Journal of Solid Mechanics
http://jsm.iau-arak.ac.ir/
Journal of Solid Mechanicsendaily1Thu, 30 Sep 2021 00:00:00 +0330Thu, 30 Sep 2021 00:00:00 +0330Dynamic Response of Bi-Directional Functionally Graded Materials (BDFGMs) Beams Rested on Visco-Pasternak Foundation Under Periodic Axial Force
http://jsm.iau-arak.ac.ir/article_678358.html
Since the temperature or stress distribution in some advanced machines such as modern aerospace shuttles and craft develops in two or three directions, the need for a new type of FGMs is felt whose properties vary in two or three directions. On the other hand, dynamic buckling behavior of structures is a complicated phenomenon which should be investigated through the response of equations of motion. In this paper, dynamic response of beams composed of bi-directional functionally graded materials (BDFGMs) rested on visco-Pasternak foundation under periodic axial force is investigated. Material properties of BDFGMs beam vary continuously in both the thickness and longitudinal directions based on the two types of analytical functions (e.g. exponential and power law distributions). Hamilton's principle is employed to derive the equations of motion of BDFGMs beam according to the Euler-Bernoulli and Timoshenko beam theories. Then, the generalized differential quadrature (GDQ) method in conjunction with the Bolotin method is used to solve the differential equations of motion under different boundary conditions. It is observed that a good agreement between the present work and the literature result. Various parametric investigations are performed for the effects of the gradient index, length-to-thickness ratio and viscoelastic foundation coefficients on the dynamic stability region of BDFGMs beam. The results show that the influence of gradient index of material properties along the thickness direction is greater than gradient index along the longitudinal direction on the dynamic stability of BDFGMs beam for both exponential and power law distributions.Dynamic and Vibration Analysis for Geometrical Structures of Planetary Gears
http://jsm.iau-arak.ac.ir/article_683915.html
In industry applications, planetary gear systems are widely used in power transmission systems. In planetary gears, dynamic loads, noise and reduction the structural life are produced by system vibrations. For gear transmission systems, the parametric excitation which introduced by the periodically time&ndash;varying mesh stiffness of each gear oscillation is the main source of vibration. Generally, there are two methods to evaluate the gear mesh stiffnesses, the finite element method and the analytical method. In this wok, the periodically time&ndash;varying mesh stiffness of planetary gears is investigated. The influence of pressure angles on mesh stiffness of meshing gears is shown and the dynamic model of planetary gear sets is studied. When planets of the single&ndash;stage spur planetary gear system are meshed by new planets, the system is converted to special type of system with meshed planets. Vibration for geometrical structures (symmetric and anti&ndash;symmetric) of planetary system with meshed planets is investigated. Mesh stiffness of meshing gears by estimation function is obtained and numerical results of natural frequencies and vibration modes are derived.Study on Vibration Band Gap Characteristics of a Branched Shape Periodic Structure Using the GDQR
http://jsm.iau-arak.ac.ir/article_678297.html
In this study, a new periodic structure with special vibration band gap properties is introduced. This structure consists of a main beam and several cantilever beam elements connected to this main beam in the branched shape. Two models with different number of beam elements and geometrical parameters are considered for this periodic structure. The transverse vibrations of beams are solved using the generalized differential quadrature rule (GDQR) method to calculate the first four band gaps of each model. Investigating the influences of geometrical parameters on the band gaps shows that some bands are close to each other for specific ranges of geometrical parameters values. Furthermore, as the number of beam elements increases, the number of close band gaps increases. Having more than two close band gaps means that this periodic structure has a relatively wide band gap in total. Furthermore, this wide band can move to low frequency ranges by changing the geometrical parameters. Absorbing vibrations over a wide band gap at low frequency ranges makes this periodic structure a good vibration absorber. Verification of the analytical method using ANSYS software shows that the GDQR method can be used for vibration analysis of beam-like structures with high accuracy.Buckling and Free Vibrations of a Magneto-Electro-Elastic Sandwich Panel with Flexible Core
http://jsm.iau-arak.ac.ir/article_684115.html
This paper presents the buckling and out-of-plane free vibration response of a sandwich panel with flexible core for the different boundary condition. In the desired configuration of the sandwich panel, the top and bottom plates are made of magneto-electro-elastic (MEE) plates. Moreover, the in-plane electric and magnetic potential fields are neglected for the derivation of the required relations. The sandwich structure is subjected to axial force in both longitudinal and transverse directions; in addition, and the top and bottom plates are exposed to electric and magnetic fields. The governing equations of motion for MEE sandwich panel with a flexible core are derived based on the first-order shear deformation theory by neglecting the displacement of the mid-plate and using the Hamilton&rsquo;s principle. Furthermore, the derived partial differential equations (PDEs) are solved. According to the obtained numerical results, the core thickness, variation of electric field, variation of magnetic field and plate length are introduced as the most influential parameters on the free vibration response of the panel as well as the critical force of buckling. &nbsp;As one of the results, the electric potential is inversely related to the natural frequency and buckling load, so that with increasing the electric potential, the natural frequency and critical load of the structure is also increased.Moreover, the magnetic potential is directly related to the natural frequency and buckling load of the system, and increasing trends of natural frequency and critical load are observed by increasing the magnetic potential.Investigation of Stress State of the Layered Composite with a Longitudinal Cylindrical Cavity
http://jsm.iau-arak.ac.ir/article_683397.html
The article presents the study of the stress state of a two-layer composite with a cylindrical cavity located parallel to the surfaces of the layers. Displacements are set on the cavity and the upper and lower boundaries of the upper and lower layers, respectively. The three-dimensional elasticity solution has been obtained by the analytical-numerical generalized Fourier method with respect to the system of Lame equations in local cylindrical coordinates associated with cavity and Cartesian coordinates associated with boundaries of the layers. The infinite systems of linear algebraic equations resulting from satisfying the boundary conditions are solved by the reduction method. As a result, displacements and stresses have been obtained at various points of the elastic body. We have compared the stress-strain state of a two-layer structure with a cylindrical cavity located in either of the layers. The analysis included various geometrical parameters and boundary functions; the results obtained were compared with a single-layer holed structure.Dispersion of SH-Wave in a Heterogeneous Orthotropic Layer Sandwiched Between an Inhomogeneous Semi-Infinite Medium and a Heterogeneous Elastic Half-Space
http://jsm.iau-arak.ac.ir/article_684260.html
The aim of this paper is to investigates the existence of the dispersion of SH-wave in a heterogeneous orthotropic layer lying over a heterogeneous elastic half-space and underlying an inhomogeneous semi-infinite medium. Hyperbolic variation in upper semi-infinite associated with directional rigidities and density has been considered while linear variation in the intermediate layer associated with initial stress, density, shear moduli and lower half-space associated with rigidity and density has been considered. The dispersion equation of SH-wave has been obtained in a closed form by using variable separation method. The effects of inhomogeneities of the assumed media are illustrated by figures using MATLAB programming. The Earth's composition is heterogeneous that incorporates extremely hard layers. The propagation of SH-wave across crustal layer of the Earth very much depends upon heterogeneity and orthotropic properties. In fact, the observation reveals that the phase velocity of SH-wave is directly proportionate to inhomogeneity parameter, orthotropic parameter and heterogeneity parameter. That means as inhomogeneity parameter and heterogeneity orthotropic parameter increases, the phase velocity of SH-wave increases proportionately. Moreover, the obtained dispersion equation of SH-wave coincides with the classical result of Love wave as initial stress, inhomogeneities, and the upper semi-infinite medium is neglected. This analysis may be helpful to expound the nature of the dispersion of seismic waves in elastic media.Free Vibration Analysis of Composite Grid Stiffened Cylindrical Shells Using A Generalized Higher Order Theory
http://jsm.iau-arak.ac.ir/article_681359.html
The present study analyzes the free vibration of multi-layered composite cylindrical shells and perforated composite cylindrical shells via a modified version of Reddy&rsquo;s third-order shear deformation theory (TSDT) under simple support conditions. An advantage of the proposed theory over other high-order theories is the inclusion of the shell section trapezoidal form coefficient term in the displacement field and strain equations to improve the accuracy of results. The non-uniform stiffness and mass distributions across reinforcement ribs and the empty or filled bays between the ribs in perforated shells were addressed via a proper distribution function. For integrated perforated cylindrical shells, the results were validated by comparison to other studies and the numerical results obtained via ABAQUS. The proposed theory was in good consistency with numerical results and the results of previous studies. It should be noted that the proposed theory was more accurate than TSDT.&nbsp;Deformation Field Produced by a Doublet Source in a Half-Space Model
http://jsm.iau-arak.ac.ir/article_683917.html
Using Galerkin vector approach closed-form analytic expressions for the displacements and stresses caused by a doublet source buried in a homogenous, isotropic, perfectly elastic half-space have been obtained. Further, the viscoelastic deformation field has been obtained by applying the correspondence principle of linear viscoelasticity, assuming the medium to be elastic in dilatation and Kelvin, Maxwell, or SLS (Standard linear solid) type viscoelastic in distortion. The effect of Poisson&rsquo;s ratio on the deformation field due to a doublet source is examined in elastic half-space. The effect of relaxation time on displacement and stress fields is studied due to a doublet source in viscoelastic half-space. The variation of the displacements and stresses with the epicentral distance is studied graphically using MATLAB software. Stresses for a doublet with axis parallel to x-axis attain minimum value for Poissonian half- space. Viscoelastic displacements and stresses attain maxima for the Maxwell model and minima for the Kelvin model.Thermoelastic Analysis of Annular Sector Plate Under Restricted Boundaries Amidst Elastic Reaction
http://jsm.iau-arak.ac.ir/article_683353.html
An analytical framework is developed for the thermoelastic analysis of annular sector plate whose boundaries are subjected to elastic reactions. The exact expression for transient heat conduction with internal heat sources is obtained using a classical method. The fourth-order differential equation for the thermally induced deflection is obtained by developing a new integral transformation in accordance with the simply supported elastic supports that are subjected to elastic reactions. Here it is supposed that the movement of the boundaries is limited by an elastic reaction, that is, (a) shearing stress is proportional to the displacement, and (b) the reaction moment is proportional to the rate of change of displacement with respect to the radius. Finally, the maximum thermal stresses distributed linearly over the thickness of the plate are obtained in terms of resultant bending momentum per unit width. The calculation is obtained for the steel, aluminium and copper material plates using Bessel's function can be expressed in infinite series form, and the results are depicted using a few graphs.&nbsp;A Comparison Between the Linear and Nonlinear Dynamic Vibration Absorber for a Timoshenko Beam
http://jsm.iau-arak.ac.ir/article_683324.html
Dynamic vibration absorbers (DVAs) play an important role in the energy dissipation of a vibrating system. Undesirable vibrations of structures can be reduced by using the absorbers. This paper investigates the effect of an attached energy sink on the energy dissipation of a simply supported beam subjected to harmonic excitation. The aim is to design an optimal linear energy sink (LES) and a nonlinear energy sink (NES) and then compare them with each other. Each absorber includes a spring, a mass, and a damper. For each absorber, the optimum mass, stiffness, and damping coefficients are obtained in order to minimize the beam&rsquo;s maximum amplitude at the resonant frequencies. The optimization problem is minimizing the maximum amplitude of the beam subjected to an arbitrary harmonic force excitation. For consideration of the effects of rotary inertia and shear deformation, the Timoshenko beam theory is used. The mathematical model of beam with DVA is verified by using the ANSYS WORKBENCH software. Finally, by considering the uncertainty on the DVA parameters it was observed that the LES is more robust than the NES.Experimental and Numerical Investigation of the Impact of a Blunt Projectile with a Perforated Plate
http://jsm.iau-arak.ac.ir/article_683543.html
This paper experimentally and numerically investigated the impact of a blunt projectile to perforated steel targets. In this study, projectiles were made of AISI 52100 and perforated plates were made of AISI 1045. In order to investigate the effect of the hole diameter on the projectile, three different diameters of the hole were considered, along with the effect of the projectile overlap with the hole. After examining different hitting states, the projectile was deviated from its movement direction after hitting the hole and changed from vertical hit to skew. The deviation of the projectile increased when the diameter of the hole increased or the amount of projectile overlap with the hole increased. Then, numerical modeling of impacting the projectile was performed by ABAQUS software and the results were compared with experimental results and the accuracy of the model was confirmed. And this model was used to investigate the effect of initial projectile speed on deviation of the projectile, accordingly, an increase in the initial velocity of the impact led to an increase in the deviation of the projectile.Nonlinear Investigation of Magnetic Influence on Dynamic Behaviour of Non-Homogeneous Varying Thickness Circular Plates Resting on Elastic Foundations
http://jsm.iau-arak.ac.ir/article_683918.html
In this work, a nonlinear investigation of non-homogeneous varying thickness circular plates resting on elastic foundations under the influence of the magnetic fieldis investigated. The non-homogeneity of the circular plates&rsquo; material is presumed to occur due to linear and parabolic changes in Young&rsquo;s modulus likewise the density along the radial direction in a unique manner. The geometric Von K&aacute;rm&aacute;n equations are used in modelling the governing differential equations. The transverse deflection is approximated using an assumed single term mode shape while the central deflection in form of Duffing&rsquo;s equation is obtained using the Galerkin method.&nbsp; Subsequently, the semi-analytical solutions are provided using the Optimal Homotopy Asymptotic Method (OHAM), the analytical solutions are used for parametric investigation. The results in this work are in good harmony with past results in the literature. From the results, it is realized that the nonlinear frequency of the circular plate increases with an increase in the linear elastic foundation. Also, the results showed that clamped edge and simply supported edge condition produced the same hardening nonlinearity. However, varying taper and non-homogeneity lower the nonlinear frequency ratio. Also, maximum deflection occurs when excitation force is zero, and attenuation of deflection is observed due to the presence of a magnetic field, varying thickness, homogeneity, and elastic foundation. It is anticipated that the discoveries from this research will boost the design of structures subjected to vibration.Study of the Mechanical Behavior of Municipal Solid Waste Landfill Using a Viscoplastic Constitutive Model
http://jsm.iau-arak.ac.ir/article_683354.html
As long as there is the need for disposal of&nbsp; household&nbsp; waste there will be the need to understand&nbsp; the phenomena taking place in storage facilities for nonhazardous waste (municipal solid waste landfill). The understanding of landfill technology is of great importance because of its ever-changing state, whether mechanical, chemical or hydrological. In this context, there is a need to better understand the stress-strain behavior evolution with time of the landfilled waste. Based on triaxial and oedometric compression tests of municipal solid waste samples&nbsp; ranging from fresh&nbsp; to degraded waste, a viscoplastic constitutive model (Burgers creep-viscoplastic model) is used to describe the behavior of the municipal solid waste under loading. This model is able to adequately capture the stress-strain and pore water pressure response of the municipal solid waste at different ages. To illustrate its applicability, settlements due to the incremental loading of waste with time are predicted for a typical municipal solid waste landfill. The proposed model predicts the total settlement of a storage facilityin a range similar to results published in the literature. An extension of the studied municipal solid waste landfill was also investigated.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Large Deformation Hermitian Finite Element Coupled Thermoelasticity Analysis of Wave Propagation and Reflection in a Finite Domain
http://jsm.iau-arak.ac.ir/article_683919.html
In the present paper, a finite element nonlinear coupled thermoelasticity formulation is presented for analysis of the wave propagation, reflection, and mixing phenomena in the finite length isotropic solids. The governing equations are derived based on the second Piola-Kirchhoff stress and the full form of Green&rsquo;s strain-displacement tensors to account for the large deformations and finite strains. In contrast to the available researches, the assumption of very small temperature changes compared to the reference temperature is released in the present research. Galerkin&rsquo;s method, a weak formulation, and cubic elements are employed to obtain the time-dependent non-linear finite element governing equations. The proposed solution procedure to the resulting highly nonlinear and time-dependent governing equations employs an updating algorithm and Newmark&rsquo;s numerical time integration method. The wave propagation and reflection phenomena are investigated for both the mechanical and thermal shocks and time variations of distributions of the resulting displacements, temperature rises, and stresses are illustrated graphically and discussed comprehensively. Furthermore, the effects of the non-linear terms are discussed comprehensively. Results reveal that in the non-linear analysis, no fixed speed of wave propagation can be defined.&nbsp;Memory Response in Thermoelastic Plate with Three-Phase-Lag Model
http://jsm.iau-arak.ac.ir/article_683540.html
In this article, using memory-dependent derivative (MDD) on three-phase-lag model of thermoelasticity, a new generalized model of thermoelasticity theory with time delay and kernel function is constructed. The governing coupled equations of the new generalized thermoelasticity with time delay and kernel function are applied to two dimensional problem of an isotropic plate. The two dimensional equations of generalized thermoelasticity with MDD are solved using state space approach. Numerical inversion method is employed for the inversion of Laplace and Fourier transforms. The displacements, temperature and stress components for different thermoelastic models are presented graphically and the effect of different kernel and time delay on the considered parameters are observed.Anisotropic and Isotropic Elasticity Applied for the Study of Elastic Fields Generated by Interfacial Dislocations in a Heterostructure of InAs/(001)GaAs Semiconductors
http://jsm.iau-arak.ac.ir/article_682342.html
This work is a study of the elastic fields&rsquo; effect (stresses and displacements) caused by dislocations networks at a heterostructure interface of a InAs / GaAs semiconductors thin system in the cases of isotropic and anisotropic elasticity. The numerical study of this type of heterostructure aims to predict the behavior of the interface with respect to these elastic fields satisfying the boundary conditions. The method used is based on a development in Fourier series. The deformation near the dislocation is greater than the other locations far from the dislocation.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Static and Dynamic Stability Analysis of Thick CNT Reinforced Beams Resting on Pasternak Foundation Under Axial and Follower Forces
http://jsm.iau-arak.ac.ir/article_685144.html
In this paper, a numerical solution is presented for static and dynamic stability analysis of carbon nanotube (CNT) reinforced beams resting on Pasternak foundation. The beam is considered to be exposed to compressive axial and follower forces at its free end. The beam is modeled based on the Reddy&rsquo;s third order shear deformation theory and governing equations and external boundary conditions are derived using Hamilton&rsquo;s principle. The set of governing equations and boundary conditions are solved numerically using differential quadrature method. Convergence and accuracy of results are confirmed and effect of various parameters on the stability region of the beam is investigated including volume fraction and distribution of CNTs, width and thickness of the beam and elastic and shear coefficients of the foundation.An Approximate Thermo-Mechanical Solution of a Functionally Graded Cylinder Using Hybrid Integral Transform and Finite Element Method
http://jsm.iau-arak.ac.ir/article_685417.html
This article introduces a novel mixed method that combines the Fast Fourier Transform technique and a conventional Finite Element Method for investigating thermo-mechanical behavior of a thick functionally graded cylinder under asymmetric loadings. Material properties are assumed to vary along the radial direction according to a power function. Thermo-elastic governing equations of the cylinder are derived using principle of virtual work in cylindrical coordinates. Plane strain assumption is considered for a long cylinder during the analysis. Fast Fourier Transform technique is utilized in circumferential direction to discretize equations and related boundary conditions. Finite element method is then applied to remaining equations. For convergence study, the results obtained from this method are compared with those extracted from exact and complete FE solutions. It is observed from the results that the method has a super algebraic convergence behavior in circumferential direction. Influence of the mesh refinement is also investigated in the radial direction. According to ability of the mixed FFT-FE method for asymmetric analyzing, two kinds of loadings are considered here and results are presented. In thermo-elastic analyzing of the long cylinder, it&rsquo;s obvious that the present method benefits from some features such as fast convergence and low computational cost in comparison with FE solution.Fatigue Life Assessment for an Aluminum Alloy Piston Using Stress Gradient Approach Described in the FKM Method
http://jsm.iau-arak.ac.ir/article_684965.html
Engine piston is one of the most complex components among all automotive. The engine can be called the heart of a car and the piston may be considered the most important part of an engine. In fact, piston has to endure thermo-mechanical cyclic loadings in a wide range of operating conditions. This paper presents high cycle fatigue (HCF) life prediction for an aluminum alloy piston using stress gradient approach described in the Forschungskuratorium Maschinenbau (FKM) method. For this purpose, first Solidworks software was used to model the piston. Then Ansys Workbench software was used to determine temperature and stress distribution of the piston. Finally, in order to study the fatigue life of the piston based on HCF approach, the results were fed into the nCode Design Life software. The numerical results showed that the temperature maximum occurred at the piston crown center. The results of finite element analysis (FEA) indicated that the stress and number of cycles to failure have the most critical values at the upper portion of piston pin and piston compression grooves. To evaluate properly of results, stress analysis and HCF results is compared with real samples of damaged piston and it has been shown that critical identified areas, match well with areas of failure in the real samples. The lifetime of this part can be determined through FEA instead of experimental tests.An Interval Parametric Approach for the Solution of One Dimensional Generalized Thermoelastic Problem
http://jsm.iau-arak.ac.ir/article_684966.html
This paper is presenting the solutions of the one dimension generalized thermo-elastic coupled equations by considering some thermo-elastic constants as interval numbers. As most of the elastic constants are obtained using the experimental methods. Thus there might be some deficiency of exactness to obtain such constants. This kind of deficiency might cause the results on a micro-scale.&nbsp; L-S model has been considered to study the effect of such an interval parametric approach to generalized thermoelasticity. Laplace transform method applied to obtain a system of coupled ordinary differential equations. Then the vector-matrix differential form is used to solve these equations by the eigenvalue approach in Laplace transformed domain. The solution in the space-time domain obtained numerically. The numerical solutions obtained by using some suitable inverse transformation method. The solutions are graphically represented for different values of the parameter of interval parametric form and the significance of obtained results are described along with the behavior of the solutions.Finite Crack in a Thermoelastic Transversely Isotropic Medium Under Green-Naghdi Theory
http://jsm.iau-arak.ac.ir/article_684963.html
In this paper, we have studied a model of finite linear Mode-I crack in a thermoelastic transversely isotropic medium under Green Naghdi theory. The crack is subjected to a prescribed temperature and a known tensile stress. The plane boundary surface is considered as isothermal and all the field variables are sufficiently smooth. The heat conduction equation is written under two temperature theory (2TT) for Green Naghdi model which contains absolute temperature as well as conductive temperature. The analytical expressions of displacement components, stress components and temperature variables are obtained by normal mode analysis and matrix inversion method. Comparisons have been made within Green Naghdi (G-N) theory of type I, type II and type III for displacement, stress and absolute temperature variables against the crack width for a transversely isotropic material (Cobalt) by virtues of graphs. Also, Comparison have been made among displacement, thermal stress and absolute temperature for different depths.&nbsp;The Frequency Response of Intelligent Composite Sandwich Plate under Biaxial In-Plane Forces
http://jsm.iau-arak.ac.ir/article_673985.html
This paper investigates the frequency response of a smart sandwich plate made of magnetic face sheets and reinforced core with nano-fibers. The effective elastic properties of composite core reinforced with carbon nanotube are estimated by the extended rule of Mixture. The orthotropic visco-Pasternak foundation is examined to study orthotropic angle, damping coefficient, normal, and shear modulus. The top and bottom face sheets of the sandwich are magnetic and their vibrations are controlled by a feedback control system and magneto-mechanical couplings. Also, the sandwich plate is subjected to the compression and extension in-plane forces in both x and y directions. Five coupled equations of motion are derived using Hamilton&rsquo;s principle. These equations are solved by the differential quadrature method. The analysis performed by the third-order shear deformation theory (Reddy&rsquo;s theory) shows useful details of the effective parameters such in-plane forces, modulus of elastic foundation, core-to-face sheet thickness ratio and controller effect of velocity feedback gain on the dimensionless frequency of the sandwich plate. The analysis of such structures can be discussed in the military, aerospace and civil industries.Magneto-Rheological Response in Vibration of Intelligent Sandwich Plate with Velocity Feedback Control
http://jsm.iau-arak.ac.ir/article_674337.html
This study deals with the free vibration of the sandwich plate made of two smart magnetostrictive face sheets and an electro-rheological fluid core. Electro-rheological fluids are polymer-based material that changes its viscosity under the applied electric field. A feedback control system follows the magnetization effect on the vibration characteristics of the sandwich plate when subjected to the magnetic field. It is assumed that there is no slip between layers, so the stress-strain relations of each layer are separately considered. Energy method is utilized in order to derive the five coupled equations of motion. These equations are solved by differential quadrature method (DQM). Results of this study show the rheology response of fluid in presence of electric field where the core gets hard and the dimensionless frequency increases. Also, the significant effect of thickness and aspect ratios and velocity feedback gain are discussed in detail. Such intelligent structures can replace in many of the systems used in automotive, aerospace and building industries as the detector, warning, and vibration absorber etc.Thermodynamic Stability of Sandwich Micro-Beam with Honeycomb Core and Piezoelectric / Porous Viscoelastic Graphene Facesheets
http://jsm.iau-arak.ac.ir/article_677554.html
Thermodynamic stability of sandwich micro beam with honeycomb core and piezoelectric / porous visco graphene sheets resting on visco Pasternak. In order to consider size effect, strain gradient theory is utilized. Using energy method and zigzag theory, final motion equations of sandwich micro beam are derived and solved by Galerkin method. The effects of parameters such as small scale, temperature changes, core to face sheets ratio, intensity of electric fields and elastic medium on the thermal dynamic stability of sandwich micro beam are investigated. Results indicated that by increasing temperature changes, the origins of the instability regions moves to lower excitation frequencies and decreases the width of the instability region of sandwich micro beam at a certain dynamic load factor. In addition, increasing porosity indexes leads to increase excitation frequencies and consequently cause to more stable system . The results of present work can be used to optimum design and control of micro-thermal/electro-mechanical devices.Analytical solutions of Finite Wedges Coated by an Orthotropic Coating Containing Multiple Cracks and Cavities
http://jsm.iau-arak.ac.ir/article_682153.html
This paper presents a general formulation for an isotropic wedge reinforced by an orthotropic coating involving multiple arbitrarily oriented defects under out of plane deformation. The exact closed form solution of the problem weakened by a screw dislocation in the isotropic wedge is obtained by making use of finite Fourier cosine transform. Also, the closed-form solutions of the out of plane stress and displacement fields are obtained. After that, by making use of a distributed dislocation approach, a set of singular integral equations of the domain involving smooth cavities and cracks subjected to out of plane external loading are achieved. The cracks and cavities are considered to be only in the isotropic wedge. The presented integral equations have Cauchy singularity and must be evaluated numerically. Multiple numerical examples will be presented to show the applicability and efficiency of the presented solution. The geometric and point load singularities of the stress components are obtained and compared with the available data in the literature.Transient Dynamic Analysis of Grid-Stiffened Composite Conical Shells
http://jsm.iau-arak.ac.ir/article_683575.html
In this study, the transient dynamic analysis of grid-stiffened composite conical shells is discussed. The transient dynamic response of the composite conical shell with simply supported boundary conditions under the lateral impact load, which is applied extensively and uniformly on a certain surface, is obtained using the convolution integral and based on the method of addition of modes. The validation of the obtained results has been done with the help of references and ABAQUS finite element software. The effects of various parameters such as fiber angle, geometric ratios, type, etc. have been investigated in forced vibrations. Finally, the effect of reinforcing the conical shell with the help of grid-stiffened structures has been studied.The effects of various parameters such as fiber angle, geometric ratios, type, etc. have been investigated in forced vibrations. Finally, the effect of reinforcing the conical shell with the help of grid-stiffened structures has been studied.grid-stiffened structures has been studied.Improved High-order Analysis of Linear Vibrations of a Thick Sandwich Panel With an Electro-rheological Core by Using Exponential Shear Deformation Theory
http://jsm.iau-arak.ac.ir/article_683752.html
In In this paper, the behavior of free vibrations of the thick sandwich panel with multi-layer face sheets and an electrorheological (ER) fluid core using Exponential Shear Deformation Theory were investigated. For the first time, Exponential shear deformation theory is used for the face sheets while the Displacement field based on the second Frostig's model is used for the core. The governing equations and the boundary conditions are derived by Hamilton&rsquo;s principle. Closed form solution is achieved using the Navier method and solving the eigenvalues. Primary attention is focused on the effects of electric field magnitude, geometric aspect ratio,and ER core layer thickness on the dynamic characteristics of the sandwich plate. The rheological property of an ER material, such as viscosity, plasticity, and elasticity may be changed when applying an electric field. When an electric field is applied, the damping of the system is more effective. The effects of the natural frequencies and loss factors on the dynamic behaviorof the sandwich plate are studied.the natural frequency of the sandwich plate increases and the modal loss factor decreases. With increasing the thickness of the ER layer, the natural frequencies of the sandwich plate are decreased.The Fracture Toughness of the Welding Zone in Gas Transfer Steel Pipes by Experimental and Numerical Methods
http://jsm.iau-arak.ac.ir/article_684701.html
Fracture toughness is a criterion to determine the resistance of materials against small longitudinal and peripheral cracks, which can be created in the effect of welding or peripheral effects. Therefore, it is extremely important to scrutiny the factors that impress crack treatment and the way that it grows. In this research, fracture toughness was investigated on the peripheral welding zone in gas and oil transfer pipelines made in steel API X65. The fracture toughness is derived by using two different methods. At first, the three-point bending test method was used on samples that made up of the peripheral welding zone. Then, with a numerical simulation it was calculated by ABAQUS software v6/10. The comparison of experimental results and computer simulation results shows good agreement from two methods. The fracture toughness of the welded zone, obtained in this study, was compared with that of the base metal. The results showed that fracture toughness on the welding zone in gas and oil transfer steel pipelines decreased 43% compared to the base metal. This issue shows that peripheral welding on gas and oil transfer pipelines has more talent for crack growth compared to the base metal.Assessment of Different Mathematical Models for Analysis of Low-Velocity Impact on Composite Plates in Presence of Pre-loads
http://jsm.iau-arak.ac.ir/article_684737.html
In this paper, the low-velocity impact response of composite plates in the presence of pre-loads is investigated using three new models for contact force estimation. The boundary conditions are considered as simply supported and the behavior of the material is linear elastic. The equations are based on both classical and first order shear deformation theory and the Fourier series method is used to solve the governing equations. The mass of the impactor is considered to be large mass and therefore the impact response is categorized as quasi-static. In the first impact model, the contact force history is first considered as a half-sine and then the maximum contact force and contact duration are calculated. In the second model, an improved two degree of freedom (ITDOF) spring-mass system is expressed by calculating the effective contact stiffness using a fast-iterative scheme. In the third model, which is expressed for the first time in this paper, the plate is considered as a series of masses and springs constructing a multi degree of freedom (MDOF) spring-mass system and the average forces applied to springs is introduced as the contact force. Validation of these models is done by comparing the results with the analytical, numerical and experimental results and shows good agreement. Results show that the new MDOF spring-mass system is more accurate for calculating the contact force rather than the ITDOF spring-mass system.