Sharif Digital Repository

Structures that change shapes are often called morphing structures. Smart morphing composites refer to the morphing structures that can detect the change in conditions and, through a control mechanism, command the actuators to maintain the stability and/or perform a new task. The present report provides a framework on the eld of smart morphing composite structures. The emphasis on this work is on, particularly, multi-stable composite structures with capability to detect the new conditions and adapt themselves to properly respond to them. Due to cycling nature of applied load on morphing, these structures are vulnerable to failure due to fatigue. A failure control mechanism utilizing a... 

In this research, a new Kirchhoff plate model based on the modified couple stress theory has been utilized to derive the corresponding closed-form expression for the buckling load. Moreover, a numerical mesh-less method, Reproducing Kernel Particle Method (RKPM), in combination with Corrected Collocation Method (CCM) has been employed to model the nano-plate and calculate its buckling load in the framework of the modified couple stress theory. To this end, two kinds of nano-plates have been modeled, the square nano-plates with all edges simply supported 1) in the presence of the nano-void and 2) without the nano-void. It should be noted that the analytical and numerical solutions for the... 

Characterization and simulation of carbon nanotube-reinforced composites at large scale have been a concern of researchers in the past decade. This is due to the computational complication of considering many embedded carbon nanotubes (CNTs). However a simple meshing of organized CNT distribution in the matrix can ease this obstacle. In this study, a finite element approach is employed to investigate the elastodynamic behavior of a wavy CNT-reinforced composite structure. A three dimensional structure with up to 6400 uniformly distributed wavy CNTs is embedded in a polymer matrix. Each wavy nanotube is represented by a set of beam elements. The effect of nanotube waviness and volume fraction... 

This paper investigates the behavior of the Y-shaped bracing system. Because of the special type of eccentricity in this system, the behavior of the frame is strongly dependent on the geometrical changes of the braces. So that even in the elastic region, it shows the geometrically nonlinear behavior. The amount of eccentricity is very effective on the nonlinear behavior of the frame. Also the ratio of cross sections of the bracing members has a very important impact on the expected performance of the frame. The results show that this system tolerates large displacements, and can act like a base isolation system. Firstly, using a two-dimensional accurate modeling related to the geometrical... 

Duringfalling a viscous liquid freely on a surface, the viscous thread bends due to a phenomenon called buckling. The gravity force in this process could be replaced by an electric force in electrospinning process. In the present thesis, we have designed a number of setups in order to investigate the buckling phenomenon in two categories of helical and non-helical buckling by using direct electrospinning process. By making the collector moving, the electrospun fibers show several shapes including coiling, meander, figure of 8 shape, etc. There are three effective forces acting in this process which are viscous force, electric force and inertia. Also there are three distinct regimes defined... 

This study presents the bending analysis of laminated conical panels under transverse compression with various boundary conditions. Equations was derived using first order shear deformation theory (FSDT) and solved using generalized differential quadrature (GDQ) method. Using this method results in the capability of studying any combinations of boundary conditions on four edges of the panel. Results are compared and validated with the results available in the literature. Effect of boundary conditions, panel length, semi-vertex angle and subtended angle on deflection of the panel was investigated.The buckling analysis of cross-ply laminated conical shell panels with simply supported boundary... 

Due to restrictions on connecting beams to columns in steel structures when moment-resisting connections in two perpendicular directions are employed, the use of ordinary wide-flange sections or fabricated boxes becomes impractical. Application of Cruciform sections, especially when fabricated from two split-I sections (IPE sections) seems to be a reasonable solution to this problem. In this study, using Finite Elements Method and a commercial FEM software, the nonlinear behaviour of a number of cruciform columns, already tested by others, were modeled numerically. After reaching results in acceptable agreement with those of the tests, potentially suitable sections for fabrication of... 

Since previous models can not give a complete description for electrospinning electrical instability, using polymer solutions with diifferent properties, the aim of the existing thesis is to propose a new model that covers a range of materials from non-conducting to conducting and from viscous to elastic and also the initial jet’s tension. In addition, since the previous models have used large wave length approxiamtions, using accurate calculations we showed that the new model has better results for small wavelengths of about two times the jet’s radii. To compare the model to experimental results, we designed and made a proper setup to record the electrospinning process for a PEO solution... 

Finding suitable locations for installing conventional concentric bracings such as X and V, without interfering with building architecture and its openings, is a routine challenge in building design. One of the less known forms of concentric bracings which can be used to solve this issue, is the y-shaped bracing composed of three braces. In the current thesis, results of analytical studies, computer modeling and experimental tests are presented to extend the knowledge of structural behavior of y-bracings. As the first step, effective buckling lengths of braces with rigid connections were found from equilibrium equations incorporating the effect of axial force on rotational stiffness of... 

In the present study, buckling and free vibration of two joined conical shells made from isotropic and generally laminated composites are presented. The joined conical shells can be considered as the general case that can be used in analysis of single cylindrical and conical shells, joined cylindrical-conical shells, joined cylinder-plates or cone-plates, cylindrical and conical shells with stepped thicknesses, annular plates, laminates with ply drop-off or any case that the stiffness of the laminate changes in the shell. Governing equations are obtained using thin-walled shallow shell theory of Donnell type and Hamilton’s principle. The joining of shells is exerted using various methods and... 

In this thesis, buckling of truncated conical shells made of composite laminates with general lamination sequence is investigated. The conical shell is considered under axial compression with simply supported or clamped boundary condition. First, Donnel type nonlinear equations and boundary conditions for doubly curved shells are obtained using Hamilton principle. Second, using adjacent equilibrium criterion, the nonlinear equations was linearized then with defining lame parameters and curvature radius, the linear equations of conical shell was extracted. The power series and Galerkin method was used to solve differential equations. The obtained results are in good agreement with available... 

In the present study, the buckling of conical sandwich panel with composite faces and flexible core is investigated. At first, the nonlinear differential equations based on Donnell and Novozhilov theories with relevant boundary conditions for conical shells are derived using energy method and Hamilton principle. In the following, by applying adjacent-equilibrium criterion, the equations are linearized and the equations of conical shell are obtained. Then, the results obtained from these theories are compared, and based on the benefits and application domain of the theories, Novozhilov theory is selected to model composite faces of the sandwich panel. High-order sandwich theory is used for... 

In the present study, the buckling of generally laminated truncated conical shells having thickness variation expressed by a linear function, subjected to axial compression with simply or clamped supports has been considered. To begin with, the fundamental relations for a conical shell with variable thickness have been derived applying thin-walled shallow shell theory of Donnell-type and theorem of minimum potential energy; non-linear terms of Donnell equations by the help of adjacent-equilibrium criterion are linearized. Governing equations are solved using power series method and are applicable for all combinations of classical boundary conditions. The results are validated with Galerkin... 

In this dissertation, elasto-plastic analysis of deformation, buckling and stability of sandwich cylindrical shell panel with orthotropic core under axial compression and lateral uniform pressure is perfomed. A new study on behavior of sandwich cylindrical shell panels under elasto-plastic deformation is done. In contrast of available analyses in which the core layer assumed to be isotropic and elastic, present analysis includes the sandwich shell having orthotropic elasto-plastic core. The deformation analysis of sandwich shell is performed based on two different theories; one is adopted for sandwiches having a stiff core and the other is proper for sandwiches having a flexible core. Based... 

One of the methods of forming the metal parts is to apply a localized strain field to the workpiece. This field can be generated by creating a deformation in an actuator connected to the workpiece, or directly by a localized imposing heat (thermal localized strain) to the workpiece. For example in laser forming process, the workpieces in the forms of sheet and tube can be deformed by creating localized strain field induced from thermal field caused by laser irradiation. The main mechanisms in laser forming are temperature gradient mechanism, upsetting mechanism and buckling mechanism. It is worth mentioning that until now, the localized strain field induced by laser irrediation is... 

The purpose of this thesis parametric study the natural frequencies and the criti-cal buckling multilayer composites truncated cone with the effect of lateral shear deformation. For this purpose five-bending tensile deformation equation of motion of the truncated cone shell in a suitable coordinate system have been studied. Then solve the five-coordinate movement for power series-are consid-ered. The natural frequencies and critical buckling force for the various truncat-ed cones with four different boundary conditions are calculated and the results with the results of similar conical shells with the same boundary conditions, tak-ing into account the effect of lateral shear deformation and... 

Placement of control and bracing systems in a structure is one of the most important factors affecting the effectiveness of the system in reducing responses to earthquakes. In other words, a control system with a proven effectiveness in earthquake does not reduce the structure responses unless used with proper placement. The performance of Ribbed Bracing System (RBS) in enhancing seismic response of structures, especially in preventing the buckling of bracing under compression and removing residual displacements, is approved by analytical and experimental studies, but optimal placement of such systems in structures has not been studied yet. Hence, in this research the optimal placement... 

The aim of this project is buckling and post-buckling analysis of laminated composite circular cylindrical shells under external pressure on the basis of different shell theories. Based on Donnell, Love, and Sanders nonlinear shell theories within the first-order shear deformation model and von Karman geometric nonlinearity, the potential energy of composite circular cylindrical shells under external pressure with simply supported edges is extracted and by minimizing of the total potential energy and implementing the Ritz method, buckling pressure, the nonlinear post-buckling analysis and the curves of static equilibrium paths are presented. Furthermore, the effect of the external energy due... 

In order to enhance the behavior of structures during an earthquake, various system have been proposed and used in recent years. The main purpose of these systems is to provide enough deuctility to dissipate the input energy of the earthquake. Buckling restrained braces are used extensively in seismic-restraint structures due to their sutiable cyclic behavior. They consist of a core energy dissipation and external restraining component. The purpose of this study is to improve the behavior of BRBs using FRP strips as a restraining component. In this study ABAQUS is used to model analyze the structure. Concrete Damage Plasticity (CPD) is used to model concrete, Hashin model used for FRP strips... 

The thesis addresses the buckling and post-buckling analysis of an elastic conical shell under non-uniform axial loading using finite element method. Non-uniform axial load is applied to one end of the truncated cone in the form of two equal-length loaded zones, diametrically opposite to each other. Material used in this thesis is isotropic with linear elasticity. The results are presented for different boundary condition. The results show that the buckling strength obtained by nonlinear analysis may be upto 40% less than the buckling strength obtained by linear analysis. The effects of boundary conditions and geometry on the results has been investigated