Glass Fibre Reinforced Polymer Sandwich Research Articles

Connection development and in-plane response of glass fiber reinforced polymer sandwich panels with reinforced cores

This paper presents the findings of an experimental research project that was conducted in two phases to study the behavior of glass fiber reinforced polymer (GFRP) sandwich panels with reinforced cores under in-plane loading conditions. The tested panels consisted of two GFRP face skins separated by a polymeric foam core. The foam core was reinforced with different configurations of through-thickness fiber insertions and through-thickness GFRP web skins. In the first phase the performance of three different types of structural connections was tested — namely, bolted, bonded, and so-called enhanced bolted connections. The findings indicate that bolted connections to thinner and more flexible panels exhibited lower strength and a higher degree of nonlinear behavior compared with the bonded connections to the same panels. In contrast, the bolted connections to thicker and stiffer panels were generally stronger and stiffer than their bonded counterparts. The findings further indicate that the ultimate strength of the connections can be increased by up to 26% by bonding a steel reinforcing plate to the face skins of the panel prior to bolting. In the second phase three full-scale sandwich panels (1400 mm × 1400 mm) with different panel configurations were tested under proportional, biaxial, in-plane loading. The applied loads were selected to simulate the in-plane loading conditions in sandwich panels that are subjected primarily to in-plane loads, such as webs of deep beams and shear walls in lightweight structures. The full-field strains and displacements of the panels were measured using a digital image correlation-based (DIC) non-contact measurement system. The findings indicate that the through-thickness core reinforcements effectively prevented localized buckling, debonding, and separation of the panels’ face skins. The findings also demonstrated that slender panels exhibit shear–compression buckling failures, whereas less slender panels exhibit shear–tension rupture failures.

GFRP-Balsa Sandwich Bridge Deck: Concept, Design, and Experimental Validation

The concept, design, and experimental validation of the new Avançon Bridge in Bex, Switzerland, are described. The lightweight glass fiber–reinforced polymer (GFRP) sandwich bridge deck adhesively bonded to steel girders, reduced the traffic disruption period by approximately 40 days or 80% compared to a cast-in-place concrete bridge, and also enabled the bridge to be widened to two lanes. The semi-integral bridge concept allows the application of a continuous asphalt layer across the abutments without expansion joints and thus facilitates and reduces maintenance. The GFRP sandwich deck with structural balsa core fulfils all the requirements concerning serviceability, ultimate limit state, and fatigue. The bridge deck dimensions significantly depended on the selected and applied design recommendation. In the case of the Avançon Bridge, the German and British recommendations provided the most conservative sets of material factors, the Dutch recommendation specified the least conservative, with the Eurocomp recommendation lying somewhere in between. In particular, the selected material factor applied to stiffness influenced the deck composition and material consumption.

Geometry and restraint effects on the bending behaviour of the glass fibre reinforced polymer sandwich slabs under point load

The behaviour of structural glass fibre reinforced polymer (GFRP) composite sandwich slab was investigated under static point load. In this paper, the effects of dimensions aspect ratio, skin fibre orientations, overall thickness, boundary restraints, and boundary conditions on the static behaviour of the GFRP slab were presented. It was found that the ultimate load of the fibre composite sandwich slab is reducing with increasing panel dimension aspect ratio. The experimental results also showed that the fibre orientation of the skin has an effect on the failure mode and stiffness of the slab. As expected, the flexural stiffness of 18mm thick slab is higher than the 15mm thick slab. Finally, the restraint conditions did not affect much on the failure load and stiffness of the one-way and two-way slab systems.

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.

Experimental and numerical analysis of an innovative GFRP sandwich floor panel under point load

A new glass fibre reinforced polymer (GFRP) sandwich panel has been developed for flooring system. The new panel is made of modified phenolic core and E-CR glass skins. This paper presents the results of the experimental behaviour and the non-linear finite element analysis (FEA) of the GFRP sandwich panel. The experimental works investigate the behaviour of the GFRP sandwich panel, skin–core interaction, and core behaviour. A non-linear finite element model was developed to simulate the behaviour of the skin–core interaction, and the model was verified by comparing the results with those obtained from testing. The non-linear FE model was applied to a single span GFRP sandwich floor panel under point load test. The GFRP sandwich floor panel demonstrated a linear behaviour under point load. The results of the numerical simulations show a good agreement with the experimental results.

The Effects of Air and Underwater Blast on Composite Sandwich Panels and Tubular Laminate Structures

The resistance of glass-fibre reinforced polymer (GFRP) sandwich panels and laminate tubes to blast in air and underwater environments has been studied. Procedures for monitoring the structural response of such materials during blast events have been devised. High-speed photography was employed during the air-blast loading of GFRP sandwich panels, in conjunction with digital image correlation (DIC), to monitor the deformation of these structures under shock loading. Failure mechanisms have been revealed by using DIC and confirmed in post-test sectioning. Strain gauges were used to monitor the structural response of similar sandwich materials and GFRP tubular laminates during underwater shocks. The effect of the backing medium (air or water) of the target facing the shock has been identified during these studies. Mechanisms of failure have been established such as core crushing, skin/core cracking, delamination and fibre breakage. Strain gauge data supported the mechanisms for such damage. These studies were part of a research programme sponsored by the Office of Naval Research (ONR) investigating blast loading of composite naval structures. The full-scale experimental results presented here will aid and assist in the development of analytical and computational models. Furthermore, it highlights the importance of support and boundary conditions with regards to blast resistant design.

Static and fatigue bending behavior of pultruded GFRP sandwich panels with through-thickness fiber insertions

This paper presents the findings of a research program that was undertaken to evaluate the static and fatigue characteristics of an innovative 3-D glass fiber reinforced polymer (GFRP) sandwich panel proposed for civil infrastructure and transportation applications. The research consists of analytical modeling verified by experimental results. A rational analytical model is presented and used to evaluate the effective elastic modulus, shear modulus and degree of composite interaction of the panels to resist one-way bending. The experimental program was conducted in two phases to study the static and fatigue behavior of the panels. In the first phase a total of 730 sandwich beams were tested to evaluate the effect of different parameters on the fundamental behavior of the panel. The parameters considered include the pattern and density of through-thickness fiber insertions, the overall thickness of the panels, and the number of FRP plies in the face skins. The study indicates that the shear behavior and degree of composite interaction of the panels is sensitive to the configuration of the panel core. The second phase of the experimental program included testing of 24 additional sandwich panels to evaluate the fatigue behavior. The results of the experimental program indicate that the panels with stiffer cores generally exhibited a higher degree of degradation than panels with more flexible cores. The findings of this study indicate that the proposed panels represent a versatile construction system which can be configured to achieve the specific design demands for civil engineering infrastructure applications.

Thermomechanical Behavior of Multifunctional GFRP Sandwich Structures with Encapsulated Photovoltaic Cells

The feasibility of encapsulating solar cells into the glass fiber-reinforced polymer (GFRP) skins of load-bearing and thermally insulating sandwich elements with foam cores has been evaluated. Exposure of the encapsulated cells to artificial sunlight led to a significant temperature increase on the top sandwich surface, which almost reached the glass transition temperature of the resin. Mechanical loading up to serviceability limit loads did not cause any damage to the solar cells. Stresses of less than 20% of the material strength arose in the face sheets due to thermal and mechanical loading up to failure. Composite action through the face sheets with encapsulated cells was maintained and no debonding between face sheets and foam core was observed. Thanks to the superior mechanical and thermal sandwich behavior, thin-film silicon cells are more appropriate than polycrystalline silicon cells for use in multifunctional GFRP sandwich structures, although they are less efficient.

Two-way bending behavior of 3-D GFRP sandwich panels with through-thickness fiber insertions

This paper presents the details of a research program that was conducted to evaluate the two-way bending behavior of 3-D glass fiber reinforced polymer (GFRP) sandwich panels. The panels consist of GFRP skins with a foam core and through-thickness fiber insertions. While the behavior of these panels under one-way bending is relatively well understood the behavior under two-way bending has not yet been investigated. An experimental program was conducted to evaluate the effect of the fiber insertion pattern and the panel thickness on the two-way bending behavior under the effect of a concentrated load. The experimental results were used to verify a non-linear, static finite element model which was used to introduce a simplified method to predict the behavior. The measured and predicted responses indicate that at lower deflections the panel behavior is dominated by plate bending action while for higher deflections membrane action dominates. The finite element analysis was extended to study the effect of different parameters which were not tested in the experimental program. The parametric study indicates that increasing the relative flexural or shear rigidities of the panel alters the behavior towards the plate bending mechanism thereby reducing the percentage of load carried by membrane action.