Glass Fibre-reinforced Polymer Face Sheets Research Articles

Investigation of quasi-static indentation on sandwich structure with GFRP face sheets and PLA bio-inspired core: Numerical and experimental study

Composite materials incorporated in naval, aerospace, and automobile structures are exposed to unforeseen damages, which seriously damage their mechanical performance. In particular, the existence of hardly visual impairment on the in-service composite structures is a critical issue that highlights the severity of structural safety in an aircraft. The ability of these materials to sustain multiple impacts requires an understanding of the impact energy absorption to improve the material’s damage tolerance. The present study investigates the energy absorption, load response, failure modes, and damage mechanics under the quasi-static indentation of a sandwich structure. The structure comprises bio-inspired Poly-lactic Acid (PLA) core and Glass Fibre Reinforced Polymer (GFRP) laminates, used in real naval and aeronautical structures, under repeated low-velocity impact with reduced energies and quasi-static indentation. In addition, a lightweight sandwich structure’s damage performance is greatly influenced by its core geometry. Therefore, choosing an appropriate core structure is critical. A Numerical model is developed for the composite structure under quasi-static indentation loads, considering suitable material properties and damage models for the core and face sheets. These results are then compared with the experimental investigation. The load–displacement response and the energy absorption characteristics of the sandwich structure showed good agreement for the experimental and numerical analysis results.

Bending performance of curved sandwich panels comprising GFRP face sheets and web cores: Experimental investigation and theoretical model

Composite sandwich-walled shells composed of glass fiber reinforced polymer (GFRP) face sheets and web cores manufactured using a new multistage filament winding (MFW) technique is a type of novel structure. The paper uses a three-point bending test and analytical model to study its mechanical response under lateral external load. The analytical model can accurately predict the deformation and ultimate bearing capacity, and it is shown that the web parameters have a crucial influence on the deformation and failure modes. The results provide a theoretical basis for the parameter design and optimization of this type of curved sandwich panel.

Flexural Behavior of Slab-Rib Integrated Bridge Decks with GFRP Skin and Polyurethane Foam Core

This paper presents experimental and analytical studies on flexural behavior of slab-rib integrated Sandwich composite decks. The influences of layers of glass fiber-reinforced polymer (GFRP) facesheets, foam densities, and the existence of webs and cross beams are discussed herein. The test results showed that the existence of vertical webs remarkably improved the debonding of the facesheets from the foam core, thus increasing the ultimate load by 59% compared with the specimens without webs. However, the existence of horizontal webs has insignificant effect on the failure mode and ultimate load. Increasing the number of layers of GFRP facesheets from 2 to 4 and 6 results in 100% and 214% increments in ultimate loads, respectively, while the specimen with lower density of foam had a higher ultimate load than the specimen with higher density of foam due to deformation compatibility between GFRP skins and foam core with low density. The analysis software Abaqus Explicit was used to simulate the flexural behavior of test specimens, and the numerical results agreed well with the test data. The verified finite element model was extended to analyze the influences of the number of GFRP layers on the top of decks and the height of vertical webs. Based on equivalent method and compatibility of shear deformation, the flexural and shear rigidities were estimated. Then, analytical solution for displacement of the slab-rib integrated Sandwich composite decks subjected to four-point load was derived out. Comparison of analytical and experimental results shows that the displacements can be precisely predicted by the present theoretical model.

Numerical analysis on flexural behaviour of GFRP sandwich roof panel with multilayer core material

In this study, the flexural performance of Glass Fibre Reinforced Polymer (GFRP) sandwich roof panel with multilayer polyurethane foam core was investigated using commercial FEM software ANSYS WORKBENCH. The GFRP sandwich panel is composed of thin GFRP face sheets at top and bottom infilled with Polyurethane (PU) foam core of two different densities. GFRP sandwich panels with different stacking sequences of the multilayer core was considered to determine the best sequence in which the different layers of core material can be laid on top of each other. The optimum panel size was obtained from parametric study conducted with number of GFRP plies and thickness of core as parameters. Alternatively, the flexural behaviour of GFRP sandwich panel with three different web core configurations were also studied, which includes trapezoidal shaped GFRP webs infilled with PU foam (Type 1), rhombus shaped GFRP webs infilled with PU foam (Type 2), and wave shaped GFRP webs infilled with PU foam (Type 3). Based on the finite element analysis, GFRP sandwich panel with Type 3 core configuration (wave shaped GFRP webs infilled with PU foam) with lesser deformation represented a feasible model to be used as a roofing panel for small residential buildings and prefabricated modular constructions.

Strain energy release rate of sandwich composite beams for different densities and geometry parameters

In this paper, fracture behaviour of marine sandwich structured composite beams manufactured by vacuum-assisted resin infusion process with a PVC foam core, and different thicknesses of upper and lower glass fibre-reinforced polymer face sheets have been investigated. Fracture toughness in terms of strain energy release rate of sandwich composite beam is obtained using three end notched flexure test (3 ENF) by analytical method, finite element simulation using J integral and virtual crack closure technique (VCCT). Experimental testing has been applied with more accurate loading values for finite element modelling (FEM) simulations. The good agreement between experimental and numerical results shows that the finite element model is acceptable. A parametric study is carried out to observe the effects of core thickness, density of core, length of specimens, loading directions of the specimens on strain energy release rate (SERR) of sandwich composite beams under mode II loading. It is developed for the different core thicknesses with varying density combinations. The variations of maximum SERR value are presented graphically using numerical method and compared with analytical solution.

Experimental, analytical and numerical study of mechanical properties and fracture energy for composite sandwich beams

In this study, the mechanical and fracture behaviour of marine sandwich-structured composite that is manufactured by vacuum-assisted resin infusion process with a PVC foam-web core, and different thicknesses of upper and lower glass fibre-reinforced polymer face sheets used as outer and inner side of the hull have been examined. The properties of PVC core, face sheet material, and composite sandwich structures are presented. Failure modes include sandwich flatwise tension, core flatwise compression, sandwich edgewise compression, and face sheet bending of manufactured composites have been investigated experimentally for marine application. The analytical solution is derived to calculate the flexural rigidity, shear stresses and maximum tensile, compression stresses in three-point bending specimens for marine sandwich composites. 3 End Notched Flexure test method has been applied to calculate the strain energy release rate. Moreover, the finite element study is carried out by using a 2D model to calculate the fracture energy (J) value numerically and virtual crack closure technique. Reasonably good results are obtained between analytical and numerical methods.

A Methodology for Enhancing the Shear Response of Sandwich Composite Panel: Sandwich Composite Panel with Stair Keys

Objectives: In composite sandwich panel, delamination between the foam core and face sheet is due to inability to withstand shear load. Hence a methodology of introducing shear keys for enhancing the shear response to resist delamination is analysed in the present study. Methods/Statistical Analysis: The conventional sandwich panel under analysis is composed of Glass Fibre Reinforced Polymer (GFRP) skin with PVC (Polyvinyl chloride) foam core impregnated with epoxy resin. The present study is to introduce stair keys in between GFRP and PVC which are made by overlapping GFRP face sheets, with the length and depth to get the required step size. Parametric Finite Element (FE) investigation using ANSYS software has been performed to evaluate the foam core performance by grooving the foam material as stepped shapes. The effect of different length of the stepped grooves in foam material are analysed and its results are compared with conventional sandwich panel. The stair key response for number of steps ranging from n = 1, 3, 5 and 7 are investigated. Findings: The FE results showed an improvement in the shear stress response of the sandwich panel with stair grooved foam core with stair keys compared to conventional model. Also the stair inserts between the GFRP skin and the foam core increases the initial shear stiffness and ultimate shear strength of the proposed model of the sandwich panel. Application/Improvements: The present methodology acts as a new model of peel stopper mechanism, where the shear failure due to debonding of face sheet and foam core is rerouted to foam core. Also it is free from initial damage as there is no loss of solidarity of the bulk material at the foam core, cost effective and easy to design and manufacture compared to other pinning and stitching process.

A STUDY ON GLASS FIBER REINFORCED POLYMER-CLAY NANOCOMPOSITES WITH SANDWICH STRUCTURE

Glass fiber reinforced polymer (GFRP) has been found attractive due to high strength-to-weight ratio, high stiffness-to-weight ratio, and corrosion and fatigue resistance. The properties of GFRP are further enhanced by adding very small amount of nanometer size particles. The use of sandwich composites with GFRP face sheets is becoming popular in structural design because of their ability to substantially decrease weight while maintaining mechanical performance. In this study face sheets of sandwich composites are modified using nanoclay particles. The sandwich structure composed of bidirectional E-glass fiber, Closite 30B nanoclay, epoxy resin and high density thermocol. Hand layup method was used for fabrication of sheets also the nanoclay percentage was varied subjected to various test. The use of nano composite increases the bending strength up to 41% as compared to virgin epoxy. The natural degradation of bending specimen with neat epoxy showed the maximum degradation up to 10% and it was 5% in case of specimens with nano composite sheets. The water resistance property of epoxy was improved by the addition of both glass fibre and nanoclay. The tensile strength is raised by 33% by using 3% of clay in the epoxy. The SEM and XRD were performed for characterization of the nano composites.

Analysis of ultrasonic waveforms from smart sandwich composite structures under creep bending at elevated temperature

Sandwich structures with polyurethane foam core and glass fiber–reinforced polymer facesheets with three orientations were investigated experimentally and numerically under three-point bending tests at 80 °C, at a relatively low load level associated with a linear viscoelastic response. Off-the-shelf piezoelectric transducers were inserted inside one of the facesheets and were interrogated in pitch-catch at low ultrasonic frequencies during testing. The objective of this article is to investigate ability and sensitivity of the embedded transducers to detect creep deformation. The denoised received waveforms were analyzed in the time domain, where guided wave speeds were found to exhibit a drop due to temperature changes (most significant in the sandwich samples with off-axis orientation), followed by an increase, eventually reaching an asymptotic value. The waveforms were also processed in the joint frequency–time domain, with a novel signal processing technique built upon Gabor wavelet transforms and their contour lines. It is shown that this wavelet contour technique indirectly captures the trend of physically measured displacements and can differentiate among the three different fiber orientations in the facesheets, and among room temperature and 80 °C. This technique has the potential to effectively track creep time-dependent response and life performance in smart sandwich composites.

A comparative study of the impact properties of sandwich materials with different cores

Sandwich panels are made of two high strength skins bonded to either side of a light weight core and are used in applications where high stiffness combined with low structural weight is required. The purpose of this paper is to compare the mechanical response of several sandwich panels whose core materials are different. Sandwich panels with glass fibre-reinforced polymer face sheets were used, combined with five different cores; polystyrene foam, polypropylene honeycomb, two different density Balsa wood and Cork. All specimens were subjected to low velocity impact and their structural response (Force-displacement curves) were compared to quasistatic response of the panel tested using an hemispherical indenter.

Contribution to Shear Wrinkling of GFRP Webs in Cell-Core Sandwiches

Glass-fiber-reinforced polymer (GFRP) cell-core sandwiches are composed of outer GFRP face sheets, a foam core, and a grid of GFRP webs integrated into the core to reinforce the shear load capacity. One of the critical failure modes of cell-core sandwich structures is shear wrinkling, a local buckling failure in the sandwich webs because of shear loading. The shear wrinkling behavior of GFRP laminates with different laminate sequences, stabilized by a polyurethane foam core, was experimentally and numerically investigated. Shear wrinkling was simulated by a biaxial compression–tension setup. The results show that an increasing transverse tension load significantly decreases the wrinkling load. The decreasing effect of tension is explained by the lateral contraction because of Poisson’s effect, which causes an increase in the initial imperfections and subsequent accelerated bending.