Composite Honeycomb Sandwich Research Articles

Vibroacoustic performance of composite honeycomb structures

This paper is concerned with the prediction of vibroacoustic performance of the honeycomb sandwich panels in a close-fitting enclosure. The acoustical transfer function of this panel in the close-fitting enclosure are presented. The noise reduction performance of the honeycomb sandwich panels is investigated through a set of experiments verifying the potential and usefulness of the honeycomb panel in practice. The results have confirmed that the absorption at the mass-spring-mass resonance in the case of a honeycomb panel (comparatively stiff) with a thin plate is more efficient with minimum weight. Adding absorption minimizes the effect of the 'mass-air-mass' resonance that usually impairs the low-frequency transmission loss, and offers good performance at higher frequencies. The potential of composite honeycomb sandwich panels for reducing low frequency noise (<500 Hz) is demonstrated.

A Study on the Mechanical Properties of the Honeycomb Sandwich Composites made by VARTM

To prove the suitability the honeycomb composites structure with VARTM, the mechanical properties of the skin materials and honeycomb composites structure were evaluated with the static strength tests. The mechanical properties of honeycomb composites structure made by VARTM were satisfied with the real using conditions instead of the composites structure made by autoclave process. Accordingly, the honeycomb sandwich composites made by VARTM is available for manufacturing various composites parts. VARTM was very effective method to manufacture the honeycomb sandwich composites. It was possible that the manufacturing process was changed from autoclave process to VARTM to solve the problems on the autoclave process.

Strength Characteristics and Deformation Behavior of Aluminum Honeycomb Sandwich Plates under Three-Point Bending Loads

The strength characteristics as well as local deformation behaviors of honeycomb sandwich composite (HSC) structures under three-point bending loads were investigated in consideration of various failure modes such as skin layer yielding, interface-delamination as well as shear deformation and local buckling in the core layer. Various types of aluminum honeycomb core and skin layer were used for this study. Their finite-element simulation was performed to analyze stresses and deformation behaviors of honeycomb sandwich plates. The results were very comparable to the experimental ones. Consequently, thicker skin layer, smaller cell size of honeycomb core and less delamiantion had dominant effects on the improvement in strength and deformation behaviors of honeycomb sandwich plates.

Effect of Temperature on the Low-velocity Impact Behavior of Composite Sandwich Panels

Composite sandwich panels constructed from glass-fiber-reinforced facesheets surrounding both foam-filled and nonfilled honeycomb cores are impacted using a drop-weight impactor at three energy levels and three temperatures. The effects of core material, temperature, and impact velocity on the absorbed energy, peak impact force, and damage mechanisms were studied. The foam-filled samples were subsequently subjected to four-point bend tests to investigate the effect of impact velocity and temperature on the damage tolerance and residual strength of the composites. It was found that the temperature can have a significant effect on the energy absorbed and maximum force encountered during impact, although the effect of the impact temperature on the residual bending stiffness and strength of the composites was mixed. In addition, the nature of the core material greatly influenced the damage mechanisms and impact force transfer in the honeycomb sandwich composites.

Mechanics of Composite Sinusoidal Honeycomb Cores

Lightweight and heavy-duty fiber-reinforced polymer (FRP) composite honeycomb sandwich structures have been increasingly used in civil infrastructure. Unique cellular core configurations, such as sinusoidal core, have been applied in sandwich construction. Due to specific core geometry, the solutions for core effective stiffness properties are not readily available. This paper presents a mechanics of materials approach to evaluate the effective stiffness properties of sinusoidal cores. In particular, the internal forces of a curved wall in a unit cell are expressed in terms of resultant forces, and based on the energy method and principle of equivalence analysis, the in-plane stiffness properties of sinusoidal cores are derived. Both finite-element modeling and experimental testing are carried out to verify the accuracy of the proposed analytical formulation. To illustrate the present analytical approach as an efficient tool in optimal analysis and size selection of sinusoidal cores, several design plots are provided and discussed. The simplified analysis and formulation presented for sinusoidal cores can be used in design application of FRP honeycomb sandwich and optimization of efficient cellular core structures.

Failure Analyses of Polymer Matrix Composite (PMC) Honeycomb Sandwich Joint Panels

The objective of this paper is to investigate the structural behavior and material failure characteristics of polymer-matrix composite (PMC) honeycomb sandwich joint panels under several transverse loads which resulted in web bending as typically experienced by aircraft wing skin. Several PMC honeycomb sandwich joint panels were fabricated as part of the demonstration test elements to provide structural concepts for the High-Speed Civil Transport (HSCT) wing. Test elements were preliminarily designed and sized under design-integration trade studies (DITS) task. Test elements selected for this study included two PMC honeycomb sandwich joint panels; one panel consisted of a honeycomb sandwich wing skin bolted joint by two fiber-reinforced composite spar caps to a honeycomb sandwich spar web; the other panel had the same structural concept except that the composite spar caps were replaced with the titanium ones. Essential components in the sandwich construction were composite face sheets, honeycomb cores, and core-to-facing bonding material. By statically loaded test elements to failure in room temperature, the test was designed to simulate flight load condition of 15 psi fuel over pressurization against the wing spar during supersonic maneuver. Geometric linear and nonlinear finite element models were constructed to simulate the structural behaviors of these test panels. Failure theories such as the Yeh-Stratton, Tsai-Wu, Tsai-Hill, and Maximum Stress and Strain criteria were utilized to predict the first ply failure and the results were compared with experimental data.

Dynamic response of doubly curved honeycomb sandwich panels to random acoustic excitation. Part 1: Experimental study

A set of four doubly curved, composite honeycomb sandwich panels has been tested with broad band, random acoustic excitation in a progressive wave tube facility. This paper presents the experimental results in the form of dynamic face plate strain measurements taken from various points close to the centre of the panels, on both the inner and outer face plates. The panels were tested at overall sound pressure levels up to 164 dB (ref. 2×10 −5 Pa , over a frequency bandwidth of 60– 600 Hz ). The response was found to be linear, with a maximum measured root mean square strain of 250με. The doubly curved geometry was found to have a profound effect on the ratio of inner-to-outer face plate strain, which was compared with ratios reported for flat and singly curved geometries. The second part of this study concentrates on three methods for predicting the response of the doubly curved panels to random acoustic excitation.

Optimal sizing of a composite sandwich fuselage component

This paper looks at structural optimisation techniques applied to real aerospace vehicle shell systems, e.g. the fuselage of a commercial transport aircraft. The objective of this study was to determine the effectiveness of a commercially available, gradient-based structural optimisation tool to minimise the weight of an advanced polymer matrix composite (PMC) honeycomb sandwich barrel representing a fuselage section of a future high speed civil transport. The finite element method using MSC/NASTRAN was chosen for the structural analysis. The key contributions of this study are the demonstration of the application of state-of-the-art structural optimisation techniques to the sizing of a complex shell representative of a realistic vehicle fuselage structure and the lessons learned from this demonstration.

THE EFFECTS OF VARIOUS DESIGN PARAMETERS ON THE FREE VIBRATION OF DOUBLY CURVED COMPOSITE SANDWICH PANELS

Sandwich panels have a very high stiffness to weight ratio, which makes them particularly useful in the aerospace industry where carbon fibre reinforced plastics and lightweight honeycomb cores are being used in the construction of floor panels, fairings and intake barrel panels. In the latter case, the geometry of the panels can be considered doubly curved. This paper presents an introduction to an ongoing study investigating the dynamic response prediction of acoustically excited composite sandwich panels which have double curvature. The final objective is to assess and hopefully produce an up to date set of acoustic fatigue design guidelines for this type of structure. The free vibration of doubly curved composite honeycomb sandwich panels is investigated here, both experimentally and theoretically, the latter using a commerically available finite element package. The design and manufacture of three test panels is covered before presenting experimental results for the natural frequencies of vibration with freely supported boundary conditions. Once validated against the experimental results, the theoretical investigation is extended to study the effects of changing radii of curvature, orthotropic properties of the core, and ply orientation on the natural frequencies of vibration of rectangular panels with various boundary conditions. The results from the parameter studies show curve veering, particularly when studying the effect of changing radii and ply orientation, however, it is not clear whether this phenomenon is due to the approximation method used or occurs in the physical system.

Evaluation of the In-Service Performance Behavior of Honeycomb Composite Sandwich Structures

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.

Composite robot end effector for manipulating large LCD glass panels

Recently, the design and the manufacture of light robot end effectors with high stiffness have become important in order to reduce the deflection due to the self-weight and weight of glass panel, a part of LCD, as the size of glass panels as well as robot end effectors increases. The best way to reduce the deflection and vibration of end effectors without sacrificing the stiffness of end effectors is to employ fiber reinforced composite materials for main structural materials because composite materials have high specific stiffness and high damping. In this work, the end effector for loading and unloading large glass panels were designed and manufactured using carbon fiber epoxy composite honeycomb sandwich structures. Finite element analysis was used along with an optimization routine to design the composite end effector. A box type sandwich structure was employed to reduce the shear effect arising from the low modulus of honeycomb structure. The carbon fiber epoxy prepreg was hand-laid up on the honeycomb structure and cured in an autoclave. A special process was used to reinforce the two sidewalls of the box type sandwich structure. The weight reduction of the composite end effector was more than 50% compared to the weight of a comparable aluminum end effector. From the experiments, it was also found that the static and dynamic characteristics of the composite end effector were much improved compared to those of the aluminum end effector.

Low Velocity Impact Response of Resin Infusion Molded Foam Filled Honeycomb Sandwich Composites

In this study the low-velocity impact and post-impact response of low-cost resin infusion molded sandwich composites utilizing a foam filled honeycomb core with graphite and S2-glass fabric facesheets (skins) has been investigated. The foam filled honeycomb core provides combined advantages of the traditional foam core and honeycomb sandwich composites in that it possesses high shear and bending stiffness, and cell wall stability. The low velocity impact response of 101.6 mm x 101.6 mm sandwich plates is studied at five energy levels representative of damage initiation and propagation. The low velocity damage is correlated to ultrasonic C-scan images, vibration resonance frequency and optical microscopy observations. The results indicate that the damage tolerance is enhanced by the foam filled honeycomb core and that load required to initiate damage is independent of the facesheet type for any specific core/facesheet thickness. The sandwich composites with S2-glass facesheets are found to possess more damage tolerance as compared to the graphite facesheets.

CRITICAL AND COINCIDENCE FREQUENCIES OF FLAT PANELS

Critical and coincidence frequencies of panels are important in studying their behaviour under acoustic excitation. Most spacecraft structural panels are of honeycomb sandwich construction and many of them have face sheets made of composite material. The critical and coincidence frequencies of such panels are discussed here. Expressions for critical and coincidence frequencies of thick isotropic and thin as well as thick symmetric composite panels are derived. It is shown that the orthotropic behaviour and transverse shear flexibility of the panels affects the critical and coincidence frequencies. The critical frequency of a typical composite honeycomb sandwich panel obtained using the above expressions match well with experimental results.

Water Intrusion in Thin‐Skinned Composite Honeycomb Sandwich Structures

Thin-skinned composite honeycomb sandwich structures from the trailing edge of the U.S. Army's Apache and Chinook helicopters have been tested to ascertain their susceptibility to water intrusion as well as such intrusions' effects on impact damage and cyclic loading. Minimum-impact and fatigue conditions were determined which would create microcracks sufficiently large to allow the passage of water through the skins; damage sufficient for this to occur was for some skins undetectable under a 40X-magnification optical microscope. Flow rate was a function of moisture content, damage, applied strain, and pressure differences.

Optimum design of composite honeycomb sandwich panels subjected to uniaxial compression

Sandwich construction provides a very lightweight structural configuration for many load conditions. The use of composite materials with their high stiffness, high strength, and anisotropy makes sandwich construction even more competitive for many applications. It is very desirable to design these structures for minimum weight to insure their most effective use. Closed-form analytical solutions are presented herein for the analysis and design of minimum weight, composite material hex-cell and square cell honeycomb core sandwich and panels subjected to in-plane uniaxial compressive loads. These methods account for overstressing, overall buckling, core shear instability, face wrinkling, and monocell buckling. The optimum face thickness, core depth, cell wall thickness, and cell size are analytically determined. The methods insure minimum weight, as well as provide methods to compare various material systems, compare honeycomb sandwich construction with other panel architectures, and assess the weight penalties associated with using nonoptimum honeycomb sandwich constructions. A comparison of various polymer, metal, and ceramic matrix composite materials is made by way of example.