جستجوی مقالات مرتبط با کلیدواژه "high order theory" در نشریات گروه "مکانیک"

The present study investigated the bending behavior of a curved sandwich beam with flexible core and carbon nanotube reinforced face sheets. Carbon nanotubes are considered as functional graded material in the thickness of the face sheets and their properties change along the thickness of the face sheets. In order to model the behavior of the sandwich beam, the Euler-Bernoulli theory was applied for the face sheets and the quasi 3D elasticity was applied for the core, which allowed us to investigate the flexibility of the core. In this regard also, the compatibility condition between the face sheets and the core is used. The governing differential equations were extracted by using the principle of virtual displacement. In order to verify the accuracy of the formulation and present method, the results were compared with the existing results in this domain and was verified the validity of the extracted and solved equations. Therefore, the effect of different patterns of carbon nanotubes distribution have been investigated and compared on the radial deflection, the tangent displacement, the axial force, and the bending moment in the faces and the radial and shear stresses in the core. Also, the effect of the volume fraction of the carbon nanotubes, the ratio of the core thickness to the faces, and the beam curvature radius and angle have been investigated on results.

In this paper, free and forced vibrations of a cylindrical sandwich shell with orthogonal stiffeners using high-order theory were analyzed. The sandwich structure is consists of two orthotropic composite face sheets and a flexible foam core and longitudinal and environmental stiffeners. The face sheets and core are perfectly glued together and there is no relative displacement between them at the interfaces. To analyze this shell under simply supported boundary conditions, the face sheets’ displacements are based on Kant's third-order theory and in the core, the second Frostig’s model is used. The Rayleigh-Ritz method to solve free vibration and the assumed modes method to analyze forced vibration were used. In the forced vibrations section, sinusoidal loading is applied uniformly and radially to the shell. The vibrations of the stiffened sandwich shell are simulated with Abaqus software. Finally, the effect of various parameters as length to radius ratio, thickness to radius ratio, core thickness to total thickness, structure and material of face sheets and core on the vibration response of the structure has been investigated. To validate, the results of free and forced vibrations obtained from the present analysis were compared with the results of other references and Abaqus software.

In this study, vibration analysis of axial symmetric circular cylindrical shell has been investigated. The high-order theory is used to approximate the transverse displacement in this study. Hence, the transverse displacement based on the Fourier expansion is extended to three terms. Due to the symmetry of the cylindrical shell, only the axial mode has been investigated. The strain and kinetic energies are obtained for the circular cylindrical shell. The Hamiltonian principle was used to derive the equations of motion. The stiffness and mass matrices have been obtained by applying Galerkin method and finite element method. For this purpose, the linear shape function is used for all unknowns. In order to validate the research, comparing the axisymmetric frequencies of the results with previous studies has been used. Finally, the axisymmetric frequencies and axial mode shapes of the circular cylindrical shell for various boundary conditions are given, including simply support-simply support, clamped-clamped, clamped-simply support and clamped-free.

In the fiber metal laminated shell with determination the proper fiber angle orientation is achieved the arrangement with maximum performance. For this purpose in this study the fiber angle orientation of composite layers of the fiber metal laminate circular cylindrical shells are changed frequently and each cases being subjected to lateral load and the tension of all composite layers are calculated for all cases. Then the fiber angle orientation that cause to maximum stiffness based on maximum tension fracture criterion is selected. For this purpose an analytical program linked to the numerical program is used and calculated result. The buckling analysis is applied to determine the performance of design process. The results of buckling analyses show that determination of the optimum fiber angle orientation causes to improvement of the fiber metal laminated shell stability. Comparing the effect of variation of the fiber angle orientation, variation of the metal layer properties and variation of the thickness shell on the buckling load is the another innovation of this study and it is determined that for various amount of metal volume fraction with change in which item the maximum stability is achived.in order to improve the result accuracy high order shear deformation theory is utilized for buckling analysis.

This study dealt with the flutter and biaxial buckling of composite sandwich panels based on a higher order theory. The formulation was based on an enhanced higher order sandwich panel theory that the vertical displacement component of the face sheets were assumed as quadratic one while a cubic pattern was used for the in-plane displacement components of the face sheets and the all displacement components of the core. The transverse normal stress in the face sheets and the in-plane stresses in the core were considered. For the first time, the continuity conditions of the displacements, transverse shear and normal stress at the layer interfaces, as well as the conditions of zero transverse shear stresses on the upper and lower surfaces of the sandwich panel are simultaneously satisfied. The aerodynamic loading was obtained by the first-order piston theory. The equations of motion and boundary conditions were derived via the Hamilton principle. Moreover, effects of some important parameters like lay-up of the face sheets, length to width ratio, length to panel thickness ratio, thickness ratio of the face sheets to panel, fiber angle, elastic modulus ratio and thickness ratio of the face sheets on the stability boundaries were investigated. The results were validated by those published in the literature. The results revealed that by increasing length to width ratio, length to panel thickness ratio and elastic modulus ratio of the face sheets, the stability boundaries were decreased and the largest nondimensional buckling load was occurred at the angle ply sandwich panel.