Circular Sandwich Panels Research Articles

A novel design method of circular sandwich panels with gradient continuous controllable core based on space-filling design and 2D-Voronoi method

In this paper, a novel method based on the space-filling design and 2D Voronoi method was proposed to design the in-plane gradient continuous controllable honeycomb (GCCH) structures. Low-velocity impact tests were carried out using the sandwich panels with GCCH core layers, which were all made of Aluminium alloy material and fabricated with the wire-cut machine. A concise theoretical solution for loading capacity and denting profile was developed and verified. Three-dimensional finite element models were implemented in ABAQUS/Explicit to model sandwich panels.The FE models were validated with experimental results and, subsequently, the simulation results were further extended to study the impact response and energy absorption characteristics. Results show that the method proposed in this work was effective to design multi-cell structures with graded mechanical properties in the radius direction and approximately homogeneous in the circumferential direction by controlling the distribution of the sites. Sandwich panels with GCCH core layers had better energy absorption properties compared with sandwich panels whose core layers were hexagonal honeycomb with similar cell wall lengths.

Natural frequency and bending analysis of heterogeneous polar orthotropic-faced sandwich panels in the existence of in-plane pre-stress

In this paper, the effects of plane pre-stresses on the free vibration and static analyses of circular and annular sandwich panels are examined based on an accurate formulation, as first time. It is assumed that initially pre-stresses consist of in-plane normal (tensile/compressive) and pure bending stresses. New first-order shear deformation theory together with a layerwise approach for sandwich panel is utilized. The sandwich panels are made up of either orthotropic or heterogeneous polar orthotropic materials. Furthermore, piecewise-defined linear local in-plane displacements are adopted based on zigzag theory. The governing partial differential equations are extracted by implementing principle of minimum total potential energy. A unified analytical solution procedure is developed based on power series method for the analysis of heterogeneous initially stressed annular and circular sandwich panels with arbitrary boundary conditions. The transverse shear stress is precisely calculated by considering three-dimensional theory of elasticity. To validate the proposed formulation, the obtained results are compared with those of finite element method. After numerically demonstrating the accuracy of the method, the effects of different geometrical and material parameters, boundary conditions and in-plane pre-stresses on the free vibration and static behavior of circular and annular sandwich panels are investigated.

Investigation on the dynamic response of circular sandwich panels with the bio-inspired gradient core

Abstract A circular bio-inspired in-plane gradient core is designed based on the Royal Water Lily venation structure. The dynamic responses of various clamped circular sandwich panels with the bio-inspired gradient core under blast loadings are investigated using a combined numerical and theoretical approach. Four groups of gradient cores, such as negative, hybrid, non-gradient, and positive cores, are obtained by adjusting cell wall thickness. The classical circular sandwich panel model under blast loading is modified by introducing the in-plane gradient of the core. The blast resistance of the in-plane gradient clamped circular sandwich panels are studied using the modified theoretical model. Simulation results are consistent with the theoretical predictions for clamped circular sandwich panels with various gradient cores. In comparison with other three kinds of gradient sandwich panels, the proposed sandwich panels with negative gradient cores have higher specific energy absorption and lower deflection of the back face sheet. Results show that a reasonable design of the density of the gradient core can effectively improve the mechanical behaviors of the sandwich structure without adding additional mass in the structure. Such results can provide guidance for the in-plane design of sandwich structures.

Nonlinear vibration of Al-Al based high entropy alloy circular sandwich panel

Circular sandwich panels were designed with Aluminium being core material, steel and Al-Al-based high entropy alloy (Al-based HEA) as the surface board materials, respectively. The dynamic response and influence of small changes in thickness and inherent properties (poisson ratio and density) of the sandwich panels are investigated by a three-dimensional finite element modeling. The nonlinear vibration of the sandwich panel changes from steady state to multiple-periods-bifurcation and chaotic vibration state by changing the forced excitation frequency, amplitude and the initial conditions. Compared with Al-steel sandwich panel, Al-based HEA sandwich panel has good stability under high excitation frequency. Our research shows that Al-Al HEA has potential advantages to be a aircraft and aerospace sandwich panel candidate.

An Approximate Solution to the Plastic Indentation of Circular Sandwich Panels

The plastic indentation response of circular sandwich panels loaded by the flat end of a cylinder is investigated employing a velocity field model. Using the principles of virtual velocities and minimum work, an expression for the indenter load in relation to the indenter displacement and displacement field of the deformed face sheet is derived. The analytical solutions obtained are in good agreement with those found by simulations using the ABAQUS code. The radial tensile strain of the deformed face sheet and the ratio of energy absorption rate of the core to that of the face sheet are discussed.

Sound transmission analysis of MR fluid based-circular sandwich panels: Experimental and finite element analysis

Magnetorheological Fluids (MR) have been recently utilized in sandwich panels to provide variable stiffness and damping to effectively control vibrations. In this study, the sound transmission behavior of MR based-sandwich panels is investigated through development of an efficient finite element model. A clamped circular sandwich panel with elastic face sheets and MR Fluid as the core layer has been considered. A finite element model utilizing circular and annular elements has been developed to derive the governing equations of motion in the finite element form. The transverse velocity is then calculated and utilized to obtain the sound radiated from the panel and subsequently the sound transmission loss. In order to validate the simulated results, a test setup including two anechoic spaces and an electro-magnet has been designed and fabricated. The magnetic flux density generated inside the electromagnet is simulated using magneto-static finite element analysis and validated with the measured magnetic flux density using Gaussmeter. The results from magneto-static analysis is used to derive an approximate polynomial function to evaluate the magnetic flux density as a function of the plate’s radius and applied current. The STL and first axisymmetric natural frequency of the MR sandwich panels with aluminum face sheets are simulated and compared with those obtained experimentally. Finally, a parametric study on the effect of applied magnetic field, the thickness of the core layer and the thickness of face sheets on the STL and natural frequency of the adaptive sandwich panel are presented.

Load-Carrying Capacity of Circular Sandwich Plates at Large Deflection

AbstractThe load-carrying capacity of circular sandwich panels under the quasi-static loading applied in the central area is investigated in this paper. The panels consist of two metallic face shee...

Dynamic response of circular metallic sandwich panels under projectile impact

The dynamic response of circular sandwich panels with aluminium honeycomb and corrugated cores under projectile impact was investigated experimentally and numerically. Impulse loaded on the panel was controlled by projectile launching velocity and the deformation process of sandwich panels was recorded by a high-speed camera in the experiments. Typical deformation/failure modes of face-sheets and cores were obtained and analysed. The back face-sheet deflections and strain histories of face-sheets were measured and discussed. A parametric study was conducted by LS-DYNA 3D to analyse the effect of geometrical configuration on energy absorption mechanism and back face-sheet permanent deflection of circular sandwich panels. The results indicated that the impact resistance of the structure was sensitive to geometrical configuration. Increasing face-sheet thickness and core relative density significantly improved sandwich structure impact resistance. Increasing foil thickness improved the panel impact resistance more efficiently than decreasing wall side length. The results have important reference value to guide engineering application of the sandwich structure subjected to impact loading.

Delamination in sandwich panels due to local water slamming loads

We study delamination in a sandwich panel due to transient finite plane strain elastic deformations caused by local water slamming loads and use the boundary element method to analyze motion of water and the finite element method to determine deformations of the panel. The cohesive zone model is used to study delamination initiation and propagation. The fluid is assumed to be incompressible and inviscid, and undergo irrotational motion. A layer-wise third order shear and normal deformable plate/shell theory is employed to simulate deformations of the panel by considering all geometric nonlinearities (i.e., all non-linear terms in strain–displacement relations) and taking the panel material to be St. Venant–Kirchhoff (i.e., the second Piola–Kirchhoff stress tensor is a linear function of the Green–St. Venant strain tensor). The Rayleigh damping is introduced to account for structural damping that reduces oscillations in the pressure acting on the panel/water interface. Results have been computed for water entry of (i) straight and circular sandwich panels made of Hookean materials with and without consideration of delamination failure, and (ii) flat sandwich panels made of the St. Venant–Kirchhoff materials. The face sheets and the core of sandwich panels are made, respectively, of fiber reinforced composites and soft materials. It is found that for the same entry speed (i) the peak pressure for a curved panel is less than that for a straight panel, (ii) the consideration of geometric nonlinearities significantly increases the peak hydrodynamic pressure, (iii) delamination occurs in mode-II, and (iv) the delamination reduces the hydroelastic pressure acting on the panel surface and hence alters deformations of the panel.

An axisymmetric elastic analysis for circular sandwich panels with functionally graded cores

This paper presents an analytical solution in the framework of the elasticity theory, which is useful in describing the elastic bending response of axisymmetric circular sandwich panels with functionally graded material cores and homogeneous face-sheets. The Young’s modulus of the core is assumed to be exponentially dependant on the transverse direction and the Poisson’s ratio as well as uniform and equal to the face-sheets ratio. The elastic solution is obtained using a Plevako representation, which reduces the problem to the search of potential functions satisfying linear fourth-order partial differential equations. We explicitly obtain the analytical solution by writing the potential functions as Fourier Bessel expansions with respect to the radial coordinate. A comparative study of functionally graded versus a homogeneous sandwich core is presented by considering the first term of the expansion as the loading condition. In this way, the solution is written in a closed form and furnishes a benchmark to accurately investigate the agreement with the structural theory results.

On the dynamic response of sandwich panels with different core set-ups subject to global and local blast loads

The recent increase in blast and impact threats has led to an emerging interest in sandwich structures due to their superior performance in such loading environments. The optimised architecture of this class in conjunction with additional benefits of high strength-to-weight and stiffness-to-weight ratios vital to weight-sensitive military applications has led to numerous research works on the topic. In this study, the dynamic response of four circular sandwich panel constructions with different core designs under global and local blast loading conditions has been investigated. Numerical finite element (FE) models have been set up to study the effect of additional core interlayers on blast resistance enhancement of these sandwich panels. The objectives are (1) to assess the existing blast resistance capacity, (2) to increase the dynamic energy absorption, (3) to improve the stress distribution through plastic deformation, and (4) to ensure sacrificial damage to the additional core layers; hence, to avoid the main part of the core being damaged by excessive shear deformation, the dominant failure mode in conventional sandwich panels. A ductile elastomeric layer of polyurea, and a fairly compressible Divinycell-H200 foam layer have been selected as the additional core interlayers, and they have been placed in different arrangements to improve the overall blast resistance of the standard sandwich panel with glass-fibre-reinforced plastic (GFRP) face-sheets, and balsawood core. Dynamic explicit FE analyses were carried out using the commercial package ABAQUS 6.9-1. Comparison of specific kinetic and strain energies shows the effect of additional core layers on the blast energy absorption of a sandwich system. The study shows the improvement in shear failure prevention of the core as a result of the use of additional core layers and a reduction in the level of kinetic and strain energies in the protected core in both absolute and relative terms. The stress contours show a smoother stress distribution in enhanced cases. These conclusions are confirmed and explained by using a qualitative two-degree-of-freedom system with an elastic–viscoplastic spring element representing the integral effects of sacrificial additional core interlayers and a nonlinear spring representing the stiffness of the conventional sandwich system and comparing the results of dynamic analysis with a similar qualitative single-degree-of-freedom model of a conventional sandwich panel.

The influence of core height and face plate thickness on the response of honeycomb sandwich panels subjected to blast loading

This paper reports on an investigation into the behaviour of circular sandwich panels with aluminium honeycomb cores subjected to air blast loading. Explosive tests were performed on sandwich panels consisting of mild steel face plates and aluminium honeycomb cores. The loading was generated by detonating plastic explosives at a pre-determined stand-off distance. Core height and face plate thickness were varied and the results are compared with previous experiments. It was observed that the panels exhibited permanent face plate deflection and tearing, and the honeycomb core exhibited crushing and densification. It was found that increasing the core thickness delayed the onset of core densification and decreased back plate deflection. Increasing the plate thickness was also found to decrease back plate deflection, although the panels then had a substantially higher overall mass.

LOAD-CARRYING CAPACITIES FOR CIRCULAR METAL FOAM CORE SANDWICH PANELS AT LARGE DEFLECTION

This paper is concerned with the load-carrying capacities of a circular sandwich panel with metallic foam core subjected to quasi-static pressure loading. The analysis is performed with a newly developed yield criterion for the sandwich cross section. The large deflection response is estimated by assuming a velocity field, which is defined based on the initial velocity field and the boundary condition. A finite element simulation has been performed to validate the analytical solution for the simply supported cases. Good agreement is found between the theoretical and finite element predictions for the load-deflection response.

Low velocity impact denting of HSSA lightweight sandwich panel

Slow speed impact by a small mass can cause residual denting without perforation of a fibrous core sandwich panel that has thin facesheets. Denting depends on the kinetic energy, compliance and nose shape of the colliding body as well as the compliance and mass density of the sandwich panel. Collision experiments were carried out with fibrous core sandwich panels of different sizes struck by colliding spheres at small velocities. Analytical models based on either quasi-static or dynamic deformation of plates were developed to calculate the impact force during low speed impact on circular sandwich panels. Finite element analysis using ABAQUS was performed to calculate impact damage on sandwich panels. Results of the analytical and numerical models and the experimental measurements were compared. The dependence of damage on both structural parameters and impact variables was investigated.

Modal Frequencies of Circular Sandwich Panels

Axisymmetric and non-axisymmetric modes of vibration of circular sandwich panels are investigated by applying first-order shear theory (Mindlin-Reissner Plate). Solutions are obtained for boundary conditions with free, simply supported, and clamped edges. Numerical finite element method (FEM) simulation using ABAQUS is applied to validate the analytical modeling. Both analytical and numerical calculations are compared with experimental measurements of the first few modes of vibration; the frequency differences are less than 4%.

Dynamic Stability of Circular Cylindrical Sandwich Panels

A theoretical study of the dynamic stability of simply supported sandwich plates and circular cylindrical sandwich panels with dissimilar face-sheets and orthotropic cores is presented. The uniformly distributed periodic edge loads consist of steady components and oscillating components which are impulsive or vary according to an arbitrary piecewise constant law. It was observed that stable regions exist when the steady component of the applied load exceeds the static buckling load. For the particular combination of parameters associated with these regions the oscillating component of the load has a stabilizing effect on the structure. It was further observed that the mathematical structure of the equations governing the dynamic stability of simply supported sandwich plates and circular cylindrical sandwich panels is the same as that for the corresponding simply supported, homogeneous plates and panels, and a complete analogy exists between them.