molecular dynamics approach is employed to investigate thermal properties of silicon. Since simulation results rely upon interatomic potentials, thermal expansion coefficient (TEC) and lattice constant of bulk silicon have been obtained using different potentials (SW, Tersoff, MEAM, and EDIP) and results indicate that SW has a better agreement with the experimental observations. To investigate effect of size on TEC of silicon nanowires, further simulations are performed using SW potential. To this end, silicon nanowires of different sizes are examined and their TEC is calculated by averaging in different directions ([100],... 

The main objective of the current work is to utilize Lattice Boltzmann Method (LBM) for simulating buoyancy-driven flow considering the hybrid thermal lattice Boltzmann equation (HTLBE). After deriving the required formulations, they are validated against a wide range of Rayleigh numbers in buoyancy-driven square cavity problem. The performance of the method is investigated on parallel machines using Message Passing Interface (MPI) library and implementing domain decomposition technique to solve problems with large order of computations. The achieved results show that the code is highly efficient to solve large scale problems with excellent speedup. Copyright © 2004 by ASME  

This paper is concerned with the stability analysis of bridged single walled carbon nanotubes (SWCNT) under temperature changes. A molecular structural mechanics model is utilized to investigate the free vibration frequencies and thermal buckling of SWCNT. In comparison with most of the previous studies, a temperature-variable thermal-expansion-coefficient is used that is negative under a certain temperature. Also thermal variation of Young's modulus of the CNTs is considered. Several studies are performed to investigate the critical temperature change due to heating and cooling of SWCNTs with different chiralities and slenderness ratios and the stability boundaries are determined  

In this paper, using the multiplicative decomposition of the deformation gradient into mechanical and thermal parts, both kinematic and kinetic aspects of finite deformation thermoelasticity are considered. At first, the kinematics of the thermoelastic continua in the purely thermal process of nonisothermal deformation is investigated for finite deformation thermoelasticity. Also, a linear relation between the thermal expansion tensor and the rate of the thermal deformation tensor is presented. In order to model the mechanical behavior of thermoelastic continua in the stress-producing process of nonisothermal deformation, an isothermal effective stress-strain equation based on the... 

The present simulation aims to investigate adding NEPCM nanoparticles to water in the natural convection inside a cavity by using FVM method and SIMPLE algorithm. Nano-encapsulated phase change material (NEPCM) consists of a shell and core with phase change property. The NEPCM particles in base fluid have the ability to transfer heat by absorbing and dissipating heat in the liquid-solid phase change state. In this study, the energy wall phenomenon due to the phase change of NEPCM core has appeared that the whose energy transfer strength is proportional to the latent heat of NEPCM core and the thickness of the energy wall. Moreover, the relationship between the energy wall and the heat... 

Conic shell structures are widely used in aerospace industries. In the literature various models have been proposed to failure analysis of composite materials. Clearly, each model has a favorable range of applications. In this paper tensile, compressive, shear and thermal expansion properties of tape-wounded Carbon/Phenolic composites are firstly measured at various temperatures in range 23–200°C. The captured properties are then taken into account to progressive failure analysis of a conic Carbon/Phenolic structure under internal pressure and thermal loadings. For this end, a particular failure criterion is proposed to predict failure in the composite structures with a reasonable margin of... 

The determination of the thermo-mechanical stress field in and around a spherical/ cylindrical inhomogeneity surrounded by a functionally graded (FG) coating, which in turn is embedded in an infinite medium, is of interest. The present work, in the frame work of Boussinesq/Papkovich-Neuber displacement potentials method, discovers the potential functions by which not only the relevant boundary value problems (BVPs) in the literature, but also the more complex problem of the coated inhomogeneities with FG coating and sliding interfaces can be treated in a unified manner. The thermo-elastic fields pertinent to the inhomogeneities with multiple homogeneous coatings and various combinations of... 

Applying flexible variable shape control surfaces (wing and elevator) structures is a way to increase efficiency and maneuverability of the planes, which is recently under research. In this paper, modeling of the flight of an unmanned ultra light plane is discussed. The modeling is done based on a real ultra light plane presented recently. To increase maneuverability of the plane, flexible variable shape structures are designed for the wing and the elevator. In design procedure, having an ultra light plane is considered. The elevator and the wing are used as control surfaces for longitudinal and lateral maneuvers respectively. Shape memory alloys (SMA) are used for reshaping the flexible... 

Solids usually show complex material behavior. If deformation is finite, the description of the kinematics makes the mechanical model complicated. In fact, one of the basic questions in the formulation and analysis procedures of finite deformation thermoelasticity is: "How can the finite deformation thermoelasticity response be best accounted for in the kinematic formulation?" A rather attractive way to proceed is to use the approach of small strain analysis, and decompose the total strain into a mechanical part and a thermal part. In this paper, based on the multiplicative decomposition of the deformation gradient, the mechanical and thermal strains are defined in the power and exponential... 

This is the first research on the vibration and buckling analysis of a graphene nanoplatelet composite (GPLRC) microdisk in the framework of a numerical based generalized differential quadrature method (GDQM). The stresses and strains are obtained using the higher-order shear deformable theory (HOSDT). Rule of the mixture is employed to obtain varying mass density, thermal expansion, and Poisson's ratio, while the module of elasticity is computed by modified Halpin-Tsai model. Governing equations and boundary conditions of the GPLRC microdisk are obtained by implementing Extended Hamilton's principle. The results show that outer to inner ratios of the radius (Ro/Ri), ratios of length scale... 

The purpose of this work is to develop a physical simulation model for the purpose of studying the effect of various design parameters on the performance of a packaged liquid chiller. A computer model which simulates the steady-state cyclic performance of a vapor compression chiller is developed for the purpose of performing detailed physical design analysis of actual industrial chillers. The model can be used for optimizing design and for detailed energy efficiency analysis of packaged liquid chillers. The simulation model takes into account presence of all chiller components such as compressor, shell-and-tube condenser and evaporator heat exchangers, thermostatic expansion valve and... 

In this work, the group contribution approach has been used in combination with the linear isotherm regularity (LIR) equation of state to estimate pvT properties of primary, secondary and tertiary alcohols, ketones and 1-carboxylic acid. In addition, the isothermal compressibility and thermal expansion coefficient of these compounds have been predicted. We assume each of these organic compounds as a hypothetical mixture of methyl, methylene and a functional group, in which the interaction potential of each pair is assumed to be the average effective pair potential. Then, the LIR equation of state (EOS) has been extended to such a hypothetical mixture. Three basic compounds, namely propane,... 

LM13 alloy is widely used in piston industry, due to its low coefficient of thermal expansion, excellent castability and hot tear resistance. In this research effect of casting process on wear behavior of LM13 alloy was investigated. First, samples were produced using two casting processes and heat treated. Then wear behavior of these samples under dry sliding condition was examined. Results of hardness and strength tests indicated that squeeze cast specimens exhibited higher mechanical properties. Wear experiment results showed that in both squeeze and gravity cast specimens, amount of weight loss increases with increase in sliding distance which is accompanied by reduction in wear rate and... 

This research studied the effect of adding TiO2 nanoparticles along with Al2O3 and Y2O3 additives on the physical and mechanical properties of a SiC-matrix composite. The samples were fabricated through a pressureless process at 1900 °C. The results showed that the addition of TiO2 nanoparticles up to 4.5 wt% inhibited the excessive growth of SiC grains. According to the investigations, the microstructure and final properties of composites were affected by density, synthesized phases as well as their distribution in the matrix, and grain size. The highest density, Young's modulus, hardness, indentation fracture resistance, and flexural strength, alongside with the lowest brittleness index... 

Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) have been widely applied in fixed partial prostheses as well as dental uses i.e. a substructure for crowns. However, Y-TZP has limited applications, which is due to the presence of defects in its microstructure introduced during the manufacturing process. Accordingly, due to Y-TZP limitations, the novel (X)Y-TZP- 20Al2O3-(80-X) SiO2 (X = 65, 70 and 75) ceramic nanocomposites were successfully fabricated via the powder metallurgy method. X-ray diffraction (XRD) patterns of commercial powders showed the stabilization of monoclinic zirconia (ZM) by increasing the silica content. In order to determine the fracture load and micro-bending... 

A pressureless sintering method was utilized to fabricate metal/ceramic joints out of yttria-stabilized zirconia (3Y-TZP) and stainless steels (SS). Ultrafine (150 nm) and nanoscale (75 nm) 3Y-TZP particles and micrometric 17-4PH, 316L, and 420 SS (<31 μm) powders were tested. Isothermal and nonisothermal sintering behaviors of the powders and composite layers in hydrogen, argon, and vacuum atmospheres were examined. It was found that the mismatch strain between the zirconia ceramic and SS during cosintering is significant, which leads to bond cracking and joint failure. Nevertheless, interlayer diffusion of Zr, Fe, and Cr and the formation of a reaction zone, particularly during vacuum... 

Thermal loadings in saturated (two-phase) clays induce excess pore water pressure due to the difference in the thermal expansion coefficient of the pore volume and the pore water. The gradual dissipation of the excess pore water pressure causes thermal volume reduction which is known as thermal consolidation. However, thermal consolidation in a three-phase soil system such as unsaturated soil is more sophisticated. In this paper, an analytical model for thermal consolidation around a heat source embedded in unsaturated clay or in calyey soils containing two immiscible fluids is developed based on the effective stress concept. Governing equations, including energy, mass, and momentum balance...