Composite sandwich structures with Grid stiffened core (SSGSC) are one of the new structural configurations applied in advanced industries such as aerospace, that are made of two thin face sheet layers attached to the top and bottom of a Grid stiffened core. Due to the good advantages such as high specific strength, not only in aerospace but also they are used in other engineering applications, such as military industry, ship building, rail transport, oil platform etc. In the present study three composite SSGSC samples made of different material and thiknesses are fabricated with hand lay-up method using a silicon rubber mold and epoxy resin. Also, two metallic samples of the same dimensions as the copmposite ones, including a monolithic and a SSGSC samples made of aluminum are fabricated. In order to study their behavior subjected to the quasi-static transverse loads, the samples undergo three-point bending tests. Results of the practical tests on the composite samples showed that beyond the failure of the face sheets, the Grid stiffened core will tolerate the load, also there are no delamination between the face sheet layers due to good curing process. It was found that changing the fibers of the face sheet from Glass to Carbon with the same thikness, improves strength-to-weight ratio of the SSGSC samples rather than increasing the thickness of the face sheet of the same material.

A composite Grid sandwich panel consists of a core with a composite Grid structure and two faces on both sides of the core. This study investigated low-velocity impact in Grid sandwich panels with Grid cores experimentally and numerically by constructing and performing experimental tests using Abaqus finite element software. In the experimental part, three sandwich panels with Grid cores were made for the low-velocity impact test. In the numerical part, three-dimensional elements were used, and damage was solved via programming in the Fortran language in Abaqus software. The results showed that the use of foam in the core of these structures reduced deflection due to impact despite a slight increase in the final weight of the structures.

In the present study three composite sandwich structures with Grid stiffened core (SSGSC) samples made of different materials and thicknesses are fabricated with hand lay-up method using a silicon rubber mold and epoxy resin. Also, two metallic samples of the same dimensions as the composite ones, including a monolithic and a SSGSC samples made of aluminum are fabricated. In order to study their behavior subjected to the quasi-static transverse loads, the samples undergo three-point bending tests. Results of the practical tests on the composite samples showed that beyond the failure of the face sheets, the Grid stiffened core will tolerate load, also there are no delamination between the face sheet layers due to good curing process. The experimental modal testing is achieved on all the samples. The frequency response, mode shape as well as damping coefficients are obtained from each experiment. Finally, numerical modal analysis is done and the results are compared with the experiments.

In the present study, the buckling behavior of moderately thick spherical sandwich panels with Grid stiffened core and shape-memory wires (SMA) reinforced layer is studied for the first time. The core of the panel is a Grid structure and its cells are tetrahedral, and the outer layers are reinforced by SMA wires with a uniform, one-way distribution. The finite element method is used to perform the simulations. The Brinson model is used for SMA super-elastic behavior definition and fuzzy transformations are applied using the UMAT subroutine in ABAQUS software. The effect of effective geometric and mechanical parameters such as the radius of curvature of the shell, the volume fraction of SMA wires, and their prestressing on the buckling loads of the shell are verified. The results show that SMA wires cause recycled stresses that are applied as a tensile force on the upper layers of the shell. This characteristic increases the stiffness of the shell and leads the buckling load growth. If α,=0. 1, Increasing the volume fraction of SMA wires from 0 to 0. 6% leads to the buckling load growth by 325%. In addition, the buckling load per unit volume of the shell with Grid core and without Grid core is 0. 71 and 0. 79, respectively, which indicates that the presence of Grid core increases the specific buckling load by 11%. This increase, along with the reduction in the weight of the structure, highlights the importance of using sandwich structures with Grid cores.

In this study, the transient dynamic analysis of Grid-stiffened composite conical shells is discussed. The transient dynamic response of the composite conical shell with simply supported boundary conditions under the lateral impact load, which is applied extensively and uniformly on a certain surface, is obtained using the convolution integral and based on the method of addition of modes. The validation of the obtained results has been done with the help of references and ABAQUS finite element software. The effects of various parameters such as fiber angle, geometric ratios, type, etc. have been investigated in forced vibrations. Finally, the effect of reinforcing the conical shell with the help of Grid-stiffened structures has been studied.

Laminated composite conical shells are used as components of aerospace, marine industries and civil engineering structures. In this research free vibration of Grid stiffened composite conical shell with simply support boundary condition is studied. No study has yet been done on vibration analysis of these structures. Smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of shell in order to obtain the equivalent stiffness parameters of the whole structure. The stiffeners are considered as a beam and support shear loads and bending moments in addition to the axial loads. Geodesic path is applied to the stiffeners. Equations were derived using classical shell theory of Donnell type and were solved using energy functional with the Rayleigh-Ritz method. A 3D finite element model was built using ABAQUS software. Results were compared and validated for Grid stiffened structure with ABAQUS software. Comparisons and validations revealed good agreements. The effects of shell geometrical parameters and variations in the cross stiffeners angle on the natural frequencies were investigated. Results given are novel and can be used as a benchmark for further studies.

Rotating cylindrical shells are applied in different industrial applications, such as gas turbine engines, electric motors, rotary kilns and rotor systems. So, it is of great interest to conduct some researches to improve the understanding of vibrational characteristics of rotating cylindrical shells. Grid stiffened laminated composite cylindrical shells are used as components of aerospace, marine industries and civil engineering structures. In this research free vibration of rotating Grid stiffened composite cylindrical shell with various boundary conditions using the Fourier series expansion method is presented. Smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of shell in order to obtain the equivalent stiffness parameters of the whole structure. The stiffeners are considered as a beam and support shear loads and bending moments in addition to the axial loads. Strain displacement relations from Sanders's shell theory are employed in the analysis. Using the Fourier series expansion and Stokes’ transformation, frequency determinant of laminated cylindrical shells is derived.The effects of shell geometrical parameters and changes in the cross stiffeners angle and axial loading on the natural frequencies are investigated. Results given are novel and can be used as a benchmark for further studies.

Protective steel doors are widely used in buildings due to their high resistance against the impact loads. However, its heavy weight has been always considered as a major drawback for these doors. In this paper, a new optimized stiffened impact-protective steel door incorporating sandwich panel with aluminum foam core (OSSA) is examined. This door consists of two face sheets, main and secondary stiffeners, and aluminum foam as the inner core. In order to optimize the door, at first the rigidity and weight functions of the stiffened steel door were extracted. Then an optimal door weighing 42% less than the primary door was obtained. Due to the high energy absorption capacity of the combined foam core and stiffened steel door structure, the use of aluminum foam core in the optimized steel door was proposed. By doing numerical analysis, and depending on the thickness of the face sheet of OSSA, 20 to 32% reduction in the maximum displacement was observed. The results also showed that, with 67% increase in the peak overpressure, OSSA has kept almost the same maximum displacement as that of the steel door without an aluminum foam. In other words, by using aluminum foam core in the optimized stiffened door, the door will resist 67% more impact load.

Nowadays, Grid stiffened composite shells have many applications in aerospace. These structures include an external shell in which some helical and circumferential ribs placed in the inner surface of the shell are being used to reinforce it. Conical shells are one type of these structures that is used in the construction of space projectile body. In this study, buckling behavior of Grid stiffened composite conical shells under axial loading have been investigated. For this purpose, both smeared and finite element methods have been used and effects of external shell winding, helical ribs angle, ribs number and vertex angle of cone parameters on the buckling load of these structures were investigated. In analytical method, stringers by a shell that have equivalent stiffness were smeared. Based on this analysis, the extensional, coupling and bending matrices associated with the stiffeners were determined. Then, by use of Ritz method, buckling load was calculated. Also, in the finite element method, conical shells by use of ANSYS software were modeled and analyzed. In finite element analysis, two kinds of mode shape for these structures were observed. Also, the results from smeared method showed that the structure with ribs of 30 degrees and shell winding angle between 70 to 80 degrees can be a modify case for design.

This study aims to the investigation of the effect of Grid geometry on the modal response and buckling strength of a composite conical lattice structure under static axial loading by Finite Element Method (FEM). For this purpose, four structures with similar geometry have been designed through four Grid structures. Abaqus finite element software has been used for modeling and analyzing the structures. The experimental results of Zamani and Ahmadifar study [1] have been used to validate the results of FEM. Given the results of numerical and experimental analysis, there is an accordance between the results and the FEM efficiency. The results show the contiguous natural frequency of the structures so that their negligible difference is due to the variations of structures’ weight and stiffness. Changing the Grid does not affect the shape of the modes. The isoGrid bears a higher buckling loading than the anisoGrid. Reducing the rib angle is an effective parameter, which increases the buckling loading on the structure. Although peripheral ribs play a role in load bearing, adding their numbers increases the total weight of the structure, therefore, it has no significant effect on increasing the stability of the structure.