Behaviour Of Composite Sandwich Panels Research Articles

Experimental study on the fire resistance of all-composite and hybrid web-core sandwich panels for building floors

Fibre-reinforced polymer (FRP) composites and polymeric foams used in construction are susceptible to elevated temperatures, but little is known about the behaviour of composite sandwich panels under fire exposure. This paper presents an experimental study on the fire resistance of web-core composite sandwich panels with polyurethane foam infill for building floors. Two panel variants were considered: (i) an all-composite panel, with glass-FRP (GFRP) face sheets and webs; and (ii) a hybrid panel, with an additional fibre reinforced concrete (FRC) top layer. Five full-scale specimens were loaded in a four-point bending configuration, subjected to a constant service load, and subsequently exposed to a standard fire (ISO 834) on their bottom face. The effectiveness of passive fire protection systems, consisting of calcium silicate boards installed either adherent to the panels or forming an air cavity, was assessed. The following features were investigated: (i)temperature progression across the thickness of the panels, (ii)their mechanical response, (iii)failure modes, and (iv)fire resistance. The results obtained indicate that despite the vulnerability of composite sandwich panels to fire, relatively high fire resistances of 44 min and 49 min were obtained for the unprotected web-core all-composite and hybrid variants, respectively. The failure mechanism of the sandwich panels generally involved local compression and in-plane shear failure of the webs. The use of suitable passive fire protections provided significant fire resistance increases of at least 45 min (adherent) and 60 min (with air cavity), allowing to exceed the 90 min threshold.

Non-linear vibration and parametric optimization of sandwich composite curved shell panels with graphene reinforced skins and auxetic honeycomb core

This study aims to investigate the non-linear free vibration behavior of composite sandwich panels composed of Graphene-reinforced composite (GRC) skins and honeycomb auxetic core. Here, modified Halpin-Tsai micromechanics and bottom-up multi-scale-based schemes are employed to compute the spatial-dependent elastic properties of Graphene nanocomposite and auxetic honeycomb core, respectively. The non-linear kinematic field is based on Kant’s higher-order shear-deformation theory and the Green strain. Using the Hamilton principle, the nonlinear governing equations are affirmed and solved further through Picard’s iteration-based 2D-isoparametric finite element approximations via Lagrangian elements. The mesh convergence and validation tests are executed to confirm the consistency and correctness of the developed model. The established sandwich model is further employed for various parametric conditions by varying the core-to-face sheet thickness, auxetic honeycomb properties, graphene volume fraction, shell configurations, temperature, and support conditions. These numerous results exemplify the non-linear frequencies at small-to-large amplitudes for the sandwich shell structures and are discussed in detail. In addition, parametric optimization is conducted using the response surface method to investigate the optimal values of auxetic honeycomb parameters, resulting in maximum frequency response. Findings confirm that, within the selected ranges of the geometric parameters of auxetic honeycomb core, higher values of the thickness of the cell rib (∼1.9 cm) and the length of the vertical cell rib (∼0.15 cm) and lower value of the core thickness (∼5 cm) yield the maximum frequency.

High-speed impact analysis of reinforced GFRP sandwich structure with lattice core using experimental and finite element methods

ABSTRACT High-speed impact behaviour of composite sandwich panels reinforced by nano-SiO2 has been studied in the present article. The sandwich panels were manufactured by glass/fibre epoxy composite face sheets and an M-shaped core using the vacuum-assisted resin transfer moulding (VARTM) method. To enhance the mechanical strength of the matrix, especially impact resistance, the nanoparticles were added to the resin epoxy matrix as filler. A scanning electron microscope (SEM) was utilised to observe the microscopic structure of the composites. The experimental results indicated that adding 1–3 wt-% of nano-SiO2 into the matrix remarkably increased the impact resistance of the composite. In order to validate the results, the experimental data were compared to the finite element models, and good agreement was observed.

Assessment of high-velocity impact effects on carbon fiber reinforced polymer sandwich panel with M-shaped core reinforced by nano-SiO2: Experimental and numerical study

This paper describes the high-velocity impact behavior of composite sandwich panels with different amounts of nano-SiO2. The sandwich panels were manufactured by carbon/fiber epoxy composite face sheets and an M-shaped core using the vacuum-assisted resin transfer molding method. To enhance the mechanical strength of the matrix, especially impact resistance, the nanoparticles were added to the resin epoxy matrix as filler with the ratios of 1%, 2%, and 3% of the composite's total weight. A scanning electron microscope was utilized to observe the microscopic structure of the composites, and it revealed an exceptional homogeneous mixture of nano-SiO2 particles in the resin epoxy matrix. Afterward, high-velocity impact tests were carried out using a single-stage gas gun test machine. A spherical steel projectile with a diameter of 8.7 mm was used for the test with a speed of 235 m/s. The experimental results indicated that adding 1–3 wt% of nano-SiO2 into the matrix remarkably increased the impact resistance of the composite. Moreover, the results showed that when the projectile collides with the core of the sandwich panel, it remains in the sandwich panel and its output velocity becomes zero, while when the projectile does not collide with the core, its output velocity is not zero. In order to validate the results, the experimental data were compared to the finite element models, and good agreement was observed.

Vibro-Acoustic Behavior of Rubber Filled Composite Sandwich Panel

This paper investigates the vibro-acoustic behavior of composite sandwich panels with different cellular sandwich cores. In these designs, two face sheets are made of carbon/ glass hybrid fiber bonded to the hexagonal honeycombs or chiral structure, and the filler is thermoplastic vulcanized rubber. Numerical simulation and model experiments are performed to obtain the vibration and sound radiation of composite sandwich panels with and without rubber. It is found that numerical results including vibration acceleration and sound pressure agree well with the corresponding experimental results. The analysis shows that the rubber filler is able to effectively reduce the vibro-acoustic response of composite sandwich panels. The effect of cellular sandwich core parameters on the vibration and sound radiation of composite sandwich panels is also discussed, which proves that the chiral structure can present superior dynamic properties.

Energy absorption and impact behavior of composite sandwich panels under high-velocity spherical projectile

In this research, the impact behavior and energy absorption of sandwich panels with composite foam cores under high velocity (50 - 220 m/s) impact were experimentally investigated. The dynamic deflection of rear sheets was captured and analyzed using three dimensional digital image correlation technique with high-speed cameras. The effects of density, thickness and multi-layer of cores on the anti-penetration and energy absorption performance of sandwich panels were evaluated. The study results showed that the penetration could only produce the slightly local permanent deformation around the impact position for rear sheets. The plug and petalling were the typical failure modes of front and rear sheets, respectively. The increase in density and thickness of cores both could result in an obvious improvement in the ballistic limit velocity of panels. In addition, the energy absorption efficiency of panels could be effectively improved by increasing the thickness and density of cores. However, the effect of thickness of cores on the attenuation of energy absorption efficiency of panels was negligible under the same density of cores. Particularly, the multi-layer cores presented negligible effect on the anti-penetration and energy absorption performance of panels in this study.

On the subject of analyzing the post-buckling behavior of composite sandwich panels with thin skins of variable stiffness under longitudinal compression

The use of variable stiffness panels can be considered as one of the measures to improve the weight efficiency of aircraft structures. The object of research in this work is three-layer panels of variable stiffness loaded with longitudinal compressive forces. The purpose of the work is to evaluate the overcritical behavior of the specified panels when geometrically nonlinear relations are used. The variable parameter of three-layered panels in the case under consideration is the height of the rigid filler, which varies linearly. An analytical solution of the problem of determining the stress-strain state by the Bubnov-Galerkin method is given. The deflection of a panel is represented by two terms, and the problem is reduced to the solution of a nonlinear system of two unknown equations with respect to the values of the deflection amplitudes. Analytical expressions for calculating membrane stresses are given. The practical significance of the work lies in the possibility of estimating the overcritical behavior of a three-layer panel of variable stiffness under compression and the possibility of constructing an algorithm for the optimal design of the panels.

Mechanical behaviour of composite sandwich panels with foamed concrete core reinforced with natural fibre in four-point bending

The four-point bending behaviour of composite sandwich panels made of corrugated steel faces and foamed concrete (FC) cores with a density of 700 kg/m3 is reported. Plain FC (PFC) core and fibre-reinforced FC (FRFC) core, reinforced with an alkaline-treated natural fibre (henequen fibre) at a volume fraction of 1%, were used. FRFC core reinforced with polypropylene fibre was also used as a reference. The results showed that panels with FRFC cores exhibited greater initial failure load, maximum load and energy absorption when compared to the PFC cored panels, which was associated with the enhancements of ductility and toughness of the FRFC cores produced by the fibres. Several energy absorbing mechanisms were observed in the panels, including the development of major tension and shear cracks in the FC core, face wrinkling and face–core debonding. The finite element simulations showed that the face–core bonding plays a crucial role in the structural performance of the panels. The findings presented herein encourage further investigations to assess the use of sandwich panels with natural-fibre reinforced cores for construction applications.

Low-velocity impact resistance of composite sandwich panels with various types of auxetic and non-auxetic core structures

This work describes the low-velocity impact behavior of composite sandwich panels with different types of auxetic (negative Poisson’s ratio) and non-auxetic prismatic core structures. Sandwich panels have been manufactured with carbon/fiber epoxy composite face sheets, polyurethane rigid foam core or 3D printed PLA plastic cellular honeycombs head (hexagonal, re-entrant, hexachiral and arrowhead). The material properties of the constituents have been determined via tensile and compression tests. The cellular core topologies have the same wall thickness and number of cells (39x4, except for the hexachiral topology). A rigid striker with a hemispherical head tip is dropped on the specimens with a speed of 2.6 m/s. Explicit finite element (FE) models are validated by the experimental results. Parametric numerical analyses using the validated FE have been carried out with different impact energies of 10, 20, 30, 40, 50, 60 and 76 J to identify the best core designs. The results show that non-auxetic cores could have advantages over the auxetic ones at small deformation (impact energy is equal to 10 J) thanks to the larger contact surface and higher thickness of the cellular structure. The auxetic core, however, provides greater impact resistance and energy absorption capability as the impact energy increases due to the larger densification and lower indentation during collapse. The arrowhead-based panels in particular possess 25%, 13% and 11% larger crash efficiency than the other samples for impacts with 50, 60 and 76 J. The hexachiral lattice provides the best performance at 10, 20 and 30 J, and also possesses advantages over the other cellular configurations (except for the arrowhead core) in the case of 40, 50, 60 and 76 J impact loading. As a result, the arrowhead and hexachiral configurations are those mostly recommended for applications involving impacts under large deformations.

Compression behaviour of composite sandwich panels with corrugated core

The corrugated-core of composite structures is low-density for sandwich panels and has excellent anisotropic properties. More efforts are needed to understand the behaviour of such composites under...

Experimental investigation on creep behaviour of composite sandwich panels constructed from polystyrene/cement-mixed cores and thin cement sheet facings

ABSTRACTComposite sandwich panels have gradually become more popular due to their typical benefits including strength, weight, ease of handling, durability, versatility, thermal and acoustic properties. Many researchers are aware of these benefits and have undertaken detailed research and publicised large amounts of scientific papers on composite sandwich panels. With the variety of loads that could possibly be applied to a structure, often the in-service life behaviour is significant. Reviewing whether it will function correctly and without excessive deformations is a factor that can sometimes impact the performance. Polystyrene/Cement-mixed cores and thin cement sheet facings composite sandwich panels are Australian products made of cement–polystyrene beaded mixture encapsulated between two thick cement board sheets. The creep and creep recovery properties of these sandwich panels are relatively unknown. Therefore, in this study, in order to understand the creep and creep recovery behaviour of those sandwich panels, a series of experimental tests have been performed and the outcomes have been explained and discussed. Based on the results of this study, values for immediate recovery, creep recovery and irrecoverable creep strain are determined and proposed. In addition, typical creep and creep recovery design curves have been developed and presented for practical applications in structural engineering.

Structural Behavior of Durable Composite Sandwich Panels with High Performance Expanded Polystyrene Concrete

Sandwich panels comprising prefabricated ultra-high performance concrete (UHPC) composites can be used as eco-friendly and multi-functional structural elements. To improve the structural and thermal performance of composite sandwich panels, combinations of UHPC and expanded polystyrene (EPS) beads were investigated. High-performance expanded polystyrene concrete (HPEPC) was tested with various EPS bulk ratios to determine the suitability of the mechanical properties for use as a high-strength lightweight aggregate concrete. As a core material in composite sandwich panels, the mechanical properties of HPEPC were compared with those of EPS mortar. The compressive strength of HPEPC is approximately eight times greater than that of EPS mortar, and the thermal conductivity of approximately a quarter that of EPS mortar. The structural behavior of composite sandwich panels was empirically analyzed using different combinations of cores, face sheets, and adhesive materials. In the flatwise and edgewise compression tests, sandwich panels with HPEPC cores had high peak strengths, irrespective of the type of face sheets, as opposed to the specimens with EPS mortar cores. In the four-point bending tests, the sandwich panels with HPEPC cores, or reinforced UHPC face sheets combined with adhesive mortar, exhibited higher peak strengths than the other specimens, and failed in a stable manner, without delamination.

Residual bending behaviour of sandwich composites after impact

This work investigates the residual mechanical behaviour of composite sandwich panels in bending after impact loading conditions. The sandwich panels were made of an epoxy/glass face sheet with three different core materials: styrene acrylonitrile foam, polyethylene terephthalate foam and Balsa wood. A three-point bending test was performed in order to determine the reference stiffness. A low-velocity impact test and thereafter the three-point bending test were performed with the same specimens. The failure modes during bending tests were captured using a high-speed camera. It was found that multiple shear cracks with progressive failure were present in the core of styrene acrylonitrile and polyethylene terephthalate panels in bending after impact tests, whereas single shear crack with sudden failure was the case for Balsa panels. The initial bending stiffness decreased approximately 30.5, 35.2 and 55.6% for Balsa, styrene acrylonitrile and polyethylene terephthalate panels, respectively, in bending after impact tests due to the influence of the pre-damage from the low-velocity impact tests. The reduction in collapse force was also quantified for Balsa, styrene acrylonitrile and polyethylene terephthalate panels as 22.8, 4.9 and 22.1%, respectively.

Numerical modelling of the creep behaviour of GFRP sandwich panels using the Carrera Unified Formulation and Composite Creep Modelling

Sandwich panels often need to be designed to sustain significant permanent loads, raising the need to accurately account for long-term creep deformation. However, the accurate prediction of creep in sandwich panels is not trivial, particularly owing to their composite multi-layered nature, the multitude of possible face and core material combinations, and the possible existence of through-thickness shear reinforcement (ribs/webs). This paper presents numerical investigations on the creep behaviour of composite sandwich panels produced by vacuum infusion with glass-fibre reinforced polymer (GFRP) faces and ribs, and polyurethane (PUR) and polyethylene terephthalate (PET) foam cores. Carrera Unified Formulation (CUF) is implemented, for the first time using 1D elements with an equivalent single layer (ESL) methodology, to model the creep response of simple and ribbed panels by adopting a Composite Creep Modelling (CCM) approach. Previous experimental results from creep tests carried out on such sandwich panels and their constituent materials are used to obtain time-dependent constitutive relations for the materials in various layers and validate the numerical results. Additionally, results from analytical beam models using Timoshenko beam theory (TBT) with multi-layered sections are used to further validate the numerical outputs obtained with CUF. The developed numerical models were able to predict the experimental creep behaviour of the full-scale sandwich panels with reasonable accuracy. Differences observed between the CUF and TBT models mainly stem from the inherent approximations concerning the shear correction factors used with TBT, which contrast with the solutions provided by CUF, where such factors do not need to be considered when higher degrees of approximation are used.

Identification and prediction of cyclic fatigue behaviour in sandwich panels

The work describes the development of analytical model to identify and predict the cyclic fatigue behaviour of composite sandwich panels subjected to cyclic fatigue loading under 3-point bending conditions. Sandwich samples made from CFRP skin and Nomex core have been loaded with a mean displacement corresponding to 60% of the failure deformation, and subsequently subjected to cyclic loading under displacement control with different loading levels. The fatigue tests show that the stiffness degradation over the number of cycles is characterised by three different phases according to the loading level used. The evolution of the energy dissipated per unit volume versus the number of cycles has also been considered. The cyclic history of the stiffness degradation is developed here following an alternative approach to the one currently adopted. The approach involves the use of interpolation through empirical functions of the experimental data, with the coefficients of the interpolation based on the material properties of the sandwich structure and the type of loading. The alternative modelling approach presented in this work allows the prediction of the fatigue behaviour in sandwich structures without using a large number of test data currently needed in fatigue testing of sandwich panels.

Experimental, Theoretical and Numerical Investigation of the Flexural Behaviour of the Composite Sandwich Panels with PVC Foam Core

This study presents the main results of an experimental, theoretical and numerical investigation on the flexural behaviour and failure mode of composite sandwich panels primarily developed for marine applications. The face sheets of the sandwich panels are made up of glass fibre reinforced polymer (GFRP), while polyvinylchloride (PVC) foam was used as core material. Four-point bending test was carried out to investigate the flexural behaviour of the sandwich panel under quasi static load. The finite element (FE) analysis taking into account the cohesive nature of the skin-core interaction as well as the geometry and materials nonlinearity was performed, while a classical beam theory was used to estimate the flexural response. Although the FE results accurately represented the initial and post yield flexural response, the theoretical one restricted to the initial response of the sandwich panel due to the linearity assumptions. Core shear failure associate with skin-core debonding close to the loading points was the dominant failure mode observed experimentally and validated numerically and theoretically.

Insight into the shear behaviour of composite sandwich panels with foam core

While sandwich construction offers well-known advantages for high stiffness with light weight, the problem of designing the sandwich structure to withstand shear loading remains an important problem. This problem is more difficult with lower stiffness foam cores under high shear loading because the core is typically the weakest component of the structure and is the first one to fail in shear under the assuming of perfect contact between the skin and the foam core. In the present study, the shear response of the composite sandwich panels with Polyvinylchloride (PVC) foam core was investigated. The PVC H100 foam core is sandwiched between Glass Fiber Reinforced Polymer (GFRP) skins using epoxy resin to build a high performance sandwich panel to be investigated. Experiments have been carried out to characterise the mechanical response of the constituent materials under tension, compression and shear loading. Static shear tests for the sandwich panel reveal that the main failure mode is the delamination between the skin and the core rather than shearing the core itself due to the considerable value of the shear strength of the PVC foam. The Finite Element Analysis (FEA) of the sandwich structure shows that shear response and failure mode can be predicted, but that accurate predictions require a consideration of the non-linear response of the foam core. The results have a direct application in predicting the ability of the sandwich structure to withstand the shear loading.

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

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 tests are carried out by using a material test system and a drop weight machine, respectively. The load-displacement response, energy absorption and energy-absorbing effectiveness of sandwich panels are obtained and compared for quasi-static and impact tests. Effects of some key parameters on the overall energy absorption behavior of the panels are explored, such as impact energy, face sheets and core thickness, core density and indenter nose shape.

GFRP sandwich panels with PU foam and PP honeycomb cores for civil engineering structural applications

PurposeThe purpose of this paper is to present experimental investigations on the structural behaviour of composite sandwich panels for civil engineering applications. The performance of two different core materials – rigid plastic polyurethane (PU) foam and polypropylene (PP) honeycomb – combined with glass fibre reinforced polymer (GFRP) skins, and the effect of using GFRP ribs along the longitudinal edges of the panels were investigated.Design/methodology/approachThe experimental campaign first included flatwise tensile tests on the GFRP skins; edgewise and flatwise compressive tests; flatwise tensile tests on small‐scale sandwich specimens; and shear tests on the core materials. Subsequently, flexural static and dynamic tests were carried out in full‐scale sandwich panels (2.50×0.50×0.10 m3) in order to evaluate their service and failure behaviour. Linear elastic analytical and numerical models of the tested sandwich panels were developed in order to confirm the effects of varying the core material and of introducing GFRP ribs.FindingsTests confirmed the considerable influence of the core, namely of its stiffness and strength, on the performance of the unstrengthened panels; in addition, tests showed that the introduction of lateral reinforcements significantly increases the stiffness and strength of the panels, with the shear behaviour of strengthened panels being governed by the ribs. The unstrengthened panels collapsed due to core shear failure, while the strengthened panels failed due to face skin delamination followed by crushing of the skins. The models, validated with the experimental results, allowed simulating the serviceability behaviour of the sandwich panels with a good accuracy.Originality/valueThe present study confirmed that composite sandwich panels made of GFRP skins and PU rigid foam or PP honeycomb cores have significant potential for a wide range of structural applications, presenting significant stiffness and strength, particularly when strengthened with lateral GFRP ribs.

Structural behaviour of composite sandwich panels with plain and fibre-reinforced foamed concrete cores and corrugated steel faces

This paper studies the four-point bending response and failure mechanisms of sandwich panels with corrugated steel faces and either plain or fibre-reinforced foamed concrete core. Mechanical properties of both plain and polyvinyl alcohol fibre-reinforced foamed concrete were obtained, which are needed for the design of sandwich panel and numerical modelling. It is found that the fibre-reinforcement largely enhances the mechanical behaviour of foamed concrete and composite sandwich panels. Finite element code Abaqus/Standard was employed to investigate the influence of face/core bonding and fastening on the four-point bending response of the sandwich panels. It was found that face/core bonding plays a crucial role in the structural performance while the influence of fastening is negligible.