Bottom Face Sheets Research Articles

English

A composite structure consist of two face sheets made from material such as metal or fibre composite bonded to light weight material called as core. This light weight composite structure used in application of aircrafts, wind turbine blades, marine and also in other industrial sectors. In this composite structure have top and bottom side mild steel face sheets are used and for core material selected glass fiber reinforced polymer (E-glass/epoxy). In this way minimum weight and increasing of strength can be obtained. In this paper analysis of composite structure is done in Ansys work bench and Total deformation and equivalent stress is analyzed. The model of composite structure is generated in CATIA. The rectangular core composite structure results are compared with circular core composite structure and V core composite structure of with same weight and same boundary conditions and loading.

Improved extended high order analysis of sandwich beams with a bilinear core shear behavior

The response of a sandwich panel with bilinear constitutive behavior for shear stress of a core is presented based on a proposed improved extended high order sandwich panel theory. In this theory the face sheets are analyzed based on the first order shear deformation theory that is hitherto not applied in the conventional extended high order sandwich panel theory. Besides, the two-dimensional (2D) elasticity is used for the core. The field equations are derived using the Ritz-based solution which is suitable for any essential boundary condition. In each type of boundary conditions, the effects of plastic shear modulus of the core on transverse shear stress distribution within the core, transverse normal stresses at top and bottom face sheet–core interfaces, displacement components through the thickness of the core, as well as the force and moment resultants and transverse displacements in the face sheets are studied in detail. Also, all results based on the bilinear material assumption of the core are compared with the linear elastic ones. The results reveal that initial plastic regions are created at core edges. Furthermore, the absolute value of shear stresses in the plastic zones based on the bilinear analysis is lower than those obtained from linear elastic one for both types of the boundary conditions. It is seen that, unlike the case of the clamped edges, the plastic regions predicted by bilinear material behavior are much more extensive than ones resulted from elastic material behavior in the simply supported case. Finally, in the case of the linear elastic analysis, the results of the transverse deflections and shear stresses are compared with finite element simulation.

The Failure Behavior of Geometrically Asymmetric Metal Foam Core Sandwich Beams Under Three-Point Bending

The failure behavior of geometrically asymmetric sandwich beams with a metal foam core is analytically and experimentally investigated. New initial failure modes of the asymmetric sandwich beams are observed under three-point bending, i.e., face yield, face wrinkling, core shear A, core shear AB, core shear A-AB, and indentation. It is shown that the initial failure modes of sandwich beams depend on the span of the beam, the thicknesses of top and bottom face sheets, core height and material properties. We derived the analytical formulae for the initial failure loads and then constructed the initial failure mechanism maps for the geometrically asymmetric sandwich beams. It is shown that the analytically predicted initial failure mechanism maps are in good agreement with the experimental results, which are clearly different from the symmetric sandwich beams. As a preliminary application, the minimum weight designs are presented for asymmetric metal sandwich beams.

Damage behavior of potting materials in sandwich composites with pinned joints

Abstract The damage behavior of the potting materials around a pinhole, being used in the mechanical joints of sandwich composites, is investigated experimentally. The sandwich composite panels used in the tests were manufactured by the vacuum-assisted resin infusion technique. Each of the top and bottom face sheets of the panels consisted of two woven E-glass/epoxy layers. As the core material, PVC foam (AIREX® C70.55) was used. The potting material consists of an epoxy resin and hardener system mixed with short E-glass fibers (4 wt%). The diameter of the potting material D and the edge distance to the center of pinhole E were considered as the two main varied dimensions. They were chosen as D=10, 12, 15, and 18 mm and E=15, 20, and 25 mm. The damage mechanisms of the potting material and sandwich sections are presented by using load-displacement variations and images of the damaged samples, subjected to in-plane pin loading.

Experimental study on the compression properties and failure mechanism of 3D integrated woven spacer composites

The compressive experiments on the 3D integrated woven spacer composites with different core heights are performed in the flat and warp direction. Macro-fracture morphology and SEM micrographs have been examined to understand the deformation and failure mechanism. The results show that the core height is an important parameter to influence the compressive properties and failure mechanism. For flat compression, the compressive properties decrease with the core height and load–displacement curves exhibit elastic, plasticity plateau and densification stages. For high core height, yet more than one peak load appears. For warp compression, the compressive properties increase greatly with the core height and the curves only have obvious elastic stage. Meanwhile, the failure mechanism is significantly different under the flat and warp compression. For flat compression, core fiber bundles dominate the failure and three typical failure mechanisms have been obtained for different core heights. For warp compression, it is the face sheet rupture and dislocation between the top and bottom face sheets that dominate the failure of the composites.

Analytical stress analysis of annular FGM sandwich plates with non-uniform shear and normal tractions, employing a zigzag-elasticity plate theory

Present paper is devoted to stress and deformation analysis of functionally graded annular sandwich plates subjected to non-uniform normal and/or shear tractions. In spite of its wide applications, analytical stress analysis of plates under shear or combinations of normal and shear tractions has not been performed so far, especially for the sandwich plates. Furthermore, it is the first time that a power solution is developed for the annular functionally graded sandwich plates. The governing equations are derived based on principle of minimum potential energy and a double superposition zigzag theory. The transverse shear stresses are determined based on the three-dimensional theory of elasticity. The resulting governing equations may cover symmetric and asymmetric layups, various boundary conditions, and arbitrary non-uniform tractions on the top and bottom face sheets. The obtained results are verified by comparing them with results of the three-dimensional theory of elasticity. While the present approach is accurate, it is computationally more economic than the three-dimensional elasticity approach. Finally, a parametric study including evaluating effects of various parameters on the stress and displacement distributions of the annular sandwich FGM plates is accomplished.

Shear fatigue characterization of fire resistant syntactic foam core sandwich beam

Eco-Core is syntactic foam made by high volume percent of flyash and a small amount of phenolic resin. Because of very low volatile content in the mixture, it has demonstrated to be a fire resistant material for composite sandwich structural applications. Its superior mechanical and fire safety properties were established previously. Its fatigue performance under compression, shear and flexure loading are being investigated. Objective of this paper is to establish shear stress–life relationship and failure modes of sandwich beams. The Eco-Core sandwich specimens made of FGI 1854 glass/vinyl ester face sheet were designed to fail in core shear and were tested by shear fatigue loading at a frequency of 2 Hz and load ratio of R = 0.1. The Eco-Core density was about 0.5 g/cm3. The fatigue test was conducted at maximum shear stress ( τmax) values of 0.7 τc to 0.9 τc using four-point bend load specimen, where τc is the static shear strength of the core. Shear fatigue failure of the core material was found to be three types: shear crack on-set, crack propagation and ultimate shear failure (represented by shear crack linking to top and bottom face sheets and finally interface delamination). These failures were found to be represented by 2, 5 and 7% change in compliance. The fatigue stress–life (S–N) relationship was found to follow the power law equation, τmax/ τc = AoNα. Constants of the equation were established for all three modes of failure. Based on 1 million cycles limit, the endurance limit was determined to be 0.66 τc, 0.68 τc and 0.69 τc, respectively, for damage onset, propagation and ultimate failure. The typical shear fatigue failure was a 45° crack in the core, followed by crack propagation to face sheet and finally interfacial delamination between face sheet and core.

Energy-Release Rate and Mode Mixity of Face/Core Debonds in Sandwich Beams

Closed-form algebraic expressions for the energy-release rate and the mode mixity are obtained for a debonded sandwich (trimaterial). The most general case of an “asymmetric” sandwich is considered (i.e., the bottom face sheet not necessarily of the same material or thickness as the top face sheet). The energy-release rate is obtained by use of the J-integral, and the expression is derived in terms of the forces and moments at the debond section. Regarding the mode mixity, a closed-form expression is derived in terms of the geometry, material, and applied loading, and it is proven that, in the trimaterial case, just as in the bimaterial case, the mode mixity can be obtained in terms of a single scalar quantity , which is independent of loading; the value for a particular geometry and material can be extracted from a numerical solution for one loading combination. Thus, this analysis extends the existing formulas in the literature, which are for either a delamination in a homogeneous composite or an interface crack in a bimaterial. These new “trimaterial with a crack” formulas are also proven to yield the formulas for the limits of a bimaterial or for a homogeneous section with a crack.

Dynamic response of clamped sandwich beam with aluminium alloy foam core subjected to impact loading

The dynamic response of clamped sandwich beam with aluminium alloy open-cell foam core subjected to impact loading is investigated in the paper. The face sheet and the core of the sandwich beam have the different thickness. And the sandwich beam is impacted by a steel projectile in the mid-span. The impact force is recorded by using accelerometer. The results show that tensile crack and core shear are the dominant failure modes. And the impact velocity and the thickness of the face sheet and the foam core have a significant influence on the failure modes and the impact forces. Combining with the inertia effect and experimental results, the failure mechanisms of the sandwich beams are discussed. The thickness of the foam core plays an important role in the failure mechanism of the sandwich beam. In present paper, the failure of the sandwich beam with a thin core is dominated by the bending moment, while the sandwich beam with a thick core fails by bending deformation in the front face sheet and the bottom face sheet in opposite direction due to the plastic hinges in the front face sheet.

Lightweight damping of composite sandwich beams: Experimental analysis

The purpose of this article is to experimentally study the damping of composite sandwich beams with lightweight honeycomb core. The top and bottom facesheets are made of carbon/epoxy layers with partial interleaved viscoelastic layers. A new damping approach consisting of selectively targeting the inflection points of the bending mode shapes is proposed. At the nodes, the shearing deformation in the beam is maximal, and so is the strain in the viscoelastic layers. The experimental investigation of damping is made by means of standard impact tests using an instrumented hammer performed on beam specimens. The nodes are determined experimentally by moving a small accelerometer along the beam axis and by measuring the amplitude of the acceleration at each point. This novel damping approach keeps the damping ratio as high as the ratio obtained with standard (full coverage) surface damping treatment while reducing the added mass by almost 50%. A comparison of the results obtained in this study with experimental and numerical results found in the literature leads to the conclusion that the most efficient way of damping this type of sandwich structure is to modify and/or improve the viscoelastic properties of the core.

The Development of a Multi-Functional Composite Embedded Smart-Skin Antenna Structure

This paper focuses on the research and development of the “Multi-functional Composite Embedded Smart-Skin Antenna (MECSSA) Structure” with load-bearing, shape maintaining and communication capabilities. MECSSA structure consists of top and bottom composite thin facesheet, honeycomb core, 4 by 8 micro-strip antenna arrays located among honeycomb core and some adhesive. Simulation and experiment methods were used to study the performance of MECSSA structure. Through the study we found that adhesive is the significant factor of affecting the electrical performance of MECSSA structure, especially for radio frequency (RF) and it must take into account in the research. There may be two ways to avoid the influence of adhesive: compensation and separation. Three point bending test indicated that the strength of MECSSA structure satisfies design requirements.

Finite element buckling analysis of laminated composite sandwich panels with transversely flexible core containing a face/core debond

In this article, a new three-dimensional finite element modeling approach with less computing time and space is introduced to study the buckling behavior of sandwich panels, containing a face–core debond. The finite element model presented in this study relates the motion of the face sheets to the core through constraint equations utilizing the concept of slave and master nodes, thus representing a more realistic model of the sandwich panel. The composite face sheets are modeled with shell elements, and the core is modeled using the 3D structural solid elements capable of taking transverse flexibility into consideration. In order to model the debond, the constraints between the nodes of the face sheet and the core are removed and replaced with contact elements in the debonded region to avoid interpenetration. The model is validated through comparison with experimental results reported in the literature. The validated model is then used to study the effects of the size, shape, aspect ratio of the debond, as well as fiber orientation of the face sheets and the influence of core stiffness on the buckling load of the panel subject to different boundary conditions on the top and bottom face sheets of the panel.

On the impact response of sandwich composites with cores of balsa wood and PVC foam

Abstract This paper presents an experimental investigation on impact response of sandwich composite panels with PVC foam core and balsa wood core. A number of tests were performed under various impact energies. Damage process of the sandwich composites is analyzed from cross-examining load–deflection curves, energy profile diagrams and the damaged specimens. The primary damage modes observed are; fiber fractures at upper and lower skins, delaminations between adjacent glass–epoxy layers, core shear fractures, and face/core debonding. After visual inspection of the top and bottom face-sheets, initial examination, damage mechanisms at the interior layers and cores were ascertained through destructive analysis, i.e. sectioning by an abrasive water-jet machine, of samples. In addition to the single impacts, repeated impact response of the samples is also investigated.

Development of a New Finite Element for the Analysis of Sandwich Beams with Soft Core

A new super convergent sandwich beam finite element formulation is presented in this article. This element is a two-nodded, six degrees of freedom (dof) per node (3 dof u0, w, φ for top and bottom face sheets each), which assumes that all the axial and flexural loads are taken by face sheets, while the core takes only the shear loads. The beam element is formulated based on first-order shear deformation theory for the face sheets and the core displacements are assumed to vary linearly across the thickness. A number of numerical experiments involving static, free vibration, and wave propagation analysis examples are solved with an aim to show the super convergent property of the formulated element. The examples presented in this article consider both metallic and composite face sheets. The formulated element is verified in most cases with the results available in the published literature.

Quasi-static indentation tests on aluminium foam sandwich panels

Abstract Mechanical response and energy absorption of aluminium foam sandwich panels subjected to quasi-static indentation loads were investigated experimentally. These sandwich panels consisted of two aluminium face-sheets and a closed cell aluminium foam core (ALPORAS®). Quasi-static indentation tests were conducted using an MTS universal testing machine, with sandwich panels either simply supported or fully fixed. Force–displacement curves were recorded and the total energy absorbed by sandwich panels was calculated accordingly. Videos and photographs were taken to capture the deformation of top face-sheets, foam cores and bottom face-sheets. Effects of face-sheet thickness, core thickness, boundary conditions, adhesive and surface condition of face-sheets on the mechanical response and energy absorption of sandwich panels were discussed.

Free Vibration Analysis of Sandwich Plates with a Uniformly Distributed Attached Mass, Flexible Core, and Different Boundary Conditions

The free vibration analysis of rectangular sandwich plates with a flexible core both with and without a uniformly distributed attached mass on the top facesheet is carried out using the finite element method (FEM) through ANSYS parametric design language, which is validated by several literatures through some numerical examples. The model uses the 8-node shell 99 element to model the composite laminates of the top and bottom facesheets of the sandwich plate and 20-node high-order solid 95 element in order to model the flexible PVC core. The validated finite element model is then used to study the parametric effects of geometry such as aspect ratio, length-to-thickness ratio, core thickness-to-plate thickness ratio, the size and the stiffness of the attached mass on the natural frequencies of the sandwich plate as well as the normal and shear stresses. The use of FEM also allows studying the effect of different boundary conditions for both the top and the bottom facesheets of sandwich plates with or without distributed attached mass. Numerical results that hitherto not reported in the literature have been presented in this article. The results presented in this investigation could be useful to acquire a better insight into the behavior of sandwich laminates carrying attached mass for engineering designers of sandwich structures. The results are presented and compared with the latest Numerical results found in literature.

Ultralight X-type lattice sandwich structure (I): Concept, fabrication and experimental characterization

A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density.

Impact and Damage Prediction of Sandwich Beams with Flexible Core Considering Arbitrary Boundary Effects

In this study, a higher-order impact sandwich beam model is presented to simulate the response of a soft-core sandwich beam subjected to a foreign object impact. The effects of asymmetric lay-up of the sandwich and arbitrary boundary conditions are accounted for in the analysis, and the solution is obtained by employing a finite difference method (FDM). A static and free vibration problem of sandwich beams is first solved, and the results are validated by comparing with the numerical finite element predictions of ABAQUS. The validity of the impact response is then examined using the LS-DYNA model. The contact force and deflection history as well as the propagation of axial, shear, and transverse normal stresses in the sandwich beams during the impact are analyzed. The local effect at the boundary and the loading location is captured by the present model, and the influences of boundary conditions (i.e., the top face sheet free and the bottom pin—pin supported versus both the top and bottom face sheets clamped) and the load spreading process on the impact behavior are discussed. The calculated stresses under the foreign object impact are further incorporated with the failure criteria to assess the failure location, time, and mode in the sandwich beams. The damage induced by the impact process is predicted and comprehensively compared with the experimental results. The higher-order impact model of sandwich beams with the FDM provides accurate predictions of the generated stresses and induced damage, and it can be used effectively in design analysis of anti-impact structures made of sandwiches.

Explicit local buckling analysis of rotationally restrained composite plates under uniaxial compression

A variational formulation of the Ritz method is used to establish an eigenvalue problem for the local buckling behavior of composite plates elastically restrained along their four edges (the RRRR plates) and subjected to compression along one axis, and the explicit solution in terms of the rotational restraint stiffness ( k ) is presented. Based on the different boundary and loading conditions, the explicit local buckling solution for the rotationally restrained plates is further simplified to several special cases (e.g., the SSSS, SSCC, CCSS, SSRR, RRSS, CCRR, and RRCC plates) with a combination of simply supported ( S ) , clamped ( C ) , and/or rotationally restrained ( R ) edge conditions. The unique deformation shape function combining the harmonic and polynomial functions is proposed by considering the effect of elastic rotational restraint stiffness ( k ) along the four edges of the orthotropic plate. The explicit local buckling solutions of the RRSS and SSRR cases are validated with the exact transcendental solutions. A parametric study is conducted to evaluate the influences of the rotational restraint stiffness ( k ) and the aspect ratio ( γ ) on the local buckling stress resultants of various rotationally restrained plates. The applicability of the explicit solutions of restrained composite plates is illustrated in the discrete plate analysis of two composite structures: short thin-walled composite columns and honeycomb sandwich cores. The local buckling strength values of plate panels in short FRP box columns and core walls between the top and bottom face sheets of sandwich are predicted, and they are in excellent agreement with the numerical finite element solutions and experimental results. The simplicity of the “explicit” local buckling solution of elastically restrained composite plates facilitates analysis, design, and optimization of composite structures.

Response of In-plane Linearly Prestressed Composite Sandwich Panels with Transversely Flexible Core to Low-velocity Impact

The problem of transverse low-velocity impact on a linearly in-plane prestressed sandwich panel has been considered in this article. The panel may be subjected to initial in-plane biaxial normal and shear stresses along the edges of the panel. Impact is assumed to occur normally over the top or the bottom face-sheets, at arbitrary location. The boundary conditions of the top and the bottom face-sheets are independent. The interaction between the impactor and the panel is modeled with the help of the system having three-degrees-of-freedom (TDOF) consisting of springs-masses-dashpot (SMD) or springs-masses (SM). The effects of initial biaxial stresses and transverse flexibility of the core are considered analytically. In order to determine all components of the displacements, stresses and strains in the face-sheets and the core, a numerical procedure based on improved higher-order sandwich plate theory (IHSAPT) and Galerkin’s method, are employed. The deflections and the corresponding stresses in the panel with higher initial stresses are smaller than those with lower initial stresses. The effects of in-plane initial shear stresses on impact response are slightly greater than that of the other in-plane normal loading states.