Showing papers on "Sandwich-structured composite published in 2004"
TL;DR: In this article, a model based on inelastic column theory incorporating strain hardening was able to predict the lattice truss core's compressive peak strength capacity in both the annealed and age hardened conditions, for all relative densities tested.
298 citations
TL;DR: In this article, the three-point bending collapse strength of composite-polymer foam sandwich beams with composite faces and polymer foam cores has been analyzed and an indentation model for elastic faces and an elastic-plastic core has been developed.
253 citations
TL;DR: In this paper, an approach for characterizing the structural performance of all-metallic sandwich panels with truss and prismatic cores is presented and demonstrated for panels with pyramidal truss cores.
243 citations
TL;DR: In this paper, the high velocity impact response of a range of novel aluminium foam sandwich structures has been investigated using a nitrogen gas gun, and it has been shown that these novel systems offer excellent energy absorbing characteristics under high-velocity impact loading conditions.
223 citations
TL;DR: In this paper, a free vibration analysis of sandwich panels with a flexible core based on the high-order sandwich panel theory approach is presented, which is valid for any type of loading scheme, localized as well as distributed, and distinguish between loads applied at the upper or lower face.
193 citations
TL;DR: In this article, multifunctional sandwich panels with corrugated and prismatic diamond cores have been analyzed and their behavior compared with panels designed using truss and honeycomb cores.
167 citations
TL;DR: In this paper, two types of sandwich panels with carbon epoxy skins and aluminium honeycomb core were subjected to low velocity impacts and then the damaged panels tested for their compression-after-impact (CAI) strength.
94 citations
TL;DR: In this paper, a finite element simulation of the core shear response was performed and the results demonstrated robust behavior beyond the limit load, when combined with the constitutive properties of the face sheet material.
Abstract: Metallic sandwich panels with tetrahedral truss cores have been fabricated and their structural performance evaluated. A fabrication technique involving deformation-shaping and brazing has been used. The responses of the structure in core shear and panel bending have been measured. The results demonstrate robust behavior beyond the limit load. A finite element simulation of the core shear response duplicates the features found experimentally. When combined with the constitutive properties of the face sheet material, these shear characteristics have been shown to predict, with good fidelity, the limit load for panels in bending. @DOI: 10.1115/1.1757487#
90 citations
TL;DR: In this article, a parametric study on impact damage resistance and residual strength of carbon fiber sandwich panels with carbon fiber-vinylester faces and PVC foam core is conducted. But the results of the study were limited to two different impactor geometries.
Abstract: A plastic micro buckling approach is investigated in order to see whether it can be used to analytically predict the residual strength of carbon fiber sandwich structures. A parametric study on impact damage resistance and residual strength of sandwich panels with carbon fiber-vinylester faces and PVC foam core is conducted. Two sandwich configurations are studied. The first configuration consists of thin faces and an intermediate density core, representative of a panel from a superstructure. The second configuration consists of thick faces and a high density core, representative of a panel from a hull. Two different impactor geometries are used. One spherical impactor and one pyramid shaped impactor are used in a drop weight rig to inflict low velocity impact damage of different energy levels in the face of the sandwich. The damages achieved ranges from barely visible damages to penetration of one face. Residual strength is tested using in-plane compression of the sandwich plates either instrumented with strain gauges or monitored with digital speckle photography.
87 citations
TL;DR: In this paper, the core material is polyurethane foam made from polymeric isocyanate (Part A) and reacting with polyol (Part B), and spherical nanoparticles such as TiO2 of about 29 nm in diameters were dispersed in Part A of liquid polyurethene through an ultrasonic cavitation process.
Abstract: It is well known that in a sandwich structure, the core plays an important role in enhancing the flexural rigidity and by controlling the failure mechanisms. If the core is made from foam, the strength of the core material and the debond strength at the core–skin interface almost entirely dictate the performance of structural sandwich composites especially under flexure. In this investigation attempts have been made to improve the performance of the sandwich by strengthening the core but partially sacrificing the debond fracture toughness of the sandwich construction. Strengthening of the core has been accomplished by infusing nanoparticles into the parent polymer of the core material when it was in the liquid stage. The core material is polyurethane foam made from polymeric isocyanate (Part A) and reacting with polyol (Part B). Spherical nanoparticles such as TiO2 of about 29 nm in diameters were dispersed in Part A of liquid polyurethane through an ultrasonic cavitation process. The amount of nanoparticles infused into liquid foam varied from 1 to 3% by weight. Once Part A was doped with nanoparticles, it was mixed with Part B, and was cast in a rectangular mold to produce the nanophased polyurethane foam. The nanophased foam was then used with regular S-2 Glass fiber preforms and SC-15 epoxy to manufacture sandwich composites in a VARTM set up. Test coupons were then extracted from foam as well as from sandwich panels to conduct flexural and various other chemical tests. A parallel set of control panels were also made with neat polyurethane core materials. Thermogravimetric and SEM analyses have indicated that the decomposition temperature of the nanophased foams increases by about 27 °C and the cell size almost doubles with nanoparticle infusion. A significant improvement in flexural strength and stiffness has also been observed with 3% loading of TiO2 nanoparticles. Debond fracture toughness parameters (Gc) were also determined for both categories of sandwich constructions, and it was seen that nanoparticle infusion reduces the value of Gc by almost a factor of three. Despite this reduction, strength of nanophased sandwich increased by about 53% over the neat system. Details of manufacturing and analyses of test results are included in the paper.
85 citations
TL;DR: A survey of recent developments and contemporary trends in the modeling of the deformation and buckling behavior of sandwich shells is presented in this paper, where the basic ideas and features of this model are outlined and compared to alternative recent approaches presented by other authors.
Abstract: The area of sandwich construction has been an active field of research for more than five decades. During this period, a large number of mathematical models for structural sandwich panels has been provided, ranging from the early sandwich membrane models to more sophisticated recent approaches. Especially during the past decade, the increasing demand for high-performance, lightweight structures has stimulated a strong trend toward the develoment of refined models for sandwich plates and shells. The main focus of the present paper is a survey of recent developments and contemporary trends in the modeling of the deformation and buckling behavior of sandwich shells. The development of refined sandwich models is illustrated by an approach recently proposed by the authors. The basic ideas and features of this model are outlined and compared to alternative recent approaches presented by other authors.
TL;DR: An efficient 6-noded triangular element based on refined plate theory was developed for analysis of sandwich plates with stiff laminated face sheets and is applied to a free vibration problem in this article.
Abstract: An efficient 6-noded triangular element based on refined plate theory was developed for analysis of sandwich plates with stiff laminated face sheets and is applied to a free vibration problem in this paper. The plate theory represents parabolic through thickness variation of transverse shear stresses with continuity at the layer interfaces, which introduces discontinuity at these interfaces for the shear strains. The authors note that the plate theory requires unknowns at the reference plane only. Moreover, it ensures a shear stress-free condition at the top and bottom surfaces of the plate. Thus, the plate theory has all necessary features for an accurate modeling of laminated sandwich plates. The plate theory suffers from a problem in its finite element implementation since it requires C-sup-1 continuity of transverse displacement at the element interfaces. As very few elements based on this plate theory exist, and these possess certain disadvantages, an attempt has been made to develop this new element. It has been utilized to study some interesting problems of laminated sandwich plate.
TL;DR: In this paper, an exact analytical solution based on the propagator matrix method and a semianalytical solution, based on a higher-order mixed approach (displacement and stress interpolation), has been presented to evaluate the natural frequencies as well as the stress and displacement mode shapes of simply supported, cross-ply laminated and sandwich plates.
Abstract: An exact analytical solution based on the propagator matrix method and a semianalytical solution based on a higher-order mixed approach (displacement and stress interpolation) have been presented in this paper to evaluate the natural frequencies as well as the stress and displacement mode shapes of simply supported, cross-ply laminated and sandwich plates. Continuity of the transverse stresses and displacements has been maintained at the laminae interfaces. Results have been presented for orthotropic plates, symmetric as well as nonsymmetric cross-ply composite and sandwich laminates. Results from the propagator matrix agree well with the published results for frequencies as well as for displacement and stress mode shapes. Furthermore, the frequencies and displacement and stress eigenvectors obtained from the proposed layerwise mixed method are in excellent agreement with those obtained by three-dimensional elasticity theory. Results obtained from the present equivalent single layer theory are in good agreement with those obtained from the displacement based higher order methods. The high accuracy of the present methods is further confirmed by comparing the response of a sandwich plate with significantly different layer properties for which the conventional displacement based formulations yield inaccurate solutions.
TL;DR: In this article, non-crimp fabric (NCF) composite face sheet sandwich panels have been tested in compression after impact (CAI). Damage in the face sheets was characterised by fractography.
Abstract: In the present study, non-crimp fabric (NCF) composite face sheet sandwich panels have been tested in compression after impact (CAI). Damage in the face sheets was characterised by fractography. Co ...
TL;DR: In this paper, the effects of sea-water on foam cored composite sandwich structures under long-term exposure were investigated by means of computational fracture mechanics, and the effects on the fracture behavior of foam materials and on face/core interfacial debonding fracture were investigated experimentally.
Abstract: This article concerns the effects of sea-water on foam cored composite sandwich structures under long-term exposure. Special attention is focused on sea-water induced damage in foam materials, weight gains and expansional strains, as well as on possible degradation in the properties of foam materials due to such extended exposure. In addition, sea-water effects on the fracture behavior of foam materials and on face/core interfacial debonding fracture are investigated experimentally and interpreted by means of computational fracture mechanics.
TL;DR: In this article, the problem of the dynamic response of sandwich flat panels exposed to blast loadings is addressed, and the implications of the explosive charge, stand-off distance, directionality property of face sheets material, damping ratio, geometric nonlinearity, initial geometric imperfection, and of the characteristics of the blast, on dynamic response and dynamic magnification factor are put into evidence via a parametric study, and pertinent conclusions are outlined.
Abstract: The problem of the dynamic response of sandwich flat panels exposed to blast loadings is addressed. The sandwich model includes a number of non-classical effects such as the anisotropy and heterogeneity of face sheets, transverse orthotropy of the core layer, the geometrical non-linearities considered in the von Karman sense, as well as the initial geometric imperfections. As concerns the blast pulses considered in this analysis, these are due to either an underwater/in-air explosion, or are due to a pressure wave traveling across the panel span. Implications of the explosive charge, stand-off distance, directionality property of face sheets material, damping ratio, geometric non-linearity, initial geometric imperfection, and of the characteristics of the blast, on dynamic response and dynamic magnification factor are put into evidence via a parametric study, and pertinent conclusions are outlined.
TL;DR: In this article, a multi-parameter optimization procedure for ultralightweight truss-core sandwich panels is presented, which incorporates objectives from various structural performances of the material system at many loading cases simultaneously.
TL;DR: In this paper, the authors used a Winkler-type elastic foundation to model the core of a sandwich, and formulated an interaction equation that can be used as a criterion of wrinkling under compression in the principal directions.
Abstract: The problem of face wrinkling in sandwich structures was identified as an important failure mode and first analyzed in 1940 by Gough et al. (1), who used a Winkler-type elastic foundation to model the core. This work was followed by experiments and further analysis by many others. Until 1966 all of the research was devoted to uniaxial compression loading. However, in many applications, such as naval and aircraft structures, panels are subjected to biaxial loading. Such loadings were first analyzed by Plantema in 1966 (2) for the case of sandwich constructed of isotropic materials. Sullins et al. (3) suggested an interaction equation that can be used as a criterion of wrinkling under compression in the principal directions. This equation is formulated in terms of the ratios of the principal compressive stresses to the corresponding wrinkling stresses. More recently Fagerberg (4, 5) and Vonach and Rammerstorfer (6) considered the case of sandwich with orthotropic facings. The present work attacks the subject problem using three different models for the core. One model uses a simple Winkler elastic foundation approach. The second model, following Hoff and Mautner (Hoff, N.J. and Mautner, S.E. (1945). The Buckling of Sandwich-Type Panels, Journal of the Aeronautical Sciences, 12: 285-297.), uses a linear model for the decay in deformation from the core-facing interface, while the third model, following Plantema (Plantema, F.J. (1966). Sand- wich Construction, John Wiley & Sons, Inc., New York.), uses an exponential decay.
TL;DR: In this article, the authors used the higher-order theory for sandwich panels (HSAPT), a two-dimensional finite element analysis, and classical sandwich theory to predict the vibration response of a cantilever soft-core sandwich beam.
Abstract: The natural frequencies and corresponding vibration modes of a cantilever sandwich beam with a soft polymer foam core are predicted using the higher-order theory for sandwich panels (HSAPT), a two-dimensional finite element analysis, and classical sandwich theory The predictions of the higher-order theory are shown to be in good agreement with experimental measurements made with a simple experimental setup, as well as with finite element analysis Experimental observations and analytical predictions show that the classical sandwich theory is not capable of accurately predicting the free vibration response of soft-core sandwich beams It is shown that the vibration response of the cantilever soft-core sandwich beam consists of a group of five lower frequency shear (antisymmetric) modes that are followed by a group of four thickness-stretch (symmetric) modes For the higher frequency range, the vibration modes alternate between groups of one-two antisymmetric and symmetric modes For very high frequencies,
TL;DR: The in situ fracture toughness of six core materials was measured using a new test method as discussed by the authors, and the materials tested were seven composite sandwich panels fabricated using vacuum assisted resin transfer (VASTR).
Abstract: The in situ fracture toughness of six core materials was measured using a new test method. The materials tested were seven composite sandwich panels fabricated using vacuum-assisted resin transfer ...
TL;DR: In this article, the authors considered local bending effects induced in the vicinity of inserts in sandwich panels and associated them with an increase of bending stresses in the sandwich faces and normal and shear stresses in sandwich core.
Abstract: The paper considers local bending effects induced in the vicinity of inserts in sandwich panels. Such local bending effects are associated with an increase of bending stresses in the sandwich faces and normal and shear stresses in the sandwich core. An earlier developed analytic model [Proceedings of the Sixth International Conference on Sandwich Structures (ICSS-6) (2002) 551] is adapted for the case of a sandwich panel with circular insert, with elastic properties differing from those of the core. The locally induced stresses in the faces and core due to presence of the insert are expressed via simple analytic relations (and charts) enabling an estimation of these local stresses. Finite element analysis is employed to demonstrate the applicability of the analytic model, and a good correspondence between the numerical and the analytical data is found. A study case related to marine applications, namely a circular insert in a sandwich deck panel used for mounting of a rigging fixture, is considered, and optimization of an existing design is carried out.
TL;DR: In this article, a finite element model that predicts temperature distribution in a composite panel exposed to a heat source, such as fire, is described, where the panel is assumed to be composed of skins consisting of polymer matrix reinforced with fibres and a lightweight core.
Abstract: A finite element model that predicts temperature distribution in a composite panel exposed to a heat source, such as fire, is described. The panel is assumed to be composed of skins consisting of polymer matrix reinforced with fibres and a lightweight core (the paper concentrates on the crucial aspect of the problem, i.e. the behaviour of the ‘hot’ skin of the panel. The core is assumed not to decompose, and the ‘cold’ skin is treated exactly as the ‘hot’ skin.) It is assumed that the polymer matrix undergoes chemical decomposition. Such a model results in a set of coupled non-linear transient partial differential equations. A Galerkin finite element framework is formulated to yield a fully implicit time stepping scheme. The crucial input parameters for the model are carefully identified for subsequent experimental determination. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: The fracture properties and impact response of a series of aluminum foam sandwich structures with the glass fiber-reinforced polypropylene-based fiber-metal laminate (FML) skins have been studied in this article.
Abstract: The fracture properties and impact response of a series of aluminum foam sandwich structures with the glass fiber–reinforced polypropylene-based fiber-metal laminate (FML) skins have been studied. Initially, the manufacturing process for producing the FML skins was optimized to obtain a strong bond between the composite plies and the aluminum layers. The degree of adhesion between the composite plies and the aluminum was characterized by conducting single cantilever beam tests. Here, it was found that the composites could be successfully bonded to the aluminum using a simple short stamping procedure. A detailed examination of the fracture surfaces indicated that crack propagation occurred within the composite ply in the fiber-metal laminates and along the composite-aluminum foam interface in the sandwich structures. The low velocity impact response of the FMLs and the sandwich structures was investigated using an instrumented drop-weight impact tower and a laser-Doppler velocimeter. The energy absorption characteristics of the sandwich structures were investigated along with the failure processes. Finally, a series of tensile tests on the damaged FMLs and thermoplastic sandwich structures showed that both systems offer promising residual load-bearing properties. Here, shear failure in the aluminum foam was observed in the sandwich structures, indicative of a strong bond between the FML skins and the aluminum core. Polym. Compos. 25:499–509, 2004. © 2004 Society of Plastics Engineers.
TL;DR: In this paper, a series of tests of localized, penetrating impact on sandwich panels were conducted in quasi-static conditions and at approximately 70 and 93 m/s, with three different impactor tip geometries.
Abstract: Part I of this article describes a series of tests of localized, penetrating impact on sandwich panels. The sandwich panel size was 500 500 mm2 with a thickness of 46 mm. Three types of panel configuration were tested. Penetration was carried out in quasi-static conditions and at approximately 70 and 93 m/s. Impactor mass was 1 kg with an impactor diameter of 50 mm and with three different impactor tip geometries. For each of the 27 combinations, the total energy absorption was measured, and the damage patterns are described and quantified.
TL;DR: In this paper, the authors developed a B-spline finite strip method for predicting the natural frequencies of vibration and the buckling stresses of rectangular sandwich panels, each panel comprises a flat sandwich main plate which is reinforced by a number of longitudinal compact plate stiffeners attached to the faceplates, and the core of the main plate is represented as a three-dimensional solid whilst the faceplate and the stiffening plates may in general be composite laminates which are represented, in turn, as either shear-deformable plates or classically thin plates.
TL;DR: In this paper, the development and the optimization of a thermoforming process (compression molding) for thermoplastic sandwich panels are reported. But the authors focus on the use of two different types of core material, a PP foam and a PP honeycomb.
Abstract: This paper reports on the development and the optimization of a thermoforming process (compression molding) for thermoplastic sandwich panels. The skins of the panels are fabricated from polypropylene (PP)/continuous glass fibers dry prepregs in the form of a commingled fabric. The use of two different types of core material has been used, a PP foam and a PP honeycomb. Additionally, two alternative methods for the thermoforming process have been analyzed, using either a one-stage or a two-stage process. In the one-step process, skin molding and skin-core bonding are carried out simultaneously. In the two-stage process, the skins are first thermoformed and then bonded to the core as the second stage. The influence of the selected process parameters on the mechanical properties of the panels has been experimentally investigated, leading to the identification of the preferred processing conditions. Polym. Compos. 25:307–318, 2004. © 2004 Society of Plastics Engineers.
TL;DR: In this paper, the transition from face wrinkling failure to face sheet compression failure, induced by local buckling at fibre level, so called face sheet microbuckling, was investigated on small sandwich panels subjected to uni-axial compression.
Abstract: This paper investigates the transition from face wrinkling failure to face sheet compression failure, the latter induced by local buckling at fibre level, so called face sheet microbuckling. An experimental series is performed on small sandwich panels subjected to uni-axial compression. Two different face sheet lay-ups are used in conjunction with a range of PVC core material densities. The results are compared to analytical wrinkling formulae and the correlation is found to be very good. The experimental results also clearly show the transition from wrinkling failure to face sheet microbuckling failure when the core modulus exceeds a certain value. The localised failure surfaces are inspected by microscope and some different characteristics of the failure modes are indicated.
TL;DR: In this paper, low-velocity instrumented impact tests were carried out on sandwich panels made of glass fiber-reinforced plastic facesheets and polyurethane foam core.
Abstract: Low-velocity instrumented impact tests were carried out on sandwich panels made of glass fiber-reinforced plastic facesheets and polyurethane foam core. The tests were carried out using a drop weight instrumented impact tester, connected to a data acquisition system. Four different types of sandwich samples using polyester/e-glass and epoxy/e-glass facesheet materials and polyurethane foam were considered for investigation. Two different face sheet materials were chosen to experimentally examine the effect of their elastic modulus on the impact response of the sandwich structures. The data acquisition system records the impact data such as impact force, penetration time and depth of penetration, and plots impact force versus depth of penetration and penetration time versus depth of penetration curves. From the recorded data the impact parameters such as maximum impact force, penetration time and depth of penetration versus impact energy were plotted to study the impact behavior. The results show that high...
TL;DR: In this article, experimental and numerical results were used to improve the design rules of fully profiled sandwich panels with slender plates, and the results showed that these design rules could not be extended to slender plates in their present form.
Abstract: Past research into the local buckling behaviour of fully profiled sandwich panels has been based on polyurethane foams and thicker lower grade steels. The Australian sandwich panels use polystyrene foam and thinner and high strength steels, which are bonded together using separate adhesives. Therefore a research project on Australian sandwich panels was undertaken using experimental and finite element analyses. The experimental study on 50 foam-supported steel plate elements and associated finite element analyses produced a large database for sandwich panels subject to local buckling effects, but revealed the inadequacy of conventional effective width formulae for panels with slender plates. It confirmed that these design rules could not be extended to slender plates in their present form. In this research, experimental and numerical results were used to improve the design rules. This paper presents the details of experimental and finite element analyses, their results and the improved design rules.
TL;DR: Based on sandwich panel penetration experiments and the observed damage patterns, the individual energy contributions are estimated from simple physical mode in this article, where the authors proposed a simple physical model to estimate individual energy contribution.
Abstract: Based on sandwich panel penetration experiments and the observed damage patterns, as described in Part I of this article, the individual energy contributions are estimated from simple physical mode...