Honeycomb Core Sandwich Panels Research Articles

Quieting a rib-framed honeycomb core sandwich panel for a rotorcraft roof.

A rotorcraft roof composite sandwich panel has been redesigned to optimize sound power transmission loss (TL) and minimize structure-borne sound for frequencies between 1 and 4 kHz where gear meshing noise from the transmission has the most impact on speech intelligibility. The roof section, framed by a grid of ribs, was originally constructed of a single honeycomb core/composite facesheet sandwich panel. The original panel has acoustic coincidence frequencies near 600 Hz, leading to poor TL across the frequency range of 1 to 4 kHz. To quiet the panel, the cross section was split into two thinner sandwich subpanels separated by an air gap. The air gap was sized to target the fundamental mass-spring-mass resonance of the panel system to less than 500 Hz, well below the frequency range of interest. The panels were designed to withstand structural loading from normal rotorcraft operation, as well as 'man-on-the-roof' static loads experienced during maintenance operations. Thin layers of viscoelastomer were included in the facesheet ply layups, increasing panel damping loss factors from about 0.01 to 0.05. Transmission loss measurements show the optimized panel provides 6-11 dB of acoustic transmission loss improvement, and 6-15 dB of structure-borne sound reduction at critical rotorcraft transmission tonal frequencies. Analytic panel TL theory simulates the measured performance within 3 dB over most frequencies. Detailed finite element (FE)/boundary element (BE) modeling simulates TL slightly more accurately, within 2 dB for frequencies up to 4 kHz, and also simulates structure-borne sound well, generally within 3 dB.

Sound transmission loss characteristics of sandwich aircraft panels: Influence of nature of core

Sandwich panel which has a design involving acoustic comfort is always denser and larger in size than the design involving mechanical strength. The respective short come can be solved by exploring the impact of core geometry on sound transmission characteristics of sandwich panels. In this aspect, the present work focuses on the study of influence of core geometry on sound transmission characteristics of sandwich panels which are commonly used as aircraft structures. Numerical investigation has been carried out based on a 2D model with equivalent elastic properties. The present study has found that, for a honeycomb core sandwich panel in due consideration to space constraint, better sound transmission characteristics can be achieved with lower core height. It is observed that, for a honeycomb core sandwich panel, one can select cell size as the parameter to reduce the weight with out affecting the sound transmission loss. Triangular core sandwich panel can be used for low frequency application due to its increased transmission loss. In foam core sandwich panel, it is noticed that the effect of face sheet material on sound transmission loss is significant and this can be controlled by varying the density of foam.

Sound radiation and transmission loss characteristics of a honeycomb sandwich panel with composite facings: Effect of inherent material damping

This paper presents the results of numerical studies carried out on vibro-acoustic and sound transmission loss behaviour of aluminium honeycomb core sandwich panel with fibre reinforced plastic (FRP) facings. Layered structural shell element with equivalent orthotropic elastic properties of core and orthotropic properties of FRP facing layer is used to predict the free and forced vibration characteristics. Followed by this, acoustic response and transmission loss characteristics are obtained using Rayleigh integral. Vibration and acoustic characteristics of FRP sandwich panels are compared with aluminium sandwich panels. The result reveals that FRP panel has better vibro-acoustic and transmission loss characteristics due to high stiffness and inherent material damping associated with them. Resonant amplitudes of the response are fully controlled by modal damping factors calculated based on modal strain energy. It is also demonstrated that FRP panel can be used to replace the aluminium panel without losing acoustic comfort with nearly 40 percent weight reduction.

Free-Vibration Analysis of Sandwich Panels with Randomly Irregular Honeycomb Core

An analytical framework has been proposed to analyze the effect of random structural irregularity in honeycomb core for natural frequencies of sandwich panels. Closed-form formulas have been developed for the out-of-plane shear moduli of spatially irregular honeycombs following minimum potential energy theorem and minimum complementary energy theorem. Subsequently an analytical approach has been presented for free-vibration analysis of honeycomb core sandwich panels to quantify the effect of such irregularity following a probabilistic paradigm. Representative results have been furnished for natural frequencies corresponding to low vibration modes of a sandwich panel with high length-to-width ratio. The results suggest that spatially random irregularities in honeycomb core have considerable effect on the natural frequencies of sandwich panels.

Influence of nature of core on vibro acoustic behavior of sandwich aerospace structures

This paper presents the study of influence of core geometry on vibration and acoustic response characteristics of sandwich panels which are used as aerospace structures. Sandwich panels considered in this research work are: (a) Honeycomb core, (b) Truss and Z core, (c) Foam core. The present study has found that (i) For a honeycomb core sandwich panel in due consideration to space constraint, the better acoustic comfort can be achieved by reducing the core height and increasing the face sheet thickness. (ii) It is demonstrated that, for a honeycomb core sandwich panel, vibration and acoustic response is not sensitive to the cell size. (iii) It is observed that, triangular core gives better acoustic comfort for the truss core sandwich panel compared to other type of core. (iv) For foam core sandwich panels, it is observed that sandwich panel with carbon-epoxy (high stiffness) face sheet radiates less sound in the lower frequency range (0–100 Hz). While the sandwich panel with Titanium (high density) face sheet radiates less sound at the higher frequencies. In order to reduce the preprocessing time and computational effort throughout the analysis in the present study, equivalent 2D elastic properties are calculated and used to find out the vibration and acoustic response characteristics.

Design Optimization of Honeycomb Core Sandwich Panels for Maximum Sound Transmission Loss

This study focuses on sound transmission frequency response through honeycomb core sandwich panels with in-plane orientation. Specifically, an optimization technique has been presented to determine the honeycomb unit cell geometric parameters that maximize the sound transmission loss (STL) through a sandwich panel, while maintaining constraints of constant mass and overall dimensions of panel length and height. The vibration characteristics and STL response of a sandwich panel are parameterized in terms of four honeycomb unit cell independent geometric parameters; two side lengths, cell wall thickness, and interior cell wall angle. With constraints of constant mass and overall dimensions, relationships are determined such that the number of independent variables needed to define the honeycomb cell and panel geometry is reduced to three; the integer number of unit cells in the longitudinal direction of the core, number of unit cells in the height direction, and interior cell wall angle. The optimization procedure is implemented by linking a structural acoustic finite-element (FE) model of the panel, with modefrontier, a general purpose optimization software. Optimum designs are obtained in representative frequency ranges within the resonance region of the STL response. Optimized honeycomb geometric solutions show at least 20% increase in STL response compared to standard hexagonal honeycomb core panels. It is found that the STL response is not only affected by the cell wall angle, but strongly depends also on the number of unit cells in the horizontal and vertical direction.

GS0319 CFRPを表面板に用いたハニカムコアサンドイッチパネルの局部圧縮疲労特性に関する研究 : 表面板繊維方向が及ぼす影響

When honeycomb core sandwich panel (hereafter, HSP for brevity) is used as a floor panel, a dent will be formed on the face sheet of the HSP. If the high toughness material such as Carbon fiber reinforced plastics (hereafter, CFRP for brevity) is used as the face sheet, it is thought that the period for use as the floor panel will extend. In this study, by using HSPs on which 4-ply CFRP of [(0/90),(+45/-45)]s and [(0/90)_4]_T was used as the face sheet(hereafter, CFRP-HSP for brevity), local compression fatigue tests were carried out in consideration of usage condition as floor panel. The fatigue life was similar for both CFRP-HPSs. The rigidity was superior to CFRP-HSP used face sheet of [(0/90),(+45/-45)]s rather than CFRP-HSP used face sheet of [(0/90)_4]_T.

Modelling of Honeycomb Core Sandwich Panels with Fibre Reinforced Plastic Facesheets and Analysing the Mechanical Properties

Using experimentally obtained specific material properties, numerical finite element models were created, one was honeycomb core sandwich structure other neat FRP composite structure was designed and experimentally verified. The honeycomb core sandwich composite comprised facesheets from wound glass fibre and polyvinylester resin and a core from recycled paper hexagonal honeycomb impregnated with polyvinylester resin and neat FRP composite structure consisted only two thin layers of facesheets. The model was used to obtain the optimal thickness of facesheet in honeycomb core sandwich structure at which the effective strength and stiffness properties can be obtained. It was determined that thickness of the facesheets had a significant effect on stiffness properties when the length between the supports are high.

Vibration Based Health Monitoring Of Honeycomb Core Sandwich Panels Using Support Vector Machine

Abstract Honeycomb sandwich structures are extensively used in aerospace, aeronautic, marine and automotive industries due to their high strength-to-weight ratios, high energy absorption capability and effective acoustic insulation. Unfortunately, either presence of disbond along the skin-core interface or emergence of disbond due to repeated loading, aging or an intensive load can jeopardize the integrity and safety of the whole structure The current work presents a new array based technique for health monitoring of these structures using support vector machine (SVM). The proposed technique is first used on simulated mode shape data of the structure and then the technique is validated using experimental mode shape data. The experimental set up has been developed in laboratory and Laser Doppler Vibrometer (LDV) is used to extract the experimental mode shapes. The results have been obtained using both support vector classification and regression analysis and it is found that that the former is better at prediction of debond location

GS0320 二層積層ハニカムコアサンドイッチパネルの落錘衝撃特性 : セルサイズおよびセル壁厚さの影響

GS0320 二層積層ハニカムコアサンドイッチパネルの落錘衝撃特性 : セルサイズおよびセル壁厚さの影響

Thermo-mechanical response of superalloy honeycomb sandwich panels subjected to non-steady thermal loading

This paper investigates heat-shielding performance and 3D thermal deformation behavior of two superalloy honeycomb-core sandwich panels in time-varying thermal environment by using a self-developed transient aerodynamic heating simulation system and a novel active imaging stereo-digital image correlation (stereo-DIC) technique. To facilitate deformation measurement of large objects using stereo-DIC, a simple but practical technique is adopted for fabricating high-temperature speckle patterns on large measuring areas. The results indicate that the sandwich panels provide good thermal shielding performance under 900°C with the thermal insulation effect stabilizing at around 30%. The measured high-temperature deformation fields of the test sandwich panels reveal that an in-plane homogeneous thermal expansion occurs as expected, while the out-of-plane deformation shows evident axisymmetric distributions with the maximum deflections dependent on the temperature differences between the back and front facets. The results provide a foundational understanding on the thermal–mechanical characteristics of superalloy honeycomb-core sandwich panels, which is essential to the structural design of a superalloy honeycomb sandwich thermal protection system.

Multi-objective optimisation of viscoelastic damping inserts in honeycomb sandwich structures

The Double-Shear Lap Joint (DSLJ) is a novel damping insert sited internally within a structure which is particularly well suited for lightweight sandwich structures with internal voids, such as honeycomb core sandwich panels. In high performance lightweight structures, the insertion of relatively more dense dampers of any type may increase the total mass substantially and alter the mass distribution significantly. The objective herein was to determine the optimum location, number and orientation of DSLJ inserts within a typical sandwich panel, and thereby to assess the efficacy of two different optimisation approaches to this problem; a parametric optimisation and the Adaptive Indicator-Based Evolutionary Algorithm (IBEA). Both approaches were used to maximise the damping while minimising the additional mass of the damping inserts applied to the structure. Although the parametric approach was faster and easier to implement, the Adaptive IBEA identified significantly better configurations in many cases, especially where veering occurred, in one case improving modal loss factors more than fourfold vs the parametric method. Solutions were identified with large increases in modal loss factors but only small increases in mass vs the empty structure.

Vibro‐acoustic analysis of post‐impacted sandwich panels

In this study, the vibro‐acoustic behaviour of centrally damaged honeycomb cored sandwich panels is investigated experimentally. For this purpose, experimental evaluations are completed by the followings: (I) honeycomb sandwich panels with two different core materials and the same skin materials are considered, (II) low‐velocity impact measurements with three different projectiles are obtained, (III) vibration and vibro‐acoustic tests are performed to present the vibration characteristics of the post‐impacted sandwich panels with two different boundary conditions. Effect of core material and projectile geometry on modal and sound characteristics is examined. The results are given in tabular and graphical forms.

Compressive strength of aluminum honeycomb core sandwich panels with thick carbon–epoxy facesheets subjected to barely visible indentation damage

An experimental study of damage tolerance under quasi-static indentation (QSI) was performed for sandwich composite panels consisting of 16-ply carbon–epoxy facesheets bonded to an aluminum honeycomb core. To determine how indentation damage and compression strength after indentation depend on the facesheet layup, three facesheet stacking sequences were used, varying the maximum ply angle change and placement of the outermost 0° ply. Similarly, to determine the effect of core parameters on damage and strength following indentation, three cores with varying density and thickness were studied. Specimens were indented in QSI to the barely visible indentation damage threshold by spherical indenters of 25.4 or 76.2 mm diameters. Damaged specimens were tested to failure in compression to determine the post-indentation compressive strength and resulting failure mode. Compression-after-indentation (CAI) strength is compared to the undamaged strength obtained from edgewise-compression tests of specimens with the same geometry type. Three distinct failure modes were observed in the CAI experiments: compressive fiber failure, delamination buckling and global instability. Post-indentation compressive strength was independent of indenter size and there was no clear propensity for a particular failure mode dependent on a given specimen geometry. Specimens with a high core density and facesheets with a primary ply angle change of 90° were found to be the most damage resistant. Specimens with facesheets having the outer 0° plies closest to the center of the laminate were found to be the most damage tolerant.

OS1328-147 衝撃荷重によるCFRP積層板およびCFRPサンドイッチパネルの損傷評価と材料特性変化

In the present paper, damage development within carbon fiber reinforced plastic (CFRP) laminates and CFRP/Al honeycomb core sandwich panels by impact loading was evaluated, and change in material properties due to the damage development was investigated. Falling weight impact tests, cross section observation and 3-point bending tests were carried out. As results, it is obtained that reduction rate of bending elastic modulus in a laminate is lower than that in an upper face-sheet of the sandwich panel, and difference in the reduction rate between them becomes maximum at 5.1J. As a result of investigating the relationship between reduction in bending elastic modulus and internal damage development, the reduction is caused by delamination mainly. Since total length of cracks in CFRP/Al core sandwich panels is smaller than that in laminates, the sandwich panels have high impact tolerance.

OS7-5 Study on Deformation Characteristics of Honeycomb Core Sandwich Panel Subjected to Local Compression(Stress and strain measurement II,OS7 Stress and strain measurement,MEASUREMENT METHODS)

OS7-5 Study on Deformation Characteristics of Honeycomb Core Sandwich Panel Subjected to Local Compression(Stress and strain measurement II,OS7 Stress and strain measurement,MEASUREMENT METHODS)

The Effect of Honeycomb Core Geometry on the Sound Transmission Performance of Sandwich Panels

Abstract The authors present numerical results for a systematic parametric study of the effect of honeycomb core geometry on the sound transmission and vibration properties of in-plane loaded honeycomb core sandwich panels using structural acoustic finite element analysis (FEA). Honeycomb cellular structures offer many distinct advantages over homogenous materials because their effective material properties depend on both their constituent material properties and their geometric cell configuration. From these structures, a wide range of targeted effective material properties can be achieved thus supporting forward design-by-tailoring honeycomb cellular structures for specific applications. One area that has not been fully explored is the set of acoustic properties of honeycomb and understanding of how designers can effectively tune designs in different frequency ranges. One such example is the insulation of target sound frequencies to prevent sound transmission through a panel. This work explored the effect of geometry of in-plane honeycomb cores in sandwich panels on the acoustic properties the panel. The two acoustic responses of interest are the general level of sound transmission loss (STL) of the panel and the location of the resonance frequencies that exhibit high levels of sound transmission, or low sound pressure transmission loss. Constant mass honeycomb core models were studied with internal cell angles ranging in increments from −45 deg to +45 deg. Effective honeycomb moduli based on static analysis of honeycomb unit cells are calculated and correlated to the shift in resonance frequencies for the different geometries, with all panels having the same total mass. This helps explain the direction of resonance frequency shift found in the panel natural frequency solutions. Results show an interesting trend of the first resonance frequencies in relation to effective structural properties. Honeycomb geometries with smaller core internal cell angles, under constant mass constraints, shifted natural frequencies lower, and had more resonances in the 1–1000 Hz range, but exhibited a higher sound pressure transmission loss between resonant frequencies.

Honeycomb core sandwich panels for origami-inspired deployable shelters: Multi-objective optimization for minimum weight and maximum energy efficiency

Rapidly deployable shelters, which can be packaged small but offer a high volume expansion ratio, are a critical asset for forward operating bases and can also be effective for disaster relief. Origami-inspired deployable shelters provide significant design advantages, including that (1) the rigid folded plates of these structures provide enhanced structural performance in the deployed form and (2) origami folds permit easy packaging in a small volume. Key design priorities include that the structure be lightweight and that it have thermal insulation for energy efficiency in heating and cooling. Energy efficiency is particularly critical for forward operating bases where fuel is at a premium. Honeycomb core sandwich panels, which provide a high stiffness to mass ratio, offer a lightweight option for rigid-wall origami-inspired shelters and can provide thermal insulation. A challenge in using this material, however, is the wide variety of options for material selection (for the face and core) and the thickness of each component. To achieve weight and energy efficiency priorities, this paper presents a multi-objective optimization procedure to design material properties of honeycomb core sandwich panels for minimum weight and maximum thermal resistance within the context of origami-inspired shelters. The novelty of this work includes the specific application to origami shelters, the simplified approach employed which approximates the structural behavior of the panels to avoid time-intensive finite element analyses, and a focus on selecting commercially available materials. While final design would require a three-dimensional finite element analysis, this procedure offers designers a valuable, simplified tool to rapidly narrow-in on sandwich panel configurations which are lightweight while offering thermal insulation. This approach is demonstrated for one origami-inspired topology which carries loads prescribed by the US Army Natick Soldier Research, Development & Engineering Center.

Evaluation of elastic constants of A3003 honeycomb core with varying hexagonal cell geometries through finite element approach

Aluminum honeycomb core is one of the most sought after material for the sandwich panel for light weight applications. While the aluminum face sheet is isotropic, the honeycomb core assumes orthotropic characteristics due to its configuration and strenuous load transfer paths. It is now well established that stiffness, dynamic, and low velocity impact response of the honeycomb core sandwich panel are critically dependent on the elastic constants of the core. An attempt is made to determine the elastic constants of orthotropic core through finite element approach simulating the load transfer and fixity boundary conditions likely to be prevalent in the unit cell of the honeycomb core. The cell wall thickness and the cell shape dictated by plastic bending limitations have also been simulated to determine their influence on the elastic constants. Further, the cell wall thickness and the bend radius have been varied and their influence on orthotropic elastic constants has been determined. The results of the study have been compared with analytical solutions proposed by researchers. The finite element procedure evolved is a simple, efficient, and quick solution methodology to accurately predict elastic constants of honeycomb core depicting the exact cell size and shape.

Testing and modeling of Nomex™ honeycomb sandwich Panels with bolt insert

Nomex™ honeycomb core sandwich panels with a bolt insert were load tested and modeled. The objective was to predict the honeycomb local buckling load and to identify a Nomex™ honeycomb constituent material model. Sandwich specimens were subjected to bolt pull-out load tests. The same sandwich structure was also tested in flat-wise tension with strain gages installed on the honeycomb walls. Finite element models of the flat-wise tension and bolt pull-out tests were built. The honeycomb geometry and strain gages were modeled with shell elements. An orthotropic honeycomb material model was identified by comparing the two test models to the experimental data. The material parameters identified are in the mid-range of previously published values. The pull-out test model was used to predict honeycomb wall buckling with a nodal rotation vector sum criterion. The buckling loads predictions closely corresponded to the start of the experimental load/displacement slope transition zone.