Collapse mechanisms of sandwich beams with composite faces and a foam core, loaded in three-point bending. Part II: experimental investigation and numerical modelling (original) (raw)
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Collapse of clamped and simply supported composite sandwich beams in three-point bending
Composites Part B: Engineering, 2004
Composite sandwich beams, comprising glass -vinylester face sheets and a PVC foam core, have been manufactured and tested quasistatically. Clamped and simply supported beams were tested in three-point bending in order to investigate the initial collapse modes, the mechanisms that govern the post-yield deformation and parameters that set the ultimate strength of these beams. Initial collapse is by three competing mechanisms: face microbuckling, core shear and indentation. Simple formulae for the initial collapse loads of clamped and simply supported beams along with analytical expressions for the finite deflection behaviour of clamped beams are presented. The simply supported beams display a softening post-yield response, while the clamped beams exhibit hardening behaviour due to membrane stretching of the face sheets. Good agreement is found between the measured, analytical and finite element predictions of the load versus deflection response of the simply supported and clamped beams. Collapse mechanism maps with contours of initial collapse load and energy absorption are plotted. These maps are used to determine the minimum mass designs of sandwich beams comprising woven glass face sheets and a PVC foam core. q
International Journal of Solids and Structures, 2008
Analytical predictions are presented for the plastic collapse strength of lightweight sandwich beams having pin-reinforced foam cores that are loaded in 3-point bending. Both polymer and aluminum foam cores are considered, whilst the facesheet and the pins are made of either composite or metal. Four different failure modes are account for: metal facesheet yield or composite facesheet microbuckling, facesheet wrinkling, plastic shear of the core, and facesheet indentation beneath the loading rollers. A micromechanics-based model is developed and combined with the homogenization approach to calculate the effective properties of pin-reinforced foam cores. To calculate the elastic buckling strength of pin reinforcements, the pin-reinforced foam core is treated as assemblies of simply supported columns resting upon an elastic foundation. Minimum mass design of the sandwich is then obtained as a function of the prescribed structural load index, subjected to the constraint that none of the above failure modes occurs. Collapse mechanism maps are constructed and compared with the failure maps of foam-cored sandwich beams without pin reinforcements. Finite element simulations are carried out to verify the analytical model and to study the performance and failure mechanisms of the sandwich subject to loading types other than 3-point bending. The results demonstrate that the weaker the foam is, the more optimal the pin-reinforced foam core becomes, and that sandwich beams with pin-reinforced polymer foam cores are structurally more efficient than foam-or trusscored sandwich beams.
Collapse of truss core sandwich beams in 3-point bending
International Journal of Solids and Structures, 2001
Sandwich beams, comprising a truss core and either solid or triangulated face-sheets, have been investment cast in an aluminium±silicon alloy and in silicon brass. The macroscopic eective stiness and strength of the triangulated facesheets and tetrahedral core are estimated by idealising them as pin-jointed assemblies; tests show that this approximation is adequate. Next, the collapse responses of these sandwich beams in 3-point bending are measured. Collapse is by four competing mechanisms: face-yield, face-wrinkling, indentation and core shear, with the active collapse mode dependent upon the beam geometry and yield strain of the material. Upper bound expressions for the collapse loads are given in terms of the eective properties of the faces and core of the sandwich beam; these upper bounds are in good agreement with the measured beam response, and are used to construct collapse mechanism maps with beam geometrical parameters as the axes. The maps are useful for selecting sandwich beams of minimum weight for a given structural load index. The optimisation reveals that truss core sandwich beams are signi®cantly lighter than the competing concept of sandwich beams with a metallic foam core.
Zenodo (CERN European Organization for Nuclear Research), 2007
This paper deals with analysis of flexural stiffness, indentation and their energies in three point loading of sandwich beams with composite faces from Eglass/epoxy and cores from Polyurethane or PVC. Energy is consumed in three stages of indentation in laminated beam, indentation of sandwich beam and bending of sandwich beam. Theory of elasticity is chosen to present equations for indentation of laminated beam, then these equations have been corrected to offer better results. An analytical model has been used assuming an elastic-perfectly plastic compressive behavior of the foam core. Classical theory of beam is used to describe three point bending. Finite element (FE) analysis of static indentation sandwich beams is performed using the FE code ABAQUS. The foam core is modeled using the crushable foam material model and response of the foam core is experimentally characterized in uniaxial compression. Three point bending and indentation have been done experimentally in two cases of low velocity and higher velocity (quasi-impact) of loading. Results can describe response of beam in terms of core and faces thicknesses, core material, indentor diameter, energy absorbed, and length of plastic area in the testing. The experimental results are in good agreement with the analytical and FE analyses. These results can be used as an introduction for impact loading and energy absorbing of sandwich structures.
Experimental investigations on the sandwich composite beams and panels with elastomeric foam core
Journal of Sandwich Structures & Materials, 2017
In this paper, the load-carrying capacity and failure mechanisms of sandwich beams and panels with elastomeric foam core and composite laminate face sheets are investigated. For this purpose, the flexural behavior of laminated composite beams and panels (applied as face sheets) is firstly investigated under three-point bending and central concentrated loads, respectively. Then, the same examination is conducted for the sandwich beams and panels, in which the proposed elastomeric foam is utilized as the core material. It is shown that the failure mechanisms which are associated to the core in the sandwich structures with crushable foams are not considered in the examined sandwich structures. The collapse of the sandwich specimens, examined here, is observed due to the failure of the skins in some steps. By multi-step collapse of these specimens via separately failure of the top and bottom skins, a considerable amount of energy is absorbed between these steps. Due to non-brittle behav...
Ecf17 Brno 2008, 2013
An investigation was conducted on failure of composite sandwich beams under threepoint bending and in cantilever beams under end loading. The beams consisted of unidirectional carbon/epoxy facings and a variety of core materials, including aluminum honeycomb, PVC closedcell foams, polyurethane foam and balsa wood. The constituent materials were fully characterized and in the case of the core materials, failure envelopes were developed for biaxial states of stress. Deformation and failure mechanisms include core shear failure and compression facing wrinkling. Results were obtained for stress (strain) distributions in the linear and nonlinear/plastic range of the core, critical failure loads due to shear core failure and compression facing wrinkling and their dependence on geometrical dimensions, material parameters and loading conditions. w
Failure of sandwich beams consisting of alumina face sheet and aluminum foam core in bending
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005
Applications of sandwich structures, comprising alumina face sheets and aluminum foam core, depend critically on their mechanical performance. Four point bend tests are performed on sandwich beams with varying geometries to identify competing failure modes, such as core indentation, face sheet cracking and core shear. Analytical formulae for the identified failure modes are obtained. A failure mode map was constructed based on the analytical calculations in the non-dimensional parameters of beam geometry for a given face sheet to core strength ratio. The tested geometries are simulated using a finite element program: the beam stiffness and the failure load calculations were found to be in good agreement with the experimental and analytical results within experimental scatter.
Influence of core properties on the failure of composite sandwich beams
Journal of Mechanics of Materials and Structures, 2009
The initiation of failure in composite sandwich beams is heavily dependent on properties of the core material. Several core materials, including PVC foams and balsa wood were characterized. The various failure modes occurring in composite sandwich beams are described and their relationship to the relevant core properties is explained and discussed. Under flexural loading of sandwich beams, plastic yielding or cracking of the core occurs when the critical yield stress or strength (usually shear) of the core is reached. Indentation under localized loading depends principally on the square root of the core yield stress. The critical stress for facesheet wrinkling is related to the core Young's and shear moduli in the thickness direction. Experimental mechanics methods were used to illustrate the failure modes and verify analytical predictions.