Sandwich Composite Shells Research Articles

Smart analysis of sandwich foldable cylinders as gymnastic accessories

A novel smart analysis of sandwich composite cylindrical shell is presented in this article. It is assumed that the sandwich shell is manufactured from the graphene origami reinforced copper core between two intelligent layers. The proposed structure in this article can be used as an idealized model for cylinder shapes in gymnastic sport and physical therapy units. The virtual work principle in the piezo elasticity framework and the cylindrical coordinate system is extended to derive governing equations. To arrive at more accurate results, a third order shear deformable model is extended for kinematic relations. The electro elastic responses are explored using the analytical method to seek impact of main parameters of the composite structure such as foldability parameter, graphene content percent, and applied electric potential on the electro elastic strain, deformation and stress results.

Nonlinear poro-thermo-forced vibration in curved sandwich magneto-electro-elastic shells under hygrothermal environment

This research employs a multiple scales perturbation approach to evaluate the nonlinear wave propagation behaviors of a doubly curved sandwich composite piezoelectric shell with a flexible core in a hygrothermal environment. Stress and strain calculations for the flexible core and face sheets are carried out using Reddy's third-order shear deformation theory (TSDT) and third-order polynomial theory, respectively. The study explores the synergistic effects of a multilayered shell, flexible core, and magneto-rheological layer (MR) in revealing the nonlinearity of both in-plane and vertical moment within the core. The Halpin–Tsai model is employed to derive the properties of polymer/carbon nanotube/fiber (PCF) and polymer/graphene platelet/fiber (PGF) three-phase composite shells. The governing equations for the multiscale shell are derived using Hamilton's formulation. The research investigates temperature variations, diverse distribution patterns, curvature ratios, and magnetic fields through numerical analysis, presenting the results graphically and prior research has demonstrated the accuracy of these methods. Notably, these factors exert significant influence on the frequency-amplitude curves of the smart structure.

Weight Optimization of Design Structural Parameters of Sandwich Composite Shells

Weight Optimization of Design Structural Parameters of Sandwich Composite Shells

Nonlinear vibrations of doubly curved composite sandwich shells with FDM additively manufactured flexible honeycomb core

Nonlinear vibrations of doubly curved composite sandwich shells with FDM additively manufactured flexible honeycomb core

Effect of temperature and porosity on free vibration characteristics of a doubly-curved skew laminated sandwich composite structures with 3D printed PLA core

This paper deals with the investigation of the influence of temperature and porosity on the vibration response of the doubly-curved skew laminated sandwich composite (DSLSC) shells. The temperature-reliant properties of the graphite–epoxy face sheet and the 3D printed polylactic acid (PLA) core are considered for the numerical analysis. The coupled thermo-elastic finite element (FE) model is developed using the first-order shear deformation theory (FSDT) to study the influence of uniform temperature rise on the modal behavior of the DSLSC shells. The stiffness generated due to thermal exposure is accounted to introduce the initial stress stiffness matrix. Further, the initial stress stiffness matrix is developed using nonlinear strain–displacement relations, while the mechanical stiffness matrices are characterized using linear strain–displacement relations. A comprehensive parametric study has been performed to appreciate the effect of temperature, geometric restraints, and material constraints of a laminated composite sandwich spherical, hyperbolic, ellipsoidal, cylindrical shells, and flat plates. Series of experiments are performed to understand the influence of temperature on the natural frequency of glass–epoxy laminated composite sandwich plates with 3D printed PLA core. Further exploration is dedicated to comprehending the experimental challenges involved in studying the vibration performance of sandwich structures with 3D printed PLA core in the thermal environment.

Nonlinear buckling analysis of a sandwich composite semi-ellipsoidal shell under hydrostatic pressure: A numerical and experimental investigation

In this study, nonlinear buckling response of composite sandwich semi-ellipsoidal shell subjected to uniform hydrostatic external pressure is investigated numerically and experimentally. The face sheet of the sandwich shell is made up of laminated composite layers and the honeycomb core is considered as reinforced with and without strips. The various honeycomb core configurations with strip reinforcements are employed in the sandwich semi-ellipsoidal shell. The numerical buckling analysis of the sandwich shell is performed using the commercially available software ANSYS®. The geometric nonlinearity and material nonlinearity of the shell structures are included through the arc length method while solving the nonlinear differential equations and identifying the critical pressure of the structure. The efficacy of the numerical modeling and analysis are verified by comparing the critical pressure obtained through the experimental investigations performed on a composite semi-ellipsoidal sandwich shell and results available in the literature. The various parametric investigations are performed on the composite sandwich shell to study the effect of honeycomb configurations, ply orientation of face sheets, aspect ratio and slenderness of the structure, geometric imperfections on the critical pressure. It was seen that the semi-ellipsoidal sandwich shell having double strip reinforcement core yields higher critical pressure among the various configurations of honeycomb cores. However, the semi-ellipsoidal sandwich shell with the single strip reinforcement in between the core having [0°]6s face sheet composite ply configuration yields higher stiffness to weight ratio which leads to the highest critical pressure among the various configurations of sandwich shell.

Universal asymptotic modeling of composite sandwich shells in a dynamic framework

As an extension of the previous work, this paper is concerned with the modeling of composite sandwich shells in a dynamic framework. The variational-asymptotic method is first used to construct an equivalent shell model taking into account inertial and transverse deformation effects, but still providing the zeroth-order approximation. At this time, each layer of the sandwich structure is individually considered as a shell in which all material constitutive constants have the same order. Next, the sandwich shell is regarded as the assembly of three curved layers with mismatched material and geometric properties, whereby an order transition in the transverse deformations occurs. By imposing continuity conditions on the interfaces between layers, a universal model with a three-dimensional recovery relation is systematically derived, allowing the mechanical behaviors of composite sandwich shells to be predicted. Finally, preliminary validations are implemented to demonstrate the capabilities and accuracy of the present approach.

Influence of multi‐walled carbon nanotubes reinforced honeycomb core on vibration and damping responses of carbon fiber composite sandwich shell structures

AbstractIn the present study, vibration and damping characteristics of the multi‐walled carbon nanotubes (MWCNT) reinforced honeycomb embedded sandwich composite shell structures have been investigated numerically using finite element (FE) method. The efficacy of the FE method by deriving the governing equations using higher order theory is verified by comparing the natural frequencies assessed using ABAQUS 3D FE model. The influence of MWCNT reinforcement, support condition, and radius of curvature on the dynamic performance of honeycomb sandwich shell with carbon fiber reinforced polymer (CFRP) composite face sheets are explored. In addition, the optimal ply orientations of the various configurations of CFRP sandwich shells with MWCNT/GFRP honeycomb are identified using the developed FE model coupled with genetic algorithm (GA) to enrich the natural frequencies and loss factors. Further, it can be observed that the reinforcement of MWCNTs in honeycomb core, geometry of shell structure, and optimal ply orientations significantly influences the natural frequencies and loss factors of the sandwich composite shell structures.

Acoustic insulation characteristics of sandwich composite shell systems with double curvature: The effect of nature of viscoelastic core

A viscoelastic model is proposed in this approach to determine the sound transmission loss coefficient of a sandwich shell system with double curvature. The structure is composed of a double-walled composite shell subjected to a viscoelastic core. Investigating the efficient impresses of rotary inertia and shear deformation, vibration equations of both outer and inner shells are extracted within the framework of shear deformation shallow shell theory. Besides, the Zener mathematical model is used for viscoelastic material, which is based on a spring connected in series with a parallel mixture of spring and dashpot. This model presents the dynamic response in the whole frequency domain at which shear modulus and bulk complex modulus are frequency dependent. Since the performed studies on the sound transmission loss of this kind of structures are insignificant, the outcomes of plate models with a viscoelastic core are used to provide a reliable sound transmission loss comparison. The results show that the applied strategy can improve the acoustic characteristics of the system at high frequencies compared to that of a single-layer one with the same mass. This issue is more highlighted while the thickness of the viscoelastic layer enhances, which confirms the positive performance of the viscoelastic materials in this range of frequency, particularly in the resonant frequency. In addition to the curvature effect on acoustic features, the vibration response of the system is configured based on various frequencies and materials.

Effect of carbon nanotubes reinforcement on eigenmodes of multi‐smart core sandwich composite cylindrical shell panels

AbstractThis study investigates the dynamic responses of carbon nanotubes (CNT) reinforced composite sandwich shells with multi magnetorheological elastomer (MRE) core. The CNT reinforced composite skin layers are made by using hand layup technique. An experimental modal test has been carried for with and without CNT reinforced composite cylindrical shells under clamped free condition. The 3D finite element model is verified by comparing the obtained natural frequencies with experimental results. The numerical results indicate that the CNT reinforced composite multi‐MRE cylindrical sandwich shell greatly influences the natural frequencies compared with single‐MRE cylindrical sandwich shell. The effect of many parameters on the natural frequencies of the CNT reinforced composite multi‐MRE cylindrical sandwich shells is also discussed, including the weight percent of CNT, magnetic fields, and support conditions.

The buckling of spherical-cylindrical composite shells by external pressure

Spherical-cylindrical composite shells are widely used in the fields of ocean engineering, and the ultimate bearing capacity is a key indicator for evaluating the structures’ performance. A new approximate analytical model is presented for buckling analysis of spherical-cylindrical honeycomb sandwich shells subjected to uniform external pressure in this paper. The effect of the hemispherical shell on the cylindrical shell is equivalent to elastic support with the stiffness, so the problem is transformed into solving the buckling of a sandwich cylindrical shell with fixed-elastically supported boundary subjected to uniform external pressure. The analytical solutions for the critical buckling pressure are obtained using the generalized Galerkin method by considering the transverse shear strain, and verified by comparison with finite element model. Consequently, the results show good agreements. The formulas not only provide an efficient tool for quick and reliable calculations of the critical buckling pressure of honeycomb sandwich spherical-cylindrical composite shells by external pressure but also apply to spherical-cylindrical composite sandwich shells with other material properties.

Analysis of forced and free vibrations of composite porous core sandwich cylindrical shells and FG-CNTs reinforced face sheets resting on visco-Pasternak foundation under uniform thermal field

The radial basis function and Newmark-beta methods were used to investigate the vibrational behavior of composite sandwich cylindrical shells with porous core and functionally graded carbon nanotube. The porous core material is a kind of open-cell metal foam, whose, depending on the porosity coefficient and the core thickness, mechanical properties vary. The Hamilton principle was used to extract its motion equations. In this cylindrical sandwich shell, temperature variations are uniformly distributed and resting on the visco-Pasternak foundation with different boundary conditions. Parametric studies were presented to investigate the influence of FG porosity, temperature change, visco-Pasternak foundation, volume fraction, geometrical properties, and distribution of carbon nanotubes on natural frequencies and response dynamics of the sandwich composite cylindrical shell. The numerical outcomes express the distribution of CNTs and volume fraction play a pivotal role in the natural rates and dynamic response of the cylindrical sandwich shell. It is also perceived that there is an increase in the cylindrical shell deformation amplitude with an increase in temperature, damping, and core porosity.

Scaling Methodology Applied to Buckling of Sandwich Composite Cylindrical Shells

Studying buckling behavior of large shell structures through full-scale test articles can be complex and expensive. Therefore, reduced-scale structures are often preferred for investigating buckling behavior. However, designing reduced-scale structures that are representative of the full-scale structure can be difficult. An analytical scaling methodology for compression-loaded sandwich composite cylindrical shells based on the nondimensionalization of the buckling equations is presented herein. The methodology was used to develop scaled configurations that show similar buckling responses to the full-scale baseline configuration. Finite element analysis results showed that both a baseline and a scaled configuration buckled similarly, when the nondimensional stiffness, defined as the ratio between the nondimensional load and nondimensional displacement, was matched between the different scale models. Limitations of the methodology are discussed and are believed to be a result of neglecting the flexural anisotropy and the transverse shear compliance. A preliminary material failure assessment for the different scales is also considered.

An Experimental Investigation of Modal Densities of Composite Honeycomb Sandwich Cylindrical Shells

Honeycomb sandwich composite cylindrical shells are widely used in aerospace structures. Experimentally observed modal densities of such shells are not reported. In this work, modal densities of a typical honeycomb sandwich composite cylinder are obtained experimentally by measuring the drive point admittance. The results are in good agreement with those estimated theoretically that incorporated transverse shear deformation. Its limitations at higher frequencies are investigated and the frequency beyond which the estimation is in error is determined. The results provide an example to prove the need for measuring the imaginary part of the driving point admittance and using it in the determination of the modal densities of honeycomb sandwich-type structures. Experiments are carried out with two boundary conditions for the cylinder and the results provide experimental evidence for the fact that the modal densities at high frequencies do not depend on the boundary conditions. At higher frequencies, it is expected that both of the face sheets vibrate independently. This frequency can be approximately estimated as the fundamental bending mode frequency of the wall of the honeycomb core. The modal density determined through the measured driving point admittance will have a sharp reduction at this frequency and this feature can be used in identifying this phenomenon. The experimental results are in very good agreement with the above results.

Numerical analysis of thermal post-buckling strength of laminated skew sandwich composite shell panel structure including stretching effect

The computational post-buckling strength of the tilted sandwich composite shell structure is evaluated in this article. The computational responses are obtained using a mathematical model derived using the higher-order type of polynomial kinematic in association with the through-thickness stretching effect. Also, the sandwich deformation behaviour of the flexible soft-core sandwich structural model is expressed mathematically with the help of a generic nonlinear strain theory i.e. Green-Lagrange type strain-displacement relations. Subsequently, the model includes all of the nonlinear strain terms to account the actual deformation and discretized via displacement type of finite element. Further, the computer code is prepared (MATLAB environment) using the derived higher-order formulation in association with the direct iterative technique for the computation of temperature carrying capacity of the soft-core sandwich within the post-buckled regime. Further, the nonlinear finite element model has been tested to show its accuracy by solving a few numerical experimentations as same as the published example including the consistency behaviour. Lastly, the derived model is utilized to find the temperature load-carrying capacity under the influences of variable factors affecting the soft-core type sandwich structural design in the small (finite) strain and large deformation regime including the effect of tilt angle.

Free vibration analysis of rotating pretwisted composite sandwich conical shells with multiple debonding in hygrothermal environment

This paper presents a finite element based method to study the influence of elevated temperature and moisture absorption on the free vibration behavior of rotating pretwisted sandwich conical shells consisting of two composite face-sheets and a synthetic foam core. The sandwich structure is assumed to contain single or multiple debonding present either in the face-sheets or at the interface between the face-sheets and core. The finite element formulation consists of an eight-noded isoparametric shell element having five degrees of freedom at each node. Lagrange’s equation is employed to derive the governing equation for free vibration analysis at moderate rotational speeds while the multi-point constraint algorithm is used to model the debonding region present in the composite sandwich shells. Numerical results are presented to depict the effects twist angle, thickness ratio of core to face-sheets, rotational speed and single or multiple debonding on the natural frequency of the composite sandwich conical shells at elevated temperature and moisture concentration.

Buckling analysis of composite lattice sandwich shells under uniaxial compression based on the effective analytical equivalent approach

In this paper, a new effective equivalent analytical approach is presented to compute the global buckling of composite lattice sandwich shells under uniaxial compression based on the first-order shear deformation theory (FSDT). The lattice core was transformed into a solid skin, as the middle skin of the sandwich shell by considering the transverse shear strains and the new force and moment effect analysis on the selected unit cell. The equivalent stiffness of the composite lattice sandwich shells is then calculated by superimposing the stiffness contribution of outer, middle and inner skins. Using the FSDT and Rayleigh-Ritz method, the related eigenvalue equations are solved, and the critical buckling load is obtained. Furthermore, a 3D finite element model is built using ABAQUS software for validation. For various test examples with different slenderness ratio, outer/inner thickness and ply stacking sequence, stiffener thickness and the number of unit cells, the efficiency and accuracy of the presented equivalent approach are confirmed by comparing the obtained results with FE and other work results. It is shown that for thick sandwich shells, the use of FSDT for determining their critical buckling load is necessary, more suitable and can give high computational efficiency.

Underwater Dynamic Collapse of Sandwich Composite Structures

An experimental investigation is conducted to study the mechanics of underwater implosion of cylindrical bonded sandwich composite shells. Sandwich structures comprised of concentric carbon-fiber/epoxy shells with PVC foam cores of different densities are imploded in a large-diameter pressure vessel. High-speed photography in conjunction with Digital Image Correlation (DIC) measurements are employed to obtain full-field displacements of the dynamic collapse process. Local dynamic pressure histories are also simultaneously recorded to investigate fluid structure interaction during implosion. Observations of collapse mode, radial displacement and velocity of collapse, interaction between the concentric shells and the foam core and post-buckling failure sequence are made. Increasing foam core shear modulus linearly increases the experimental buckling pressures. Weaker growth of incipient modal deformations are understood to play a pivotal role in obtaining higher critical buckling pressures from bonded sandwich shells than previously studied unbonded sandwich constructions. Three dynamic collapse behaviors as determined by the relative orientation of collapse between the inner and outer shell are observed. Core foam density and imperfections also strongly influence the impulse, energy and pressure pulses released from the implosions.

New hail impact simulation models on composite laminated wing leading edge

PurposeThe risk of hail-impact occurrence that can decrease local strength property must be taken into account in the design of primary airframe structures in aviation, energy and space industries. Because of the high-speed of hail impact in operation, it can affect the load carrying capacity. Testing all impact scenarios onto real structure is expensive and impractical. The purpose of this paper is to present a cost-effective hybrid testing regime including experimental tests and FEM-based simulations for airframe parts that are locally exposed to the impacting hail in flight.Design/methodology/approachTested samples (specimens) are flat panels of laminated and sandwich carbon/epoxy composites that are used in designing lightweight new airframes. The presented numerical simulations provide a cost effective and convenient tool for investigating the hail impact scenarios in the design process. The smoothed particle hydrodynamics (SPH) technique was selected for the simulation of projectiles. The most commonly used shape of projectiles in hail impact tests is the ice ball with a defined diameter. The proposed simulation technique was verified and validated in tests on flat composite panels (specimens).FindingsIntegration of the numerical analyses with high-speed impact tests of hail onto flat laminated and sandwich composite shells has been presented, and a developed simulation model for impact results assessment was obtained.Originality/valueThe tested coupons (specimens) are flat panels as representative of structural design deployed in real aircraft structures. These numerical simulations provide a cost effective and convenient tool for hail impact scenarios in the design process.

An analytical approach for global buckling of composite sandwich cylindrical shells with lattice cores

In this paper, a new analytical approach is developed for global buckling of composite sandwich cylindrical shells with lattice cores under uniaxial compression by using the smeared stiffener method. The stiffness contribution of stiffeners is evaluated through the new force and moment effect analysis of the stiffener network on a general unit cell. In these analyses, outer skin-stiffener and inner skin-stiffener interactions are considered, appropriately. The equivalent stiffness of the composite sandwich cylindrical shells with lattice cores is then computed by superimposing the stiffness contribution of stiffeners, outer and inner skins. The critical buckling load is calculated by Rayleigh–Ritz method. Finally, various test examples with different scales of the structure, outer and inner skins ply stacking sequence, outer and inner skins thicknesses were analyzed and the results were compared with results obtained by finite element methods and other works. The results show that the proposed approach has high prediction accuracy and low computational cost for the global buckling analysis of composite sandwich shells with lattice cores. Also, another advantage of the developed approach is able to prediction of the global buckling load of stiffened composite cylindrical shells with better accuracy. Therefore, the proposed approach is highly attractive for the preliminary design of composite sandwich structures in the aerospace industry.