فهرست مطالب

Solid Mechanics - Volume:9 Issue: 1, 2017
  • Volume:9 Issue: 1, 2017
  • تاریخ انتشار: 1396/01/24
  • تعداد عناوین: 16
|
  • F. Esmaeili *, S. Barzegar, H. Jafarzadeh Pages 1-11
    In this research, the influence of bolt preload on the fatigue strength of 2024-T3 aluminium alloy double lap bolted joints has been studied experimentally and numerically. To do so, three sets of the specimens were prepared and each of them subjected to tightening torque of 1,2.5 and 5 N-m and then fatigue tests were conducted under various cyclic axial load levels. In the numerical method, the influence of bolt preload on the fatigue life of double lap bolted joints were studied using the values of fatigue notch factor obtained by volumetric approach. In order to obtain stress distribution around the notch (hole) which is required for volumetric approach, nonlinear finite element simulations were carried out. To estimate the fatigue life, the S-N curve of plain (un-notched) specimen and the fatigue notch factors obtained from volumetric method were used. The estimated fatigue life was compared with those obtained from the experiments. The investigation reveals that there is a good agreement between the life predicted by the volumetric approach and the experimental results for various specimens with different amounts of bolt preload. The volumetric approach and experimental results showed that the fatigue strength of specimens were improved by increasing the bolt preload as the result of compressive stresses which appeared around the bolt hole.
    Keywords: Clamping force, Bolted joint, Hybrid joint, Tightening torque
  • M.M. Alipour, M. Shaban* Pages 12-23
    Bending analysis of multilayer graphene sheets (MLGSs) subjected to non-uniform shear and normal tractions is presented. The constitutive relations are considered to be non-classical based on nonlocal theory of elasticity. Based on the differential transformation method, numerical illustrations are carried out for circular and annular geometries. The effects of nano scale parameter, radius of circular and annular graphene sheet, number of layers as well as distance between layers in the presence of van der Waals interaction forces are investigated. In addition, the effects of different boundary conditions are also examined. The numerical results show that above mentioned parameters have significant effects on the bending behavior of MLGSs under the action of non-uniform shear and normal tractions.
    Keywords: Graphene, Multilayer, Nonlocal, Shear, normal traction
  • R. Kumar *, R. Vohra, M.G. Gorla Pages 24-38
    A dynamic two dimensional problem of thermoelasticity with double porous structure has been considered to investigate the disturbance due to normal force and thermal source. Laplace and Fourier transform technique is applied to the governing equations to solve the problem. The transformed components of stress and temperature distribution are obtained .The resulting expressions are obtained in the physical domain by using numerical inversion technique. Numerically computed results for these quantities are depicted graphically to study the effect of porosity. Results of Kumar & Rani [42] and Kumar & Ailawalia [43] have also been deduced as special cases from the present investigation.
    Keywords: Thermoelasticity, Thermomechanical sources, Double porosity, Laplace, Fourier transforms
  • K. Malekzadeh Fard, H. Malek Mohammadi * Pages 39-53
    In this paper, the behavior of free vibrations and buckling of the sandwich panel with a flexible core was investigated using a new improved ýhigh-order sandwich panel theory. In this theory, equations of motion were formulated based on shear stresses in the core. First-order shear deformation theory was ýapplied for the procedures. In this theory, for the first time, incompatibility problem of velocity and acceleration field existing in Frostig's ýfirst theory was solved using a simple analytical method. The main advantage of this theory is its simplicity and less number of equations than the ýsecond method of Frostig's high-order theory. To extract dynamic equations of the core, three-dimensional elasticity theory was utilized. ýAlso, to extract the dynamic equations governing the whole system, Hamilton's principle was used. In the analysis of free vibrations, the ýpanel underwent primary pressure plate forces. Results demonstrated that, as plate pre-loads got closer to the critical buckling loads, the natural frequency of the panel tended zero. The results obtained from the present theory were in good correspondence with the ýresults of the most recent papers.
    Keywords: Free Vibration, Buckling, Plate sandwich, Flexible core, Navier's methods
  • A.R. Ghasemi *, M. Moradi Pages 54-62
    The principal effects of mass degradation on polymer matrix composites (PMCs) are the decay of mechanical properties such as strength, elongation, and resilience. This degradation is a common problem of the PMCs under thermal cycling conditions. In this article, composite degradation was investigated by measurement of total mass loss (TML) using the Taguchi approach. Thermal cycling tests were performed using a developed thermal cycling apparatus. Weight loss experiments were performed on the glass fiber/epoxy laminates under different number of thermal cycles and temperature differences. Also, The specimens had various fiber volume fractions and stacking sequences. Statistical analysis is performed to study contribution of each factor. Based on weight loss rates, a regression model was presented to evaluate the TML of laminated composite materials samples. It was found that the temperature differences and fiber volume fraction are the most effective factors of surface degradation with 61 and 22 percent contribution. Also, under the similar experimental conditions, the [0]8 layups exhibits 44 and 35.7 percent more mass loss than the [0/±45/90]s and [02/902]s layups, respectively.
    Keywords: Thermal cycling, Total mass loss, Polymer matrix composites (PMCs), Taguchi method, Stacking sequence
  • A. Behravan Rad* Pages 63-85
    Present paper is devoted to stress and deformation analyses of heated variable thickness functionally graded (FG) circular plate with clamped supported, embedded on a gradient elastic foundation and subjected to non-uniform transverse load. The plate is coupled by an elastic medium which is simulated as a Winkler- Pasternak foundation with gradient coefficients in the radial and circumferential directions during the plate deformation. The temperature distribution is assumed to be a function of the thickness direction. The governing state equations are derived in terms of displacements and temperature based on the 3D theory of thermo-elasticity. These equations are solved using a semi-analytical method to evaluate the deformation and stress components in the plate. Material properties of the plate except the Poisson's ratio are assumed to be graded continuously along the thickness direction according to an exponential distribution. A parametric study is accomplished to evaluate the effects of material heterogeneity indices, foundation parameters, temperature difference between the top and bottom surfaces of the plate and thickness to radius ratio on displacements and stresses. The results are reported for the first time and the new results can be used as a benchmark solution for the future researches.
    Keywords: Functionally graded, Circular plate, Gradient foundation, Thermo-mechanical, Semi-analytical, Non-uniform
  • R. Kumar *, P. Sharma Pages 86-99
    In this paper the propagation of harmonic plane waves in a homogeneous anisotropic magneto-piezothermoelastic diffusive body with fractional order derivative is studied. The governing equations for a homogeneous transversely isotropic body in the context of the theory of thermoelasticity with diffusion given by Sherief et al. [1] are considered as a special case. It is found that three types of waves propagate in one dimension anisotropic magneto-piezothermoelastic diffusive body, namely quasi-longitudinal wave (QP), quasi-thermal wave (QT) and quasi-diffusion wave (QD). The different characteristics of waves like phase velocity, attenuation coefficient, specific heat loss and penetration depth are computed numerically and presented graphically for Cadmium Selenide (CdSe) material. The effect of fractional order parameter on phase velocity, attenuation coefficient, specific heat loss and penetration depth has been studied.
    Keywords: Piezothermoelastic, Magneto, Harmonic plane wave, Phase velocity, Attenuation coefficient
  • M. Jabbari, M. Zamani Nejad *, M. Ghannad Pages 100-114
    In this paper, thermo-elastic analysis of a rotating thick truncated conical shell subjected to the temperature gradient, internal pressure and external pressure is presented. Given the existence of shear stress in the conical shell due to thickness change along the axial direction, the governing equations are obtained based on first-order shear deformation theory (FSDT). These equations are solved by using multi-layer method (MLM). The model has been verified with the results of finite element method (FEM). Finally, some numerical results are presented to study the effects of thermal and mechanical loading, geometry parameters of truncated conical shell.
    Keywords: Pressurized conical shells, Variable thickness, Thermo-elastic analysis, Rotation, Multi, layer method (MLM)
  • J.J. Tripathi *, G.D. Kedar, K.C. Deshmukh Pages 115-125
    A two dimensional generalized thermoelastic problem of a thick circular plate of finite thickness and infinite extent subjected to continuous axisymmetric heat supply and an internal heat generation is studied within the context of generalized thermoelasticity. Unified system of equations for classical coupled thermoelasticity, Lord-Shulman and Green-Lindsay theory is considered. An exact solution of the problem is obtained in the transform domain. Inversion of Laplace transforms is done by employing numerical scheme. Mathematical model is prepared for Copper material plate and the numerical results are discussed and represented graphically.
    Keywords: Thermoelasticity, Classical coupled, Lord-shulman, Green-lindsay, Internal heat generation, Axisymmetric heat supply
  • A. Ehsani, J. Rezaeepazhand* Pages 126-137
    The present paper investigates the advantages of a new class of composite grid structures over conventional grids. Thus far, a known grid structure such as orthogrid or isogrid has been used as an orthotropic layer with at most in-plane anisotropy. The present laminated grid is composed of various numbers of thin composite grid layers. The stiffness of the structure can be adjusted by choosing proper stacking sequences. This concept yields to a large variety of laminated grid configurations with different coupling effects compare to conventional grids. To illustrate the advantages of the laminated grids, the stiffness matrices and the bending response of the laminated and conventional grids are compared. Furthermore, a progressive failure analysis is implemented to compare the failure resistance of laminated and conventional grids. The results indicate that, thoughtful selection of stacking sequences of the laminated grid enhances the stiffness and response of the laminated grids without significant effect on the failure index.
    Keywords: Laminated grid, Composite, Stiffness, Orthogrid, Plate bending, Progressive failure
  • K. Torabi *, H. Afshari, H. Najafi Pages 138-156
    In this paper, exact solution for two-plane transverse vibration analysis of axial-loaded multi-step Timoshenko rotor carrying concentrated masses is presented. Each attached element is considered to have both translational and rotational inertia. Forward and backward frequencies and corresponding modes are obtained using transfer matrix method (TMM). The effect of the angular velocity of spin, value of the translational and rotational inertia, position of the attached elements and applied axial force on the natural frequencies are investigated for various boundary conditions.
    Keywords: Whirling analysis, Timoshenko rotor, Multi, step, Axial load, Concentrated mass, Rotational inertia, Transfer matrix method (TMM)
  • R. Kumar *, Sh Devi, V. Sharma Pages 157-171
    The main aim is to study the two dimensional axisymmetric problem of thick circular plate in modified couple stress theory with heat and mass diffusive sources. The thermoelastic theories with mass diffusion developed by Sherief et al. [1] and kumar and Kansal [2] have been used to investigate the problem. Laplace and Hankel transforms technique is applied to obtain the solutions of the governing equations. The displacements, stress components, temperature change and chemical potential are obtained in the transformed domain. Numerical inversion technique has been used to obtain the solutions in the physical domain. Effects of couple stress on the resulting quantities are shown graphically. Some particular cases of interest are also deduced.
    Keywords: Modified couple stress, Axisymmetric heat sources, Heat generation, Laplace, Hankel transforms
  • R. Ghajar *, S. Peyman, J. Sheikhi, M. Poorjamshidian Pages 172-185
    In this paper, the interface crack of two non-homogenous functionally graded materials is studied. Subsequently, with employing the displacement method for fracture of mixed-mode stress intensity factors, the continuous variation of material properties are calculated. In this investigation, the displacements are derived with employing of the functional graded material programming and analysis of isoparametric finite element; then, with using of displacement fields near crack tip, the mixed-mode stress intensity factors are defined. In this present study, the problems are divided into homogenous and non-homogenous materials categories; and in order to verify the accuracy of results, the analytical and numerical methods are employed. Moreover, the effect of Poisson's ratio variation on mixed-mode stress intensity factors for interface crack be examined and is shown in this study. Unlike the homogenous material, the effect of Poisson’s ratio variations on mixed-mode stress intensity factors at interface crack between two nonhomogenous is considerable.
    Keywords: Interface crack, Displacement method, Nonhomogeneous materials
  • S.A. Mohajerani, A. Mohammadzadeh *, M. Nikkhah Bahrami Pages 186-197
    In this paper vibration of ferromagnetic rectangular plates which are subjected to an inclined magnetic field is investigated based on classical plate theory and Maxwell equations. Levy type solution and Finite element method using Comsol software are used to obtain the frequency of the plate subjected to different boundary conditions, good agreements is obtained when computed results are compared with those obtained by Comsol software, the results have shown that the frequency of the plates increases with the magnetic field and the effect of magnetic field is similar to the Winkler’s foundation.
    Keywords: Free Vibration, Magnetic field, Ferromagnetic plate, Exact solution, Levy type
  • R. Moradi Dastjerdi, G. Payganeh *, M. Tajdari Pages 198-212
    In this paper, the effects of carbon nanotube (CNT) orientation and aggregation on the static behavior of functionally graded nanocomposite cylinders reinforced by CNTs are investigated based on a mesh-free method. The used nanocomposites are made of the straight CNTs that are embedded in an isotropic polymer as matrix. The straight CNTs are oriented, randomly or aligned or local aggregated into some clusters. The volume fractions of the CNTs and clusters are assumed variable along the thickness, so mechanical properties of the carbon nanotube reinforced composite cylinders are variable and are estimated based on the Eshelby–Mori–Tanaka approach. The obtained mechanical properties are verified by experimental and theoretical results that are reported in literatures. In the mesh-free analysis, moving least squares (MLSs) shape functions are used for approximation of displacement field in the weak form of equilibrium equation. Also, the effects of CNT distribution type and cylinder thickness are investigated on the stress distribution and displacement field of these cylinders.
    Keywords: Nanocomposite cylinder, Aggregation, Mori-Tanaka, Static behavior, Functionally graded, Mesh-Free
  • P.K. Vaishnav *, S. Kundu, S.M. Abo Dahab, A. Saha Pages 213-224
    The present paper studies the possibility of propagation of torsional surface waves in an inhomogeneous anisotropic layer lying between two heterogeneous half-spaces (upper and lower half-space). Both the half-spaces are assumed to be under compressive initial stress. The study reveals that under the assumed conditions, a torsional surface wave propagates in the medium. The dispersion relation of torsional surface wave has been obtained in the presence of heterogeneity, initial stress and anisotropic, and it is observed that the inhomogeneity factor due to quadratic and hyperbolic variations in rigidity, density and initial stress of the medium decreases the phase velocity as it increases. The result also shows that the initial stresses have a pronounced influence on the propagation of torsional surface waves. In the absence of anisotropy, Initial stress, inhomogeneity and rigidity of the upper half-space, then the dispersion relation coincide with the classical dispersion relation of Love wave.
    Keywords: Torsional wave, Heterogeneity, Initial stress, Phase velocity, Dispersion relation