Behavior Of Composite Sandwich Beams Research Articles

Finite Element Analysis of Hybrid Skin Sandwich Composite

Sandwich structured composite is a particular classification in composite materials. This type of structure has been mainly used in recent studies because of its high specific strength, low density, and stiffness. It is increasingly more commonly employed in structural designs due to its features and performance. The sandwich composites used in this investigation are made of aluminium alloys and areca fibre. The sandwich composite’s face sheet comes in a variety of thicknesses. The adhesive skin layer is also varied to investigate the effect of using natural fibre. The sandwich composite is subjected to 3 point bend test. The modal analysis is investigated using the finite element method. The 3D model of sandwich composites is modelled using solid works 2020. Using Altair Hyper Works, the boundary conditions and meshing is carried out. ANSYS Mechanical APDL is used to analyse the sandwich composites. This investigation analyses the behaviour of composite sandwich beams.

The flexural behaviour of composite sandwich beams with a lattice-web reinforced wood core

In this study, the flexural behaviour of lattice-web reinforced composite sandwich beams was investigated. The innovative composite sandwich beams consisted of glass fibre reinforced composite materials as the surface layer and web, Paulownia wood and South Pine as the core material. While keeping the external size unchanged, 1, 2, 3, 4 and 5 wood cores were formed by the vacuum infusion process at one time, to develop a different number of lattice-webs. In addition, the wood beam was used as a control. A four-point bending test was carried out on all specimen beams. The equivalent bending stiffness, equivalent shear stiffness, mid-span deflection of the specimens and bearing capacity were analysed. There is a larger plateau stage in the latter part of the load-midspan deflection curve of the beams strengthened by the lattice-web, which means the beams had ductile failure characteristics. Furthermore, the type of wood core greatly influenced the flexural behaviour of the composite sandwich beam, and the optimum lattice-web number of the Paulownia specimen is 2, and that of the South Pine specimen is 3.

Bending behaviour of composite sandwich beams manufactured by 3D printing with continuous fibre reinforcement

Additive manufacturing with FFF (Fused Filament Fabrication) technology using continuous fibre, allows more complex structure designs with more technical materials than conventional manufacturing processes. The present paper is focused on analysing the bending behaviour of sandwich beams with unidirectional carbon fibre skins and honeycomb type core. The nobelty of the research is focused on printed materials (polyamide 6 reinforced with continuous carbon fibres) and the fact that the core has been manufactured directly in the printig process. The study variable consisted of the spatial arrangement of the beam; for the first type of beams the skins are positioned in parallel with the base plate, whereas for the second type of beams, the skins are placed perpendicullary with respect to the base plate. Thus, in both cases skins are obtained with the same fibre orientation, but with different manufacturing strategies. Otherwise, those configurations where skins are placed in parallel with respect to the base plate, the influence of reinforcing the hexagons of the core with carbon fibres following different strategies has been analysed. On the one hand, the hexagons are reinforced depositing continous carbon fibre following concentric deposition strategy, forming hexagonal rings in each hexagon independently. On the other hand, the overall core is reinforced toghether with continous carbon fibres following the external perimeter of the core. Results show that the beams whose skins have been manufactured in parallel with respect to the base plate have higher stiffness. In the same way, those structures with reinforced cores have a higher stiffnes compared to those with non-reinforced cores.

Effect of shear span-to-depth ratio on the mechanical behavior of composite sandwich beams with GFRP ribs and balsa wood core materials

Abstract This study investigated the effect of shear span-to-depth (a/d) ratio on the mechanical behavior of composite sandwich beams, composed of glass fiber reinforced polymer (GFRP) skins, balsa wood core, and GFRP ribs. Three-point bending tests were carried out on fifteen specimens to verify the effects of the a/d ratio, varying from 1 to 6, and GFRP ribs on the deflections, failure load, and failure modes of sandwich beams. Test results indicated that the a/d ratio plays a major role in beam deflections, which decreased 74–1418% as the a/d ratio varying from 1 to 6. All beams exhibited deflections at failure of span/124 to span/35. Specimens failed in balsa wood core shear failure while a/d ≤ 4, whereas it failed in top skin compression failure when a/d ratio equal to 6. Increasing the GFRP ribs thickness from zero to 2.4 mm, the failure load of sandwich beams increased by 23–75%. Moreover, the ultimate moment increased by 70–323% as the a/d ratio increases from 1 to 6. In addition, for specimens with a/d equal to 4, the failure load and stiffness of sandwich structures with balsa wood core was 79–209% and 90–246% higher than those of specimens with different densities of light-weight foam core. A simplified analytical model accounting for the influence of GFRP ribs on stiffness and strength of the sandwich beam was developed and validated against experimental results. Analysis shows that flexure became more dominant as the a/d ratio increases. The shear deformation contribution of the balsa wood core is over 50% in beams with a/d ≤ 3, while the value is only 20% for beams with a/d equal to 6. The proposed analytical model which accounts for the combined effect of the GFRP ribs agrees well with the experimental results.

Fatigue behaviour of composite sandwich beams strengthened with GFRP stiffeners

This paper investigated the fatigue behaviour of composite sandwich beams, which consisted of glass fibre reinforced plastic (GFRP) skins and a foam core, strengthened with transverse or longitudinal GFRP stiffeners. A total of 42 specimens were prepared using vacuum-assisted resin transfer molding technology. The effects of GFRP stiffeners (transverse or longitudinal) on failure mode, bending deflection behaviour and fatigue life of specimens were investigated. Experimental results revealed that for beams with transverse stiffeners, the failure initiated from core shear and interface debonding between stiffeners and foam core; while for beams with longitudinal stiffeners, the failure was due to GFRP skins compression failure or longitudinal GFRP stiffeners buckling or fracture failure. Moreover, the bending strengths and failure fatigue cycle numbers of beams with longitudinal GFRP stiffeners were all larger than those of common beams or beams with transverse GFRP stiffeners. Lastly, a fatigue damage model was developed to predict the failure cycle number under different loading levels. The validity of the proposed model has been verified to estimate the fatigue behaviour of sandwich beams strengthened with GFRP stiffeners.

Flexural testing and analysis of full-strain-fields in sandwich composites

The objective of this work was to characterize the full-field flexural behavior of composite sandwich beams. Finite element analysis was used to estimate the behavior of sandwich beams under three- and four-point-bending tests and were compared with experimental results obtained via digital image correlation and strain-gages. Two different core thicknesses and two different sandwich lengths were used to simulate short- and long-beam. Two distinct sandwich beams were fabricated by bonding basalt fiber reinforced polymer composite face sheets (laminates) to polyurethane core and aluminum face sheets glued to polyurethane core with an adhesive film. Full-strain-fields and flexural displacements were obtained by means of strain-gages and digital image correlation technique. Experimental results were in good agreement with predictions and digital image technique attested to be a complementary method to strain-gages in experimental full-strain-fields analysis.

Flexural creep behavior and life prediction of GFRP-balsa sandwich beams

In this paper, the flexural creep behavior of composite sandwich beams with glass fiber- reinforced polymer (GFRP) face sheets and a balsa wood core was investigated. First, static three-point bending tests for the beams were conducted, and an average ultimate bearing capacity of 6.08 kN was obtained. Then, ten bending creep test devices were designed and manufactured based on the principle of leverage. Creep experiments were carried out for a period of 3000 h at four different load levels corresponding to 20%, 40%, 60% and 80% of the ultimate bearing capacity. The results show that the creep behavior exhibits linear viscoelastic properties when the load level is less than 40%, while creep failure occurs in all specimens at load levels of 60% and 80%. Specimens subjected to the 60% load level exhibit two failure modes, i.e., core shear failure and overall bending failure, while specimens subjected to the 80% load level exhibit only bending failure. Furthermore, the experimental creep curves at the 20% and 40% load levels are successfully fitted by the Bailey-Norton and Findley models, and a life prediction method is proposed to predict the creep life of the beams at any load level.

Flexural behavior of composite sandwich beams with different kinds of GFRP ribs in flatwise and edgewise positions

This paper investigated the flexural behavior of composite sandwich beams, composed of glass fiber reinforced polymer (GFRP) skins and a polyurethane (PU) foam core with different kinds of GFRP ribs reinforcement, in flatwise and edgewise positions. The GFRP ribs, consisted of longitudinal, transverse and horizontal ribs, respectively, were embedded inside of the PU foam core. Twenty specimens were tested under four-point bending to verify the influence of the GFRP ribs and beam orientation on the bending stiffness, ultimate load bearing capacity, and failure modes of sandwich beams. It was found that changing the beam orientation from flatwise to edgewise change the beam failure mode from foam core shear failure to skin compressive failure. The sandwich beam's high stiffness and ultimate load bearing capacity can be efficiently utilized by placing them in edgewise position, and the longitudinal ribs played a major role on the bending stiffness and ultimate load bearing capacity compared with the transverse and horizontal ribs in flatwise position. Furthermore, an analytical model accounting for shear and flexural rigidities was proposed to predict the deflection and ultimate load bearing capacity of composite sandwich beams with different kinds of GFRP ribs in flatwise and edgewise positions. The analytical results were agreed well with test results.

The effect of interface debonding on flexural behaviour of composite sandwich beams

In the current article, the behaviour of sandwich beams with and without initial core–skin debonding is studied under flexural loads through numerical and experimental procedures. Sandwich beams with three different lengths of 100, 180 and 280 mm and two types of composite skin layups of [0/90]2 and [45/–45]2 are fabricated. An initial artificial debonding is created between core and face sheets during manufacturing the flawed sandwich beams. Numerical simulations and experiments of the short- and medium-sized intact beams revealed that the dominant failure mode is foam yielding and crushing. Thus, the composite skins layup sequence has almost no effect on the failure initiation and growth of those beams. However, in the long-sized sandwich beams, the layup sequence changed the load–displacement response of the beams. Moreover, ignoring the nonlinear behaviour of the composite skins caused a remarkable deviation from the experiment. It is shown that sandwich beams with initial debonding placed in tension side had a negligible effect on the loading capacity of the beams, while those on the compression side had remarkable effects. For instance, the ultimate load of the long-sized beam decreased by 56% compared to the intact sandwich beam. Similarly, in the medium-sized beam, the core–skin debonding in the compressive side caused near 20% reduction in the loading capacity compared to the corresponding intact beam. The cohesive zone model and the extended finite element method were utilized successfully to capture crack initiation and propagation between the core–skin interfaces as well as inside the foam core. Acceptable agreement was observed between the experiment and numerical results.

Effect of integral viscoelastic core on the nonlinear dynamic behaviour of composite sandwich beams with rectangular cross sections

This paper deals with geometrically nonlinear transient analysis of sandwich beams with viscoelastic cores and laminated composite skins. The formulation is based on the Full Layerwise theory (FLWT) and the Boltzmann's superposition principle and using weakly singular Koltunov-Rzhanitsyn kernel for modelling the viscoelastic core. The nonlinear governing integro-partial differential equations (IPDEs) of the sandwich beams are derived using Hamilton's principle. The Galerkin method in combination with the Newmark-Beta procedure, which is coupled to the Newton-Raphson algorithm, are employed to solve the obtained nonlinear IPDEs. The effects of using integral model and considering the history of strain for viscoelastic core on the dynamic response of sandwich beams are investigated. The results indicate that, employing the integral model with Koltunov-Rzhanitsyn kernel in the constitutive equation affects the amplitude and the frequency of the dynamic response of sandwich beam. For comparison purpose, the finite element analysis is carried out within ANSYS software environment and the user-material subroutine is developed to model the Koltunov-Rzhanitsyn kernel. The results of the used semi-analytical model agree well with those obtained from finite element method (FEM) of analysis. It should be noted that, because of employing a large number of degrees of freedom in the FEM analysis for accurate modelling of the viscoelastic sandwich beams, the FEM analysis is rather computationally inefficient in comparison to the presented method. Moreover, the Koltunov-Rzhanitsyn kernel is capable of modelling the viscoelastic behaviour accurately with lower number of rheological parameters in comparison to the Prony series.

Numerical simulation of the nonlinear static behavior of composite sandwich beams with a magnetorheological elastomer core

In this work the static behavior of magnetorheological elastomer (MRE) sandwich beams is studied in flexion with transverse shear. The beam is formed by two aluminum skins bonded to a core of elastomeric silicone oil and loaded with iron particles at 30%. The rigidity of the beam is given by the addition of a usual stiffness matrix of two aluminum skins and an MRE complex stiffness matrix. The latter is a function of the magnetorheological properties of the MRE. The results show the influence of MRE adaptive stiffness and the loss factor in the static behavior of the sandwich studied. The structure proposed can be directly applied to civil engineering, for example, building foundations, mechanical engineering and aircraft wings.

Behaviour of fibre composite sandwich structures under short and asymmetrical beam shear tests

The behaviour of structural fibre composite sandwich beams made up of glass fibre composite skins and phenolic core material was investigated under three-point short beam and asymmetrical beam shear tests. The effect of the shear span-to-depth ratio (a/D) on the strength and failure behaviour of the composite sandwich beams was examined. The results showed that with increasing a/D ratio, the failure load of the sandwich beam is decreasing. On the contrary, the coupling effect of flexural stresses increases with increasing a/D ratio. Noticeably, the fibre composite sandwich beams tested under asymmetrical beam shear exhibited higher failure load compared to beams tested under short beam shear. Analysis showed that the shear stress in the core is more dominant than flexural stress when the a/D ratio is 1 for the sandwich beams under short beam test and 1–3 for the sandwich beams tested under asymmetrical beams shear test. The proposed prediction equation which accounts for the combined effect of shear and flexural stresses due to the changing a/D ratio, presented a good agreement with the experimental results, showing that it can reasonably estimate the failure load of structural fibre composite sandwich beams.

Quasi-static and dynamic fracture behavior of composite sandwich beams with a viscoelastic interface crack

Fracture analysis of sandwich beams with a viscoelastic interface crack under quasi-static and dynamic loading has been studied. Firstly, a three-parameter standard solid material model was employed to describe the viscoelasticity of the adhesive layer. And a novel interfacial fracture analysis model called three material media model was established, in which an interface crack was inserted in the viscoelastic layer. Secondly, a finite element procedure based on Rice J-integral and Kishimoto J-integral theories was used to analyze quasi-static and dynamic interface fracture behavior of the sandwich beam, respectively. Finally, the influence of viscoelastic adhesive layer on the quasi-static J-integral was discussed. In addition, comparison of quasi-static Rice J-integral with Kishimoto J-integral under various loading rates was carried out. The numerical results show that the oscillating characteristic of dynamic J-integral is more evident with shorter loading rise time.

FEM analysis of dynamic flexural behaviour of composite sandwich beams with foam core

The dynamic flexural behaviour of sandwich beams, with composite face-sheets and a foam core, was analysed by developing a 3D finite-element model. To model the core behaviour, a crushable foam model was used. The Hou criteria were used to predict the failure of the face-sheets. Dynamic bending tests were performed to validate the numerical model. The comparison between numerical and experimental results in terms of contact-force histories, peak-force values, absorbed energy, and maximum displacement of both face-sheets was satisfactory. It was revealed that the collapse of the foam core under the impact region favoured the failure of the upper face-sheet.

Nonlinear Stress and Deformation Behaviour of Composite Sandwich Beams

The nonlinear load-displacement and normal stress distribution in composite sandwich beams made of unidirectional carbon/epoxy facings and PVC foam cores under bending was studied. The carbon/epoxy after an initial linear response exhibits a stiffening nonlinearity in tension and a softening nonlinearity in compression with the longitudinal strength in tension higher than that in compression. The foam core also presents a nonlinear stress-strain response. It was obtained that the load-displacement behaviour of the beam, after an initial linear part, is not linear. This behavior was modeled by an incremental strength of materials nonlinear analysis. The theoretical predictions were in good agreement with the experimental results. Furthermore, it was obtained that the neutral axis of sandwich beams under bending does not pass through the centroid of the cross section, but is displaced toward the tensile side of the beam. Experimental results by moiré measurements of the in-plane horizontal displacements of the core material corroborated the analytical predictions. These findings imply higher compressive and smaller tensile stresses in the core, than those predicted for facings with identical stress-strain behaviour in tension and compression, and should be taking into consideration in the failure analysis of sandwich beams.

Failure modes of composite sandwich beams

A thorough investigation of failure behavior of composite sandwich beams under three-and four-point bending was undertaken. The beams were made of unidirectional carbon/epoxy facings and a PVC closed-cell foam core. The constituent materials were fully characterized and in the case of the foam core, failure envelopes were developed for general two-dimensional states of stress. Various failure modes including facing wrinkling, indentation failure and core failure were observed and compared with analytical predictions. The initiation, propagation and interaction of failure modes depend on the type of loading, constituent material properties and geometrical dimensions.

Failure of Composite Sandwich Beams

A thorough investigation of failure behaviour of composite sandwich beams under three- and four-point bending was undertaken. The beams were made of unidirectional carbon/epoxy facings and a PVC closed-cell foam core. The constituent materials were fully characterised and in the case of the foam core, failure envelopes were developed for general two-dimensional states of stress. Various failure modes including facing wrinkling, indentation failure and core failure were observed and compared with analytical predictions. The initiation, propagation and interaction of failure modes depend on the type of loading, constituent material properties and geometrical dimensions.

Nonlinear behavior of composite sandwich beams in three-point bending

The load-deflection behavior of a composite sandwich beam in three-point bending was investigated. The beam was made of unidirectional carbon/epoxy facings and a polyvinyl chloride closed-cell foam core. The load-deflection curves were plotted up to the point of failure initiation. They consist of an initial linear part followed by a nonlinear portion. A nonlinear mechanics of materials analysis that accounts for the combined effect of the nonlinear behavior of the facings and core materials (material nonlinearity) and the large deflections of the beam (geometric nonlinearity) was developed. The theoretical predictions were in good agreement with the experimental results. It was found that the effect of material nonlinearity on the deflection of the beam is more pronounced for shear-dominated core failures in the case of short span lengths. It is due to the nonlinear shear stress-strain behavior of the core. For long span lengths, the observed nonlinearity is small and is attributed to the combined effect of the facings nonlinear stress-strain behavior and the large deflections of the beam.

Fabrication, testing and analysis of composite sandwich beams

The objective of this work was to determine experimentally the flexural behavior of composite sandwich beams and compare the results with predictions of theoretical models. Sandwich beams were fabricated by bonding unidirectional carbon/epoxy face sheets (laminates) to aluminum honeycomb cores with an adhesive film. All constituent materials (composite laminates, adhesive and core) were characterized independently. Special techniques were developed to prevent premature failures under the loading pins and to ensure failure in the test section. Sandwich beams were tested under four-point and three-point bending. Strains to failure in the face sheets were recorded with strain gages, and beam deflections, and strains in the honeycomb core were recorded by using moiré techniques. The beam face sheets exhibited a softening non-linearity on the compression side and a stiffening non-linearity on the tension side. Experimental results were in good agreement with predictions from simple models which assume the face sheets to behave like membranes, neglecting the contribution of the honeycomb core, and accounting for the non-linear behavior of the face sheets.

Sensitivity Of Bonded And Composite Beams

In this paper the sensitivity of the modal damping and natural frequencies of adhesively bonded and composite beams to small pre-deformations is investigated. Originally, a set of experiments was conducted on adhesively bonded beams in order to assess the extent to which damping could be influenced by the joint's location. As a part of the study, the experiments were repeated a number of times, and it was observed that the data exhibited a large amount of scatter. After further investigation, it was found that the scatter in the damping data could be correlated with small, initially undetected pre-deformations of the beams, and that the pre-deformation also caused significant changes in the beams' natural frequencies. In order to study this phenomenon further, a finite element model of the specimen was developed that could be used to calculate its mode shapes, natural frequencies and modal damping. The finite element model exhibited behavior that was consistent with the experiments. The calculations also indicated that if the frequencies were plotted as a function of the amplitude of the pre-deformation, then some pairs of frequencies crossed while others veered away from each other, and that the crossings and veerings could be closely related to mode shape changes and damping variations. In addition, the finite element program was used to simulate the behavior of composite sandwich beams and it was predicted that they would exhibit analogous behavior. Lastly, sets of experiments were conducted on both adhesively bonded and composite beams in which the amplitudes of the pre-deformation, the natural frequencies and the modal damping were measured and compared with predictions from the finite element model. The correlation between the predictions and the experimental data was good and the amount of scatter was reduced to acceptable levels once pre-deformation was taken into account.