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poisson-ratio
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General solution for mechanical and thermal stresses in a functionally graded hollow cylinder due to nonaxisymmetric steady-state loads
, Article Journal of Applied Mechanics, Transactions ASME ; Volume 70, Issue 1 , 2003 , Pages 111-118 ; 00218936 (ISSN) ; Sohrabpour, S ; Eslami, M. R ; Sharif University of Technology
2003
Abstract
In this paper, the general theoretical analysis of two-dimensional steady-state thermal stresses for a hollow thick cylinder made of functionally graded material is developed. The temperature distribution is assumed to be a function of radial and circumferential directions with general thermal and mechanical boundary conditions on the inside and outside surfaces. The material properties, except Poisson's ratio, are assumed to depend on the variable r and they are expressed as power functions of r. The separation of variables and complex Fourier series are used to solve the heat conduction and Navier equations
Experimental Investigation for FINDING a Suitable Additive (Nanoparticle) to Design Required Elastic Cement for Iranian Oil/Gas Wells
, M.Sc. Thesis Sharif University of Technology ; Taghikhani, Vahid (Supervisor) ; Soltanian, Hamid (Supervisor) ; Moghadasi, Jamshid (Supervisor) ; Samsam Sokheiravi, Mohammad (Co-Advisor)
Abstract
Previous studies indicate that increasing cement compressive strength can’t prevent loss of zonal isolation and casing collapse in worse case during well operations or formation loading. Since standard cements with high compressive strength can’t solve these problems, so application of elastic cements with low Young’s modulus and high Poisson’s ratio becomes important. These cements sustain generated stresses during well operations and prevent creation of point loads when formation creep occurs. For this purpose, a new additive was designed in order to improve the cement elasticity and tensile strength. It is a nanoparticle and named EX-RIPI (by Research Institute of Petroleum Industry,...
Investigating the Effect Strain Rate on the Poisson’s Ratio of Auxetic Polyurethane Foams
, M.Sc. Thesis Sharif University of Technology ; Nourani, Amir (Supervisor)
Abstract
Auxetic materials have a negative Poisson ratio (NPR), which is their most distinguishable characteristic as compared to regular materials. Test specimens were made of conventional polyurethane (PU) foams according to ASTM ; then, with a thermo-mechanical process, the foam was converted to auxetic PU foam. The reproducibility of specimens' fabrication was checked with CoV= for the final foam thickness. With regard to the fact that changing loading conditions can vary Poisson's ratio, in this study, the variations occurred in Poisson's ratio due to changing loading conditions are investigated. The applied strain and strain rate were altered in experiments and statistical analysis was...
Molecular dynamics study of two dimensional silicon dioxides with in-plane negative poisson's ratio
, Article Computational Materials Science ; Volume 153 , 2018 , Pages 258-267 ; 09270256 (ISSN) ; Tavakoli, R ; Jafary Zadeh, M ; Sharif University of Technology
Abstract
In the present work, the mechanical properties, in particular, the Poisson's ratio of four two-dimensional silica structures, called here α,β,γ and δ are studied by means of molecular dynamics simulations. The α structure has been synthesized experimentally and the others have been reported as the most stable low-energy structures that reveal in-plane negative Poisson's ratio based on the first principles calculations. Among these structures, β-silica exhibits the largest in-plane negative Poisson's ratio which is 2–4 times higher than penta-graphene. Our results illustrate that the classical molecular dynamics simulation reproduces results in agreement with those of the first principles...
Hybrid anisotropic pentamode mechanical metamaterial produced by additive manufacturing technique
, Article Applied Physics Letters ; Volume 117, Issue 6 , 2020 ; Movahhedy, M. R ; Shishkovsky, I ; Hedayati, R ; Sharif University of Technology
American Institute of Physics Inc
2020
Abstract
Pentamode metamaterials are a type of extremal designer metamaterials, which are able to demonstrate extremely high rigidity in one direction and extremely high compliance in other directions. Pentamodes can, therefore, be considered as building blocks of exotic materials with any arbitrarily selected thermodynamically admissible elasticity tensor. The pentamode lattices can then be envisioned to be combined to construct intermediate extremal materials, such as quadramodes, trimodes, and bimodes. In this study, we constructed several primary types of anisotropic pentamode lattices (with midpoint positioning of 10%, 15%, 20%, 25%, 30%, 35%, and 42% of the main unit cell diagonal) and then...
A thermoelasticity solution of sandwich structures with functionally graded coating
, Article Composites Science and Technology ; Volume 67, Issue 6 , 2007 , Pages 1073-1080 ; 02663538 (ISSN) ; Haftbaradaran, H ; Asghari, M ; Sharif University of Technology
2007
Abstract
An exact thermoelasticity solution for a two-dimensional thick composite consisting of homogeneous and functionally graded layers is presented. The thermomechanical properties of functionally graded layers are assumed to vary exponentially through the thickness while the Poisson's ratio is taken to be constant. The heat transfer problem is solved under steady state condition accounting for the heat convection. Utilizing the stress function the governing equation reduces to a fourth order inhomogeneous partial differential equation which is solved exactly using Fourier series method. A comparative study is done between two sandwich structures with homogeneous and functionally graded coatings,...
Sensitivity analysis of torque transmission efficiency of a half-toroidal CVT
, Article 2006 SAE World Congress, Detroit, MI, 3 April 2006 through 6 April 2006 ; 2006 ; 01487191 (ISSN) ; Zohoor, H ; Sharif University of Technology
SAE International
2006
Abstract
In this research a computer model based on elasto hydrodynamic fluid film lubrication is developed in order to calculate the torque transmission efficiency of a half-toroidal CVT variator. Validation of this model is verified by comparing the experimental and the model results. Sensitivity of torque transmission efficiency to eleven parameters is investigated. These parameters are: dimensionless roller curvature, aspect ratio, half cone angle, fluid viscosity index, pressure constant for Roelands model, input rotational velocity, absolute viscosity at atmospheric pressure, Young modulus of disks and power rollers, Poisson ratio of disks and power rollers, number of power rollers and variator...
Evaluation of the equivalent mechanical properties in a novel composite cruciform honeycomb using analytical and numerical methods
, Article Composite Structures ; Volume 275 , 2021 ; 02638223 (ISSN) ; Ashrafian, M. M ; Gharehbaghi, H ; Nazari, R ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
In the present study, a novel theoretical model is developed, based on the energy method, to predict the equivalent mechanical properties of a new morphing structure with zero Poisson's ratio, which is composed of continuous fiber reinforced composite struts. Due to the employing glass fiber in fabricating the proposed cruciform honeycomb, higher strength than the structures made of pure isotropic materials is obtained. The use of cells with a zero Poisson's ratio also increases the flexural strength of the structure. In the continuation of the paper, by examining the geometric effects on the equivalent properties, a parametric study is performed. Then, using the appropriate failure...
Cone tip resistance in sand: Modeling, verification, and applications
, Article Canadian Geotechnical Journal ; Volume 42, Issue 4 , 2005 , Pages 977-993 ; 00083674 (ISSN) ; Bryne, P. M ; Campanella, R. G ; Sharif University of Technology
2005
Abstract
A numerical modeling procedure is presented to evaluate cone tip resistance in sand. The procedure involves a moving boundary simulating cone penetration. The soil is modeled as a Mohr-Coulomb elastic-plastic material with stress-dependent parameters. The procedure is verified by comparing predicted numerical values of cone tip resistance with published experimental measurements from calibration chamber tests. The selected database. consists of 59 calibration chamber tests on Ticino sand with different relative densities, overconsolidation ratios, stresses, and boundary conditions. Several applications of the modeling procedure are also presented. The computer program FLAC is used to carry...
Thermoelastic analysis of thick-walled finite-length cylinders of functionally graded materials
, Article Journal of Thermal Stresses ; Volume 28, Issue 4 , 2005 , Pages 391-408 ; 01495739 (ISSN) ; Angoshtari, A ; Naghdabadi, R ; Sharif University of Technology
2005
Abstract
A semianalytical thermoelasticity solution for thick-walled finite-length cylinders made of functionally graded (FG) materials is presented. The governing partial differential equations are reduced to ordinary differential equations using Fourier expansion series in the axial coordinate. The radial domain is divided into some virtual subdomains in which the power-law distribution is used for the thermomechanical properties of the constituent components. Imposing the necessary continuity conditions between adjacent subdomains, together with the global boundary conditions, a set of linear algebraic equations are obtained. Solution of the linear algebraic equations yields the thermoelastic...
Material property identification of artificial degenerated intervertebral disc models - comparison of inverse poroelastic finite element analysis with biphasic closed form solution
, Article Journal of Mechanics ; Volume 29, Issue 4 , 2013 , Pages 589-597 ; 17277191 (ISSN) ; Hsu, Y. C ; Haghpanahi, M ; Parnianpour, M ; Wang, J. L ; Sharif University of Technology
2013
Abstract
ABSTRACT Disc rheological parameters regulate the mechanical and biological function of intervertebral disc. The knowledge of effects of degeneration on disc rheology can be beneficial for the design of new disc implants or therapy. We developed two material property identification protocols, i.e., inverse poroelas-tic finite element analysis, and biphasic closed form solution. These protocols were used to find the material properties of intact, moderate and severe degenerated porcine discs. Comparing these two computational protocols for intact and artificial degenerated discs showed they are valid in defining bi-phasic/poroelastic properties. We found that enzymatic agent disrupts the...
Detecting and estimating the time of a step-change in multivariate Poisson processes
, Article Scientia Iranica ; Volume 19, Issue 3 , June , 2012 , Pages 862-871 ; 10263098 (ISSN) ; Khedmati, M ; Sharif University of Technology
2012
Abstract
In multi-attribute process monitoring, when a control chart signals an out-of-control condition indicating the existence of a special cause, knowing when the process has really changed (the change point) accelerates the identification of the source of the special cause and makes the corrective measures to be employed sooner. This, of course, results in a considerable amount of savings in time and money. Since many real world multi-attribute processes are Poisson and most process changes are step-change, a new method is proposed, in this paper, to derive the maximum likelihood estimator of the time of a step-change in the mean vector of multivariate Poisson processes. In this method, two...
Multi-parameter sensitivity analysis for guided needle insertion through soft tissue
, Article Proceedings of 2010 IEEE EMBS Conference on Biomedical Engineering and Sciences, IECBES 2010, 30 November 2010 through 2 December 2010, Kuala Lumpur ; 2010 , Pages 97-100 ; 9781424476008 (ISBN) ; Jahed, M ; Sharif University of Technology
2010
Abstract
Soft tissue needle insertion characterization has been a focus of many medical and biomedical recent studies. In this study the constrained prostate soft tissue deformation through a finite element model is evaluated. The study considers a sensitivity analysis of the target reaching error with respect to the mechanical, insertion and anatomical parameters in presence of the kinematics constraint on the tissue. The needle insertion into the soft tissue is simulated using the proposed Finite Element Method (FEM). Based on acquired results, the insertion of needle induces a considerable rotation of the prostate tissue due to its specific kinematics and support structure. Such rotation can...
An efficient procedure for computing an optimal (R, Q) policy in continuous review systems with poisson demands and constant lead time
, Article Scientia Iranica ; Volume 16, Issue 2 E , 2009 , Pages 128-137 ; 10263098 (ISSN) ; Eshraghnia Jahromi, A ; Modarres Yazdi, M ; Sharif University of Technology
Abstract
In this paper, a continuous review inventory system is considered in which an order in a batch of size Q is placed immediately after the inventory position reaches R. Transportation time is constant and demands are assumed to be generated by a stationary Poisson process with one unit demand at a time. Demands not covered immediately from the inventory are backordered. In a recent paper, the exact evaluation of batch-ordering policies for two-level inventory systems was derived. This evaluation is based on a recursive procedure for determining the exact policy costs in case of one-for-one replenishment policies. In this paper, we show how this result can be applied to find the optimal...
An improvement in the determination of end bearing capacity of drilled shafts in sand
, Article Journal of GeoEngineering ; Volume 14, Issue 2 , 2019 , Pages 109-119 ; 19908326 (ISSN) ; Jazebi, M ; Sharif University of Technology
Taiwan Geotechnical Society
2019
Abstract
There are many equations available in the literature using the results of CPT (cone penetration test) and SPT (standard penetration test) measurements to predict the end bearing capacity of drilled shafts in sand. However, there are few equations that use soil parameters, such as friction angle and elastic modulus, as input values. Also, these available equations usually overestimate the end bearing capacity, and at times show conflicting results with respect to the parameters they use. This paper describes a numerical procedure to overcome the above shortcomings. The results obtained in this study were compared with both experimental and numerical results available in the literature. A...
An improvement in the determination of end bearing capacity of drilled shafts in sand
, Article Journal of GeoEngineering ; Volume 14, Issue 2 , 2019 , Pages 109-119 ; 19908326 (ISSN) ; Jazebi, M ; Sharif University of Technology
Taiwan Geotechnical Society
2019
Abstract
There are many equations available in the literature using the results of CPT (cone penetration test) and SPT (standard penetration test) measurements to predict the end bearing capacity of drilled shafts in sand. However, there are few equations that use soil parameters, such as friction angle and elastic modulus, as input values. Also, these available equations usually overestimate the end bearing capacity, and at times show conflicting results with respect to the parameters they use. This paper describes a numerical procedure to overcome the above shortcomings. The results obtained in this study were compared with both experimental and numerical results available in the literature. A...
On the modeling of human intervertebral disc annulus fibrosus: Elastic, permanent deformation and failure responses
, Article Journal of Biomechanics ; Volume 102 , 2020 ; Shirazi Adl, A ; Baghani, M ; Eskandari, A. H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
As a primary load-resisting component, annulus fibrosus (AF) maintains structural integrity of the entire intervertebral disc. Experiments have demonstrated that permanent deformation and damage take place in the tissue under mechanical loads. Development of an accurate model to capture the complex behaviour of AF tissue is hence crucial in disc model studies. We, therefore, aimed to develop a non-homogenous model to capture elastic, inelastic and failure responses of the AF tissue and the entire disc model under axial load. Our model estimations satisfactorily agreed with results of existing uniaxial (along fiber, circumferential and axial directions) and biaxial tissue-level tests. The...
A meta-model analysis of a finite element simulation for defining poroelastic properties of intervertebral discs
, Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 227, Issue 6 , 2013 , Pages 672-682 ; 09544119 (ISSN) ; Hsu, Y. C ; Haghpanahi, M ; Parnianpour, M ; Wang, J. L ; Sharif University of Technology
2013
Abstract
Finite element analysis is an effective tool to evaluate the material properties of living tissue. For an interactive optimization procedure, the finite element analysis usually needs many simulations to reach a reasonable solution. The metamodel analysis of finite element simulation can be used to reduce the computation of a structure with complex geometry or a material with composite constitutive equations. The intervertebral disc is a complex, heterogeneous, and hydrated porous structure. A poroelastic finite element model can be used to observe the fluid transferring, pressure deviation, and other properties within the disc. Defining reasonable poroelastic material properties of the...
Dynamic responses of intervertebral disc during static creep and dynamic cyclic loading: A parametric Poroelastic finite element analysis
, Article Biomedical Engineering - Applications, Basis and Communications ; Volume 25, Issue 1 , 2013 ; 10162372 (ISSN) ; Haghpanahi, M ; Parnianpour, M ; Wang, J. L ; Sharif University of Technology
2013
Abstract
Low back pain is a common reason for activity limitation in people younger than 45 years old, and was proved to be associated with heavy physical works, repetitive lifting, impact, stationary work postures and vibrations. The study of load transferring and the loading condition encountered in spinal column can be simulated by finite element models. The intervertebral disc is a structure composed of a porous material. Many physical models were developed to simulate this phenomenon. The confounding effects of poroelastic properties and loading conditions on disc mechanical responses are, nevertheless, not cleared yet. The objective of this study was to develop an axisymmetric poroelastic...
Temperature and thickness effects on thermal and mechanical stresses of rotating FG-disks
, Article Journal of Mechanical Science and Technology ; Volume 25, Issue 3 , 2011 , Pages 827-836 ; 1738494X (ISSN) ; Azadi, M ; Sharif University of Technology
Abstract
In the present paper, radial and hoop thermal and mechanical stress analysis of a rotating disk made of functionally graded material (FGM) with variable thickness is carried out by using finite element method (FEM). To model the disk by FEM, one-dimensional two-degree elements with three nodes are used. It is assumed that the material properties, such as elastic modulus, Poisson's ratio and thermal expansion coefficient, are considered to vary using a power law function in the radial direction. The geometrical and boundary conditions are in the shape of two models including thermal stress (model-A) and mechanical stress (model-B). In model-A there exists no pressure in both external and...