Showing papers on "Sandwich-structured composite published in 2014"
TL;DR: In this article, the authors describe the manufacturing and testing of graded conventional/auxetic honeycomb cores, which are used to manufacture sandwich panels for flatwise compression and edgewise loading.
Abstract: The work describes the manufacturing and testing of graded conventional/auxetic honeycomb cores. The graded honeycombs are manufactured using Kevlar woven fabric/914 epoxy prepreg using Kirigami techniques, which consist in a combination of Origami and ply-cut processes. The cores are used to manufacture sandwich panels for flatwise compression and edgewise loading. The compressive modulus and compressive strength of stabilized (sandwich) honeycombs are found to be higher than those of bare honeycombs, and with density-averaged properties enhanced compared to other sandwich panels offered in the market place. The modulus and strength of graded sandwich panel under quasi-static edgewise loading vary with different failure mode mechanisms, and offer also improvements towards available panels from open literature. Edgewise impact loading shows a strong directionality of the mechanical response. When the indenter impacts the auxetic portion of the graded core, the strong localization of the damage due to the negative Poisson’s ratio effect contains significantly the maximum dynamic displacement of the sandwich panel.
176 citations
TL;DR: In this article, the polyurethane foam filled pyramidal lattice core sandwich panel is fabricated in order to improve the energy absorption and low velocity impact resistance, based on the compression tests, a synergistic effect that the foam filled sandwich panels have a greater load carrying capacity compared to the sum of the unfilled specimens and the filled polyurehane block is found.
150 citations
TL;DR: In this article, all-metallic hybrid-cored sandwich constructions with aluminum foam blocks inserted into the interstices of steel corrugated plates were fabricated and tested under three-point bending.
120 citations
TL;DR: In this article, the influence of foam infill on the blast resistivity of corrugated steel core sandwich panels was investigated experimentally using a shock tube facility and high speed photography and numerically through Finite Element Methods (FEM).
118 citations
TL;DR: In this paper, a meso-scale finite element modeling of Nomex honeycomb cores is proposed to account for strain gage local stiffening effects and thickness normalization, and the cell wall material properties are implemented in a honeycomb core finite element model and further calibrated by matching simulation results to manufacturer test data.
114 citations
TL;DR: In this paper, the authors present a blast experiment to investigate the blast-resistance of square sandwich panels with hexagon aluminum honeycomb cores and calculate the impulse loading on the panel by using the displacement history of ballistic pendulum.
108 citations
TL;DR: In this article, the authors used pulsed eddy current (PEC) and two features, representing the magnetic field intensity and conductivity, were used to characterise the different types of defects in carbon fiber reinforced plastics (CFRP) laminates and honeycomb sandwich panels.
Abstract: With the growing interest to use composite materials and honeycomb sandwich panels in industrial fields, much attention is devoted to the development of non-destructive testing (NDT) techniques for the detection and evaluation of defects. In this work, scanning pulsed eddy current (PEC) was investigated and two features, representing the magnetic field intensity and conductivity, were used to characterise the different types of defects in carbon fibre reinforced plastics (CFRP) laminates and honeycomb sandwich panels. The experimental results show that the low energy impact from 4 J to 12 J, conductive and non-conductive insert defects can be effectively detected and evaluated using the proposed methods. The effectiveness was verified and the advantages of scanning PEC were addressed through comparative studies with flash thermography and shearography.
106 citations
TL;DR: In this paper, the authors outline the testing procedure of sandwich sections made of TRC and their load-carrying behaviour subjected to tension, shear forces, and bending moments, and their results show that TRC facings can achieve a high structural capacity while satisfying structural and physical demands.
100 citations
TL;DR: The Avancon Bridge in Bex, Switzerland as discussed by the authors is a semi-integral bridge that allows the application of a continuous asphalt layer across the abutments without expansion joints and thus facilitates and reduces maintenance.
Abstract: The concept, design and experimental validation of the new Avancon Bridge in Bex, Switzerland, are described. The lightweight glass fiber-reinforced polymer (GFRP) sandwich bridge deck adhesively bonded to steel girders reduced the traffic disruption period by approximately 40 days or 80% compared to a cast-in-place concrete bridge and also enabled the bridge to be widened to two lanes. The semi-integral bridge concept allows the application of a continuous asphalt layer across the abutments without expansion joints and thus facilitates and reduces maintenance. The GFRP sandwich deck with structural balsa core fulfils all the requirements concerning serviceability, ultimate limit state and fatigue.
95 citations
TL;DR: In this article, the bending properties and failure modes of carbon fiber composite egg and pyramidal honeycomb beams were studied and presented in terms of face wrinkling, face crushing, core member crushing and debonding.
89 citations
TL;DR: In this paper, the dynamic response of corrugated sandwich panels under air blast loading was investigated using a ballistic pendulum system, and the residual deflection of the back face sheet and the deformation/failure modes of the sandwich panel under different impulse levels were analyzed.
TL;DR: In this paper, the effect of foam density variations in sandwich structure under high velocity impact loadings was investigated and it was shown that low ballistic performance in low density foam core (below 40 kg/m3) in the sandwich structure may be associated with foam's low cell wall thickness and strut.
TL;DR: In this article, a multi-objective optimization procedure is presented to design material properties of honeycomb core sandwich panels for minimum weight and maximum thermal resistance within the context of origami-inspired shelters.
TL;DR: In this paper, a composite panel is redesigned to mimic nacre's microstructure and the original composite structure is subjected to an underwater impulsive loading scenario, and their performances are compared numerically in terms of damage and deflection.
TL;DR: In this article, an adhesively bonded modular GFRP sandwich system for use in building floor construction is described, where sandwich units are formed by incorporating standard pultruded I-profiles between two girders to form built-up modular sections with considerable improvement of bending stiffness.
TL;DR: In this paper, the results of the experimental investigation into the addition of indentations of power-law profile into composite plates and panels and their subsequent inclusion into composite honeycomb sandwich panels are reported.
TL;DR: In this article, an orthogrid structure was added into the sandwich structure to raise the stiffness of soft honeycomb and therefore reduce the interfacial mismatch between carbon fiber and low-stiffness aluminum honeycomb, and three point bending tests were conducted to compare carbon fiber sandwiches with different types of core.
Abstract: The full potential of carbon-fiber and aluminum-honeycomb sandwich panels and structures has been limited by the huge property mismatch between the high-stiffness carbon fiber and low-stiffness aluminum honeycomb. In this study, an orthogrid structure was added into the sandwich structure to raise the stiffness of soft honeycomb and therefore reduce the interfacial mismatch. The core then became an aluminum orthogrid structure filled with aluminum-honeycomb blocks. Three point bending tests were conducted to compare carbon fiber sandwiches with different types of core: (1) aluminum-honeycomb core; (2) aluminum-plate orthogrid core; and (3) aluminum-plate orthogrid core filled by aluminum-honeycomb blocks. The honeycomb filled orthogrid core sandwich was a bit heavier than the honeycomb or grid sandwich, but the critical load, specific strength and energy absorption ability were all improved. The results indicated that the honeycomb filled orthogrid core sandwich with carbon fiber face sheet could provide improved structural properties for thin walled engineering structures.
TL;DR: In this article, the structural and mechanical properties of Luffa sponge are studied at different levels of its hierarchical organization from a single fiber to a segment of whole sponge, and the difference of the compressive stress-strain responses of four sets of segmental samples were also compared.
TL;DR: In this paper, the Nomex™ honeycomb core sandwich panels with a bolt insert were load tested and modeled to predict the honeycomb local buckling load and to identify a nomex® honeycomb constituent material model.
Abstract: Nomex™ honeycomb core sandwich panels with a bolt insert were load tested and modeled. The objective was to predict the honeycomb local buckling load and to identify a Nomex™ honeycomb constituent material model. Sandwich specimens were subjected to bolt pull-out load tests. The same sandwich structure was also tested in flat-wise tension with strain gages installed on the honeycomb walls. Finite element models of the flat-wise tension and bolt pull-out tests were built. The honeycomb geometry and strain gages were modeled with shell elements. An orthotropic honeycomb material model was identified by comparing the two test models to the experimental data. The material parameters identified are in the mid-range of previously published values. The pull-out test model was used to predict honeycomb wall buckling with a nodal rotation vector sum criterion. The buckling loads predictions closely corresponded to the start of the experimental load/displacement slope transition zone.
TL;DR: In this paper, carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from a carbon fiber braided net, 3D woven face sheets and various polymeric foams, and infused with an epoxy resin using a vacuum assisted resin transfer process.
TL;DR: In this paper, the authors used the solid isotropic material with penalization (SIMP) model to find the optimal distribution of a given amount of materials in a sandwich-structured composite.
Abstract: A sandwich-structured composite is a special class of composite materials that is fabricated by attaching two thin but stiff layers to a lightweight but thick core Composites analyzed in this paper consist of two different materials: auxetic and structural steel The optimization criterion is minimum compliance for the load case where the frame's top boundary is downward loaded Outer layers are made of steel while the middle layer is two-phase solid material composite Only the middle layer is optimized by means of minimization of the objective function defined as the internal strain energy In the first part of this paper we study the application of the solid isotropic material with penalization (SIMP) model to find the optimal distribution of a given amount of materials in sandwich-structured composite In the second part we propose a multilayered composite structure in which internal layers surfaces are wavy In both cases the total energy strain is analyzed
TL;DR: In this article, the authors focused on the bending behavior of an innovative sandwich panels with GFRP face sheets and a foam-web core (GFFW panels), manufactured by vacuum assisted resin infusion process.
Abstract: This study focused on the bending behavior of an innovative sandwich panels with GFRP face sheets and a foam-web core (GFFW panels), manufactured by vacuum assisted resin infusion process. An experimental study was carried out to validate the effectiveness of this panel for increasing the ultimate bending strength. Compared to the control specimen, a maximum of an approximately 410% increase in the ultimate bending strength can be achieved. The influences of web thickness, web height and web spacing on failure mode, initial bending stiffness and mid-span deflection were also investigated. Test results demonstrated that the ultimate bending strength and initial bending stiffness can be enhanced by increasing web thickness and web height. In the meantime, the indentation failure and local wrinkling failure did not occur due to the presence of the GFRP webs. Furthermore, an analytical model was proposed to predict the mid-span deflection and initial bending stiffness of GFFW panels. A comparison of the analytical and experimental results showed that the analytical model accurately predicted the ultimate bending strengths and min-span deflections of the GFFW panels loaded in four-point bending.
TL;DR: In this paper, a fire performance enhancement strategy for multilayer composite sandwich panels, which are comprised of GFRP composite facets and polyethylene foam core, is proposed with the addition of environmentally friendly, fire retardant unsaturated polyester resins and gel-coats.
Abstract: Composite materials such as glass fibre reinforced polymers (GFRPs) possess the advantages of high strength and stiffness, as well as low density and highly flexible tailoring; therefore, their potential in replacing conventional materials (such as concrete, aluminium and steel) in building facade has become attractive. This paper addresses one of the major issues that hinder the extensive use of composite structures in the high-rise building industry, which is the fire resistance. In this study, a fire performance enhancement strategy for multilayer composite sandwich panels, which are comprised of GFRP composite facets and polyethylene foam core, is proposed with the addition of environmentally friendly, fire retardant unsaturated polyester resins and gel-coats. A series of burning experimental studies including thermo-gravimetric analysis (TGA) and single burning item (SBI) are carried out on the full scale composite sandwich as well as on single constituents, providing information regarding heat release rate, total heat release, fire growth rate, and smoke production. Experimental results are compared with fire safety codes for building materials to identify the key areas for improvements. A fire dynamic numerical model has been developed in this work using the Fire Dynamics Simulator (FDS) to simulate the burning process of composite structures in the SBI test. Numerical results of heat production and growth rate are presented in comparison with experimental observations validating the computational model and provide further insights into the fire resisting process. Parametric studies are conducted to investigate the effect of fire retardant additives on the fire performance of the composite sandwich panel leading to optimum designs for the sandwich panel.
TL;DR: In this article, a ZrO 2 ceramic corrugated core sandwich panels were fabricated using gelcasting technique and pressureless sintering and the nominal density was 2.4 grams/cm 3 (42.9% of bulk ceramic).
TL;DR: In this article, the impact response of sandwich specimens with FML skins and polyurethane foam was investigated by experimental and numerical approaches using LS-DYNA to model impact of cylindrical projectile with clamped boundary condition.
TL;DR: In this paper, the authors investigated the energy-absorbing characteristics of polymer foams reinforced with small carbon fiber reinforced epoxy tubes and found that these structures should be capable of absorbing significant energy when subjected to this severe loading condition.
Abstract: This paper reports the findings of a research study investigating the energy-absorbing characteristics of polymer foams reinforced with small carbon fibre reinforced epoxy tubes. Initial attention focuses on establishing the influence of tube diameter on the specific energy absorption (SEA) characteristics of the chamfered CFRP tubes. Here, it is shown that the SEA of the tubes increases rapidly with decreasing diameter/thickness ratio, with the highest values being close to 93 kJ/kg. Similar tests were conducted at dynamic rates of strain, where it was observed that the measured values of SEA were lower than the corresponding quasi-static data, possibly due to rate-sensitive effects in the delamination resistance of the composite material. In the next stage of the investigation, the composite tubes were embedded in a range of polymer foams in order to establish the influence of both tube arrangement and foam density on the crush behaviour of these lightweight structures. In addition, a limited number of blast tests have been undertaken on structures based on these core materials. Here, extensive crushing of the composite tubes was again observed, suggesting that these structures should be capable of absorbing significant energy when subjected to this severe loading condition. Finally, the results of these tests are compared with previously-published data from studies on a range of different cores materials. Here, it has been shown that the energy-absorbing characteristics of these systems exceed values associated with other core materials, such as aluminium honeycombs, polymer honeycombs and metal foams.
TL;DR: In this paper, an experimental program of compression after impact tests (CAI) has been performed to quantitatively describe the decrease of the sandwich mechanical performance after an impact, and the results show a clear reduction of the residual strength of the damaged panels compared with undamaged ones.
Abstract: Sandwich panels are used in industrial fields where lightness and energy absorption capabilities are required. In order to increase their exploitation, a wide knowledge of their mechanical behavior also in severe loading conditions is crucial. Light structures such as the one studied in the present work, sandwich panels with aluminum skins and Nomex ™ honeycomb core, are exposed to a possible decrease of their structural integrity, resulting from a low velocity impact. In order to quantitatively describe the decrease of the sandwich mechanical performance after an impact, an experimental program of compression after impact tests (CAI) has been performed. Sandwich panel specimens have been damaged during a low velocity impact test phase, using an experimental apparatus based on a free fall mass tower. Different experimental impact energies have been tested. Damaged and undamaged specimens have been consequently tested adopting a compression after impact procedure. The relation between the residual strength of the panel and the possible relevant parameters has been statistically investigated. The results show a clear reduction of the residual strength of the damaged panels compared with undamaged ones. Nevertheless, a reduced dependency between the impact energy and the residual strength is found above a certain impact energy threshold.
TL;DR: In this paper, a series of tests have been performed at RWTH Aachen University to investigate the loadbearing behavior of sandwich panels with thin TRC-facings and resilient insulation cores applied for self-supporting facades.
TL;DR: In this paper, numerical and experimental investigations on the acoustic power, radiated by Aluminium Foam Sandwich panels, are carried out and two different Alulight® specimens, made of the same material but with different thickness and percentage of foam density, are investigated.
TL;DR: In this paper, the authors present a review of recent experimental and numerical work on the response of composite materials, sandwich structures and hybrid materials to air-blast loading, along with the results from recent experiments on plain composite laminates, polymeric sandwich panels and fibre-metal lamination.
Abstract: Composite materials are finding use in an increasing number of structural applications as a result of their high specific strength, high specific stiffness, thermal resistance and the potential for tailoring of properties to suit specific applications. Fibre-reinforced composites, foam core sandwich panels and fibre-metal laminates (FMLs) are examples of composite materials that are employed in high-performance engineering applications, for example in yachts, passenger aircraft, racing cars and sports equipment. Explosive loading is a potential threat to many of these structures, and therefore an improved understanding of the response of such systems to air-blast loading is important. This paper reviews recent experimental and numerical work on the response of composite materials, sandwich structures and hybrid materials to air-blast loading. Commonly employed experimental techniques used to simulate air-blast loading conditions are described, along with the results from recent experiments on plain composite laminates, polymeric sandwich panels and FMLs. The influence of loading distribution, materials and test geometry on the failure of composites is discussed. The latter part of paper discusses numerical modelling considerations and reports methods and results from recent numerical modelling work on the blast loading of