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Origami foldcore structures can be used in thin-walled sandwich panels to provide unique advantages over traditional honeycomb structures. For instance, their continuously connected space is available for flowing through cooling liquid or compact pipeline placement. However, origami foldcores suffer from relatively low-energy absorption. This paper proposes a new design of energy-absorbing foldcore structures for sandwich panels, including the geometric design, experimental tests, numerical parametric study, and theoretical estimation of energy absorption. Origami initiators are introduced to the Miura foldcores to induce a failure mode with more transverse folds, which is not common for regular foldcore structures. As a result, 60% higher energy absorption and tunable load uniformity can be achieved. [ABSTRACT FROM AUTHOR]

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Composite structural elements can serve dual purposes of transferring the load and insulating the buildings. This paper presents and discusses the results of experimental study carried out to understand the flexural behavior of prototype precast insulated concrete sandwich panels using truss-shaped continuous shear connectors. Experimental study consisted of four prototype concrete sandwich panels tested under four-point bending simulating one-way slab action. Panel thickness and size of wire mesh used as reinforcement in concrete wythes are the major parameters considered. Test results indicate that the truss-shaped shear connectors are effective to achieve composite action of the panels until failure. Test results also indicate that the panel thickness affects the flexural load carrying capacity, and size of wire mesh affects the ductility. Experimental and analytical studies are required in this area towards developing guidelines for design of concrete sandwich panels for field applications. [ABSTRACT FROM AUTHOR]

Sandwich panels with cellular cores are being widely used as blast mitigation materials, due to their light weight and good energy absorption properties. In the present study, the behaviour of sandwich panels against different shock loadings is evaluated using piston driven shock tube. The sandwich panels are fabricated using aluminium(Al) foam core and E-glass/epoxy composite face sheets of different thicknesses. Different shock loads were generated by varying the driven gas pressures. The foams and sandwich panels were subjected to peak shock reflected pressures ranging from 50 bars to 150 bars and the corresponding transmitted pressure pulses were recorded. The behaviour of the foams and sandwich panels under shock wave loading was evaluated by post test visual damage assessment. The effect of face sheet thickness on failure mechanisms of sandwich panel is also studied. The failure mechanisms of foams at higher shock pressures were observed to be core crushing and core fracture, whereas sandwich panels exhibited face sheet deflection, core crushing, fibre breakage at back face sheet and back face delamination. [ABSTRACT FROM AUTHOR]

The paper presents a comparative study on impact damage detection in light composite sandwich panels. Three different nondestructive testing methods were used to characterize damage in a test specimen that resulted from a controlled low velocity impact event. The analyzed test methods include the ultrasonic c-scan, vibrothermography and shearography. All considered techniques were positively verified for detecting damage in a sandwich panel. The paper gives details about the experimental procedures and equipment required to perform the tests. [ABSTRACT FROM AUTHOR]

The paper presents a comparative study on impact damage detection in light composite sandwich panels. Three different nondestructive testing methods were used to characterize damage in a test specimen that resulted from a controlled low velocity impact event. The analyzed test methods include the ultrasonic c-scan, vibrothermography and shearography. All considered techniques were positively verified for detecting damage in a sandwich panel. The paper gives details about the experimental procedures and equipment required to perform the tests. [ABSTRACT FROM AUTHOR]

To study on mechanical properties of non-metal faced sandwich panels under bending load, the force-deformation relationships of differential equations were used to derive and simplify deformation calculate formulas and bearing capacity calculate formulas of the single-span simply supported sandwich panels under uniformly distributed load and concentrated load, considering the influence of the shear deformation of core. Bending properties of two groups of sandwich panels with calcium-silicate ( CS) faces and polyurethane (PU) cores were tested through vacuum chamber loading and sandbag loading and they were analyzed through the finite element methods (FEM) with software ABAQUS. Bending deflection and bending bearing capacity of sandwich panels in serviceability limit states and bearing capacity limit states are got separately and the corresponding load-displacement curves are drew. The results show that the theoretical calculation results are identical to the experimental results and FEM results. It is concluded that the simplified formulas can be used to calculate accurately bending deflection and bending bearing capacity of non-metal faced sandwich panels. [ABSTRACT FROM AUTHOR]

Microtensile testing was used to determine the mechanical properties of individual aluminium alloy open- cell foam struts. Finite element (FE) modelling of as-tested struts was carried out using X-ray microtomography (XMT) scans of the undeformed struts to define the geometry. Strut deformation was described by continuum viscoplastic damage constitutive equations calibrated by the microtensile test data for the aluminium alloy's optimally aged condition. The as-tested strut FE model was used to develop a procedure that compensates for the effect of grip slippage inherent in the microtensile testing of metal foam struts, which results in a considerable underestimation of the elastic stiffness. The calibrated constitutive equations were then implemented into 3D FE models of open-cell metal foam core sandwich panels to study the effect of varying the strut aspect ratio on the mechanical properties of the core under uniform compression, as well as core damage visibility under localised impact scenarios. An optimal strut aspect ratio was identified through simulation that provides the greatest energy absorption per unit mass whilst ensuring core damage is accurately reflected by face sheet deformation, which is necessary for detection and repair. FE models of the panel subject to three and four point bending were created to provide a virtual standardised test to assess the core elastic properties. [ABSTRACT FROM AUTHOR]

The problem of local instability of the compressed facing of a sandwich panel is discussed in this paper. Proper estimation of wrinkling stress has become a challenging issue because of a strong tendency to optimize technical parameters and costs. The aim of the study is numerical and analytical analysis of bending of three-layer panels. Linear constitutive equations and identical elasticity modules in tension and compression are assumed. In practice, wrinkling stress depends on many factors, usually neglected in analytical solutions, though observed in experiments. In this paper we use numerical methods and hence we can allow for the loss of face adhesion or anisotropy of the core. Created models are validated and calibrated by experimental results. The analyses are carried out for various mechanical and geometrical parameters of the sandwich panel. The influence of these parameters on structural response is studied. The range of applicability of classical theoretical models is discussed basing on numerical examples. The study presented in the paper was inspired by sandwich panels producers, with the aim to increase safety and economy [ABSTRACT FROM AUTHOR]

Abstract: Sandwich panels are structural elements widely used, especially in aerospace field, because their high stiffness with a low weight. However the assessment of a detailed and reliable mechanical behaviour especially in compression is, at present, a key task for a large exploitation in primary structures. Due to the large amount and variance in manufacturing processes, the fitting of precise material model behaviour is in fact not a straightforward process. Geometry, material and technological characteristics furnished by the manufacturers are often not sufficient to build a comprehensive model that is representative of the real product. Therefore, starting from an experimental-numerical experience, based on “virtual test” approach of a flatwise compressive test on a Nomextm Honeycomb core, a parametrical analysis of the most significant parameters is carried on by means of Finite Element models. The variation influence of several parameters (wall thickness, dipping thickness, Nomex mechanical characteristic, etc) is investigated around a reference and optimal solution. The influence of the variation of these parameters on the numerical virtual model of the Honeycomb is reported and finally discussed with the aim to help the tailor process of a material behaviour model. [Copyright &y& Elsevier]

Abstract: Sandwich panels are structural elements widely used, especially in aerospace field, because their high stiffness with a low weight. However the assessment of a detailed and reliable mechanical behaviour especially in compression is, at present, a key task for a large exploitation in primary structures. Due to the large amount and variance in manufacturing processes, the fitting of precise material model behaviour is in fact not a straightforward process. Geometry, material and technological characteristics furnished by the manufacturers are often not sufficient to build a comprehensive model that is representative of the real product. Therefore, starting from an experimental-numerical experience, based on “virtual test” approach of a flatwise compressive test on a Nomextm Honeycomb core, a parametrical analysis of the most significant parameters is carried on by means of Finite Element models. The variation influence of several parameters (wall thickness, dipping thickness, Nomex mechanical characteristic, etc) is investigated around a reference and optimal solution. The influence of the variation of these parameters on the numerical virtual model of the Honeycomb is reported and finally discussed with the aim to help the tailor process of a material behaviour model. [Copyright &y& Elsevier]

A review of the investigations that have been made on adhesively bonded joints of fibre-reinforced plastic (FRP) composite structures (single skin and sandwich construction) is presented. The effects of surface preparation, joint configuration, adhesive properties, and environmental factors on the joint behaviour are described briefly for adhesively bonded FRP composite structures. The analytical and numerical methods of stress analysis required before failure prediction are discussed. The numerical approaches cover both linear and non-linear models. Several methods that have been used to predict failure in bonded joints are described. There is no general agreement about the method that should be used to predict failure since the failure strength and modes are different according to the various bonding methods and parameters, but progressive damage models are quite promising since important aspects of the joint behaviour can be modelled by using this approach. However, a lack of reliable failure criteria still exists, limiting in this way a more widespread application of adhesively bonded joints in principal load-bearing structural applications. An accurate strength prediction of the adhesively bonded joints is essential to decrease the amount of expensive testing at the design stage. [ABSTRACT FROM AUTHOR]