Showing papers on "Sandwich panel published in 2013"

A Comparative Study of Ballistic Resistance of Sandwich Panels with Aluminum Foam and Auxetic Honeycomb Cores

Abstract: An innovative auxetic-cored sandwich panel (AXP) is proposed. Its perforation resistant performance under high-velocity projectile impact was numerically analyzed using the validated finite element simulation techniques and compared with that of the aluminum foam-cored sandwich panel (AFP) of identical dimensions and weight. It has been found that the AXP is far superior to the AFP in ballistic resistance because of the material concentration at the impacted area due to the negative Poisson's ratio (NPR) effect. A parametric study was carried out to investigate the effects of several key parameters, including impact velocity, face and core thicknesses, and core density, on the ballistic resistance of the AXP and AFP. The results show that the ballistic limit and perforation energy of the AXP is greatly affected by these parameters. Meanwhile, the advantages of AXP over AFP being used as ballistic resistant structures are highlighted. The primary outcome of this research is new information on the developme...

A review of the vibroacoustics of sandwich panels: Models and experiments

Abstract: This paper reviews the most significant works in literature about the acoustic behaviour of sandwich panels, starting from the first examples of multi-layered structures, comprising a series of dif...

Deformation and Fracture of Impulsively Loaded Sandwich Panels

Abstract: Light metal sandwich panel structures with cellular cores have attracted interest for multifunctional applications which exploit their high bend strength and impact energy absorption. This concept has been explored here using a model 6061-T6 aluminum alloy system fabricated by friction stir weld joining extruded sandwich panels with a triangular corrugated core. Micro-hardness and miniature tensile coupon testing revealed that friction stir welding reduced the strength and ductility in the welds and a narrow heat affected zone on either side of the weld by approximately 30%. Square, edge clamped sandwich panels and solid plates of equal mass per unit area were subjected to localized impulsive loading by the impact of explosively accelerated, water saturated, sand shells. The hydrodynamic load and impulse applied by the sand were gradually increased by reducing the stand-off distance between the test charge and panel surfaces. The sandwich panels suffered global bending and stretching, and localized core crushing. As the pressure applied by the sand increased, face sheet fracture by a combination of tensile stretching and shear-off occurred first at the two clamped edges of the panels that were parallel with the corrugation and weld direction. The plane of these fractures always lay within the heat affected zone of the longitudinal welds. For the most intensively loaded panels additional cracks occurred at the other clamped boundaries and in the center of the panel. To investigate the dynamic deformation and fracture processes, a particle-based method has been used to simulate the impulsive loading of the panels. This has been combined with a finite element analysis utilizing a modified Johnson–Cook constitutive relation and a Cockcroft– Latham fracture criterion that accounted for local variation in material properties. The fully coupled simulation approach enabled the relationships between the soilexplosive test charge design, panel geometry, spatially varying material properties and the panel’s deformation and dynamic failure responses to be explored. This comprehensive study reveals the existence of a strong instability in the loading that results from changes in sand particle reflection during dynamic evolution of the panel’s surface topology. Significant fluid–structure interaction effects are also discovered at the sample sides and corners due to changes of the sand reflection angle by the edge clamping system.

Mechanical response of carbon fiber composite sandwich panels with pyramidal truss cores

Abstract: The combination of light carbon fiber reinforced polymer (CFRP) composite materials with structurally efficient sandwich panel designs offers novel opportunities for ultralight structures. Here, pyramidal truss sandwich cores with relative densities ρ ¯ in the range 1–10% have been manufactured from carbon fiber reinforced polymer laminates by employing a snap-fitting method. The measured quasi-static shear strength varied between 0.8 and 7.5 MPa. Two failure modes were observed: (i) Euler buckling of the struts and (ii) delamination failure of the laminates. Micro-buckling failure of the struts was not observed in the experiments reported here while Euler buckling and delamination failures occurred for the low ( ρ ¯ ⩽ 1 % ) and high ( ρ ¯ > 1 % ) relative density cores, respectively. Analytical models for the collapse of the composite cores by these failure modes are presented. Good agreement between the measurements and predictions based on the Euler buckling and delamination failure of the struts is observed while the micro-buckling analysis over-predicts the measurements. The CFRP pyramidal cores investigated here have a similar mechanical performance to CFRP honeycombs. Thus, for a range of multi-functional applications that require an “open-celled” architecture (e.g. so that cooling fluid can pass through a sandwich core), the CFRP pyramidal cores offer an attractive alternative to honeycombs.

Investigation of Various GFRP Shear Connectors for Insulated Precast Concrete Sandwich Wall Panels

Abstract: Glass fiber–reinforced polymer (GFRP) shear connectors provide much reduced thermal bridging in insulated concrete sandwich panels compared to steel connectors. In this study, 50 specimens with dimensions of 254×254×900 mm representing segments of a precast sandwich wall comprising two concrete wythes and a concrete stud surrounded by insulation foam have been tested in a double-shear configuration. Three types of GFRP connectors produced from available sand-coated and threaded rods were tested and compared to conventional steel and polymer connectors. GFRP connector diameters varied from 6 to 13 mm, and spacing varied from 80 to 300 mm. Both circular and rectangular cross sections were examined, along with various end treatments to compare with simple straight embedment. The shear strength of GFRP connectors, including the effect of friction between concrete and foam, ranged from 60 to 112 MPa, significantly higher than polymer connectors but lower than steel connectors. As the connectors bridge...

Foldcore Sandwich Structures and Their Impact Behaviour: An Overview

Abstract: This chapter gives a global overview on the family of foldcore sandwich structures with a special focus on their impact performance. Foldcore structures are produced by folding a flat sheet of material to three-dimensional zigzag structures in an origami-like manner. Relevant cell wall materials range from cardboard to plastics, from metals to composites. Different manufacturing processes and feasible cellular configurations are presented based on an extensive literature overview. The mechanical properties under compression and shear loads are assessed based on static and dynamic tests. The impact performance under low and high velocity impact with different projectiles ranging from hard body steel impactors to rubber fragments with subsequent damage assessment is addressed. In addition, a comprehensive overview on numerical modelling methods for foldcore sandwich analyses is given. Specific topics like cell wall material and imperfection modelling are discussed. Numerical foldcore geometry optimisation studies and impact simulations are presented and the robustness of such models and their relevance for industrial use is evaluated. Finally, an overview of current and potential applications of foldcore sandwich structures is given.

Impact damage detection in composite chiral sandwich panels using nonlinear vibro-acoustic modulations

Abstract: This paper reports an application of nonlinear acoustics to impact damage detection in a composite chiral sandwich panel. The panel is built from a chiral honeycomb and two composite skins. High-frequency ultrasonic excitation and low-frequency modal excitation were used to observe nonlinear modulations in ultrasonic waves due to structural damage. Low-profile, surface-bonded piezoceramic transducers were used for ultrasonic excitation. Non-contact laser vibrometry was applied for ultrasonic sensing. The work presented focuses on the analysis of the modulation intensities and damage-related nonlinearities. The paper demonstrates that the method can be used for impact damage detection in composite chiral sandwich panels.

A Comparison of Bending Properties for Cellular Core Sandwich Panels

Abstract: In this study, various sandwich panel structures with different reticulate lattice core geometries were designed and then fabricated in titanium via the electron beam melting (EBM) process. Bending tests were performed on the titanium samples, and mechanical properties such as modulus, bending strength, and energy absorption were evaluated. Different failure mechanisms were observed, and it was found that sandwich structures with auxetic cores exhibited more homogeneous deflection and bending compliance compared with other structures. It was also demonstrated that properties of auxetic sandwich structures can be tailored using different cell structure geometries to suit the needs of a given design application. Furthermore, it was found that other 3D cellular sandwich structures can also exhibit high stiffness and strength, which is desirable in potential applications.

Numerical study of blast-resistant sandwich panels with rotational friction dampers

Abstract: Blast-resistant structures are traditionally designed with solid materials of huge weight to resist blast loads. This not only increases the construction costs, but also undermines the operational performance. To overcome these problems, many researchers develop new designs with either new materials or new structural forms, or both to resist the blast loads. Friction damper, as a passive energy absorber, has been used in earthquake-resistant design to absorb vibration energy from cyclic loading. The use of friction damper in blast-resistant design to absorb high-rate impact and blast energy, however, has not been well explored. This study introduces a new sandwich panel equipped with rotational friction hinge device with spring (RFHDS) between the outer and inner plates to resist the blast loading. This device RFHDS, as a special sandwich core and energy absorber, consists of rotational friction hinge device (RFHD) and spring. The RFHD is used to absorb blast energy while the spring is used to restore the original shape of the panel. This paper studies the mechanism of RFHD by using theoretical derivation and numerical simulations to derive its equivalent force–displacement relation and study its energy absorption capacity. In addition, the energy absorption and blast loading resistance capacities of the sandwich panel equipped with RFHDS are numerically investigated by using Ls-Dyna. It is found that the proposed sandwich panel can recover, at least partially its original configuration after the loading and thus maintain its operational and blast-resistance capability after a blasting event. In order to maximize the performance of the proposed sandwich panel, parametric calculations are carried out to study the performance of RFHDS and the sandwich panels with RFHDS. The best performing sandwich panel with RFHDS in resisting blast loadings is identified. This sandwich panel configuration might be employed to mitigate blast loading effects in structural sandwich panel design.

Analysis of large scale cladding sandwich panels composed of GFRP skins and ribs and polyurethane foam core

Abstract: This paper addresses the numerical modeling of lightweight sandwich panels intended for cladding of buildings. The proposed sandwich panels are composed of woven glass fiber reinforced polymer (GFRP) skins and ribs and soft polyurethane foam core, which provides excellent insulation. The panels are designed to resist wind loading. A robust 3D FE model was developed for the large scale panels (9145×2440×78 mm3) tested under transverse loading. The model accounts for material nonlinearities; most pronounced in the soft polyurethane core and in the [0/90] GFRP ribs under shear, as well as geometric nonlinearities in the form of a reduction in panel thickness due to the soft core. The model captures both stability and material failure modes, essentially skin wrinkling and crushing in compression. It was then successfully validated using experimental results. Failure of the tension skin never occurred in this type of panels as compression skin wrinkling and crushing consistently governed. The cladding panel was shown to satisfy design code requirements in terms of strength and stiffness.

Low-velocity perforation behavior of composite sandwich panels with aluminum foam core:

Abstract: Perforation response and failure of sandwich panels with composite face sheets and aluminum foam core are investigated experimentally in this paper. Quasi-static perforation and low-velocity impact...