Showing papers on "Sandwich-structured composite published in 2011"

A literature review on computational models for laminated composite and sandwich panels

Abstract: The present paper is devoted to a state-of-the-art review on the computational treatment of laminated composite and sandwich panels. Over two hundred texts have been included in the survey with the focus put on theoretical models for multilayered plates and shells, and FEM implementation of various computational concepts. As a result of the review, one could notice a lack of a single numerical model capable for a universal representation of all layered composite and sandwich panels. Usually, with the increase of the range of rotations considered in the particular model, one can observe the decrease of the degree of complexity of the through-the-thickness representation of deformation profiles.

Mechanical behavior and failure of composite pyramidal truss core sandwich columns

Abstract: A series of analytical and experimental investigations is presented to study the response and failure of pyramidal truss core sandwich panels made of carbon fiber composite under axial compression. In the analytical part of the study, three failure modes: (i) Euler or core shear macro-buckling, (ii) face wrinkling, and (iii) face sheet crushing, were considered and theoretical relationships for predicting the failure load associated with each mode were presented. In the experimental part of the study, three different sets of specimens were manufactured to probe the three failure modes mentioned above. Pyramidal truss cores were fabricated using a hot-press molding technique and were bonded to composite face sheets made of fiber reinforced composite. The response of the sandwich panels under axial compression was measured up to failure. The measured peak loads obtained in the experiments showed good agreement with the analytical predictions. The experiments also provide insight into the post-failure response of the sandwich panels.

Novel Steel-Concrete-Steel Sandwich Composite Plates Subject to Impact and Blast Load

Abstract: This paper investigates the structural performance of steel-concrete-steel (SCS) sandwich composite system subject to impact and blast load. Novel J-hook shear connector was invented to prevent the separation of face plates from the concrete core. SCS sandwich specimens subject to 100 kg TNT blast a 5 m standoff distance were tested. The test results are reported and the factors affecting the blast resistance of SCS sandwich structures are discussed. Finite element analysis was carried out and the numerical results are verified against the blast test results. Parametric study of sandwich core strength and plate thickness is presented. Due to the superior impact performance of the proposed SCS sandwich structures, an ice caisson protective offshore structure is proposed based on the curved sandwich panel. The ultimate strength behavior of curved SCS sandwich panels is tested. The effect of arch effect is studied both experimentally and numerically.

Experimental study of the indentation of sandwich panels with carbon fibre-reinforced polymer face sheets and polymeric foam core

Abstract: This paper presents experimental studies on the quasi-static indentation of a rigid indenter into sandwich panels with carbon fibre-reinforced polymer face and polymeric foam core. It was found that both nose shape and foam core density have large influence on the indentation response of the sandwich panels in terms of absorbed energy, indentation at failure and damage area. A dependency of the indentation load on the supporting condition was observed. It was also found that the difference in indentation resistance between the sandwich panel and its corresponding core material depends on the core density.

Impact response of aluminum foam core sandwich structures

Abstract: Sandwich panels, comprised of metallic foam core and face sheets, are widely used to withstand impact and blast loadings. Based on the actual application requirements, the performance can be optimized with the proper combination of face sheets design. In this paper the impact responses of aluminum foams with various tailored face sheets, whose behavior represents elastic, elastic-ideally plastic and elastic–plastic strain work hardening, were investigated experimentally. The experiment was carried out using hemispherical indenters on blocks of aluminum foam with and without the face sheet. Competing failure modes for the initiation of failure are discussed based on comparison of energy absorption capacity. Results show that increase in thickness of foam and the use of face sheet enhances the impact energy absorption capacity. The type of face sheet not only affects the energy absorption capacity but also the failure mode for the foam blocks. Aluminum foam blocks with stainless steel sheet are strong enough to withstand the pre-designated impact loading without penetration damage. At the same time, this study also provides a comparison of the impact performance, in terms of impact energy and failure mode, among blocks with different face sheets under the low velocity impact.

Experimental research of compressive responses of multi-layered woven textile sandwich panels under quasi-static loading

Abstract: Multi-layered panels were manufactured by stacking thin monolayer panels to improve the energy absorption ability of the woven textile sandwich. Quasi-static compression experiments were conducted to get the stress–strain curves and to reveal the energy absorption mechanism. For multi-layered panels staked by monolayer of 3 mm thickness, the core piles experience the strength failure; that renders the panel high load resistance and a strain-hardening curve before the densification. The thickening of the monolayer would trigger the monolayer stack to buckle one after the other, which decreases the load resistance of the panel and renders a prolonged zigzag load–deformation curve. The peak load of the multi-layered structure is found to be close to its constituting monolayer, but much greater than a monolayer panel of the same thickness. The deformation of the multi-layered panel then becomes a multiple process of monolayer collapses. Energy absorption of the multi-layered panel is greatly enhanced and far exceeds that of the monolayer panel of the same thickness.

Experimental Investigation of Large-Scale Cladding Sandwich Panels under Out-of-Plane Transverse Loading for Building Applications

Abstract: This paper investigates large-scale sandwich panels (9,145×2,440×78 mm) subjected to out-of-plane loading. The panels comprise glass-fiber-reinforced polymer (GFRP) skins connected by orthogonal GFRP ribs and a polyurethane foam core. The lightweight insulated panel is supported at three levels along its 9,145-mm height and is proposed for cladding of buildings, where the main loading is caused by wind. A full-scale panel was tested under uniform air pressure by using a specially designed setup equipped with pressure load actuators. The panel failed at 7.5 kPa, 2.6 times the factored design pressure for the windiest region in Canada. Failure occurred by outward wrinkling and crushing of the GFRP compression skin near the middle supports. The deflection under the maximum design service wind pressure did not exceed span/360. Another test was carried out on a different specimen by using conventional mechanical loading. It confirmed the ultimate strength of the panel and also revealed a successive failure re...

Fabrication, characterization and low‐velocity impact testing of hybrid sandwich composites with polyurethane/layered silicate foam cores

Abstract: A series of nanophased hybrid sandwich composites based on polyurethane/montmorillonite (PU/MMT) has been fabricated and characterized. Polyaddition reaction of the polyol premix with 4,4'-diphenylmethane diisocyanate was applied to obtain nanophased PU foams, which were then used for fabrication of sandwich panels. It has been found that the incorporation of MMT resulted in higher number of PU cells with smaller dimensions and higher anisotropy index (cross sections RI and RII). The obtained materials exhibited improved parameters in terms of thermal insulation properties. The results also show that nanophased sandwich structures are capable of withstanding higher peak loads than those made of neat PU foam cores when subject to low-velocity impact despite their lower density than that of neat PU foams. This is especially significant for multi-impact recurrences within the threshold loads and energies studied. POLYM. COMPOS., 32:6-13, 2011. © 2010 Society of Plastics Engineers.

Response of Curved Sandwich Panels Subjected to Blast Loading

Abstract: Curved sandwich panels with two aluminium face sheets and an aluminium foam core under air blast loadings were investigated experimentally and numerically. Specimens with two values of radius of curvature and different core/face sheet configurations with the same projected area were tested for three blast intensities. All four edges of the panels were fully clamped. The experiments were carried out by a four-cable ballistic pendulum with corresponding sensors. The impulse acting on the front face of the assembly, the deflection history at the center of the back face sheet, and the strain history at some characteristic points on the back face were obtained. Then the deformation/failure modes of specimens were classified and analyzed systematically. The commercial software LS-DYNA was employed to simulate those physical processes. The finite-element (FE) model was validated by the data from experiments. Detailed deformation and energy dissipation mechanisms were further revealed by the FE models. The valuable experimental data and results from FE models show that the initial curvature of a curved sandwich panel changes the deformation/collapse mode with an extended range for bending-dominated deformation mode, which suggests that the performance of the sandwich shell structures slightly exceeds that of both their equivalent solid counterpart and a flat sandwich plate in certain blast intensity ranges.

Short fibre reinforced cores and their sandwich panels: Processing and evaluation

Abstract: Natural fibre composites (NFCs) that are replacing their synthetic counterpart in certain engineering sectors are often being underutilised, in mainly non-structural applications. Hence, in the view of adding value to current natural fibre composites, a relatively new concept of hollow cores fabricated from NFCs, has been investigated in this study. Thin continuous rolls of NFCs were produced in conical twin screw extruders which were then thermoformed into half hexagonal or sinusoidal profiles. The forming characteristics of the composites have been experimentally examined using single curvature V-bending experiments. The corrugated profiles were stacked and then bonded using ultrasonic methods to form cores for sandwich panels. The bond quality at the nodes of the cores has been experimentally determined using single-lap shear test. The mechanical properties such as compression and shear behaviour of the cores were determined by subjecting them to compressive and flexural loads, respectively. Sound absorption characteristics were determined using a standing plane wave impedance tube and the energy absorption capability was measured by subjecting the cores to quasi-static compressive loads until densification. The composites displayed good forming characteristic at the higher end of forming speed (500 mm/min) and temperatures closer to the melting temperature of the polymer matrix. The specific mechanical property values of the reinforced honeycombs after reinforcing the cell walls were more than twice of those of the un-reinforced cores. The energy absorption experiments revealed that the cores could be compressed to over 80% of their initial heights at a more or less steady stress making them suitable for packaging applications. The characteristic sound absorption of these panels at particular frequencies, coupled with good mechanical properties, make them eco-friendly and suitable in automobile, aerospace, packaging and building/construction industries.

Collapse mechanism maps for a hollow pyramidal lattice

Abstract: Cellular materials with hollow lattice truss topologies exhibit higher compressive strengths than equivalent structures with solid trusses owing to their greater resistance to plastic buckling. Consequently, hollow trusses have attracted interest as the cores for sandwich panels. Finite-element calculations are used to investigate the elastic–plastic compressive collapse of a metallic sandwich core made from vertical or inclined circular tubes, made from annealed AISI 304 stainless steel. First, the dependence of the axial compressive collapse mode upon tube geometry is determined for vertical tubes with built-in ends and is displayed in the form of a collapse mechanism map. Second, the approach is extended to inclined circular hollow tubes arranged as a pyramidal lattice core; the collapse modes are identified and the peak compressive strength is determined as a function of geometry. For a given relative density of hollow pyramidal core, the inclined tube geometry that maximizes peak strength is identified. The predicted collapse modes and loads for the pyramidal core are in excellent agreement with measurements for the limited set of experimentally investigated geometries.

Explorations of Hybrid Sandwich Panel Concepts for Projectile Impact Mitigation

Abstract: Previous studies have shown that while stainless-steel sandwich panels with pyramidal truss cores have a superior blast resistance to monolithic plates of equal mass per unit area, their ballistic performance is similar to their monolithic counterparts. Here, we explore concepts to enhance the ballistic resistance without changing the volumetric efficiency of the panels by filling the spaces within the core with combinations of polyurethane, alumina prisms, and aramid fiber textiles. The addition of the polyurethane does not enhance the ballistic limit compared with the equivalent monolithic steel plate, even when aramids are added. This poor performance occurs because the polymer is penetrated by a hole enlargement mechanism which does not result in significant projectile deformation or load spreading and engagement of the steel face sheets. By contrast, ceramic inserts deform and erode the projectile and also comminute the ceramic. The ceramic communition (and resultant dilation) results in stretching of both steel face sheets and leads to significant energy dissipation. The ballistic limit of this hybrid is about twice that of the equivalent monolithic steel plate. The addition of a Kevlar fabric to the ceramic hybrid is shown to not significantly change the ballistic limit but does reduce the residual velocities of the debris.

Temperature effects on the strength and crushing behavior of carbon fiber composite truss sandwich cores

Abstract: The effects of temperature on the mechanical behaviors of composite rods and carbon fiber composite truss sandwich cores were investigated in this paper. Strength and stiffness of composite rods in fiber-aligned direction were measured in the range of −60 °C to 260 °C and characterized as functions of temperature. The research on out-of-plane compressive properties of sandwich panels with truss cores for temperature variation indicated that strength and failure modes of sandwich panels were significantly dependent on temperature. The stiffness and strength of composite rods and sandwich panels decreased progressively as temperature increased. The decreasing of stiffness and strength at high temperature was mainly attributed to softening of the polymer matrix. The increasing of stiffness and strength at cryogenic temperature was due to reduced mobility of the polymer chains within the resin matrix and the more closely compacted molecules of resin matrix. In order to provide insight into the effect of temperature on failure mechanism, the interface between fiber and matrix was examined using scanning electron microscope, and good interfacial bonding condition was observed at cryogenic temperature. The stiffness and strength of sandwich panels at different temperatures were predicted with proposed method and compared with measured results. Good agreement was observed between the measured values and predictions.

Analysis and verification of the performance of sandwich panels with textile reinforced concrete faces

Abstract: Textile-reinforced concrete (TRC) is a composite material that recently gained renewed interest. Due to an improved durability, the usage of this composite in lightweight constructions becomes possible. In this article, the behavior of sandwich panels with TRC faces is studied. In the first part, several models are used in a finite element analysis and their advantages and disadvantages are discussed. In the second part, the calculated nonlinear behavior of the panels is compared to experimental observations.

Effects of Core Topology on Sound Insulation Performance of Lightweight All-Metallic Sandwich Panels

Abstract: An analytical study of sound transmission through all-metallic, two-dimensional, periodic sandwich structures having corrugated core is presented. The space-harmonic method is employed, and an equivalent structure containing one translational spring and one rotational spring per unit cell is proposed to simplify the analysis of the vibroacoustic problem. It is demonstrated that the core geometry exerts a significant effect on the sound insulation performance of the sandwich, so that one may tailor the core topology for specified acoustic applications. Subsequent analysis of the sound transmission loss (STL) and dispersion curves of the structure leads to fundamental insight into the physical mechanisms behind the appearance of various peaks and dips on the STL versus frequency curves. As the weight, stiffness, and acoustic property of the sandwich structures all change with the alteration of core configuration and geometry, it is further demonstrated that it is possible to explore the multifunctionality o...

An integrated assembly method of sandwich structured ceramic matrix composites

Abstract: Sandwich structured composites have been widely studied and applied at ambient temperature in aeronautical, automobile and naval applications. For high temperature applications, an integrated ceramic sandwich structure could take advantage of multiple functions such as skin stiffness and core insulation. For thermo-structural applications, skins must be made of ceramic matrix composites (CMC) because of their strength, their resistance to high temperatures (beyond 1000 °C), and their low densities. Concerning foam cores, some carbides (e.g. SiC) are, for their outstanding thermo-mechanical properties, the most appropriate. These foams can withstand long oxidative exposing conditions with low material degradation. This paper presents an assembly method of SiC based sandwich structured CMC. It is performed during sandwich manufacturing in an integrated fashion and allows the production of complex shapes at low costs. Produced flat sandwich panels, characterized by three point bending tests, showed a marked toughening behaviour.

Vibration and damping analysis of cylindrical sandwich panels containing a viscoelastic flexible core

Abstract: In the present study, vibration and damping analysis of cylindrical sandwich panels containing a viscoelastic flexible core based on the high-order theory of sandwich structures is investigated. A ...

Development of the hybrid insert for composite sandwich satellite structures

Abstract: Composite sandwich structures which are widely employed in satellite structures require many inserts for assembly. In this study, a new lightweight insert for sandwich structures was developed by reinforcing the web of insert with high strength carbon composite to increase the loading capability with reduced mass. Finite element analysis was performed to numerically predict the load capability of the new insert as well as to investigate the effects of the new insert on the structural reliability. The load capability and the failure modes of the composite sandwich structures assembled with the inserts were measured by the pull-out and shear tests and compared with the calculated results.