Quasi-Static Three-Point Bending of Carbon Fiber Sandwich Beams With Square Honeycomb Cores (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
2014
This study will present the Experimental, numerical and analytical characterizations of composite sandwich structures needed to optimize structure design. In this study, the effects of varying honeycomb core ribbon orientation and varying face sheet thickness's have on the flexural behavior of honeycomb sandwich structures was investigated. Honeycomb sandwich panels were constructed using Hexcel 6367 A250-5H carbon fiber face sheets and Hexcel Nomex HRH-10-1/8-5 honeycomb cores. The mechanical properties of the constituent materials were discovered experimentally using ASTM standards and theoretical models using honeycomb mechanics and classical beam and plate theory are described. A failure mode map for loading under three point bending is developed from previous works by Triantafillou and Gibson 26 , showing the dependence of failure mode on face sheet to core thickness and honeycomb core ribbon orientation. Beam specimens are tested with the effects of Honeycomb core ribbon orientation and unequal face sheet thickness's examined. Experimental data sufficiently agrees with theoretical predictions. A finite element model was developed in ABAQUS/CAE to validate experimental and analytical analysis and produced agreeable results. Optimal bending stiffness and strength with respect to minimum weight was analyzed. The results reveal an important role core ribbon orientation has in a sandwich beam's bending behavior, and design of unequal ply count face sheets can produce higher stiffness to weight ratios than conventional symmetric sandwich structures of similar weight when subjected to a single static load.
International Journal of Mechanical Sciences, 2004
Analytical predictions are made for the three-point bending collapse strength of sandwich beams with composite faces and polymer foam cores. Failure is by the competing modes of face sheet microbuckling, plastic shear of the core, and face sheet indentation beneath the loading rollers. Particular attention is paid to the development of an indentation model for elastic faces and an elastic-plastic core. Failure mechanism maps have been constructed to reveal the operative collapse mode as a function of geometry of sandwich beam, and minimum weight designs have been obtained as a function of an appropriate structural load index. It is shown that the optimal designs for composite-polymer foam sandwich beams are of comparable weight to sandwich beams with metallic faces and a metallic foam core.
The soft impact of composite sandwich beams with a square-honeycomb core
International Journal of Impact Engineering, 2012
The dynamic response of end-clamped monolithic beams and sandwich beams of equal areal mass have been measured by loading the beams at mid-span with metal foam projectiles to simulate localised blast loading. The sandwich beams were made from carbon fibre laminate and comprised identical face sheets and a square-honeycomb core. The transient deflection of the beams was determined as a function of projectile momentum, and the measured response was compared with finite element simulations based upon a damage mechanics approach. A range of failure modes were observed in the sandwich beams including core fracture, plug-type shear failure of the core, debonding of the face sheets from the core and tensile tearing of the face sheets at the supports. In contrast, the monolithic beams failed by a combination of delamination of the plies and tensile failure at the supports. The finite element simulations of the beam response were accurate provided the carbon fibre properties were endowed with rate sensitivity of damage growth. The relative performance of monolithic and sandwich beams were quantified by the maximum transverse deflection at mid-span for a given projectile momentum. It was found that the sandwich beams outperformed both monolithic composite beams and steel sandwich beams with a square-honeycomb core. However, the composite beams failed catastrophically at a lower projectile impulse than the steel beams due to the lower ductility of the composite material.
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
Composite Structures, 2017
In this work, mechanical response of a new sandwich beam with a hybrid core composed of epoxy resin and Alumina trihydrate (ATH) was investigated. Interactions between the indentation mode and the core shear failure mode, as well as the role of face/core debonding were evaluated as part of the failure mechanism. A digital image correlation technique (DIC) was used to capture the sequence of failure and the strain field during quasi-static loading. In addition, an explicit nonlinear finite element model was developed to predict the evolution of damage in the sandwich face sheet and core. The model includes a viscoplastic-damage model to simulate the strain rate-dependent behavior of the core material. The numerical results were compared with the impact data to demonstrate the ability of the model to follow the evolution of damage from onset to catastrophic failure. It was found that shear failure in the core plays the main role in the final failure of sandwich beams. For an impact energy below 60 J, indentation is the dominant failure mode, and its effect on the flexural response of the beam was demonstrated.
2017
The sandwich elements are multi-layered structures made of two strong and stiff thin exterior faces, bonded by a lightweight thick core, such that the structural properties of the entire assembly are superior to those of the separate components. The composite laminates are build up by stacking two or more unidirectional fibre reinforced composite laminas, with different or same fibre orientation angles, thicknesses and materials constituents. The design flexibility of composite structures is a great challenge since the advantage of orienting the composite laminas in the needed directions leads to improved structural properties of the whole assembly. The paper presents the flexural response of a sandwich beam with exterior layers made of laminated composites with different fibre orientations. The results are presented in terms of distribution of stresses on the layers of the composite sandwich beam. The failure and the damage occurrence on the plies of the laminated facings are inves...
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.
Materialwissenschaft Und Werkstofftechnik, 2014
In this study, dynamic analysis of naturally curved honeycomb sandwich beam including two surface cracks and an impact region at the facing skin is presented. Laminates of facing skin and backing skin are known as carbon fiber-plain weave composite laminates with 1.6 mm in thickness. In the first part, in order to determine mechanical properties of both the skin with no-crack/crack(s) and the honeycomb core of the composite beam, static tensile tests are conducted with respect to straingage measurement technique. In the second part, drop weight impact tests and vibration tests are performed to present the free vibration characteristics of the clamped-clamped honeycomb sandwich beam including cracks and an impactdamaged region. Corresponding to damage patterns of the sandwich beam, experimental dynamic analyses consist of six steps: (1) Vibration analysis with no-crack and no-impact region, (2) Vibration analysis with no-crack and an impact region, (3) Vibration analysis with a surface crack and no-impact region, (4) Vibration analysis with a surface crack and an impact region, (5) Vibration analysis with two surface cracks and no-impact region, (6) Vibration analysis with two surface cracks and an impact region. For these purposes, an impact hammer with a force transducer is used to excite the undamaged or damaged naturally curved honeycomb sandwich beam through the selected points. After the excitation, the responses are obtained by an accelerometer. Resonant frequencies for the modal responses of the naturally curved honeycomb sandwich beam with different damage patterns are discussed.
Failure mechanisms of composite sandwich beams under impact loading
An experimental investigation of the failure mechanisms of a composite sandwich beam under central low-velocity impact was undertaken. The beam was made of unidirectional carbon/epoxy facesheets and various core materials including aluminum honeycomb, balsa wood, polyurethane foam and foam-filled honeycomb. Damage of the beam depended on the level of impact energy and the properties of the core material. For low impact energies, the impactor after reaching the specimen bounces transferring energy back to the impactor as kinetic energy. For higher energies core crushing coupled with bending of the upper facesheet took place. The upper facesheet deforms permanently without failure. As the impact energy increases delamination of the facesheets or debonding between the core and the facesheets occurred. For much higher energies wrinkling or perforation of the upper facesheets was recorded. Damage was assessed by visual inspection and photomicrographs taken in a microscope under various magnifications. Macroscopic and microscopic failure mechanisms were recorded. Macroscopic mechanisms include indentation, surface cracking, delamination and perforation. Microscopic mechanisms include fiber breakage and matrix cracking. Results concerning the mechanisms and damage development for various core materials and impact energies were obtained.