Showing papers on "Sandwich-structured composite published in 1999"

The Behavior of Sandwich Structures of Isotropic and Composite Materials

Abstract: SANDWICH STRUCTURES: ORIGINS, ADVANTAGES, AND USES Description of Various Sandwich Constructions Advantages of Sandwich Construction over Construction Monocoque Thin Walled Construction Origins of Sandwich Construction Uses of Sandwich Construction Present Approach to Analysis Problems References ANISTROPIC ELASTICITY AND COMPOSITE LAMINATE THEORY Introduction Derivation of the Anisotropic Elastic Stiffness and Compliance Matrices The Physical Meaning of the Components of the Orthotropic Elasticity Tensor Methods to Obtain Composite Elastic Properties from Fiber and Matrix Properties Thermal and Hygrothermal Considerations Time-Temperature Effects on Composite Materials High Strain Rate Effects on Material Properties Laminae of Composite Materials Laminate Analysis [A], [B], and [D] Stiffness Matrices for a Mid-Plane Symmetric Sandwich Structure Piezoelectric Effects Problems References DERIVATION OF THE GOVERNING EQUATIONS FOR SANDWICH PLATES (PANELS) Introduction Plate Equilibrium Equations The Bending of Composite Material Laminated and/or Sandwich Plates: Classical Theory Classical Plate Theory Boundary Conditions Analysis of Composite Materials Laminated and/or Sandwich Panels Including Transverse Shear Deformation Effects Boundary Conditions for a Plate Using the Refined Plate Theory Laminated or Sandwich Plate on an Elastic Foundation Laminated or Sandwich Plates Subjected to Dynamic Loads Problems References BEAMS, COLUMNS, AND RODS OF COMPOSITE MATERIALS Development of Classical Beam Theory Some Simplified Sandwich-Beam Solutions Eigenvalue Problems of Sandwich Beams: Natural Vibrations and Elastic Stability Other Considerations Problems References ENERGY METHODS FOR SANDWICH STRUCTURES Introduction Theorem of Minimum Potential Energy Analysis of a Beam in Bending Using the Theorem of Minimum Potential Energy Reissner's Variational Theorem and Its Applications Static Deformation of Moderately Thick Beams Flexural Vibrations of Moderately Thick Beams Flexural Natural Frequencies of a Simply Supported Beam Including Transverse Shear Deformation and Rotatory Inertia Effects Minimum Potential Energy for Rectangular Plates A Rectangular Composite Material Plate Subjected to Lateral and Hygrothermal Loads In-Plane Shear Strength Determination of Composite Materials in Laminated and Sandwich Panels Problems References SOLUTIONS FOR RECTANGULAR SANDWICH PLATES Introduction Navier Solutions for Rectangular Sandwich Plates Levy Solutions for Plates of Composite Materials Perturbation Solutions for the Bending of a Composite Material Sandwich Plate, with Mid-Plane Symmetry and No Bending-Twisting Coupling Isotropic Sandwich Panels Subjected to a Uniform Lateral Load Minimum Weight Optimization for a Sandwich Panel Subjected to a Distributed Lateral Load Analysis of an Isotropic Sandwich Plate on an Elastic Foundation Subjected to a Uniform Lateral Load Static Analysis of Sandwich Plates of Composite Materials Including Transverse Shear Deformation Effects Exact Solution Other Considerations Problems References DYNAMIC EFFECTS ON SANDWICH PANELS Introduction Natural Flexural Vibrations of Sandwich Plates: Classical Theory Natural Flexural Vibrations of Sandwich Plates Including Transverse Shear Deformation Effects Forced-Vibration Response of a Sandwich Plate Subjected to a Dynamic Lateral Load Dynamic Response of Sandwich Plates to Localized Loads Large Amplitude Nonlinear Oscillations of Sandwich Plates Simply Supported on All Edges Linear and Nonlinear Oscillations of Specially Orthotropic Sandwich Panels with Various Boundary Conditions Vibration Damping Problems References THERMAL AND MOISTURE EFFECTS ON SANDWICH STRUCTURES General Considerations Derivation of the Governing Equations for a Thermoplastic Isotropic Plate Boundary Conditions General Treatment of Plate Nonhomogeneous Boundary Conditions Thermoelastic Effects on Beams Self-Equilibrium of Thermal Stress Rectangular Composite Material Plate Subjected to Lateral and Hygrothermal Loads References ELASTIC INSTABILITY (BUCKLING) OF SANDWICH PANELS General Considerations The Buckling of an Orthotropic Sandwich Plate Subjected to In-Plane Loads Classical Theory Elastic Stability of a Composite Sandwich Panel Including Transverse Shear Deformation and Hygrothermal Effects The Buckling of an Isotropic Plate on an Elastic Foundation Subjected to Biaxial In-Plane Compressive Loads The Buckling of Honeycomb Core Sandwich Panels Subjected to In-Plane Compressive Loads The Buckling of Solid- or Foam-Core Sandwich Panels Subjected to In-Plane Compressive Loads Buckling of a Truss-Core Sandwich Panel Subjected to Uniaxial Compression Elastic Stability of a Web-Core Sandwich Panel Subjected to a Uniaxial Compressive In-Plane Load Buckling of Honeycomb-Core Sandwich Panels Subjected to In-Plane Shear Loads Buckling of Solid-Core or Foam-Sandwich Panel Subjected to In-Plane Shear Loads Buckling of a Truss-Core Sandwich Panel Subjected to In-Plane Shear Loads Buckling of a Web-Core Sandwich Panel Subjected to an In-Plane Shear Load Other Considerations Problems References STRUCTURAL OPTIMIZATION TO OBTAIN MINIMUM-WEIGHT SANDWICH PANELS Introduction Minimum Weight Optimization of Honeycomb-Core Sandwich Panels Subjected to a Unidirectional Compressive Load Minimum Weight Optimization of Foam-Core Sandwich Panels Subjected to a Unidirectional Compressive Load Minimum Weight Optimization of Truss-Core Sandwich Panels Subjected to a Unidirectional Compressive Load Minimum Weight Optimization of Web-Core Sandwich Panels Subjected to a Unidirectional Compressive Load Minimum Weight Optimization of Honeycomb-Core Sandwich Panels Subjected to In-Plane Shear Loads Minimum Weight Optimization of Solid- and Foam-Core Sandwich Panels Subjected to In-Plane Shear Loads Minimum Weight Optimization of Truss-Core Sandwich Panels Subjected to In-Plane Shear Loads Minimum Weight Optimization of Web-Core Sandwich Panels Subjected to In-Plane Shear Loads Optimal Stacking Sequences for Composite Material Laminate Faces for Various Sandwich Panels Subjected to Various Loads Problems References SANDWICH SHELLS Introduction Analysis of Sandwich Cylindrical Shells under Axially Symmetric Loads A General Solution for Orthotropic-Sandwich Cylindrical Shells under Axially Symmetric Loads Shells with Mid-Plane Asymmetry Other Considerations Problems References BUCKLING OF SANDWICH CYLINDRICAL SHELLS Buckling of a Solid- or Foam-Core Sandwich Cylindrical Shell with Isotropic Faces Subjected to an Axially Symmetric Compressive End Load Buckling of a Solid- or Foam-Core Sandwich Cylindrical Shell with Orthotropic Composite Faces Subjected to an Axially Symmetric Compressive Load Buckling of a Honeycomb-Core Sandwich Cylindrical Shell with Composite Faces Subjected to an Axially Symmetric Compressive End Load Overall Buckling of Sandwich Cylindrical Shells Subjected to an Overall Bending Moment Buckling of a Sandwich Cylindrical Shell Due to External Pressure Buckling of a Sandwich Cylindrical Shell Due to Torsion Dynamic Buckling Problems References MINIMUM WEIGHT OPTIMIZATION OF SANDWICH CYLINDRICAL SHELLS General Discussion Minimum Weight Optimization of a Solid Foam-Core Sandwich Cylindrical Shell with Isotropic Faces Subjected to an Axially Compressive Load Minimum Weight Optimization of a Solid- or Foam-Core Sandwich Cylindrical Shell with Orthotropic Composite Material Faces Subjected to an Axially Compressive Load Minimum Weight Optimization of a Honeycomb-Core Sandwich Cylindrical Shell with Composite Material Faces Subjected to an Axially Symmetric Compressive Load Problems References APPENDIX 1: Core Materials APPENDIX 2: Face Materials APPENDIX 3: American Society for Testing Materials (ASTM) Standards for Sandwich Structures and Materials INDEX

The strength characteristics of aluminum honeycomb sandwich panels

Abstract: Aluminum sandwich construction has been recognized as a promising concept for structural design of lightweight transportation systems such as aircraft, high-speed trains and fast ships. The aim of the present study is to investigate the strength characteristics of aluminum sandwich panels with aluminum honeycomb core theoretically and experimentally. A series of strength tests are carried out on aluminum honeycomb-cored sandwich panel specimen in three point bending, axial compression and lateral crushing loads. Simplified theories are applied to analyze bending deformation, buckling/ultimate strength and crushing strength of honeycomb sandwich panels subject to the corresponding load component. The structural failure characteristics of aluminum sandwich panels are discussed. The test data developed are documented.

Pitch-based carbon foam heat sink with phase change material

Abstract: A process for producing a carbon foam heat sink is disclosed which obviates the need for conventional oxidative stabilization. The process employs mesophase or isotropic pitch and a simplified process using a single mold. The foam has a relatively uniform distribution of pore sizes and a highly aligned graphic structure in the struts. The foam material can be made into a composite which is useful in high temperature sandwich panels for both thermal and structural applications. The foam is encased and filled with a phase change material to provide a very efficient heat sink device.

Mechanical behaviour of cellular core for structural sandwich panels

Abstract: This paper deals with the analysis of the mechanical properties of the core materials for sandwich panels. In this work, the core is firstly a honeycomb and secondly tubular structure. This kind of core materials are extensively used, notably in automotive construction (structural components, load floors...). For this study, three approaches are developed: a finite element analysis, an analytical study and experimental tests. Structural members made up of two stiffs, strong skins separated by a lightweight core (foam, honeycomb, tube...) are known as sandwich panels. The separation of the skins by the core increases the inertia of the sandwich panel, the flexure and shear stiffness. This increase is obtained with a little increase in weight, producing an efficient structure to resist bending and buckling loads. A new analytical method to analyse sandwich panels core will be presented. These approaches (theoretical and experimental) are used to determine elastic properties and ultimate stress. A parameter study is carried out to determine elastic properties as a function of geometrical and mechanical characteristics of basic material. Both theoretical and experimental results are discussed and a good correlation between them is obtained.

Free vibration analysis of composite sandwich plates

Abstract: The fibre reinforced plastic (FRP) composite materials configured as sandwich panels are finding increased usage in a variety of structural applications. An important facet in correct usage is an understanding of the dynamic behaviour of such structural configurations. This paper addresses the issue of natural frequencies of sandwich plate panels. The closed-form solutions are obtained using Reddy's first- and higher-order shear deformation theories. The approaches are validated against results from a standard, commercially available finite element analysis package. The paper concludes with a detailed investigation of the influence of variation in material property parameters and plate geometry variables on the natural frequency.

Design of Sandwich Structures

Abstract: Failure modes for sandwich beams of GFRP laminate skins and Nomex honeycomb core are investigated Theoretical models using honeycomb mechanics and classical beam theory are described A failure mode map for loading under point bending is constructed showing the dependence of failure mode and load on the ratio of skin thickness to span length and honeycomb relative density Beam specimens are tested in point bending The e ect of honeycomb direction is also examined The experi mental data agree satisfactorily with the theoretical predictions The results reveal the important role of core shear in a sandwich beam s bending behaviour and the need for a better understanding of indentation failure mechanism High order sandwich beam theory HOSBT is implemented to extract useful infor mation about the way that sandwich beams respond to localised loads under point bending High order or localised e ects relate to the non linear patterns of the in plane and vertical displacements elds of the core through its height resulting from the unequal deformations in the loaded and unloaded skins The localised e ects are examined experimentally by Surface Displacement Analysis of video images recorded during point bending tests A new parameter based on the intrinsic material and geometric properties of a sandwich beam is introduced to characterise its susceptibility to localised e ects Skin exural rigidity is shown to play a key role in determining the way that the top skin allows the external load to pass over the core Furthermore the contact stress distribution in the interface between the central roller and the top skin and its importance to an indentation stress analysis are investigated To better model the failure in the core under the vicinity of localised loads an Arcan type test rig is used to test honeycomb cores under simultaneous compression and shear loading The experimental measurements show a linear relationship between the out of plane compression and shear in honeycomb cores This is used to derive a failure criterion for applied shear and compression which is combined with the high order sandwich beam theory to predict failure caused by localised loads in sandwich beams made of GFRP laminate skins and Nomex honeycomb under point bending loading Short beam tests with three di erent indenter s size are performed on appropriately prepared specimens Experiments validate the theoretical approach and reveal the

Bending of Curved Sandwich Panels with a Transversely Flexible Core-Closed-Form High-Order Theory:

Abstract: The bending behavior of a curved sandwich panel with a transversely flexible core, ie, "soft" in the out of plane direction is derived It is formulated using a rigorous systematic closed-form approach based on variational principles The effects of the transversely flexible core are incorporated resulting in non-linear patterns, denoted also as high-order effects, for the inplane and the transverse deformations through the height of the core The governing equations along with the associated boundary and continuity conditions for a general type of sandwich panel, ie, unidentical skins, composite laminated or metallic and a "soft" core are derived General type of boundary conditions, including spring conditions, as well as different conditions at upper and lower skins at the same section, are implemented and the effects of "stiff' edge inserts, denoted as global boundary conditions, along with the induced localized effects are considered Localized effects at support regions with or without edge stif

Method for filling and reinforcing honeycomb sandwich panels

Abstract: The present invention relates to a process for the fast and efficient filling of voids of both simple and complex shape which can be carried out at room temperature. In particular, the present invention consists of the use of free flowing thermally expanding and curing powders which are poured into the voids and then heated causing the powder to expand, coalesce and cure and thus filling or partially filling the void space as required. The process according to the present invention is particularly suitable for filling the spaces in, around and between honeycomb or pre-formed foam cores as required to produce a filled or partially filled honeycomb or foam core or any other material used in sandwich panel construction. This process is also a simple and efficient method for filling moulds suitable for use in cellular artefact production. The filled or partially filled mould or honeycomb core can then be cured to produce bonded sandwich panels or moulded cellular artefacts. In sandwich panel construction the core material can be bounded by one or more surface skins and the cured bonded panel can be cut to provide a panel having pre-sealed edges.

Evaluation of the in-service performance behavior of honeycomb composite sandwich structures

Abstract: When honeycomb composite structures are fabricated for the aerospace industry, they are designed to be closed to their operating environment for the life of the composite structure. However, once in service, this design can break down. Damage can set in motion a chain reaction of events that will ultimately degrade the mechanical integrity of the composite structure. Through thermographic analysis, the tendency of honeycomb composite structures to absorb and retain water was investigated, and an attempt was made to quantify the extent of water ingression in the Boeing 767 aircraft. Through thermographic analysis, the exterior honeycomb composite structures were found to contain less than 50 kg of water per plane. On average, over 90% of the water found on an aircraft was contained in five problematic parts, which included the outboard flap wedge, the nose landing gear doors, the main landing gear doors, the fixed upper wing panels, and the escape slide door. Kevlar lamina induced microcracking, skin porosity problems, and cracked potting compound were the root causes of water ingression and migration in these structures. Ultimately, this research will aid in the fundamental understanding and design of future honeycomb composite sandwich structures.

On the characterisation of syntactic foam core sandwich composites for compressive properties

Abstract: Sandwich structures, especially those with honeycomb and grid structures as the core material, are very commonly employed in aircraft structures. There is an increasing use of closed-pore rigid syntactic foams as core materials in sandwich constructions because they possess a number of favourable properties. The syntactic foams, owing to their structure and formation, behave differently under compression compared to other traditionally used core materials. In the present study, therefore, syntactic foam core sandwich constructions are evaluated for their behaviour under compression in both edgewise and flatwise orientations. Further, the work characterises the relative performance of two sets of sandwich materials, one containing glass-epoxy and the other, glass/carbon hybrid-epoxy skins. As non-standard geometry test specimens were involved, only a comparative evaluation was contemplated in this approach. The experiments indicate that the nature of the reinforcement fabric in the skin has a bearing on the test results in edgewise orientation. Thus, the tendency towards initiation of vertical crack in the central plane of the core material, which is a typical fracture event in this kind of material, was found to occur after a delay for the specimens containing the glass fabric in the skin. Attempts are made to establish the correlation between observations made on the test specimen visually during the course of testing and the post-compression microscopic examinations of the fracture features.

Boundary condition effects in buckling of soft core sandwich panels

Abstract: The effects of boundary conditions on the critical load level and the corresponding deflection mode shape of sandwich panels with a “soft” core due to in-plane loads are presented. The study is conducted using a closed-form high-order linearized buckling analysis that includes the influence of the transverse flexibility of the core as well as of the localized effects on the overall sandwich panel behavior, and allows the use of different boundary conditions for the upper and lower skin at the same section. The panel construction is general and consists of two skins (not necessary identical), metallic or composite-laminated symmetric, and a soft core made of foam or a low-strength honeycomb. The closed-form high-order analysis yields the general buckling behavior of the structure, which means that the solutions obtained allow for interaction between the skins and the core. The solutions are general and are \Inot\N based on separation of the buckling response on several types of uncoupled buckling modes, such as overall buckling, skins wrinkling, etc., as commonly used in the literature. The numerical scheme consists of finite differences to approximate the governing equations of the closed-form high-order formulation and to transform the set of linearized governing differential equations into an eigenvalue problem that is solved using the deflated iterative Arnoldi procedure. The influence of a general type of boundary conditions, including different conditions throughout the height of the same section and nonidentical conditions at the upper and lower skin, as well as of the core properties, on the buckling behavior of the sandwich panels is considered. The discrepancy between the Timoshenko-Reissner model and the present formulation is discussed. In particular, a partial fixity phenomenon due to the existence of the pinned boundary conditions, i.e., simply supported conditions, at the upper and lower skins at the edge is demonstrated. It is shown that the core properties affect the buckling loads and the corresponding modes of the panel in such a way that the structures with identical boundary conditions but with different cores may undergo different types of buckling such as overall and local as well as interactive loss of stability. The effect of an edge concentrated moment, induced by a couple and exerted on the skins only is also studied.

Structural behaviour of sandwich panel shear walls: An experimental analysis

Abstract: Within a comprehensive research project devoted to analyse the contributing effect of cladding panels on the structural behaviour of steel frames under horizontal loads, a suitable experimental procedure has been set up in order to characterise the main behavioural parameters of specific shear walls. In particular, with regard to light-weight sandwich panels, which are currently used in building as enclosure elements, monotonic and cyclic full-scale shear tests have been performed on both single connection specimens and pin-jointed steel frames branced by infill panels. Such an activity, whose main results are summarised in this paper, firstly provides the experimental evidence as basis for setting up numerical and analytical intepretative models. Besides, it supplies useful information on the possibility to use this panel typology as shear wall components. Finally, it points out how their shear performance can be improved through simple modifications of standard prototypes.

Thickness Effects on Pinned Joints for Composites

Abstract: Mechanical joints are commonly used for joining composite laminates, especially thick section composites. In most studies of mechanical joints, the interactions between pin diameter (D) and composite dimensions such as width (W) and distance from hole center to composite end (e), resulting in W/D and e/D ratios, are the primary parameters for joint evaluation since composite laminates are usually very thin. However, as composite thickness increases, the contact interaction between pin and composite alters. Subsequently, the composite joint stiffness and joint strength are affected. Since the contact interaction is strongly affected by pin diameter (D) and composite thickness (H), this study investigated mechanical joints with combinations of various composite thicknesses and pin diameters. Composite material made of woven glass fabric and phenolic matrix was investigated. Sixteen joint configurations based on four composite thicknesses and four pin diameters were examined. Both experiments and finite element analysis were conducted in this study It was found that the ratio of H 2 /D 2 could be used to distinguish the two primary damage modes, i.e. pin bending and bearing failure. Results also showed that thick composites with small pins and thin composites with large pins had Iower efficiencies for joint stiffness and joint strength than those having similar dimensions between pin diameter and composite thickness.

Nonlinear Behavior of Sandwich Panels with a Transversely Flexible Core

Abstract: Nonlinear behavior of sandwich panels with a transversely flexible core is presented. The study is based on a highorder nonlinear formulation that includes the influence of the transverse flexibility and shear resistance of the core on the panel behavior, thus allowing for interaction between the facings through the core thickness. The solutions obtained are general and are not based on decoupling of the local and global responses as commonly used in the literature. The governing equations along with the appropriate boundary and continuity conditions are presented, and the solution approach is outlined. The path-following algorithm devised is based on the natural parameter and the arc-length continuation techniques. The example problems discussed include a concentrated line load exerted at midspan of the panel, couples applied at the panel edges, and compression of an asymmetric sandwich panel. Mode interaction observed in the panel behavior is shown to be a result of the flexibility of the "soft" core. Variations in the boundary conditions of the sandwich panel as well as in the layout of the compressive longitudinal loads are also shown to shift its response from an imperfection-sensitive to an imperfection-nonsensitive one and vice versa.

Sandwich panel of veneer-overlaid low-density fiberboard

Abstract: Low-density sandwich panels of veneer-overlaid fiberboards of 12 mm thickness for structural use were manufactured at densities of 0.3–0.5g/cm3 using an isocyanate compound resin adhesive and steam injection pressing method. The effects of board density, veneer thickness, and resin content on the fundamental properties of sandwich panels were examined, with the following results: (1) The dry moduli of rupture and elasticity in the parallel direction of sandwich panels with thicker veneers were superior. The dry moduli of rupture and elasticity in the parallel direction of sandwich panels with 2.0 mm thick veneer at densities of 0.4–0.5 g/cm3 were 40–60 MPa, and 5–8 GPa, which were two and four times as much as those of homogeneous fiberboards, respectively. (2) The higher-density panels exhibited tensile failure at the bottom veneer surface during static dry bending in a parallel direction, whereas lower-density panels experienced horizontal shear failure in the core. (3) The dimensional stability of sandwich panels had good dimensional stability, with negligible springback after accelerated weathering conditions. (4) The thermal insulation properties of sandwich panels were found to be much superior to other commercial structural wood composite panels.

On the Response of a Sandwich Panel with a Bilinear Core

Abstract: Sandwich panels can failin a variety of ways. In the present article one type of failure is investigated and modeled that has a number of important applications, e.g., marine hulls. Here core yielding is assumed to initiate and grow in the sandwich panel while the face sheets remain bonded, unbuckled, and in the elastic range. For elastic face sheets, the core shear stresses can be determined from equilibrium of the face sheets independent of core yield. Core shear strains can then be found from the stress-strain curve and an algorithm is constructed for determining shear deflection. Bending deflection is found from the elastic solution. This approach works well except when the bilinear stress-strain behavior approaches the perfectly plastic core. With the aid of a detailed finite-element solution, it is shown that the classical sandwich theory assumptions begin to break down and that the face sheets now carry an appreciable part of the shear load. This effect is shown in detail for four-point beam bendin...

Mechanical fasteners for cladding sandwich panels:: Interpretative models for shear behaviour

Abstract: The shear performance of screwed connection systems usually adopted for lightweight sandwich panels is investigated in this paper. First of all, after brief considerations concerning the possibility to use cladding panels as diaphragm in steel building and the corresponding connecting system requirements, the results of available monotonic and cyclic experimental analyses on several connection typologies are summarised. Then mathematical models able to interpret both monotonic and cyclic behaviour of the connections are proposed. In particular, the mathematical cyclic model is based on the previously defined envelope curve, which is expressed by means of a Ramberg-Osgood type law relationship and calibrated trough monotonic tests. Finally, the comparison between experimental and numerical results is carried out, focussing on the actual dissipative capacities of such connection typologies.

Local buckling behaviour of steel plate elements supported by a plastic foam material

Abstract: Sandwich panels comprising steel facings and a polystyrene foam core are increasingly used as roof and wall claddings in buildings in Australia. When they are subjected to loads causing bending and/or axial compression, the steel plate elements of their profiled facing are susceptible to local buckling. However, when compared to panels with no foam core, they demonstrate significantly improved local buckling behaviour because they are supported by foam. In order to quantify such improvements and to validate the use of available design buckling stress formulae, an investigation using finite element analyses and laboratory experiments was carried out on steel plates that are commonly used in Australia of varying yield stress and thickness supported by a polystyrene foam core. This paper presents the details of this investigation, the buckling results and their comparison with available design buckling formulae.

Experimental Evaluation of Interactive Buckle Localization in Compression Sandwich Panels

Abstract: Experimental observations on an axially-loaded sandwich panel compare well with the recent developments in the theoretical modelling of interactive localized buckling. Comparisons of experimental collapse loads. buckle wavelengths and equilibrium paths With the theoretical model show good correlation.

Designing honeycomb panels for noise control

Abstract: Honeycomb sandwich panels which have similar mechanical properties can have significantly different acoustic properties. The mechanical properties are panel thickness, static bending stiffness and mass per unit area of the panel. The acoustic performance of the panel can be assessed by considering the panel as either a primary radiator of structure borne noise or as a transmission loss barrier. The differences in acoustic performance of the sandwich panels is determined by the bending wave speed characteristic of the panel. The key to designing honeycomb panels for noise control is to maintain a sub-sonic bending wave speed in the sandwich panel over as great a frequency range as possible. The noise control benefits of a properly designed nomex honeycomb sandwich panel are demonstrated relative to alternative non-optimum designs.