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.

Endplates are one of the most important components of polymer electrolyte membrane (PEM) fuel cell that must apply uniform contact pressure distribution on the membrane electrode assembly (MEA). For this reason, these plates must have good bending rigidity. In this research, the bending behavior of Composite sandwich plates has been investigated numerically To achieve a Composite structure with high bending stiffness for use in the endplates of PEM fuel cells. For this purpose, the bending strength of Composite sandwich panels with grid core was evaluated based on the type of material and relevant standards through numerical simulation. Numerical simulation has been performed in Abaqus software using the finite element method. The effect of different angles of fibers in three different geometries of square, triangular, and diamond grid core for C/Sic and E-Glass Epoxy materials on the bending behavior of Composite sandwich panels were analyzed. The obtained results indicate the better performance of C/Sic materials in the stress test, as well as the more suitable bending behavior of triangular mesh geometry with fiber angles (0-45-90).

The present paper investigates the effects of grid configuration on the buckling and vibration behavior of grid structures. Hence, four similar simply supported plates with equal weights and different grid patterns are considered. Using, bending stiffness matrix, the buckling load and free vibration frequency of the plates are computed. To investigate the effects of the grid orientation on the mechanical behavior, the orientation of the grids is changed in the plates. The Rayleigh–Ritz method is applied to obtain the axial and shear buckling load and free vibration frequencies. The results are compared with an angle-ply laminated Composite plate with similar inplanedimensions and equal weight. The results show, changing the grid pattern and orientation, will affect bending stiffness and consequently, significantly change the buckling and vibration behaviors of the grid plates.

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.

Background and Aim: Composite resin cores with pre-fabricated posts are commonly used to restore endodontically treated teeth. This study compared the sealing ability of core Max II and Clearfil photocore by Panavia F 2.0 cement, with and without adhesive.Materials and Methods: Crowns of sixty recently extracted human second premolar teeth were cut 3 mm above the CEJ. After preparing proximal boxes and finishing root canal therapy, the teeth were randomly divided into four groups of fifteen teeth each. The Dentatus # 2 Long pins with approximately 8 mm length were cemented in canals. In the first two groups, core Max II with adhesive (group 1) and without adhesive (group 2) was applied for cementation. Pins in the other two groups were cemented with Clearfil photocore Composite and Panavia F 2.0 cement with adhesive (group3) and without adhesive (group 4). After 24 hours, specimens were thermally cycled for 500 cycles. Then the teeth were sealed with nail varnish beyond 1 mm of restoration margins and immersed in a 0.5% fuschin solution. Afterwards samples were embedded in epoxy resin, sectioned mesiodistally and observed under 20 x magnifications. The microleakage was recorded as the amount of dye penetration in the route connecting the proximal boxes to the end of the pin. ANOVA and Tukey tests served for statistical analysis.Results: The first (61.57±14.24) and fourth (12.37±13.85) groups had the highest and the lowest value of microleakage, respectively. Using adhesive for both cements reduced microleakage (P<0.05).Conclusion: Panavia cement had less microleakage compared to core Max II. Key words: Dental Leakage - Post and core Technique - Composite Resins.Corresponding Author: Dr. Moosavi H., Assistant Professor, Department of Operative Dentistry, School of Dentistry, Mashhad University of Medical Sciences. Mashhad, Iran.

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.