DR Aghdam | AmirKabir University Of Technology (original) (raw)

Papers by DR Aghdam

Thermal bifurcation behavior of cross-ply laminated composite cylindrical shells embedded with sh... more Thermal bifurcation behavior of cross-ply laminated composite cylindrical shells embedded with shape memory alloy fibers is investigated. Properties of the constituents are assumed to be temperature-dependent. Donnell's kinematic assumptions accompanied with the von-Karman type of geometrical non-linearity are used to derive the governing equations of the shell. Furthermore, the one-dimensional constitutive law of Brinson is used to predict the behavior of shape memory alloy fibers through the heating process. Governing equilibrium equations are established by employing the static version of virtual displacements principle. Linear membrane pre-buckling analysis is performed to extract the pre-buckling deformations of the shell. Applying the well-known adjacent equilibrium criterion to the pre-buckling state of the shell, stability equations are derived. The governing equations are solved via a semi-analytical solution employing the exact trigonometric function in circumferential direction and the harmonic differential quadrature method in the longitudinal direction. Numerical results cover various cases of edge supports, cross-ply lamination, shape memory alloy fibers volume fraction and shape memory alloy fiber pre-strain. It is shown that, proper usage of shape memory alloy fibers results in considerable delay of the thermal bifurcation type of buckling.

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This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights a b s t r a c t In this study, large amplitude vibration and post-buckling analysis of variable cross-section laminated composite beams with symmetric and asymmetric lay-ups resting on nonlinear elastic foundation is investigated using the generalized differential quadrature (GDQ) method. Geometric nonlinearity of von-Karman type is considered. Various combinations of boundary conditions including free edges are considered. Furthermore, elastic foundation consists of shearing layer, linear and cubic nonlinearity. Natural frequencies are obtained for the nonlinear problem using the Picard iterative method. Results for linear and nonlinear analyses of uniform laminated beams are validated with the available data in the open literature, which show close agreement. Moreover, some new results are also presented for the nonlinear natural frequencies and buckling load of the non-uniform laminated composite beams to study effects of vibration amplitude, elastic coefficients of foundation, axial force, boundary conditions and variation of cross-section.

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This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights a b s t r a c t In this article, large amplitude vibration and thermal post-buckling of shape memory alloy (SMA) fiber reinforced hybrid composite beams with symmetric and asymmetric lay-up are analytically investigated. To predict the behavior of the smart laminated beam, the EulereBernoulli beam theory and the nonlinear von-Karman strain field are employed. Also, one-dimensional Brinson SMA model is utilized to calculate the recovery stress of SMA fibers in the case of restrained strain. Nonlinear governing equations of motion are derived via the Hamilton principle. Using an analytical approach based on the Galerkin procedure together with the simple harmonic motion assumption, a closed-form solution is obtained for the thermal post-buckling and nonlinear free vibration analysis of SMA fiber reinforced hybrid composite beams. Due to lack of any results on the free vibration and thermal stability of SMA fiber reinforced composite beams, the results obtained from the present solution for laminated composite beams without SMA fiber are compared with counterpart data in the open literature, which validate the present solution. Then, a set of parametric study is carried out to show the influence of SMA volume fraction, amount of prestrain in the SMA fiber, orientation of composite fiber, SMA-reinforced layer thickness to total thickness ratio, location of SMA layer, vibration amplitude, boundary conditions and temperature on the vibration characteristic of the laminated beam reinforced with SMA in the pre-and post-buckled domains.

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In this paper, nonlinear free vibration and primary/secondary resonance analyses of shape memory ... more In this paper, nonlinear free vibration and primary/secondary resonance analyses of shape memory alloy (SMA) fiber reinforced hybrid composite beams with symmetric and asymmetric lay-up are investigated. The simplified Brinson constitutive model and cosine phase transformation kinetics are utilized to simulate the behavior of the SMA materials and calculate the recovery stress. In order to predict the behavior of the smart laminated beam, Euler–Bernoulli beam theory and nonlinear von-Kármán strain field are employed. Two types of micromechanical models, namely Voigt and Reuss models are considered. The Galerkin procedure together with the elliptic function and multi timescales method is adopted to obtain analytical solutions for the nonlinear free vibration and primary/secondary response phenomena. Numerical results reveal that some of the geometrical and physical parameters such as the SMA volume fraction, the amount of prestrain in the SMA fiber, orientation of composite fiber, vibration amplitude and temperature are important factors affecting the free vibration characteristic in the pre/post-buckled region, and primary and secondary resonance of the laminated beams reinforced with SMA fibers. The analytical solutions and results are reported for the first time and can serve as benchmark for researchers to validate their numerical and analytical methods in the future.

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The present paper deals with the nonlinear thermal instability of geometrically imperfect sandwic... more The present paper deals with the nonlinear thermal instability of geometrically imperfect sandwich cylindrical shells under uniform heating. The sandwich shells are made of a shape memory alloy (SMA)-fiber-reinforced composite and functionally graded (FG) face sheets (FG/ SMA/FG). The Brinson phenomenological model is used to express the constitutive characteristics of SMA fibers. The governing equations are established within the framework of the third-order shear deformation shell theory by taking into account the von Karman geometrical nonlinearity and initial imperfection. The material properties of constituents are assumed to be temperature dependent. The Galerkin technique is utilized to derive expressions of the bifurcation points and bifurcation paths of the sandwich cylindrical shells. Using the developed closed-form solutions, extensive numerical results are presented to provide an insight into the influence of the SMA fiber volume fraction, SMA pre-strain, core thickness, non-homogeneity index, geometrical imperfection, geometry parameters of sandwich shells and temperature dependency of materials on the stability of shells. The results reveal that proper application of SMA fibers postpones the thermal bifurcation point and dramatically decreases thermal post-buckling deflection. Moreover, the induced tensile recovery stress of SMA fibers could also stabilize the geometrically imperfect shells during the inverse martensite phase transformation.

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Journal of Engineering Mechanics, 1996

ABSTRACT A closed-form approximate solution is obtained for the bending of a rectangular Reissner... more ABSTRACT A closed-form approximate solution is obtained for the bending of a rectangular Reissner plate with clamped edges. The governing equations are written in terms of displacement and rotations that yield a system of three second-order, partial differential equations. The solution procedure is based on the utilization of the extended Kantorovich method (EKM) to convert the governing system of equations into two systems of three second-order, ordinary differential equations. The solution to these equations is accomplished in closed form in every iteration. To show the validity of the analysis, the results are compared with the finite-element solutions.

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Composite Structures, 2010

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Applied Composite Materials, 2010

The Dynamic Relaxation (DR) technique together with finite difference discritization is used to s... more The Dynamic Relaxation (DR) technique together with finite difference discritization is used to study the bending behavior of Mindlin composite plate including geometric nonlinearity. The overall behavior of the unidirectional composite is obtained from a three-dimensional (3D) micromechanical model, in any combination of normal and shear loading conditions, based on the assumptions of Simplified Unit Cell Method (SUCM). The composite system consists of nonlinear viscoelastic matrix reinforced by transversely isotropic elastic fibers. A recursive formulation for the hereditary integral of the Schapery viscoelastic constitutive equation in multiaxial stress state is used to model the nonlinear viscoelastic matrix material in the material level. The creep tests data is used for verification of the predicted response of the current approach. Under uniform lateral pressure, the laminated plate deformation with clamped and hinged edged constraints is predicted for various time steps.

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This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights a b s t r a c t In this article, large amplitude vibration and thermal post-buckling of shape memory alloy (SMA) fiber reinforced hybrid composite beams with symmetric and asymmetric lay-up are analytically investigated. To predict the behavior of the smart laminated beam, the EulereBernoulli beam theory and the nonlinear von-Karman strain field are employed. Also, one-dimensional Brinson SMA model is utilized to calculate the recovery stress of SMA fibers in the case of restrained strain. Nonlinear governing equations of motion are derived via the Hamilton principle. Using an analytical approach based on the Galerkin procedure together with the simple harmonic motion assumption, a closed-form solution is obtained for the thermal post-buckling and nonlinear free vibration analysis of SMA fiber reinforced hybrid composite beams. Due to lack of any results on the free vibration and thermal stability of SMA fiber reinforced composite beams, the results obtained from the present solution for laminated composite beams without SMA fiber are compared with counterpart data in the open literature, which validate the present solution. Then, a set of parametric study is carried out to show the influence of SMA volume fraction, amount of prestrain in the SMA fiber, orientation of composite fiber, SMA-reinforced layer thickness to total thickness ratio, location of SMA layer, vibration amplitude, boundary conditions and temperature on the vibration characteristic of the laminated beam reinforced with SMA in the pre-and post-buckled domains.

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Journal of Engineering Mechanics, 1996

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Composite Structures, 2010

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Applied Composite Materials, 2010

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