Showing papers in "Journal of Solid Mechanics in 2011"

Free Vibration of Thick Isotropic Plates Using Trigonometric Shear Deformation Theory

Abstract: In this paper a variationally consistent trigonometric shear deformation theory is presented for the free vibration of thick isotropic square and rectangular plate. In this displacement based theory, the in-plane displacement field uses sinusoidal function in terms of thickness coordinate to include the shear deformation effect. The cosine function in terms of thickness coordinate is used in transverse displacement to include the effect of transverse normal strain. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. Results of frequency of bending mode, thickness-shear mode and thickness-stretch mode are obtained from free vibration of simply supported isotropic square and rectangular plates and compared with those of other refined theories and frequencies from exact theory. Present theory yields exact dynamic shear correction factor π2/12 from thickness shear motion of the plate.

A Power Series Solution for Free Vibration of Variable Thickness Mindlin Circular Plates with Two-Directional Material Heterogeneity and Elastic Foundations

Abstract: In the present paper, a semi-analytical solution is presented for free vibration analysis of circular plates with complex combinations of the geometric parameters, edge-conditions, material heterogeneity, and elastic foundation coefficients. The presented solution covers many engineering applications. The plate is assumed to have a variable thickness and made of a heterogeneous material whose properties vary in both radial and transverse directions. While the edge is simply-supported, clamped, or free; the bottom surface of the plate is resting on a twoparameter (Winkler-Pasternak) elastic foundation. A comprehensive sensitivity analysis including evaluating effects of various parameters is carries out. Mindlin theory is employed for derivation of the governing equations whereas the differential transform method is used to solve the resulted equations. In this regard, both the in-plane and rotary inertia are considered. Results show that degradations caused by a group of the factors (e.g., the geometric parameters) in the global behavior of the structure may be compensated by another group of factors of different nature (e.g, the material heterogeneity parameters). Moreover, employing the elastic foundation leads to higher natural frequencies and postponing the resonances. © 2011 IAU, Arak Branch. All rights reserved.

Study on the Pull-In Instability of Gold Micro-Switches Using Variable Length Scale Parameter

Abstract: In this paper, the size dependent behavior of the gold micro-switches has been studied. This behavior becomes noticeable for a structure when the characteristic size such as thickness or diameter is close to its internal length-scale parameter. The size dependent effect is insignificant for the high ratio of the characteristic size to the length-scale parameter, which is the case of the silicon base micro-beams. On the other hand, in some types of micro-beams like gold base, the size dependent effect cannot be overlooked. In such cases, ignoring this behavior in modeling will lead to incorrect results. Some previous researchers have applied classic beam theory on their models and imposed a considerable hypothetical value of residual stress to match their theoretical results with the experimental ones. In this study, by obtaining the equilibrium positions or fixed points of the gold micro-beam, a considerable difference between the obtained fixed points using classic beam theory and modified couple stress theory has been shown. In addition, it has been shown that the calculated pull-in voltages using modified couple stress theory are much closer to the experimental results than those obtained by classic beam theory. Finally, it has been shown that considering a unique value of length scale parameter, especially for the smallest values of the beam thicknesses, may leads to inaccurate results and variable length scale parameter should be considered. © 2011 IAU, Arak Branch. All rights reserved.

Optimal Nonlinear Energy Sinks in Vibration Mitigation of the Beams Traversed by Successive Moving Loads

Abstract: Optimal Nonlinear Energy Sink (NES) is employed in vibration suppression of the beams subjected to successive moving loads in this paper. As a real application, a typical railway bridge is dynamically modeled by a single-span beam and a traveling high-speed train is simulated by a series of successive moving loads. Genetic algorithm is employed as the optimization technique and optimal parameters of the NES system are accordingly obtained. It is found that the NES can remarkably suppress the vibration level particularly in vicinity of the critical speeds. A sensitivity analysis is then carried out and robustness of the optimal NES is investigated. A parametric study is performed and performance of the optimal NES is evaluated for different values of the load speeds, load magnitudes, load intervals and mass ratios.

Hygrothermal Analysis of Laminated Composite Plates by Using Efficient Higher Order Shear Deformation Theory

Abstract: Hygrothermal analysis of laminated composite plates has been done by using an efficient higher order shear deformation theory. The stress field derived from hygrothermal fields must be consistent with total strain field in this type of analysis. In the present formulation, the plate model has been implemented with a computationally efficient C 0 finite element developed by using consistent strain field. Special steps are introduced to circumvent the requirement of C 1 coninuity in the original plate formulation and C 0 continuity of the present element has been compensated in stiffness matrix calculations. The accuracy of the proposed C 0 element is established by comparing the results with those obtained by three dimensional elasticity solutions and other finite element analysis. © 2011 IAU, Arak Branch. All rights reserved.

Constrained Multi-Objective Optimization Problems in Mechanical Engineering Design Using Bees Algorithm

Abstract: Many real-world search and optimization problems involve inequality and/or equality constraints and are thus posed as constrained optimization problems. In trying to solve constrained optimization problems using classical optimization methods, this paper presents a Multi-Objective Bees Algorithm (MOBA) for solving the multi-objective optimal of mechanical engineering problems design. In the present study, a satellite heat pipe design, a space truss design and pressure vessel problems are considered. Multi-objective optimization using the bees algorithm which is a new multi-object obtain a set of geometric design parameters, leads to optimum solve. This method is developed in order to obtain a set of geometric design parameters leading to minimum heat pipe mass and the maximum thermal conductance. Hence, a set of geometric design parameters, lead to minimum pressure total cost and maximum pressure vessel volume. Numerical results reveal that the proposed algorithm can find better solutions when compared to other heuristic or deterministic methods and is a powerful search algorithm for various engineering optimization problems.

Nonlinear finite element analysis of bending of straight beams using hp-spectral approximations

Abstract: Displacement finite element models of various beam theories have been developed using traditional finite element interpolations (i.e., Hermite cubic or equi-spaced Lagrange functions). Various finite element models of beams differ from each other in the choice of the interpolation functions used for the transverse deflection w, total rotation φ and/or shear strain γxz, or in the integral form used (e.g., weak form or least-squares) to develop the finite element model. The present study is concerned with the development of alternative beam finite elements using hpspectral nodal expansions to eliminate shear and membrane locking. Both linear and non-linear analysis are carried out using both displacement and mixed finite element models of the beam theories studied. Results obtained are compared with both analytical (series) solutions and nonlinear finite element solutions from literature, and excellent agreement is found for all cases. © 2011 IAU, Arak Branch. All rights reserved.

Optimization of Functionally Graded Beams Resting on Elastic Foundations

Abstract: In this study, two goals are followed. First, by means of the Generalized Differential Quadrature (GDQ) method, parametric analysis on the vibration characteristics of three-parameter Functionally Graded (FG) beams on variable elastic foundations is studied. These parameters include (a) three parameters of power-law distribution, (b) variable Winkler foundation modulus, (c) two-parameter elastic foundation modulus. Then, volume fraction optimization of FG beam with respect to the fundamental frequency is studied. Since the optimization process is so complicated and time consuming, Genetic Algorithm (GA), a computational algorithm based on Darwinian theories that allow to solve optimization problems without using gradient-based information on the objective functions and the constraints, is performed to obtain the best material profile through the thickness to maximize the first natural frequency. A proper Artificial Neural Network (ANN) is trained by training data sets obtained from GDQ method and then is applied as the objective function in genetic algorithm by reproducing the fundamental frequency for improving the speed of the optimization process. Finally, the optimized material profile for the maximum natural frequency of a FG beam resting on elastic foundations is presented. © 2011 IAU, Arak Branch. All rights reserved.

Magneto-thermo-elastic stresses and perturbation of magnetic field vector in a thin functionally graded rotating disk

Abstract: In this paper, a semi-analytical solution for magneto-thermo-elastic problem in an axisymmetric functionally graded (FG) hollow rotating disk with constant thickness placed in uniform magnetic and thermal fields with heat convection from disk’s surfaces is presented. Solution for stresses and perturbation of magnetic field vector in a thin FG rotating disk is determined using infinitesimal theory of magneto-thermo-elasticity under plane stress conditions. The material properties except Poisson’s ratio are modeled as power-law distribution of volume fraction. The non-dimensional distribution of temperature, displacement, stresses and perturbation of magnetic field vector throughout radius are determined. The effects of the material grading index and the magnetic field on the stress and displacement fields are investigated. The results of stresses and radial displacements for two different boundary conditions are compared with the case of a thin FG rotating disk with the same loading and boundary conditions but in the absence of magnetic field. It has been found that imposing a magnetic field significantly decreases tensile circumferential stresses. Therefore, the fatigue life of the disk will be significantly improved by applying the magnetic field. The results of this investigation can be used for optimum design of rotating disks. © 2011 IAU, Arak Branch. All rights reserved.

Time-dependent thermo-electro-mechanical creep behavior of radially polarized fgpm rotating cylinder

Abstract: Time-dependent creep analysis is crucial for the performance and reliability of piezoactuators used for high-precision positioning and load-bearing applications. In this study history of stresses, deformations and electric potential of hollow rotating cylinders made of functionally graded piezoelectric material (FGPM), e.g., PZT_7A have been investigated using Mendelson’s method of successive elastic solution. Loading is composed of an internal pressure, a distributed temperature field, an inertia body force and a constant electric potential difference between the inner and outer surfaces of the FGPM cylinder. All the mechanical, thermal and piezoelectric properties are assumed to be the same power functions of the radial graded direction. Using equations of equilibrium, strain displacement, stress-strain relation and the electric potential equation a differential equation containing creep strains for displacement is derived. A semianalytical method in conjunction with the method of successive approximation has therefore been proposed for this analysis. It has been found that a major redistribution for electric potential take place throughout the thickness. Electric potentials are increasing with time in the same direction as the compressive radial stress histories. That is the electric potential histories are induced by the compressive radial stress histories during creep deformation of the FGPM cylinder. © 2011 IAU, Arak Branch. All rights reserved.

Torsional stability of cylindrical shells with functionally graded middle layer on the winkler elastic foundation

Abstract: In this study, the torsional stability analysis is presented for thin cylindrical with the functionally graded (FG) middle layer resting on the Winker elastic foundation. The mechanical properties of functionally graded material (FGM) are assumed to be graded in the thickness direction according to a simple power law and exponential distributions in terms of volume fractions of the constituents. The fundamental relations and basic equations of three-layered cylindrical shells with a FG middle layer resting on the Winker elastic foundation under torsional load are derived. Governing equations are solved by using the Galerkin method. The numerical results reveal that variations of the shell thickness-to-FG layer thickness ratio, radius-to-shell thickness ratio, lengths-to-radius ratio, foundation stiffness and compositional profiles have significant effects on the critical torsional load of three-layered cylindrical shells with a FG middle layer. The results are verified by comparing the obtained values with those in the existing literature.

Mechanical and thermal stresses in a fgpm hollow cylinder due to non-axisymmetric loads

Abstract: In this paper, the general solution of steady-state two-dimensional non-axisymmetric mechanical and thermal stresses and mechanical displacements of a hollow thick cylinder made of fluidsaturated functionally graded porous material (FGPM) is presented. The general form of thermal and mechanical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the non-homogenous system of partial differential Navier equations, using the Complex Fourier Series and the power law functions method. The material properties, except of Poisson's ratio, are assumed to depend on the radial variable r and they are expressed as power law functions. © 2011 IAU, Arak Branch. All rights reserved.

Thermal stress analysis of a composite cylinder reinforced with fg swcnts

Abstract: Thermal stress analysis of a thick-walled cylinder reinforced with functionally graded (FG) single-walled carbon nanotubes (SWCNTs) is considered in radial direction. Thick-walled cylinder is subjected to a thermal field. Two layouts of variations in the volume fraction of SWCNTs were considered in the composite cylinder along the radius from inner to outer surface, where their names are incrementally decreasing (Inc Dec) and incrementally increasing (Inc Inc). Micromechanical models based on the Mori-Tanaka is used to define effective macroscopic properties of the nano composite shell. Using equations of motion, stress-strain and their corresponding constitutive correlations of a polystyrene vessel, a second order ordinary differential equation was proposed based on the radial displacement. The higher order governing equation was solved in order to obtain the distribution of displacement and thermal stresses in radial, circumferential and axial directions. The results indicate that FG distributions of SWCNTs have significant effect on thermal stresses and displacements in axial, radial and circumferential directions, so that in Inc Inc layout, the radial and circumferential stresses are lower than of other FG structures.

Mechanical behavior of a fgm capacitive micro-beam subjected to a heat source

Abstract: This paper presents mechanical behavior of a functionally graded (FG) cantilever micro-beam subjected to a nonlinear electrostatic pressure and thermal moment considering effects of material length scale parameters. Material properties through the beam thickness direction are graded. The top surface of the micro-beam is made of pure metal and the bottom surface from a mixture of metal and ceramic. The material properties through the thickness direction follow the volume fraction of the constitutive materials in exponential function form. The governing nonlinear thermo-electro-mechanical differential equation based on Euler-Bernoulli beam theory assumptions is derived using modified couple stress theory (MCST) and is solved using the Galerkin based weighted residual method. The effects of the electrostatic pressure and temperature changes on the deflection and stability of the FGM micro-beam, having various ceramic constituent percents, are studied. The obtained results are compared with the results predicted by classic theory (CT) and for some cases are verified with those reported in the literature.

Large Amplitude Vibration of Imperfect Shear Deformable Nano-Plates Using Non-local Theory

Abstract: In this study, based on nonlocal differential constitutive relations of Eringen, the first order shear deformation theory of plates (FSDT) is reformulated for vibration of nano-plates considering the initial geometric imperfection. The dynamic analog of the von Karman nonlinear straindisplacement relations is used to derive equations of motion for the nano-plate. When dealing with nonlinearities, in the frame work of nonlocal theory, challenges are presented because of the coupling between nonlocal stress resultants and displacement terms. Governing equations are solved using differential quadrature method (DQM) and numerical results for free vibration of an imperfect single layered graphene sheet are presented. © 2011 IAU, Arak Branch. All rights reserved.

Wave Propagation and Fundamental Solution of Initially Stressed Thermoelastic Diffusion with Voids

Abstract: The present article deals with the study of propagation of plane waves in isotropic generalized thermoelastic diffusion with voids under initial stress. It is found that, for two dimensional model of isotropic generalized thermoelastic diffusion with voids under initial stress, there exists four coupled waves namely, P wave, Mass Diffusion (MD) wave, thermal (T) wave and Volume Fraction (VF) wave. The phase propagation velocities and attenuation quality factor of these plane waves are also computed and depicted graphically. In addition, the fundamental solution of system of differential equations in the theory of initially stressed thermoelastic diffusion with voids in case of steady oscillations in terms of elementary functions has been constructed. Some basic properties of the fundamental solution are established and some particular cases are also discussed.

Theoretical Formulations for Finite Element Models of Functionally Graded Beams with Piezoelectric Layers

Abstract: In this paper an overview of functionally graded materials and constitutive relations of electro elasticity for three-dimensional deformable solids is presented, and governing equations of the Bernoulli–Euler and Timoshenko beam theories which account for through-thickness power-law variation of a two-constituent material and piezoelectric layers are developed using the principle of virtual displacements. The formulation is based on a power-law variation of the material in the core with piezoelectric layers at the top and bottom. Virtual work statements of the two theories are also developed and their finite element models are presented. The theoretical formulations and finite element models presented herein can be used in the analysis of piezolaminated and adaptive structures such as beams and plates. © 2011 IAU, Arak Branch. All rights reserved.

Third Order Formulation for Vibrating Non-Homogeneous Cylindrical Shells in Elastic Medium

Abstract: Third order shear deformation theory of cylindrical shells is employed to investigate the vibration characteristics of non-homogeneous cylindrical shells surrounded by an elastic medium. The kinematic relations are obtained using the strain-displacement relations of Donnell shell theory. The shell properties are considered to be dependent on both position and thermal environment. A suitable function through the thickness direction is assumed for the non-homogeneity property. The Winkler-Pasternak elastic foundation is used to model the elastic medium. Analytical solutions are presented for cylindrical shells with simply supported boundary conditions. From the numerical studies, it is revealed that, the natural frequencies are affected significantly by the elastic foundation coefficients and environmental temperature conditions. © 2011 IAU, Arak Branch. All rights reserved.

Creep Life Forecasting of Weldment

Abstract: One of the yet unresolved engineering problems is forecasting the creep lives of weldment in a pragmatic way with sufficient accuracy. There are number of obstacles to circumvent including: complex material behavior, lack of accurate knowledge about the creep material behavior specially about the heat affected zones (HAZ),accurate and multi-axial creep damage models, etc. In general, creep life forecasting may be categorized into two groups, viz., those that are based on microscopic modeling and others that are based on macroscopic (phemenological) concepts. Many different micro-structural processes may cause creep damage .The micro-structural processes highlight the fact that the creep damages can be due to cavity nucleation and growth. Dislocation creep is another mechanism with micro-structural features such as sub-grain formation and growth, new phase formation, such as the Z phase, coarsening leading to the dissolution of the MX phase. This leads to the removal of pinning precipitates, which allow local heterogeneous subgrain growth, weakening due to this growth and also to the dissolution of the MX. These features normally lead to the earlier formation of tertiary creep and reduced life. Considering welded joints ,the development of models for practical yet sufficiently accurate creep life forecasting based on micro-structural modeling becomes even more complicated due to variation of material in the base, weld and heat-affected-zone (HAZ) and variation of the micro-structure within HAZ and their interactions. So far, and until this date, none of the micro-structural models can forecast the creep life of industrial components with sufficient accuracy in an economic manner. There are several macroscopic (phemenological) models for creep life forecasting, including: time-fraction rule, strain-fraction rule, the reference stress and skeletal stress method, continuum damage model, etc. Each of which has their own limitations .This paper gauges to a multi-axial yet pragmatic and simple model for creep life forecasting weldment operating at high temperature and subjected to an elastic-plastic-creep deformation. © 2011 IAU, Arak Branch. All rights reserved.

Study of thermo elastic damping in an electrostatically deflected circular micro-plate using hyperbolic heat conduction model

Abstract: Thermoelastic damping (TED) in a circular micro-plate resonator subjected to an electrostatic pressure is studied. The coupled thermo-elastic equations of a capacitive circular micro plate are derived considering hyperbolic heat conduction model and solved by applying Galerkin discretization method. Applying complex-frequency approach to the coupled thermo-elastic equations, TED is obtained for different ambient temperatures. Effects of the geometrical parameters on TED and the critical thickness are investigated. Furthermore, the effect of applied bias DC voltage on TED for an electrostatically deflected micro-plate is also investigated.

Analysis of Nonlinear Vibrations for Multi-walled Carbon Nanotubes Embedded in an Elastic Medium

Abstract: Nonlinear free vibration analysis of double-walled carbon nanotubes (DWCNTs) embedded in an elastic medium is studied in this paper based on classical (local) Euler-Bernoulli beam theory. Using the averaging method, the nonlinear free vibration responses of DWCNTs are obtained. The result is compared with the obtained results from the harmonic balance method for single-walled carbon nanotubes (SWCNTs) and DWCNTs. The effects of the surrounding elastic medium, van der waals (vdW) forces and aspect ratio of SWCNTs and DWCNTs on the vibration amplitude are discussed. The error percentage of the nonlinear free vibration frequencies between two theories decreases with increasing the spring constant of elastic medium. Results are also shown that if the value of the spring constant is lower than (), the nonlinear free vibration frequencies are increased. In this case, the effect of the spring constant on frequency responses is significant, while if the value of the spring constant is higher than (), the curve of frequency responses has a constant value near to 1 and therefore the effect of the spring constant on frequency responses is negligible.

Magneto-Thermo-Elastic Behavior of Cylinder Reinforced with FG SWCNTs Under Transient Thermal Field

Abstract: In this article, magneto-thermo-elastic stresses and perturbation of magnetic field vector are analyzed for a thick-walled cylinder made from polystyrene, reinforced with functionally graded (FG) single-walled carbon nanotubes (SWCNTs) in radial direction, while subjected to an axial and uniform magnetic field as well as a transient thermal field. Generalized plane strain state is considered in this study. The SWCNTs are assumed aligned, straight with infinite length. Two types of variations in the volume fraction of SWCNTs were considered in the structure of the FG cylinder along the radius from inner to outer surface, namely: functionally graded increasing (FG Inc) and functionally graded decreasing (FG Dec) which are then compared with uniformly distributed (UD) layouts. The constitutive equations of this type of reinforced polymeric cylinder are derived by Mori-Tanaka method. Following the introduction of a second order partial differential equation derived from the equations of motion and stress-strain relationships and solving by a semi-analytical method, distribution of stresses and perturbation of magnetic field vector are obtained. Results indicate that maximum radial and circumferential stresses occur in FG Inc and FG Dec layouts, respectively. Maximum perturbation of magnetic field vector is not affected by UD layout. © 2011 IAU, Arak Branch. All rights reserved.

Ductility of polymer-supported metal films with curved interfaces

Abstract: Electronic components in modern flexible electronics are connected by interconnects,having typically the form of metal films on polymer substrates.Firstly,this paper studies experimentally the ductility of a polyimide-supported Cu film with rough interface(due to sandblasting treatment) and show that,upon tensile loading along the direction of film surface,the density of surface cracks can be reduced by increasing the substrate surface roughness.The distribution of tensile stresses in the film and their effects on film cracking(initiation and propagation) are subsequently studied using the method of finite elements.It is found that a rough(curved) interface can reduce the tensile stresses along the film surface so as to restrain the cracking of the film.Finally,we employ the cohesive zone model to study the initiation and spreading of damage in the film and interfacial cracking of the curved interface.It is demonstrated that both the damage and length of interfacial crack are reduced due to interface roughening.

Effect of Boundary Condition on Pre-Existing Crack Under Fatigue Loading

Abstract: In this paper, the present investigation has been conducted keeping in mind some of the problems concerning the crack propagation direction and growth under constant loading in an inclined crack geometry. The present studies mainly focused on the development and modifications in the crack growth criterion to account the biaxial, shear loading and number of stress terms. Existing criteria for the prediction of crack initiation direction have been modified taking higher order stress terms. The effective methods of experimentally determining the stress intensity factor for a body containing a crack is to analyze the isochromatic pattern obtained from a photoelastic model. The effect of biaxial load factor, crack angle, Crack length/width of specimen and length of specimen/width of specimen were studied and a regression model was developed for geometry correction to predict stress intensity factor for tearing mode and intensity factor for shearing mode. This approach is being used to predict crack growth trajectory under biaxial cyclic loading by assuming that the crack may grow in a number of discrete steps using the vectorial method. MTS criterion (Maximum Tangential Stress criterion) is used for prediction of crack initiating angle. The crack growth trajectory has been determined by cycle simulation procedure. © 2011 IAU, Arak Branch. All rights reserved.

Performance Analysis of Different Modified MR Engines Mounts

Abstract: Increasing current vehicle development trends for small, light, front wheel drive vehicles with low idle speeds have been forced automotive industries to use hydraulic engine mounts for further improvement in vibration, noise and harshness (NVH) performance of the vehicles. However, with the development of modern vehicle designs such as hybrid vehicles and variable engine management systems which have different operational modes, more sophisticated engine mounting systems are required to effectively response to each operational mode. Magnetorheological (MR) engine mount is a semi-active hydraulic engine mount, containing MR fluid, which can alter its dynamic behavior as a result of applying magnetic field. In this paper, design concept of two MR mounts is presented and their dynamic behavior is simulated. It is shown that the simulation methods used in this paper for simulating the dynamic behaviors of the MR mounts are effective with which the dynamic characteristic analysis and design optimization of MR mounts can be performed before its prototype development. Because of increasing demands for semi-active MR mounts in automotive industries, this can ensure their low cost and high quality for development. © 2011 IAU, Arak Branch. All rights reserved.

Electro-Mechanical Buckling of a Piezoelectric Annular Plate Reinforced with BNNTs Under Thermal Environment

Abstract: In this article, axisymmetric buckling behavior of piezoelectric fiber reinforced polymeric composite (PFRPC) annular plate subjected to electro-thermo-mechanical field is presented utilizing principle of minimum potential energy. Boron-nitride nanotubes (BNNTs) are used as fibers. Full coupling between electrical, mechanical and thermal fields are considered according to a representative volume element (RVE)-based XY piezoelectric fiber reinforce composite (PEFRC) model. Assuming PFRPC material and its composite constituents to be linear, homogenous, orthotropic, and perfectly bonded with uniform applied field, the basic relation for the axisymmetric buckling of a circular plate subjected to radial compression, radial electrical field, and uniform temperature change are derived. The presented results show that BNNTs can be used as an effective supplement to improve mechanical behavior of polyvinylidene fluoride (PVDF). Also, at normal working conditions, the influence of thermal and mechanical fields is much higher than the electric one on the critical load; hence, this smart structure is best suited for applications as sensors than actuators.

Study on dynamic properties of the prestressed concrete box-girder with corrugated steel webs

Abstract: Through a dynamical test on a 30m span PC box-girder with corrugated steel webs,the natural vibrations of the box-girder was known and the theory was applied to assist the analysis and seismic design of the girder.The results show that,the modal properties of the type of girder differ from the commonly used concrete girder.The transverse and the torsion stiffness of PC box-girder with corrugated steel webs are lower than concrete box-girder and we must take care of it in our design.The fundamental frequency calculated is tally to the result of the dynamical test,and the formulation can be used to calculate the fundamental frequency of the PC box-girder with corrugated steel webs.

A constitutive law of cement-based material at large range of confining pressure state

Abstract: The triaxial compression test and hydrostatic compression test have been performed at first.Based on the experimental data,different mechanism of cement paste has been analyzed.According to thermodynamics theory,a new constitutive law is established and the damage criterion,two plastic mechanisms have been taken into account.This modelling considers also the influence of confining pressure.Numerical simulation shows that this constitutive law for cement-based materials can well explicit the main mechanical behavior at a large range of confining pressure state.

ELASTO-PLASTIC COHESIVE ZONE MODELING OF DELAMINATION OF Si/Cu INTERFACE IN A NANO-CANTILEVER

Abstract: Previous experimental tests [Thin Solid Films 516:1925-1930] have shown that nano-cantilever Si/Cu/SiN/Pt/C tends to delaminate along the interface between Cu and Si layers when subject to monotonically bending load,the measured load-displacement curve shows a clear nonlinear behavior.Based on the continuum mechanics model,this study carries out numerical simulation and analysis of the crack initiation and propagation along the interface Si/Cu,which was observed in the above tests.Exponential type cohesive zone model(CZM) using finite element method was adopted to characterize the constitutive relationship of the interface Si/Cu,where Cu layer obeys either linear elastic or Ramberg-Osgood elasto-plastic constitutive relationship.The characteristic parameters of interface bonding strength are extracted through calibration via experimental results.The simulation results show that(i) cohesive strength and cohesive energy are the dominating CZM parameters,and exponential CZM is suitable to describe the interfacial delamination between Cu and Si layers when Cu layer is linear elastic;(ii) compared with bulk Cu,nano-scale Cu has a much higher yield stress and hardening rate,which leads to little plastic deformation of the nano-cantilever specimen during the whole delamination process.These predictions are in accordance with the experimental results.

Exact Solution for Electrothermoelastic Behaviors of a Radially Polarized FGPM Rotating Disk

Abstract: This article presents an exact solution for an axisymmetric functionally graded piezoelectric (FGP) rotating disk with constant thickness subjected to an electric field and thermal gradient. All mechanical, thermal and piezoelectric properties except for Poisson’s ratio are taken in the form of power functions in radial direction. After solving the heat transfer equation, first a symmetric distribution of temperature is produced. The gradient of displacement in axial direction is then obtained by assuming stress equation in axial direction to be zero. The electric potential gradient is attained by charge and electric displacement equations. Substituting these terms in the equations for the dimensionless stresses in the radial and circumferential directions yield these stresses and using them in the mechanical equilibrium equation a nonhomogeneous second order differential equation is produced that by solving it, the dimensionless displacement in radial direction can be achieved. The study results for a FGP rotating hollow disk are presented graphically in the form of distributions for displacement, stresses and electrical potential.