فهرست مطالب keramat malekzade fard

Most of composite cylindrical shells always are used under dynamic loads not static loads in working cycle of themes and Application of dynamic loads cause to large deformation and strength reduction. One way to reduce this negative characteristic is to make the fiber metal laminated shells that named FML in abbreviation. Also dynamic loads cause to vibration in structure. In the present study, firstly the fabrication of stiffened-FML cylindrical shell is explained. Then the vibration behavior and natural frequencies of three samples of FML-stiffened cylindrical shells are derived under clamp-free boundary condition. Moreover the vibration behaviors of these shells are investigated using abaqus finite element software and the FEM results are compared with experimental results in order to shows in agreement with each other. Also the effects of various parameters are studied in this article. For this purpose the frequency response of stiffened and unstiffened FML shells are compared with together and the vibration behavior of FML-shell are compared with glass/epoxy composite shell. One of the most innovations of this study is the experimental results that can be used as a benchmark for further study.

The aim of this research work is to investigate the mechanical properties of double layer trapezoid-shape corrugated core sandwich structures under quasi-static loading conditions and to determine the failure mechanisms and energy-absorbing characteristics of the corrugated cores. In this investigation, influence of foam filling technique in double layer trapezoid-shape corrugated core by using lightweight rigid polyurethane foam is investigation. Five types of Aluminum corrugated cores both bare and foam-filled were subjected to unidirectional quasi-static compression. In the following, using numerical simulation by Abaqus software to evaluation the impact parameters, including Specific Energy Absorption (SEA) as discussed testing purposes. the energy absorbing system can be used in the aerospace industry, shipbuilding, automotive, railway industry and elevators to absorb impact energy. The FEM results are compared with Experimental results which reveal a good conformity. FEM and experimental results showed that foam filling technique can significantly increase specific absorbed energy. Finally, appropriate geometric parameters and the best examples of criteria considered with respect to the objectives, are introduced.

One of the most important, most accurate and the best of views to projectile impact and penetration phenomena in the composite target is the models related to energy discussion. In this paper previous works have been studied and it has been tried to verify and complete them. In the experimental study for the accuracy of model a reservoir of glass/epoxy is done under projectile impact and penetration of spherical pellets at different speeds. This model can investigate the ability or inability of projectile exit from the target and predict the remaining energy during passing through the target, by comparison the total energy of projectile with energy absorption mechanism, Also it is estimated the contribution of each mechanism to absorb energy at different speeds by this model. As well as ballistic velocity of projectile is estimated when it impacts to a composite target with good accuracy. This model has considered the most mechanism of energy absorption and it has been tried to add new mechanism of energy absorption; includes energy absorbed from the shift of the top cone under the projectile, energy absorbed by deformation of elastic – plastic primary fiber and energy absorbed from the friction make between the projectile and composite targets; and expresses the best and most accurate model of energy absorption. Finally, the results of this model have been compared with the results of FEM performed by ANSYS module LS.DYNA.

Free vibration characteristics of rectangular composite plate with constrained layer damping and magneto-rheological fluid (MR) core are presented.. Hamilton principal is used to obtain the equation of motion of the sandwich plate. Based on the Navier method, a closed-form solution is presented for free vibration analysis of MR sandwich plate under simply supported boundary conditions. The governing equation of motion is derived on the base of classical lamination theory for the faceplates. Only shear strain energy density of the core is considered. Using displacement continuity conditions at the interface of the layers and core, shear strain of the core is expressed in terms of displacement components of the base and constraint layers. The complex shear modulus of the MR material in the pre-yield region was described by complex modulus approach as a function of magnetic field intensity. The validity of the developed formulation is demonstrated by comparing the results in terms of natural frequencies with those in the available literature. The effects of magnetic field intensity, plate aspect ratio, thicknesses of the MR core, base layer and constrained layer for three different stacking sequences of composite faceplates on the fundamental frequency and loss factor of the first mode are discussed. The results indicate significant effect of physical and geometrical parameters on the natural frequency and loss factor associated with the first mode.

In this study, free vibration and static bending analysis of curved sandwich panel with magneto-rheological (MR) fluid layer in sheets have been studied. Sandwich panel that is studied is double curved with simply support boundary condition and it is under bending load. In order to derive the governing equations of motion, an improved high order sandwich panel theory and Hamilton's principle are used for the first time. After comparing with similar results in the domain of this issue and ensure that the accuracy of the derived equations, the effect of magnetic field on the frequency of the panel has been investigated. The effects of magnetic field intensity and changing the geometric parameters such as aspect ratio, thickness of MR layer, radius of curvature and thickness ratio on the characteristics of vibration and deflection have been studied. In the free vibration analysis section, the obtained results showed that the natural frequency of panel increases by increasing the magnetic field, also increases by increasing the panel aspect ratio, and decreases by increasing the core thickness to panel thickness ratio. Likewise the obtained results showed that the natural frequenciy for the case of double curved panel is more than single curved and flat panel. In the static bending analysis section, obtained results showed that the natural deflection of the panel decreases by increasing the magnetic field, increases by increasing the radiuses of curvatures ratio, and increases by increasing the core thickness to panel thickness ratio. Therefore, by changing these parameters, the natural frequency and deflection of the system, can be changed in the desired range, and also by having a controllable magnetic field in the system, the natural frequency and deflection of the system can be controlled.

A new improved high-order theory is presented to investigate the dynamic behavior of sandwich panels with flexible core. Shear deformation theory is used for the face sheets while the three-dimensional elasticity theory is used for the core. Displacements in the core are assumed as polynomial with unknown coefficients. Inertia forces, moments of inertia and shear deformations in the core and the face sheets are taken into consideration. Unlike the previous improved theory, the in-plane normal and shear stresses in the core are considered. The governing equations and the boundary conditions are derived by Hamilton’s principle. Closed form solution is achieved using the Navier method and solving the eigenvalues. The numerical results of present analysis are compared with the available numerical or theoretical results in the literatures. It indicates that the present new modified theory is more accurate than the other developed theories for sandwich panels. The variations of the non-dimensional natural frequency with respect to the various geometrical and material parameters are investigated.

In this paper, the problem of low-velocity transverse impact on a sandwich panel with functionally graded core has been considered. The interaction between the impactor and the panel is modeled with the help of a system having two-degrees-of-freedom consisting of springs-masses. In order to determine the contact force history, a numerical procedure is employed based on improved higher-order sandwich plate theory. Shear deformation theory is used for the face sheets while three-dimensional elasticity theory is used for the core. For the first time effect of consideration of in-plane shear stress and normal stress in the core is considered. Displacement components in the core are assumed to vary with a polynomial function with unknown coefficients. Results indicate that use of the FG core can reduce deflections and increase maximum of contact forces.