Showing papers on "Sandwich panel published in 2005"
TL;DR: In this article, the low velocity impact behavior of composite sandwich panels consisting of woven carbon/epoxy facesheets and a PVC foam core was studied experimentally and a straightforward peak impact load estimation method gave good agreement with experimental results.
Abstract: Composite sandwich structures are susceptible to low velocity impact damage and thorough characterization of the loading and damage process during impact is important. The objective of this work is to study experimentally the low velocity impact behavior of sandwich panels consisting of woven carbon/epoxy facesheets and a PVC foam core. Instrumented panels were impacted with a drop mass setup and the load, strain, and deflection histories were recorded. Damage was characterized and quantified after the test. Results were compared with those of an equivalent static loading and showed that low velocity impact was generally quasi-static in nature except for localized damage. A straightforward peak impact load estimation method gave good agreement with experimental results. A contact force–indentation relationship was also investigated for the static loading case. Experimental results were compared with analytical and finite element model analysis to determine their effectiveness in predicting the indentation behavior of the sandwich panel.
181 citations
TL;DR: In this article, a numerical simulation was performed using LS-DYNA3D transient dynamic finite element analysis code for calculating contact forces during impact along with a failure analysis for predicting the threshold of impact damage and initiation of delaminations.
138 citations
TL;DR: In this paper, a closed-form solution based on the Mindlin-Reissner plate theory is presented to describe the behavior of corrugated-core sandwich plate bending with various boundary conditions.
103 citations
TL;DR: In this paper, the authors investigate the effect of impact damage on failure mechanisms in a foam-cored sandwich panel with composite face sheets and show that residual dent growth inwards toward the midplane of a sandwich panel followed by complete separation of the face sheet is the failure mode.
Abstract: Compression-after-impact (CAI) strength of foam-cored sandwich panels with composite face sheets is investigated experimentally. The low-velocity impact by a semi-spherical (blunt) projectile is considered, producing a damage mainly in a form of core crushing accompanied by a permanent indentation (residual dent) in the face sheet. Instrumentation of the panels by strain gauges and digital speckle photography analysis are used to study the effect of damage on failure mechanisms in the panel. Residual dent growth inwards toward the mid-plane of a sandwich panel followed by a complete separation of the face sheet is identified as the failure mode. CAI strength of sandwich panels is shown to decrease with increasing impact damage size. Destructive sectioning of sandwich panels is used to characterise damage parameters and morphology for implementation in a finite element model. The finite element model that accounts for relevant details of impact damage morphology is developed and proposed for failure analysis and CAI strength predictions of damaged panels demonstrating a good correlation with experimental results.
91 citations
TL;DR: In this paper, the compressive properties, collapse modes and crushing characteristics of various types of composite sandwich panels were investigated in a series of edgewise compression tests, one of which was progressive end-crushing of the sandwich panel featured by significant crash energy absorption, feature that was highly desired since the tested hybrid composites were candidate materials for the manufacture of parts of transportation vehicles.
90 citations
TL;DR: In this paper, the transmission loss of symmetric sandwich panels with an isotropic core was derived using the consistent higher-order approach and the two-parameter foundation formulation.
80 citations
TL;DR: In this paper, a lightweight, structurally efficient sandwich panel is designed to undergo a reversible change in shape upon application of a localized thermal stimulus while supporting significant load, but no external or bias forces are required to complete the full cycle of shape change.
63 citations
TL;DR: In this paper, a two-layer panels with polymer matrix composite laminated face sheets and a thin internal sheet subjected to low velocity impact are studied in the LS-DYNA3D software, and attention is focused on the local displacement of a honeycomb core under the point of impact.
48 citations
01 Jan 2005
TL;DR: In this paper, a set of composite sandwich panels and cross-ribbed panels were analyzed and the optimal values of rib and skin thickness, rib spacing, and panel depth were obtained for minimal weight under stress and buckling constraints.
Abstract: Structural analysis and design of efficient pressurized fuselage configurations for the advanced Blended-Wing-Body (BWB) flight vehicle is a challenging problem. Unlike a conventional cylindrical pressurized fuselage, stress level in a box type BWB fuselage is an order of magnitude higher, because internal pressure primarily results in bending stress instead of skin-membrane stress. In addition, resulting deformation of aerodynamic surface could significantly affect performance advantages provided by lifting body. The pressurized composite conformal multi-lobe tanks of X-33 type space vehicle also suffered from similar problem. In the earlier BWB design studies, Vaulted Ribbed Shell (VLRS), Flat Ribbed Shell (FRS); Vaulted shell Honeycomb Core (VLHC) and Flat sandwich shell Honeycomb Core (FLHC) concepts were studied. The flat and vaulted ribbed shell concepts were found most efficient. In a recent study, a set of composite sandwich panel and cross-ribbed panel were analyzed. Optimal values of rib and skin thickness, rib spacing, and panel depth were obtained for minimal weight under stress and buckling constraints. In addition, a set of efficient multi-bubble fuselage (MBF) configuration concept was developed. The special geometric configuration of this concept allows for balancing internal cabin pressure load efficiently, through membrane stress in inner-stiffened shell and inter-cabin walls, while the outer-ribbed shell prevents buckling due to external resultant compressive loads. The initial results from these approximate finite element analyses indicate progressively lower maximum stresses and deflections compared to the earlier study. However, a relative comparison of the FEM weight per unit floor area of the segment unit indicates that the unit weights are still relatively higher that the conventional B777 type cylindrical or A380 type elliptic fuselage design. Due to the manufacturing concern associated with multi-bubble fuselage, a Y braced box-type fuselage alternative with special resin-film injected (RFI) stitched carbon composite with foam-core was designed by Boeing under a NASA research contract for the 480 passenger version. It is shown that this configuration can be improved to a modified multi-bubble fuselage which has better stress distribution, for same material and dimension.
46 citations
TL;DR: In this article, the effects of core morphology on the through-thickness elastic moduli, compressive strength and the shear strength of fibrous core sandwich panels are analyzed.
43 citations
TL;DR: In this paper, a core insert is designed to be structurally graded by means of shaping insert boundaries to be inclined with respect to the sandwich faces, which provides smoothing of material discontinuities at the junction of different materials.
TL;DR: In this article, an analytical model for static and low-velocity perforation of composite sandwich panels with woven E-glass/epoxy prepreg facesheets and aluminum honeycomb core is developed.
Abstract: Analytical models for the static and low-velocity perforation of composite sandwich panel with woven E-glass/epoxy prepreg facesheets and aluminum honeycomb core are developed. The analytical model...
TL;DR: In this paper, a one-sided handheld Magnetic Resonance (MR) sensor is used to detect water ingress inside honeycomb sandwich panels during service, which is linked to in-flight failure in some aircraft.
Abstract: Water ingress inside honeycomb sandwich panels during service has been linked to in-flight failure in some aircraft. There is an ongoing effort to develop nondestructive testing methods to detect the presence of water within the panels. Magnetic resonance (MR) represents an attractive approach in that it is sensitive to moisture. Using a unilateral MR sensor, testing can be applied directly to the surface of the panel. The viability of MR is demonstrated through laboratory imaging of both water within sandwich panels, as well as the adhesive itself. The detection of water using a one-sided handheld MR sensor is presented. It is shown that simple detection, as well as spatial localization of water within sandwich panels is possible.
01 Apr 2005
TL;DR: In this paper, a set of composite sandwich panels and cross-ribbed panels were analyzed and the optimal values of rib and skin thickness, rib spacing, and panel depth were obtained for minimal weight under stress and buckling constraints.
Abstract: Structural analysis and design of efficient pressurized fuselage configurations for the advanced Blended-Wing-Body (BWB) flight vehicle is a challenging problem. Unlike a conventional cylindrical pressurized fuselage, stress level in a box type BWB fuselage is an order of magnitude higher, because internal pressure primarily results in bending stress instead of skin-membrane stress. In addition, resulting deformation of aerodynamic surface could significantly affect performance advantages provided by lifting body. The pressurized composite conformal multi-lobe tanks of X-33 type space vehicle also suffered from similar problem. In the earlier BWB design studies, Vaulted Ribbed Shell (VLRS), Flat Ribbed Shell (FRS); Vaulted shell Honeycomb Core (VLHC) and Flat sandwich shell Honeycomb Core (FLHC) concepts were studied. The flat and vaulted ribbed shell concepts were found most efficient. In a recent study, a set of composite sandwich panel and cross-ribbed panel were analyzed. Optimal values of rib and skin thickness, rib spacing, and panel depth were obtained for minimal weight under stress and buckling constraints. In addition, a set of efficient multi-bubble fuselage (MBF) configuration concept was developed. The special geometric configuration of this concept allows for balancing internal cabin pressure load efficiently, through membrane stress in inner-stiffened shell and inter-cabin walls, while the outer-ribbed shell prevents buckling due to external resultant compressive loads. The initial results from these approximate finite element analyses indicate progressively lower maximum stresses and deflections compared to the earlier study. However, a relative comparison of the FEM weight per unit floor area of the segment unit indicates that the unit weights are still relatively higher that the conventional B777 type cylindrical or A380 type elliptic fuselage design. Due to the manufacturing concern associated with multi-bubble fuselage, a Y braced box-type fuselage alternative with special resin-film injected (RFI) stitched carbon composite with foam-core was designed by Boeing under a NASA research contract for the 480 passenger version. It is shown that this configuration can be improved to a modified multi-bubble fuselage which has better stress distribution, for same material and dimension.
TL;DR: In this paper, the effect of initial geometric imperfections in the natural waveform given by the linear stability analysis is considered, which leads to increased displacements during loading giving rise to both, an in-plane compressive strain and a varying bending strain.
Abstract: In this paper, sandwich wrinkling or local face sheet instability is treated in the context of material failure. Traditionally, test results rarely complied well with the predicted failure load and a knock down factor often had to be used. The reason for this is often referred as the effect of initial geometric imperfections. In this paper, imperfections are included in the natural waveform given by the linear stability analysis, i.e., a short wavelength sinusoidal buckling shape. These initial imperfections lead to increased displacements during loading giving rise to both, an in-plane compressive strain and a varying bending strain. These strains can then be related to material failure criteria, one for the face sheet compressive strain and one for the core normal strain. An analytical model is derived and compared with experimental results and several issues are revealed. The panel strength measured using a realistic initial imperfection amplitude agrees very well with the derived model, giving a prediction somewhat below the values obtained from the traditional approach. This verifies that the actual wrinkling failure is below the theoretical instability load. The model is able to distinguish between different failure modes, face sheet compression failure or core-adhesive joint tensile failure, giving good correlation with the experimental findings. Thus, it appears that using initial imperfections as a basis for wrinkling analysis provides a better foundation for the failure analysis than the ordinary stability analysis, and it also allows to determine which failure mode is predominant. Finally, it is shown that the choice of the core material can be made based on the theory presented to obtain a more efficient sandwich panel.
TL;DR: In this paper, the buckling capacity of fiber-reinforced polymer (FRP) sandwich deck panels with sinusoidal honeycomb core geometry was studied under out-of-plane compression.
Abstract: Fiber-reinforced polymer (FRP) sandwich deck panels with sinusoidal honeycomb core geometry have shown to be efficient in both new construction and rehabilitation of highway bridge decks. The sandwich panel consists of top and bottom laminated face sheets bonded to the honeycomb core, which extends vertically between face sheets. This paper is focused on the study of the buckling capacities of the core components under out-of-plane compression. The facesheet and core are attached by contact molding and are, therefore, not rigidly connected. Thus, this problem can be described as the instability of an FRP core panel with two rotationally restrained loaded edges. An elastic restraint coefficient is introduced to quantify the bonding layer effect between the facesheet and core, and a simple and relatively accurate test method is proposed to obtain the restraint coefficient experimentally. A combined analytical and experimental study of compression is presented. By solving a transcendental equation, the criti...
TL;DR: In this article, the authors investigate the effect of core density and debonding on the overall buckling behavior of a foam-core sandwich and find that core density has direct influence on the global buckling of the sandwich panel, while embedded delamination seem to have minimal effect on both global as well as local buckling.
Abstract: Foam–core sandwich composites have been fabricated using innovative co-injection resin infusion technique and tested under in-plane compression. The sandwich construction consisted of Klegcell foam as core materials and S2-glass/vinyl ester composites as face sheets. Tests were conducted with various foam densities and also with implanted delamination between the core and the face sheet. The intent was to investigate the effect of core density, and the effect of core–skin debonds on the overall buckling behavior of the sandwich. Analytical and finite element calculations were also performed to augment the experimental observations. It has been observed that core density has direct influence on the global buckling of the sandwich panel, while embedded delamination seem to have minimal effect on both global as well as local buckling. Detailed description of the experimental work, finite element modeling and analytical calculations are presented in this paper.
TL;DR: In this article, the authors investigated the role of localized effects within the geometrically nonlinear domain on structural sandwich panels with a compliant core and found that localized loads change the response of the panel from a strength problem controlled by stress constraints into a stability problem with unstable limit point behavior when force-controlled loads are applied.
Abstract: This paper presents the results of an investigation of the role of localized effects within the geometrically nonlinear domain on structural sandwich panels with a “compliant” core. Special emphasis is focused on the nonlinear response near concentrated loads and stiffened core regions. The adopted nonlinear analysis approach incorporates the effects of the vertical flexibility of the core, and it is based on the approach of the High-order Sandwich Panel Theory (HSAPT). The results demonstrate that the effects of localized loads, when taken into the geometrically nonlinear domain, change the response of the panel from a strength problem controlled by stress constraints into a stability problem with unstable limit point behavior when force-controlled loads are applied. The stability problem emerge as the nonlinear response develops with the formation of a small number of buckling waves in the compressed face sheet in the vicinity of the localized loads. The development of the nonlinear response is demonstr...
TL;DR: In this paper, the problem of bending a large aspect ratio simply supported sandwich panel with cross-ply facings subject to an elevated temperature or heat flux on one of the surfaces is solved exactly in the cases where long edges are either unrestrained against or completely prevented from axial displacements.
Abstract: The paper presents the solution of the problem of bending of a large aspect ratio simply supported sandwich panel with cross-ply facings subject to an elevated temperature or heat flux on one of the surfaces. The geometrically and physically linear problem for the central section is solved exactly in the cases where long edges are either unrestrained against or completely prevented from axial displacements. Wrinkling of the facings is also investigated, accounting for both thermal stresses as well as the effect of temperature on the properties of the facings and core. It is shown that thermally induced wrinkling may become the dominant mode of failure in a panel that does not wrinkle at the room temperature.
TL;DR: In this article, a method for estimating the wrinkling behavior of highly anisotropic sandwich panels under biaxial loading is presented. But the method is based on the assumption that wrinkling occurs at the angle where the ratio of applied load to sustainable wrinkling loads reaches a global maximum.
Abstract: The works that have been already published on sandwich face wrinkling consider isotropic or almost isotropic sandwich configurations. Hence, only the critical wrinkling load needs to be evaluated in the principal compressive stress direction. This is insufficient for a sandwich panel with a higher degree of anisotropy. This paper presents a method for estimating the wrinkling behavior of highly anisotropic sandwich panels under biaxial loading. The method is based on the assumption that wrinkling occurs at the angle where the ratio of applied load to sustainable wrinkling loads reaches a global maximum. In addition to the description of the analytical theories, the paper presents comparisons with finite element calculations and testing of real sandwich configurations. The results indicate that the derived model works excellently both for uni- and biaxial loadings, though a small factor of safety is required as with all other standard wrinkling theories.
Patent•
26 Jan 2005
TL;DR: In this article, the authors proposed a method of manufacturing a sandwich panel for an automobile where two skins of predetermined size and shape are provided and an intermediate substrate may be provided and attached between the two skins.
Abstract: A sandwich panel having a pair of skins and an intermediate substrate secured between the two skins creating a structural panel. The skins may be a pressboard material and a covering material may be applied to the skins forming an exterior surface. Selectively, the skins may be covered with a material. Further, an edge member may be provided that is engaged around the peripheral edge of the intermediate substrate. The edge member may include an engaging member and the engaging member may include anti-reverse fins. The edge member may also trap the covering material. A method of manufacturing a sandwich panel for an automobile where two skins of predetermined size and shape are provided. The two skins are attached to each other forming a structural panel. An intermediate substrate may be provided and attached between the skins. Further, an edge member may be provided and attached to the periphery of the structural panel.
TL;DR: In this paper, the authors show that the SBI test data produced for the intermediate scale test method, however, did not use the above mentioned mounting technique and that it is dangerous to make a fire safety assessment of a sandwich panel based on small or intermediate scale tests.
Abstract: Assessment of the fire behaviour of sandwich panels is continuously under discussion. The fire behaviour of these panels is a combination of material characteristics such as the core material and mechanical behaviour of the panels such as joints, dilations etc. The use of small or intermediate scale tests can be questioned for such types of products. Within the proposed European product standard for sandwich panels (prEN 14509) the intermediate scale test method SBI (EN 13823) has been suggested as the fire test method to certify panels. The standard does, however, use quite an artificial mounting procedure, which does not fully reflect the end-use conditions of the panels. In a previous research project conducted by Nordtest it was shown that the correlation between the SBI test method and both the ISO 9705 and ISO 13784 part 1 was insufficient. The test data produced for the SBI test method, however, did not use the above mentioned mounting technique. In this article new data for a number of products are added to the database using the mounting procedure of the product standard. The data are compared with the previous data and show that the mounting method of the product standard results in slightly more severe conditions but that there are still discrepancies with the full-scale test results. The data also show an unacceptable level of repeatability due to the fact that small dilations result in a wide variation of classification result. The new data together with the old data show once more that it is dangerous to make a fire safety assessment of a sandwich panel based on small or intermediate scale tests. (Less)
TL;DR: In this paper, a constitutive theory for FRP laminated composite materials that is designed to account for both temperature and strain rate dependent response, such as would occur during, and after, exposure to the elevated temperatures due to fire, is proposed.
TL;DR: In this paper, an analytical model to simulate the damage propagation behavior and to predict the onset of damage propagation of a low-velocity impacted composite sandwich panel subjected to increasing uniaxial compressive load is presented.
Abstract: This paper is focused on an analytical model to simulate the damage propagation behavior and to predict the onset of damage propagation of a low-velocity impacted composite sandwich panel subjected to increasing uniaxial compressive load. Major damage modes due to impact, such as the residual indentation and the locally crushed core, are included into this model. Composite sandwich panels with unsymmetrical angle-plied facesheets are studied. A consequential core-crushing mechanism is incorporated into the analysis. Good correlations between the numerical results and the experimental data have been obtained. The far-field stress corresponding to the onset of damage propagation at a characteristic location near the damage zone has been captured accurately. This quantity can be used to represent the residual load-bearing capacity of an impact-damaged sandwich panel under compression. It serves as a characteristic value in a newly proposed event-driven failure criterion named damage propagation criterion. Th...
01 Jan 2005
TL;DR: In this article, a servo-hydraulic controlled slam test system and a pressure-based transient finite element technique were used to simulate sandwich panel responses to a water slamming load.
Abstract: Dynamic experimental and theoretical methods for sandwich panel structures subjected to water slamming are described, including a unique servo-hydraulic controlled slam test system and a pressure based transient finite element technique. The pressure simulation method accurately represents the pressures observed in slamming tests, and the transient dynamic finite element modelling can simulate sandwich panel responses to a slamming load.
TL;DR: In this article, the authors describe a specific variation of composite construction called "sandwich composites", which is a structure consisting of two thin faces bonded to a thick lightweight core, and the faces are typically of aluminum or some composite laminate and the core could be a lightweight foam or a honeycomb structure.
Abstract: Interest in the development of improved composite materials has greatly increased in recent years due to their high energy dissipation characteristics and high stiffness-to-weight ratios. They are used in a variety of highly demanding structural applications, including aircraft, submarines, and military vehicles. There are numerous types of composites currently available, including carbon fibre, metal matrix, and ceramic matrix composites. Of particular interest in the current work is a specific variation of composite construction called “sandwich composites” or “sandwich panels.” The term “sandwich panel” refers to a structure consisting of two thin faces bonded to a thick lightweight core. Photographs of some typical sandwich composite structures, with a honeycomb core, are shown on Fig. 1. The faces are typically of aluminum or some composite laminate, and the core could be a lightweight foam or a honeycomb structure. 1.1. Mathematical Model
Patent•
15 Mar 2005
TL;DR: In this article, a bending fatigue test of the lightweight sandwich panel comprising a fiber reinforced plastic skin and a core having a lower specific gravity than the skin is performed by using three or four fulcrums.
Abstract: PROBLEM TO BE SOLVED: To provide a test method capable of performing a lengthy bending fatigue test of a lightweight sandwich panel automatically with high reliability. SOLUTION: In this method, a bending fatigue test of the lightweight sandwich panel comprising a fiber reinforced plastic skin and a core having a lower specific gravity than the skin is performed by using three fulcrums or four fulcrums. The method is characterized by inserting an antislipping material between the sandwich panel and the fulcrums. COPYRIGHT: (C)2006,JPO&NCIPI
Patent•
16 Mar 2005
TL;DR: In this article, a fiber reinforced resin-made thin sandwich panel is proposed to provide a light weight, shows an excellent X-ray transmission while keeping stiffness, and is suitable for a member for a medical instrument, an Xray instrument and the like.
Abstract: PROBLEM TO BE SOLVED: To provide a fiber reinforced resin-made thin sandwich panel which has a light weight, shows an excellent X-ray transmission while keeping stiffness, and is suitable for a member for a medical instrument, an X-ray instrument and the like. SOLUTION: In the fiber reinforced resin-made sandwich panel comprising a core material and skin materials of fiber reinforced resin obtained by soaking reinforcing fiber with a matrix resin, the skin materials being arranged on both surfaces of the core material, the reinforcing fiber of the skin materials contains reinforcing fiber having tensile modulus of not less than 230 GPa, the content of the reinforcing fiber of the skin material is in the range from 40 to 80 wt.%, the apparent density of the resin used for the core material is smaller than that of the skin material, and the whole thickness of the sandwich panel is in the range from 0.5 to 5 mm. COPYRIGHT: (C)2006,JPO&NCIPI
TL;DR: In this paper, the static performance of a glass fiber-reinforced polymer (GFRP) bridge deck that was installed in O'Fallon Park over Bear Creek west of the City of Denver was evaluated.
Abstract: This paper presents a study on the evaluation of the static performance of a glass fiber-reinforced polymer (GFRP) bridge deck that was installed in O’Fallon Park over Bear Creek west of the City of Denver. The bridge deck has a sandwich panel configuration, consisting of two stiff faces separated by a light-weight honeycomb core. The deck was manufactured using a hand lay-up technique. To assist the preliminary design of the deck, the stiffness and load-carrying capacities of four approximately 330 mm (13 in.) wide GFRP beam specimens were evaluated. The crushing capacity of the panel was also examined by subjecting four 330×305×190 mm (13×12×7.5 in.) specimens to compression tests. The experimental data were analyzed and compared to results obtained from analytical and finite element models, which have been used to enhance the understanding of the experimental observations. The failure of all four beams was caused by the delamination of the top faces. In spite of the scatter of the tests results, the be...
Journal Article•