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This paper aims to investigate the effect of viscoelastic behavior of polymer matrix of unidirectional fiber-reinforced laminated composite on stress distribution around the pin-loaded hole under tensile loading. The Laplace transform is used to prevent the integral form of matrix governing stress-strain relation. Applying a micromechanical model, all equilibrium equations for the fibers are written analytically in the Laplace domain. The numerical algorithm of Gaver–Stehfest is implemented, and the governing equations were solved at any given time to extract the concerned results in the time domain. The obtained results are validated against the Finite Element Method results obtained through ANSYS software. Moreover, a comparison of the results of this study at the time equal zero with elastic solutions of other references showed a good agreement. The results revealed that in the long term, the maximum tensile load in the intact fiber around the pinhole was enlarged and the tensile load in fibers far from the pinhole slightly was decreased. Moreover, the location of the maximum axial load that had occurred on pinhole edges was moved slightly toward the center over time.

This paper presents the optimization of stacking sequence of composite laminate adherends in an adhesive single lap joint under bending moment in order to minimize the amount of maximum peel and sh...

In the present work, analysis of the thermal behavior of a rubber cylinder under the repeated deformation is studied. This problem is divided into two correlated parts including transient thermal heat conduction and cyclic mechanical loading. To find the best approach-numerical method, the problem is modeled and analyzed by three approaches including coupled approach-FEM, uncoupled approach-FEM as well as Green’s function. To evaluate the dissipating energy due to hysteresis, the Prony–Mooney–Rivlin constitutive hyper-viscoelastic mathematical model is considered. To model the thermal effects and heat buildup due to dissipating energy, this energy is accounted for as a heat source inside the part in three different forms including pointwise, planar, and volumetric. It is shown that the FEM-based coupled approach presents the most accurate estimation. However, for steady-state estimation of mid-point and wall-point temperatures, the best method is Green’s function with the planar and the volumetric heat source assumptions. Moreover, a study on the effect of frequency of loading cycles in temperature distribution shows that the more the frequency, the larger the difference between the temperature of the mid-point and wall-point, and the higher maximum temperature inside the rubber.

In this research, a framework for modelling and simulation of hyper-elastic materials is proposed. The framework explains how to employ strain energy functions as a constitutive model, standard loading test data, and a powerful optimisation method to determine a mathematical function for explaining the mechanical behaviour of a hyper-elastic material using minimum types of loading test data. In the first part, a survey on hyper-elastic constitutive models is presented. Fifty models are collected and classified into six categories. Thereafter, five types of standard loading tests including uniaxial, biaxial, equi-biaxial, pure shear, and simple shear are introduced. It is shown that depending on the loading type, physical parameters, Cauchy, and nominal stress tensors, each constitutive model possesses a particular function. The genetic algorithm as a powerful optimisation method is used to determine the most accurate function for each type of loading test data. It is presented that based on the selected constitutive model and regardless of a number of existing loading types test data, a unique function can be determined for expressing and simulating the mechanical behaviour of the considered hyper-elastic material.

Present work studies the interfacial stresses in tubular single-lap adhesively bonded joints, in the presence of an annular defect (void and debond), subjected to an axial load. Using linear elasti...

The effect of the cellular core on the stress intensity factor at the tip of a crack in the adhesive layer of a five-layer sandwich composite beam is investigated. A Nomex sheet is used to model the cellular core with honeycomb, square, and triangular cells. The mechanical properties of these cells are obtained by the finite element analysis supported by theoretical two- and three-dimensional equations. Based on the deduced properties, the load-displacement curve is generated for a sandwich beam under mode I fracture. The numerical findings are validated against available experimental data. It is shown that the lowest values of the stress intensity factor are observed for a core with a honeycomb structure as compared to the other two cell shapes used in this study, which are composed of equilateral triangles or squares. An increase in the wall thickness of the cells leads to an increase in the stress intensity factor.

Dynamic analysis of functionally graded size-dependent annular nano-plate is the main concern in this study. To obtain the vibrational behavior of this plate, the stress-driven nonlocal integral elasticity, as well the strain gradient theory were used in conjunction with the classical plate theory. The resulting equilibrium equations were solved using the generalized differential quadrature rule (GDQR) and the influences of various parameters such as; size-effect parameter, material heterogeneity index, the aspect ratio of the inner to outer radii, and the effects of different boundary conditions were investigated on the vibrational behavior of the nano-plate, based on different types of boundary conditions. Results indicate that the natural frequencies increase with an increase in the heterogeneity index [Formula: see text] and the increase in size-effect parameter shows a similar effect in both models. Additionally, for the simply supported and free-edge boundary conditions (for both edges), as well as the free and knife-edges, and simply supported-free edges, the strain gradient theory predicts higher values of frequency ratios as [Formula: see text] was increased. Similar results were obtained for the remaining types of boundary conditions, with a higher sensitivity to [Formula: see text], provided the stress-driven model is used. This behavior can be interpreted as the sensitivity of the nano-plate to [Formula: see text] that is manifested by the use of the stress-driven model for the prediction of vibrational behavior of the nano-plate.

The effect of adhesive layers bonding to the core of functionally graded (FG) surface layers is investigated using the free vibration of a five-layer sandwich composite plate resting on a Winkler elastic foundation in a thermal environment. It is assumed that all layers are experiencing a steady-state temperature ΔT. The layer-wise theory is used to derive the governing equations with the help of Hamilton’s principle. The Navier solution is employed to obtain the closed-form solutions. The numerical results obtained using the present theory are compared with three-dimensional finite elements implemented by ABAQUS software. The results show that the proposed theory is not only accurate but also efficient in predicting the natural frequencies of sandwich plates resting on Winkler foundations.

Nowadays, polyethylene composes a large number of natural gas distribution pipelines installed under the ground. The focus of the present contribution is two fold. One of the objectives is to investigate the applicability of polyethylene fittings in joining polyethylene gas pipes which are electrofused onto the pipe ends and buried under the ground, by estimating stress distribution using finite element method. The second objective is to study the effectiveness of polyethylene repair patches which are used to mend the defected pipelines by performing a finite element analysis to calculate peak stress values. Buried polyethylene pipelines in the natural gas industry, can be imposed by sever loadings including the soil-structure interaction, traffic load, soil’s column weight, internal pressure, and thermal loads resulting from daily and/or seasonal temperature changes. Additionally, due to the application of pipe joints, and repair patches local stresses superimposed on the aforementioned loading effects. The pipe is assumed to be made of PE80 resin and its jointing socket, and the repair patch is PE100 material. The computational analysis of stresses and the computer simulations are performed using ANSYS commercial software. According to the results, the peak stress values take place in the middle of the fitting and at its internal surface. The maximum stress values in fitting and pipe are below the allowable stresses which shows the proper use of introduced fitting is applicable even in hot climate areas of Ahvaz, Iran. Although the buried pipe is imposed to the maximum values of stresses, the PE100 socket is more sensitive to a temperature drop. Furthermore, all four studied patch arrangements show significant reinforcing effects on the defected section of the buried PE gas pipe to transfer applied loads. Meanwhile, the defected buried medium density polyethylene gas pipe and its saddle fused patch can resist the imposed mechanical and thermal loads of 22°C temperature increase. Moreover, increasing the saddle fusion patch length to 12 inches reduces the maximum stress values in the pipe, significantly.

In this paper, a novel mathematical procedure is proposed which allows for determination of stresses in a defected adhesively bonded single lap tubular joint under torsion. It is assumed that the s...

In this study, stress distribution in a functionally graded nanodisk of variable thickness is investigated based on the strain gradient theory. It is assumed that nanodisk is subjected to thermal and mechanical loads while it is rotating with a constant angular velocity. The equilibrium equation and the corresponding boundary conditions are deduced using Hamilton's principle. A numerical scheme is used to solve the problem. The effects of angular velocity, thickness profile, material inhomogeneity parameter, external loads and temperature are investigated on the total stresses as well as radial displacements. A close examination of the results based on strain gradient and classical theories predict the same trend for variation in radial displacements along the nanodisk radius. Additionally, results show that selection of a variable thickness reduces the radial stresses. Due to coupling effect between radial stress, σ r , and high-order stresses which appear in strain gradient theory, total radial stresses at the inner and outer radii are nonzero despite the zero external loads applied at the two corresponding surfaces. Moreover, Due to very small radius of the nanodisk, the centrifugal forces due to angular velocity ω are negligible and hence, the total radial stresses are barely affected by their magnitudes.

With the increasing application of high-strength carbon steel pipes in oil and gas transport pipelines, a precise evaluation of such pipelines is of the utmost importance for the optimum an...

Predicting the failure pressure of pipelines is of paramount importance in design and integrity management in order for pipes to operate safely, efficiently, and cost-effectively in terms o...

A comprehensive literature review on the existing analytical models based on different material and geometry behaviors for both single and double-lap joints (as well as others) has been made to ass...

In this paper, the mechanical behavior of a functionally graded nano-cylinder under a radial pressure is investigated. Strain gradient theory is used to include the small scale effects in this analysis. The variations in material properties along the thickness direction are included based on three different models. Due to slight variations in engineering materials, the Poisson’s ratio is assumed to be constant. The governing equation and its corresponding boundary conditions are obtained using Hamilton’s principle. Due to the complexity of the governed system of differential equations, numerical methods are employed to achieve a solution. The analysis is general and can be reduced to classical elasticity if the material length scale parameters are taken to be zero. The effect of material indexn, variations in material properties and the applied internal and external pressures on the total and high-order stresses, are well examined. For the cases in which the applied external pressure at the inside (or outside) radius is zero, due to small effects in nano-cylinder, some components of the high-order radial stresses do not vanish at the boundaries. Based on the results, the material inhomogeneity indexn, as well as the selected model through which the mechanical properties may vary along the thickness, have significant effects on the radial and circumferential stresses.

In order to effectively design an energy harvesting system for any specific application, a model that accurately characterizes the energy harvesting parameters is needed. In the present paper a novel magneto-electro-elastic (MEE) cantilever beam has been proposed and modeled as an effective means to increase the harvested electrical power in a vibration-based energy harvesting system. The cantilever beam is composed of a linear homogeneous elastic substrate and two MEE layers with perfect bonds between their interfaces. Using the constitutive equations, Gauss's and Faraday's laws, based on the Euler–Bernoulli beam theory, the coupled magneto-electro-mechanical (MeM) differential equations are derived for a harmonic base excitation in the transversal direction with a superimposed small rotation. The resulting equations are then solved analytically to obtain the dynamic behavior as well as the harvested voltages and powers of the proposed energy harvesting system. Finally, parametric numerical studies are used to examine the effect of excitation frequency, external resistive loads, and material properties on the performance of the MEE energy harvester. The study reveals that the implementation of the coil circuit has resulted in an increase in the total useful harvested power. According to the numerical results, any increase in the Young's modulus and density of the substrate layer (across the ranges that have been studied and while the properties of the MEE layer are kept constant), increases the magnitude of the magnetoelectric harvested power in the unimorph MEE energy harvester system.

The topic presented in this research is the calibration of small-scale parameters of non-classical continuum theories such as nonlocal strain gradient theory, strain gradient theory, stress-driven nonlocal elasticity, and strain-driven nonlocal elasticity. Governing equations of vibrational behavior of circular nanoplate and associated boundary conditions for each method derived using Hamilton's principle. Obtained governing differential equations from non-classical methods were solved using the general differential quadrature rule (GDQR). Then, the first natural frequencies for different radiuses and different size parameters were obtained. On the other hand, the first natural frequencies of circular nanoplates are calculated using molecular dynamics simulation based on AIREBO and Tersoff potentials for different radiuses. Fast Fourier transform (FFT) was utilized to calculate natural frequencies based on the molecular dynamics simulation. Using the accurate size parameter is an important point in the application of non-classical continuum theories. To obtain the size parameters related to different non-classical methods, the results of molecular dynamics compared to those of nan-classical methods and simulated annealing (SA) algorithm optimization technique was utilized. Results show that stress-driven nonlocal, strain-driven nonlocal, and strain gradient methods cannot predict the behavior predicted by molecular dynamics for all ranges of radius. In other words, the responses of these three methods for any value of the size parameters (in some interval radius) and results of the molecular dynamics method are not equal for a few numbers of studied radii. In contrast to these three methods, the nonlocal strain gradient method predicts the results obtained by molecular dynamics well for all radii. The results of this paper are very useful for researchers in the field of non-classical continuum mechanics.

The aim of this research is to study the effect of a break in the laminated composite adherends on stress distribution in the adhesively single-lap joint with viscoelastic adhesive and matrix. The proposed model involves two adherends with E-glass fibers and poly-methyl-methacrylate matrix that have been adhered to each other by phenolic-epoxy resin. The equilibrium equations that are based on shear-lag theory have been derived in the Laplace domain, and the governing differential equations of the model have been derived analytically in the Laplace domain. A numerical inverse Laplace transform, which is called Gaver–Stehfest method, has been used to extract desired results in the time domain. The results obtained at the initial time completely matched with the results of elastic solution. Also, a comparison between results obtained from the analytical and finite element models show a relatively good match. The results show that viscoelastic behavior decreases the peak of stress near the break. Finally, the effect of size and location of the break, as well as volume fraction of fibers, on the stress distribution in the adhesive layer is fully investigated.

In this paper, the thermoelastic behavior of a functionally graded nanodisk is studied based on the strain gradient theory. It is assumed that the nanodisk thickness is constant, and a power-law model is adopted to describe the variation of functionally graded material properties. Furthermore, the nanodisk angular acceleration is taken to be zero while it is subjected to an axisymmetric loading. Also, it is assumed that any variation in temperature occurs only in the radial direction. The equilibrium equation and the boundary conditions are deduced from Hamilton’s principle. The obtained results are compared with those of classical theory. These results show that both theories predict the same trend for the variation in radial displacements. The differences between the stresses obtained from classical and strain gradient theories are clearly highlighted. Increasing the value of the material inhomogeneity parameter, n, considerably affects the magnitudes and the corresponding peak values of the high-order stress $$\bar{\tau }_{rrr}$$ . Any rise in temperature at the outside radius has a direct effect on the total stresses and radial displacements in the nanodisk. Also, the effects of external load at the inner and outer radii on radial displacement as well as stress components are fully investigated.

In this paper, hole stress concentrations in long fibers and their surrounding matrix bays is examined in a hybrid composite lamina. It is assumed that all fibers lie in one direction while loaded by a force p at infinity in the direction of fibers. The width of the lamina is considered to be finite and bears a hole as a defect. Due to the presence of excessive shear stress in the matrix bays bounding the hole, a yielded zone of size 2a o is developed around the hole. Shear lag model (SLM) is used to drive the displacement and stress fields. The resulting equations are solved analytically based on boundary and continuity conditions. It is shown that the shape and size of the hole, as well as length of the plastic zone, have considerable effect on stress concentrations within the lamina. Compared to a lamina with a single type fiber, a hybridized model shows lower stress concentrations in High modulus (HM) fibers bounding the hole as opposed to those of Low modulus fibers (LM) subjected to the same condition. Moreover, hole shape and size, ratio of extensional stiffness of LM to HM fibers, and size of the plastic zone seem to have considerable effect on shear and normal stresses in the matrix and fibers, respectively.

The objective of this paper is to present a coupled magneto-electro-mechanical (MEM) lumped parameter model for the response of the proposed magneto-electro-elastic (MEE) energy harvesting systems under base excitation. The proposed model can be used to create self-powering systems, which are not limited to a finite battery energy. As a novel approach, the MEE composites are used instead of the conventional piezoelectric materials in order to enhance the harvested electrical power. The considered structure consists of a MEE layer deposited on a layer of non-MEE material, in the framework of unimorph cantilever bars (longitudinal displacement) and beams (transverse displacement). To use the generated electrical potential, two electrodes are connected to the top and bottom surfaces of the MEE layer. Additionally, a stationary external coil is wrapped around the vibrating structure to induce a voltage in the coil by the magnetic field generated in the MEE layer. In order to simplify the design procedure of the proposed energy harvester and obtain closed form solutions, a lumped parameter model is prepared. As a first step in modeling process, the governing constitutive equations, Gauss's and Faraday's laws, are used to derive the coupled MEM differential equations. The derived equations are then solved analytically to obtain the dynamic behavior and the harvested voltages and powers of the proposed energy harvesting systems. Finally, the influences of the parameters that affect the performance of the MEE energy harvesters such as excitation frequency, external resistive loads and number of coil turns are discussed in detail. The results clearly show the benefit of the coil circuit implementation, whereby significant increases in the total useful harvested power as much as 38% and 36% are obtained for the beam and bar systems, respectively.

In this paper, the use of magneto-electro-elastic (MEE) composites is proposed for vibration-based energy harvesting applications as an approach to enhance the harvested electrical power density in order to create self-powering systems which are not limited by finite battery energy. The main objective of this study is analytical modeling of the response of a unimorph MEE energy harvester in the framework of a longitudinal cantilever bar which consists a MEE layer that is perfectly bonded to a lower substrate layer. This model can simplify the design procedure for determining the appropriate size and vibration levels necessary for sufficient energy to be produced and supplied to the electronic devices. As the first step, the coupled magneto-electro-mechanical differential equations based on the one dimensional bar theory and for harmonic base excitation in the longitudinal direction are derived. Subsequently, the governed coupled equations are solved to obtain the dynamic behavior, generated voltages, currents and the harvested powers by the proposed energy harvesting system. Then, the influences of the excitation frequency, electrical load resistances and number of coil turns on the performance of the MEE energy harvester are discussed in detail. This study reveals the benefit of the circuit used for the coil by increasing the total useful harvested power by as much as 37%. According to the obtained numerical results, any decrease in Young’s modulus and increase in density of the two layers increases the magnitude of the magnetoelectric harvested power in a unimorph MEE energy harvester system.

This paper presents the stress analysis of rotating nano-disk made of functionally graded materials with nonlinearly varying thickness based on strain gradient theory. The equilibrium equation and corresponding boundary conditions of nano-disk were obtained using Hamilton's principle. Because of the complexity of governing equations and boundary conditions, the equations are solved using numerical methods. Fixed boundary conditions are considered, in the numerical examples. This analysis is general and can be reduced to classical elasticity. The effect of various parameters such as graded index and thickness profile on stresses and high-order stresses were examined. Values of stresses at inner and outer radial are not zero, because stresses at inner and outer radius accumulate with stresses caused by strain gradient theory. Results show that the effects of thickness parameters are greater than the effect of graded index and the difference between the stress predicted by the classical theory and the strain gradient theory is large when the thickness of nano-disk is small.

This study aims to investigate the effect of viscoelasticity of polymeric matrix of composite materials on the transient stress concentration due to a sudden break in its fibers. The fibers were modeled as a linear elastic, and the matrix was modeled as a linear viscoelastic material. A generalized Voigt–Kelvin solid model was employed to model the viscoelastic behavior of matrix. In this study, finite difference method and an innovative semi-analytical method were used. The governing integro-differential equations have been derived by shear-lag theory and have been solved by initial and boundary conditions before and after break occurrence. The governing equations contain an integral term attributing to the viscoelastic properties of the matrix. The same analysis was conducted for the laminae and laminates with fibers arranged in square and hexagonal arrays. Results obtained from the two methods show a relatively good match. The results show that assuming viscoelastic properties decreases the peak of stress concentration factor and increases the steady stress concentration factor. Finally, the effects of size and location of break in the fibers for lamina and laminated composite were investigated.

The aim of the present study was to introduce new crushing mechanisms in terms of crushing modes for estimating the crushing force and absorbed energy of polygonal thin walled metal sections subjected to axial progressive collapse. For this purpose, two models were developed. The first model, which has been extensively used before and named as “plastic hinge model” (PHM), was modified based on new crushing modes; and as the second, a novel model was introduced by the authors named as “induced curvature model” (ICM). The latter model was considered to be more realistic than the former due to consideration of metal sheet curvatures during progressive folding process, as well as including the hardening effect of the material during plastic deformation. All possible crushing modes for a typical polygonal section were considered and discussed by combining different crushing modes of the corner elements. New expressions for the absorbed energies and crushing force were presented based on the resulting crushing modes. To evaluate the validity and efficiency of the proposed models, a detailed FE simulation was conducted using LS-DYNA. Comparison of FEM, PHM and ICM results showed the superiority of the ICM over PHM.

In this paper, the effect of charge/discharge cycles on the electrode containing nano-zirconium oxide, nanoporous carbon black and graphene nanosheets in electrochemical capacitors has been described. Surface morphology and electrochemical performance of the prepared electrode have also been conducted. The electrode prepared from graphene nanosheets (GNS), nanoporous carbon black (NCB), zirconium oxide (ZrO2), and polytetrafluoroethylene (PTFE) in molar ratio of 54:09:27:10 respectively showed a maximum specific capacitance as high as 11.84 F g−1 in the potential range between −0.45 and 0.35 V (V vs. SCE) at a scan rate of 10 mV s−1 in a 3 M NaCl electrolyte. The electrochemical results show the low ratio of the outer to total charge (q⁎O/q⁎T) which confirms the low current response and higher voltage reversal at the end potentials. SEM images confirms the ions re-deposit as agglomerates and accompanied by a drastic decrease in the surface area on the surface of the electrode after one charge/discharge cycle.

In this study, effect of morphology and pore size distribution on physicochemical properties of graphite nanosheets (GNSs)/nanoporous carbon black (NCB)/CeO2 nanoparticle electrodes were investigated in 3 M NaCl electrolyte. 90:00:00:10 (GNS:NCB:CeO2:PTFE) electrodes show a flat and smooth surface and 75:00:15:10 electrodes showed micro pores which opened on surface. In the presence of NCB particles, electrodes like 25:50:15:10 showed the macro, micro and nano pores, simultaneously. Total charge ( q T * ) of 1.73, 37.88, 208.33 C g−1 cm−2 and outer charge to total charge ( q O * /) of 0.53, 0.43 and 0.24 were obtained from 90:00:00:10, 75:00:15:10 and 25:50:15:10 electrodes, respectively. It is concluded that introducing narrower and deeper pores on surface of electrodes increases the charge storage capability and decreases the current response and power delivering capability. Flat surface of GNSs showed 3.4 F/g and also exhibited good capacitance retention of more than 80%. Additionally, nanoporous structures increased the capacitance of 25:50:15:10 electrodes up to 16.2 F/g at 10 mV s−1 in 3 M NaCl electrolyte.

The influence of clay particles on the corrosion properties of bituminous coating was studied. Different percentages of natural montmorillonite clay (Cloisite Na + ) were added to emulsified bitumen in water to make 2 wt.%, 3 wt.% and 4 wt.% of clay/bitumen nanocomposite coatings. The coatings were applied on steel 37. Optical microscopy and transmission electron microscopy (TEM) were employed to study the structure of nanocomposite. To investigate the anti-corrosion properties of the coated panels, electrochemical impedance spectroscopy (EIS) was used. The findings indicated that the addition of clay nanolayers improved corrosion resistance of the coatings. Moreover, increasing clay loading up to 4 wt.%, increased the corrosion resistance.

Mechanisms of charge storage, stability, capacitance, morphology and response current of graphene/cerium oxide (CeO2) nanoparticles as an electrode material for electrochemical capacitors have been investigated. Electrochemical properties of the assembled electrodes were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques in 3 M NaCl, NaOH and KOH electrolytes. Scanning electron microscopy (SEM) is used to characterize the microstructure and the nature of prepared electrodes. SEM images confirm the layered structure (12 nm thickness) of the used graphene. The proposed electrode shows a maximum specific capacitance as high as 11.09 F g−1 in the potential range between −0.55 and 0.3 (V vs. SCE) at scan rate of 5 mV s−1. The charge/discharge cycling test shows a good reversibility and confirms that capacitance will increase after 500 cycles by 37%.

In this paper the attenuation of Lamb waves in three-layer joints, including two elastic plates bonded together by a viscoelastic adhesive layer, is investigated in high and low frequencies using global matrix method. Theoretical boundary value problem in three-layer adhesive joints with perfect bond and traction-free boundary conditions on their outer surfaces is solved to find a combination of frequencies and modes with lowest attenuation. Characteristic equation is derived by applying continuity and boundary conditions in three-layer joints using global matrix method. Attenuation and phase velocity dispersion curves in high and low frequencies are obtained with numerical solution of this equation by a computer code for a three-layer joint, including an aluminum repair patch bonded to the aircraft aluminum skin by a layer of viscoelastic epoxy adhesive. To validate the numerical solution results of characteristic equation, wave structure curves are plotted for a special mode in two different frequencies in the adhesive joint. Also, attenuated displacement amplitude curves in a round-trip of Lamb wave along the adhesive joint are plotted to investigate the reduction of the signal amplitude generated by a single transducer. The purpose of present paper is to find a combination of frequencies and modes with minimum attenuation in high and low frequencies. These frequencies and modes are recognizable by transducers in inspections with Lamb waves because of low attenuation level.

The effect of a crack in the overlap region of a single step lap joint is studied on the shear distribution in the adhesive layer. Each adherend is considered to be a lamina with unidirectional fib...

The effect of void shape and volume fraction of fibers on the distribution of stresses in a laminated composite plate subjected to a tensile load applied in the fiber direction is investigated. The cross section of all fibers is triangular. The void can simulate an internal crack or a cylindrical hole. The shear-lag model is used to derive the field equations. By using proper boundary and bonding conditions, complete load and displacement fields in the laminate are determined. The effects of physical parameters of fibers and of void shape and its location on stress concentrations and peak shear stresses in the laminate are studied. The analytical results for stress concentration factors are compared with those given by the finite-element method, and a close agreement between them is found to exist.

In this paper, the effect of ion sizes of cations and anions on the charge storage capability of graphite nanosheets is investigated. Electrochemical properties of prepared electrodes are studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques, in 3 M NaCl, NaOH and KOH electrolytes. A scanning electron microscope (SEM) is used to characterize the microstructure and nature of prepared electrodes. SEM images and XRD patterns confirm the layered structure (12 nm thickness) of the used graphite with an interlayer distance of 3.36 A. The electrochemical results and the ratio of q O ⁎ / q T ⁎ confirm a better charge storage and charge delivering capability of prepared electrodes in 3 M NaCl electrolyte. The charge/discharge cycling test shows a good reversibility and confirms that the solution resistance will increase after 500 cycles.

Nonlinear free and forced vibration behavior of a porous functionally graded Euler-Bernoulli nanobeam subjected to mechanical and electrical loads is studied based on the nonlocal strain gradient elasticity theory. It is assumed that the porous functionally graded (FG) nanobeam is resting on a nonlinear foundation. Also, material properties of the nanobeam are assumed to vary in the thickness direction. Equations of motion are derived using Hamilton's principle. Galerkin method along with variation iteration method (VIM), Homotopy perturbation method (HPM), Hamiltonian approach method (HAM) and multiple scale method are employed to solve the governing equations based on clamped-clamped, simply-simply and clamped-simply boundary conditions. For verification purposes, the results of this study are compared with those of other studies. The effects of different parameters such as type of porosity distribution, nonlinear foundation, boundary conditions, electrical voltage and size effect parameters on the primary and secondary resonances were investigated. It was found that length-scale parameters have a crucial role on the nonlinear vibration behavior of such structures.

In this paper, the effect of viscoelasticity of adhesives on shear stress distribution in the adhesive layer of a single-lap joint under shear load is studied. The joint comprises two elastic single isotropic adherend layers joined by a viscoelastic adhesive polymer. A three-parameter viscoelastic solid model is used to deduce the governing differential equation in the Laplace domain, which is solved using residue theorem. Results show that for an impulse load of 100 N, the maximum shear stress in the adhesive layer is reduced to 39% of its initial value. Also, the ratio of viscous modulus of the adhesive to its shear modulus has an adverse effect on the peak shear stress. An increase in the thickness of the adhesive layer reduced the induced peak shear stress in the joint. Moreover, the shear strain in the adhesive layer reached its steady value after 1000 seconds.