Aerospace structures are highly vulnerable to impact loads whose damage tolerance, and its resistance vary over the range of impact velocity. Honeycomb sandwich structures are used in aerospace industries where mass efficient and impact resistant structures are needed. However, the structural integrity of these structures is reduced by impact load due to tool drop, runway debris, hailstones and improper handling of the structure. A thorough investigation of the damage behaviour of honeycomb sandwich under low-velocity impact and the post-impact residual strength determination is required to design a crashworthy lightweight structure. This paper presents the experimental evaluation of specific energy absorption using Charpy impact, residual compressive strength by compression after impact and damage evaluation of honeycomb sandwich structures having COMPOSITE FACE SHEETS. Parametric studies on COMPOSITEs and honeycombs are carried out by varying the cell size, cell thickness, core height, impact velocity, thickness and orientation of lamina. Densely packed thick honeycombs provide higher fracture energy. Under transverse compressive loading, the honeycomb core undergoes cell wall buckling, crushing and densification. Load-displacement history under in-plane compression and compression after impact for different impact energies is observed. The present study contributes for the understanding how various parameters affect the characteristics of FACE sheet indentation and plastic buckling of honeycomb sandwich structures with COMPOSITE FACE SHEETS, thereby providing useful guidelines for its potential applications in impact engineering.

The bending behavior of COMPOSITEs sandwich plates with multi-layered laminated FACE SHEETS has been investigated, using a new four-nodded rectangular finite element formulation based on a layer-wise theory. Both, first order and higher-order shear deformation, theories are used in order to model the FACE SHEETS and the core, respectively. Unlike any other layer-wise theory, the number of degrees of freedom in this present model is independent of the number of layers. The compatibility conditions as well as the displacement continuity at the interFACE ‘FACE SHEETS–core’ are satisfied. In the proposed model, the three translation components are common for the all sandwich layers, and are located at the mid-plane of the sandwich plate. The obtained results show that the developed model is able to give accurate transverse shear stresses directly from the constitutive equations. Moreover, a parametric study was also conducted to investigate the effect of certain characteristic parameters (core thickness to total thickness ratio, side-to-thickness ratio, boundary conditions, plate aspect ratio, core-to-FACE sheet anisotropy ratio, core shear modulus to the flexural modulus ratio and degree of orthotropy of the FACE sheet) on the transverse displacement variation. The numerical results obtained by our model are compared favorably with those obtained via analytical solution and numerical/experimental, results obtained by other models. The results obtained from this investigation will be useful for a more comprehensive understanding of the behavior of sandwich laminates.

In this article, bending, buckling, and free vibration of viscoelastic sandwich plate with carbon nanotubes reinforced COMPOSITE FACESHEETS and an isotropic homogeneous core on viscoelastic foundation are presented using a new first order shear deformation theory. According to this theory, the number of unknown’ s parameters and governing equations are reduced and also the using of shear correction factor is not necessary because the transverse shear stresses are directly computed from the transverse shear forces by using equilibrium equations. The governing equations obtained using Hamilton’ s principle is solved for a rectangular viscoelastic sandwich plate. The effects of the main parameters on the vibration characteristics of the viscoelastic sandwich plates are also elucidated. The results show that the frequency significantly decreases with using foundation and increasing the viscoelastic structural damping coefficient as well as the damping coefficient of materials and foundation.

In this paper, an analytical solution for the static indentation and low velocity impact response of COMPOSITE sandwich beams with an orthotropic symmetric COMPOSITE FACE-SHEETS and foam or honeycomb core is presented. The indentation force during impact loading consists of two regimes, one for small indentations of the top FACE-sheet due to bending moments and the other for larger deformation due to membrane forces. Also, the crushable core is considered a rigid-plastic foundation, and the elastic aspect is neglected. To obtain a more accurate approximation of the static indentation of the beam, both the local and global deformation of the sandwich beam are considered. The minimum potential energy method is applied for the extraction of governing equations. Furthermore, by developing a three dimensional finite element model through the ABAQUS code, the low velocity impact on COMPOSITE sandwich beams with foam core is simulated. The contact force history, maximum contact force, and upper FACE-sheet displacement results computed by the analytical model are compared with experimental and ABAQUS simulations. A good agreement between the analytical model, finite element simulation, and experimental results, is observed.

The main aim of this paper is to investigate bending behavior in sandwich plates with functionally graded carbon nanotube reinforced COMPOSITE (FG-CNTRC) FACE SHEETS with considering the effects of carbon nanotube (CNT) aggregation. The sandwich plates are assumed resting on Winkler-Pasternak elastic foundation and a mesh-free method based on first order shear deformation theory (FSDT) is developed to analyze the deflection of sandwich plates. In the FACE SHEETS, volume fraction of CNTs and their clusters are considered to be changed along the thickness. To estimate the material properties of the nanoCOMPOSITE, Eshelby-Mori-Tanaka approach is applied. In the mesh-free analysis, moving least squares (MLS) shape functions are employed to approximate the displacement field and transformation method is used for imposition of essential boundary conditions. The effects of CNT volume fraction, distribution and degree of aggregation, and also boundary conditions and geometric dimensions are investigated on the bending behavior of the sandwich plates. It is observed that in the same value of cluster volume, FG distribution of clusters leads to less deflection in these structures.