Showing papers on "Sandwich panel published in 2012"

Performance and Characterization of Shear Ties for Use in Insulated Precast Concrete Sandwich Wall Panels

Abstract: Insulated precast concrete sandwich wall panels are commonly used for exterior cladding on building structures. The insulation is sandwiched between exterior and interior concrete layers to reduce the heating and cooling costs for the structure. The panels can be designed as composite, partially composite, or noncomposite. Shear ties are used to achieve these varying degrees of composite action between the interior and exterior concrete layers. A variety of shear ties are available for domestic construction. An experimental study was conducted to assess the relative strength and response of these commercially available ties. Fourteen different shear tie types were examined, the failure modes and responses were quantified, and simplified engineer level multilinear strength curves were developed for each connection. The test results indicate that shear ties used in sandwich wall construction have considerable variation in strength, stiffness, and deformability. The maximum shear strength of the discrete tie...

Analysis of Sandwich Beams With a Compliant Core and With In-Plane Rigidity—Extended High-Order Sandwich Panel Theory Versus Elasticity

Abstract: A new one-dimensional high-order theory for orthotropic elastic sandwich beams is formulated. This new theory is an extension of the high-order sandwich panel theory (HSAPT) and includes the in-plane rigidity of the core. In this theory, in which the compressibility of the soft core in the transverse direction is also considered, the displacement field of the core has the same functional structure as in the high-order sandwich panel theory. Hence, the transverse displacement in the core is of second order in the transverse coordinate and the in-plane displacements are of third order in the transverse coordinate. The novelty of this theory is that it allows for three generalized coordinates in the core (the axial and transverse displacements at the centroid of the core and the rotation at the centroid of the core) instead of just one (midpoint transverse displacement) commonly adopted in other available theories. It is proven, by comparison to the elasticity solution, that this approach results in superior accuracy, especially for the cases of stiffer cores, for which cases the other available sandwich computational models cannot predict correctly the stress fields involved. Thus, this theory, referred to as the “extended high-order sandwich panel theory” (EHSAPT), can be used with any combinations of core and face sheets and not only the very “soft” cores that the other theories demand. The theory is derived so that all core=face sheet displacement continuity conditions are fulfilled. The governing equations as well as the boundary conditions are derived via a variational principle. The solution procedure is outlined and numerical results for the simply supported case of transverse distributed loading are produced for several typical sandwich configurations. These results are compared with the corresponding ones from the elasticity solution. Furthermore, the results using the classical sandwich model without shear, the first-order shear, and the earlier HSAPT are also presented for completeness. The comparison among these numerical results shows that the solution from the current theory is very close to that of the elasticity in terms of both the displacements and stress or strains, especially the shear stress distributions in the core for a wide range of cores. Finally, it should be noted that the theory is formulated for sandwich panels with a generally asymmetric geometric layout. [DOI: 10.1115/1.4005550]

Benefits of metal foams and developments in modelling techniques to assess their materials behaviour: a review

Abstract: A review assessing the relative benefits of metal foam core sandwich panels with respect to honeycomb, polymeric foam and truss cores has been conducted. It is noted that metal foams are able to combine low density with good bending stiffness and strength, making them attractive core materials for use in industrial applications (e.g. aircraft wing structures). The current modelling tools available for metal foams are also reviewed. These fall under three categories: analytical methods using dimensional analysis, finite element methods utilising a repeating unit cell, and finite element methods utilising the random Voronoi technique. It is noted that analytical methods do not take into account the effect of imperfections in the microstructure. Finite element methods utilising a repeating unit cell also fail to capture the natural variations in microstructure that are observed in most cellular materials. The effects of imperfections are discussed, and it is observed that these reduce the hydrostatic...

An analytical model for composite sandwich panels with honeycomb core subjected to high-velocity impact

Abstract: In this paper, an analytical model for perforation of composite sandwich panels with honeycomb core subjected to high-velocity impact has been developed. The sandwich panel consists of a aluminium honeycomb core sandwiched between two thin composite skins. The solution involves a three-stage, perforation process including perforation of the front composite skin, honeycomb core, and bottom composite skin. The strain and kinetic energy of the front and back-up composite skins and the absorbed energy of honeycomb core has been estimated. In addition, based on the energy balance and equation of motion the absorbed energy of sandwich panel, residual velocity of projectile, perforation time and projectile velocity have been obtained and compared with the available experimental tests and numerical model. Furthermore, effects of composite skins and aluminium honeycomb core on perforation resistance and ballistic performance of sandwich panels has been investigated.

Wrinkling of sandwich wide panels/beams based on the extended high-order sandwich panel theory: formulation, comparison with elasticity and experiments

Abstract: There exist several high-order sandwich panel theories, most notably, the first to be introduced high-order sandwich panel theory (HSAPT) assumes a constant shear stress in the core. Recently, the extended high-order sandwich panel theory (EHSAPT) was introduced, its novelty being that it allows for three generalized coordinates in the core (the axial and transverse displacements at the centroid of the core, and the rotation at the centroid of the core) instead of just one (shear stress in the core) of the earlier theory. In this paper, the EHSAPT formulation for predicting the critical wrinkling load is presented for a simply supported sandwich of general asymmetric construction. The cases of (i) applying the loading just on the face sheets with a linear core assumption and (ii) applying uniform strain loading throughout the thickness of the panel and a nonlinear core assumption are examined. The results are compared with a benchmark elasticity solution. In addition, edgewise compression experiments were conducted on glass face/Nomex honeycomb core and the ensuing wrinkling point is compared with the theoretical predictions. A comparison is also made with earlier edgewise compression experiments on aluminum face/granulated-cork core reported in literature. Other wrinkling formulas that are included in the comparison are: Hoff–Mautner and the HSAPT.

Servo-hydraulic System for Controlled Velocity Water Impact of Marine Sandwich Panels

Abstract: Slamming, the impact between a marine craft’s hull and the water surface is a critical load case for structural design of marine vessels. The importance of hull slamming has led to a significant body of work to understand, predict and model these impacts. There is however, a lack of experimental data for validation, particularly for deformable panels and sandwich structures. This paper describes a high-velocity panel slamming test system that enables the generation of comprehensive and reliable experimental data on slamming impacts for both rigid and flexible panel structures. The pressure magnitudes, time-histories and spatial distributions resulting from testing of a nominally rigid panel have been compared with previous analytical, semi-empirical and experimental studies. Slamming impacts of a deformable sandwich panel are shown to cause different pressures to those from a rigid panel impact, resulting in increased transverse shear loading at the panel edge.

Investigation of elastic moduli of Kraft paper honeycomb core sandwich panels

Abstract: In order to understand the influence of the thicknesses of Kraft paper honeycomb core and medium density fiberboard skins on the stiffness of the sandwich panel, the corresponding finite element models for the resulting sandwich panels were developed. The material properties for the core and skin components of these finite element models were determined using the published data and specifications. It was found that a decrease in the thickness ratio of the core to skin layer (shelling ratio) resulted in an increase in the modulus of elasticity and shear modulus of the sandwich panels. The increase was significant when the shelling ratio was smaller than six. Cell size only affected the modulus of elasticity of the sandwich panels under the flat-wise compression and panel’s inter-laminar shear modulus. Regression equations relating the stiffness of the sandwich panels to the shelling ratio and core cell size were obtained using the finite element model simulated results and were found to compare well with the existing models for layered wood composites.

Light-weight honeycomb core sandwich panels containing biofiber-reinforced thermoset polymer composite skins: Fabrication and evaluation

Abstract: The application of biofiber based paper-reinforced polymer (PRP) composites as skin materials for light-weight sandwich panel constructions was explored. Various sandwich panels with PRP composite skins and a commercial resin-impregnated aramid paper honeycomb core of different cell sizes and core heights were fabricated in the laboratory. The effects of honeycomb core height and cell size on the flexural properties of the lab-made sandwich panels were evaluated. The flexural moduli and strengths of the lab-made panels were compared to the reported values for three existing commercial products used for automotive load floor applications. The lab-made PRP composite/honeycomb core sandwich panels had comparable bending rigidity and flexural load bearing capability but lower areal weights when compared to the commercial products suggesting that PRP composites have the potential to be used as an alternative to glass fiber-reinforced polymer composites as skin materials in sandwich panel fabrication.

Design and Testing of Sandwich Structures with Different Core Materials

Abstract: The purpose of this study was to design a light-weight sandwich panel for trailers. Strength calculations and selection of different materials were carried out in order to find a new solution for this specific application. The sandwich materials were fabricated using vacuum infusion technology. The different types of sandwich composite panels were tested in 4-point bending conditions according to ASTM C393/C393M. Virtual testing was performed by use of ANSYS software to simplify the core material selection process and to design the layers. 2D Finite element analysis (FEA) of 4-point bending was made with ANSYS APDL (Classic) software. Data for the FEA was obtained from the tensile tests of glass fiber plastic (GFRP) laminates. Virtual 2D results were compared with real 4-point bending tests. 3D FEA was applied to virtually test the selected sandwich structure in real working conditions. Based on FEA results the Pareto optimality concept has been applied and optimal solutions determined.

Guided wave based detection of damage in honeycomb core sandwich structures

Abstract: We report on the Lamb wave type guided wave propagation in honeycomb core sandwich structures. An experimental study supported by theoretical evaluation of the guided wave characteristics is presented that proves the potential of Lamb wave type guided wave for detection of damage in sandwich structures. A sandwich panel is fabricated with planar dimension of 600 mm x 600 mm, having a core thickness of 7 mm, cell size of 5 mm and 0.1 mm thick aluminum face sheets. Thin piezoelectric patch actuators and sensors are used to excite and sense a frequency band limited guided wave with a central frequency. A linear phased array of piezoelectric patch actuators is used to achieve higher signal strength and directivity. Group velocity dispersion curves and corresponding frequency response of sensed signal are obtained experimentally. Linearity between the excitation signal amplitude and the corresponding sensed signal amplitude is found for certain range of parameters. The nature of damping present in the sandwich panel is monitored by measuring the sensor signal amplitude at various different distances measured from the center of the linear phased array. Indentation and low velocity impact induced damages of increasing diameter covering several honeycomb cells are created. Crushing of honeycomb core with rupture of face sheet is observed while introducing the damage. The damages are then detected experimentally by pitch-catch interrogation with guided waves and wavelet transform of the sensed signal. Signal amplitudes are analyzed for various different sizes of damages to differentiate the damage size/severity. Monotonic changes in the sensor signal amplitude due to increase in the damage size has been established successfully. With this approach it is possible to locate and monitor the damages with the help of phased array and by tracking the wave packets scattered from the damages. (C) 2012 Elsevier Ltd. All rights reserved.

Using Embedded Fiber Bragg Grating (FBG) Sensors in Smart Aircraft Structure Materials

Abstract: This paper describes the process of developing a smart material with monitoring application to the aircraft structures. A part of vertical stabilizer was selected and reproduced using carbon fiber honeycomb core sandwich panels. The sandwich panels reproduced were fabricated in accordance to the generic sandwich structure and aviation industry standards, including the materials and also the method of construction. Using a carbon fiber from Hexcel as the face-sheet, Nomex honeycomb as the core, the sandwich panel was cured using Hysol EA9330 resin according to aviation industry standard curing process. In order to make the sandwich panel as smart materials, optical sensor which has fiber bragg grating arrays, FBG, were embedded between the carbon fiber plies during the lay-out process. Using an FBG data logger, the FBG sensor signals were read before and after the FBG arrays were installed in the sandwich panels. From the initial measurement, the experiment was a success since the FBG sensors were readable and the difference in the signals was less than 1 nm. In the future, the specimen will be used for further experiment for measuring strains and establishing the existence of damage in the panel.

Global Buckling of Sandwich Beams Based on the Extended High-Order Theory

Abstract: The focus of this paper is the application of the recently introduced extended high-order sandwich panel theory to the global buckling of a sandwich beam/wide panel. Three different solution approaches using the extended highorder sandwich panel theory are presented to investigate the effects of simplifying the loading case by applying loads just on the face sheets and by including or excluding nonlinear axial strains in the core. The results are also compared with results from a benchmark elasticity solution and, furthermore, from the simple sandwich buckling formula by the earlier extended high-order sandwich panel theory. It is found that all three theories are close to the elasticity solution for “soft” cores with Ec1=E f 1 0:001, the theories diverge and the extended high-order sandwich panel theory is the most accurate.

Thermo-mechanical damage modeling of polymer matrix sandwich composites in fire

Abstract: The objective of this research is to develop a modeling and simulation approach for predicting the thermo-mechanical damage of composite materials subjected to fire environments. A 3D thermal damage model is developed for glass-reinforced polymer composite materials subject to high temperature and radiative environments. Homogenization methods are used to formulate the damaged material in terms of fiber, resin and char. The thermal damage model is implemented in Abaqus via an overlaid element approach. The solution of the mechanical response uses the existing functions in Abaqus for large-displacement analysis. Composite sandwich panels with balsa core are examined. Reasonable agreement in temperature is obtained between predictions and available experimental data. For the sandwich panels, delamination failure is predicted at the sandwich interface – consistent with the experiments. Comparisons of time-to-failure of the sandwich panel show the predictions are reasonable.

Numerical modelling of sandwich panels with soft core and different rib configurations

Abstract: This paper presents numerical modeling of the flexural behaviour of sandwich panels composed of [0/90] woven glass fibre reinforced polymer skins and polyurethane foam core, including various patterns of glass fibre reinforced polymer ribs, as well as cores of different densities. A robust finite element model has been developed. It accounts for material nonlinearities; most pronounced in soft cores and [0/90] glass fibre reinforced polymer ribs in shear, as well as geometric nonlinearities arising in panels without ribs, in the form of a reduction in panel thickness and excessive shear deformation. The model captures both material failures and stability failure, essentially skin wrinkling in compression. The model is successfully validated using a large experimental database and predicts well full flexural responses. It is shown that ribs allow compression skin to reach its full material strength. Panels without ribs fail by skin wrinkling under concentrated loads, while those under distributed loads fai...

Semi-continuous approach for the modeling of thin woven composite panels applied to oblique impacts on helicopter blades

Abstract: In aeronautics, passenger safety and reliability of structures are essential aspects. In the specific case of helicopters, blades are subjected to impact loadings. Modeling these phenomena continue to be difficult and experimental tests often replace the prediction. The following work will focus on the experimental and numerical study of an oblique impact on the skin of the blade. It is equivalent in a first approach to an impact on a sandwich panel made up of a foam core and a thin woven composite skin. The objectives are to identify the mechanisms of damage in the skin for this kind of loading and to develop a representative modeling of the chronology of damage adapted to the modeling of the complete structure. Thus, a semi-continuous F.E. explicit modeling has been developed. It relies on the development of a specific damageable element at the bundles scale. Satisfactory numerical results are obtained. They allow the identification of the damage mechanism of the woven skin.

Impact Damage Detection in Composite Chiral Sandwich Panels

Abstract: This paper demonstrates impact damage detection in a composite sandwich panel. The panel is built from a chiral honeycomb and two composite skins. Chiral structures are a subset of auxetic solids exhibiting counterintuitive deformation mechanism and rotative but not reflective symmetry. Damage detection is performed using nonlinear acoustics,involves combined vibro-acoustic interaction of high-frequency ultrasonic wave and low-frequency vibration excitation. High-and low-frequency excitations are introduced to the panel using a low-profile piezoceramic transducer and an electromagnetic shaker, respectively. Vibro-acoustic modulated responses are measured using laser vibrometry. The methods used for impact damage detection clearly reveal de-bonding in the composite panel. The high-frequency weak ultrasonic wave is also modulated by the low-frequency strong vibration wave when nonlinear acoustics is used for damage detection. As a result frequency sidebands can be observed around the main acoustic harmonic in the spectrum of the ultrasonic signal.