Honeycomb Composite Structures Research Articles

Crashworthiness of Nomex® honeycomb-filled anti-climbing energy absorbing devices

To investigate the energy-absorption characteristics of thin-walled metals and Nomex® honeycomb composite structures, Nomex® honeycombs with five different specifications were applied to anti-climbing energy absorbing devices. Based on compression tests on Nomex® honeycombs, the equivalent numerical model for honeycombs was verified. A finite element model (FEM) for anti-climbing energy absorbing devices was established in Hypermesh. On this basis, the effects of parameters of different honeycombs on absorbed energy of energy-absorbing structure were analysed through LS-DYNA. The results showed that the energy absorption capacity of the anti-climbing energy absorbing devices mainly depended on honeycomb and thin-walled tubes. A Type-2 model exhibited the highest energy absorption capacity, at about 362 kJ, ACT1-3.2-144 honeycomb and thin-walled tubes absorbed energies of 198 and 149 kJ, respectively, which accounted for more than 95% of the total energy absorbed by the whole structure. The results also revealed that the corresponding average buffer force (484 kN) and the maximum peak buffer force (1226 kN) of the Type-2 model were also much greater than those of the other four structures. The buffer force of the Type-2 model remained within 300 to 1000 kN.

Design of compact multi-layer microwave absorber for ultra-wide band applications thru shaping and RAM technologies

The present paper deals with improving the radar cross section reduction (RCSR) of a manufactured compact double-layer radar absorber material (RAM). The basic idea is to monitor the RCS performance of both operating frequency bands and electromagnetic wave (EMW) incidence angles by means of three altered structures. The interaction of EM fields with the three different structure geometries has been studied through the homogenization and/or forward-backward propagation approaches. Firstly, shaping a manufactured double-layer structure by way of uncoated periodic honeycomb is considered. Then, lonly a periodic coated honeycomb composite structure along with the expressions for its effective EM material properties are presented. Finally, multi-layered radar absorbing structure (RAS) has been studied through adding another planar thin RAM by using the extracted effective EM material properties of a periodic coated honeycomb composite structure. Genetic algorithm (GA) was applied in all RAS to optimize the thicknesses and/or material properties for better absorption of the incident EM wave. The effective material properties are measured through rectangular waveguide WR-90 and microstrip line fixtures. Comparing the results obtained from both measured and numerical solutions of the actual cross-sectional geometry, the engineered third planar layer is then manufactured to cover X, Ku and K bands up to 60̂ incident angles. The simulated results show that the designed structures an effective absorption values less than −10 dB on average in the desired bandwidths and angle of incidents for TE & TM modes. Bistatic experiment showed that the RCS values for the proposed RAS achieved more than −10 dB.

Study on Thermal Performance of Single-layer and Multi-layer Stone Aluminum Honeycomb Composite Panels

The stone aluminum honeycomb composite panel is light in weight and large in ductility. It is a sustainable building thermal insulation material. It can be used as an insulation wall for ordinary buildings and prefabricated buildings, so that the exterior walls of the building can be light, high-strength and heat-insulated. However, the current application of stone aluminum honeycomb composite panels is still rare in practice, because the reasonable core size and number of layers with the best structural optimization, the least heat transfer, and the strongest applicability are difficult to determine. In this paper, the three basic heat transfer mechanisms of heat conduction, thermal convection and heat radiation of stone aluminum honeycomb composite panel structure are systematically analyzed. Under the premise of convective heat transfer of gas in honeycomb core cavity, the surface radiation exchange of honeycomb core cavity is established. The heat and the heat transfer of the cavity and the air in the cavity play a leading role in the heat transfer mechanism. The effects of parameters such as honeycomb core layer, core size, core height and core wall thickness on heat transfer performance under steady-state heat transfer conditions were studied by experimental methods. Stone aluminum honeycomb composite panels were tested under different temperature conditions. The equivalent thermal conductivity of the structure. Based on the ANSYS finite element analysis software, based on the experiment, the fluid-solid coupling heat transfer model of stone aluminum honeycomb composite board was established to simulate the steady-state heat transfer performance of composite sheets under single-layer and multi-layer honeycomb core materials, and to study the core body. The variation of the effective thermal conductivity under different boundary conditions and different geometric parameters, the simulation results are basically consistent with the experimental results, and the results of the empirical formula are also consistent. The results show that under the condition of satisfying the feasibility of the construction process within the fixed height, the height of the honeycomb core layer, the size of the core, and the height of the core can be appropriately reduced to reduce the thermal conductivity.

Defect imaging in layered composite plates and honeycomb sandwich structures using sparse piezoelectric transducers network

Carbon fiber reinforced polymer (CFRP) plates and honeycomb composite sandwich structures (HCSS) are widely used in the aerospace industry as they exhibit excellent strength-to-weight ratio, stiffness, toughness, corrosion resistance, etc. Nevertheless, defects, such as face sheet delamination or core-sheet debonding, may appear due to the impact forces or thermo-mechanical aging and can degrade these properties. Structural health monitoring (SHM) based on the use of guided elastic waves (GW) is regarded as a promising solution to detect such defects, and consequently to reduce maintenance costs and to extend structure service time. GWs propagate over large distances while being sensitive to structural inhomogeneities. Here, a SHM system prototype is proposed. It relies on a sparse grid of piezoelectric transducers distributed over the structure, used for both actuating and sensing GWs. Defect imaging is performed by means of the correlation based algorithm, the so-called Excitelet. It computes correlation coefficients between the theoretical and experimental GW signals for each pixel on the image representing the region of interest of the structure. The theoretical signals for CFRP are computed using a model based on a 2D semi-analytical finite element formulation. Analytical prediction of theoretical signals for the HCSS being intractable, a homogenization model is applied to the honeycomb core to replace it by an equivalent orthotropic plate preserving the same modelling approach. Defect imaging results are presented for both structures, namely a CFRP plate and a HCSS. The resolution of the corresponding images can be related to the wavelength of the inspecting mode.

An Infrared-Induced Terahertz Imaging Modality for Foreign Object Detection in a Lightweight Honeycomb Composite Structure

In this paper, terahertz time-domain spectroscopy (THz-TDS) is used for the first time to detect fabricated defects in a glass fiber-skinned lightweight honeycomb composite panel. A novel amplitude polynomial regression (APR) algorithm is proposed as a preprocessing method. This method segments the amplitude–frequency curves to simulate the heating and the cooling monotonic behavior as in infrared thermography. Then, the method of empirical orthogonal function (EOF) imaging is applied on the APR preprocessed data as a postprocessing algorithm. Signal-to-noise ratio analysis is performed to verify the image improvement of the proposed APR-EOF modality from a quantitative point of view. Finally, the experimental results and the physical analysis show that THz is more suitable with respect to the detection of defects in glass fiber lightweight honeycomb composites.

A Comparative Study of Enhanced Infrared Image Processing for Foreign Object Detection in Lightweight Composite Honeycomb Structures

The interest toward lightweight composites in the aeronautical industry grows year by year. The challenge is the identification and characterization of defects by using an integration of different techniques. The use of the infrared thermography (IRT) method for the inspection of lightweight composites is poorly documented in the open literature, due to the low heat diffusion through the honeycomb cores. In this study, IRT was used to retrieve the unknown positions of internal inserted objects in three different lightweight composite structures, by using three new thermal image processing integration methods. The corresponding post-processed results were compared against the traditional principal component thermography and pulsed phase thermography image processing techniques. The comparison showed that the integrated signal smoothing processing enhanced the image quality compared to the established techniques. Then, a thermal-physical analysis corresponding to the experimental results was conducted, in order to explain the experimental results. Finally, the advantages and disadvantages of the different presented methods when applied on the different lightweight composite structures were summarized.

The energy-absorbing characteristics of carbon fiber-reinforced epoxy honeycomb structures

This paper investigates the compression properties and energy-absorbing characteristics of a carbon fiber-reinforced honeycomb structure manufactured using the vacuum-assisted resin transfer molding method (VARTM). The composite core materials were manufactured using a machined steel baseplate onto which hexagonal blocks were secured. A unidirectional carbon fiber fabric was inserted into the slots and the resulting mold was vacuum bagged and infused with a two-part epoxy resin. After curing, the hexagonal blocks were removed, leaving a well-defined composite honeycomb structure. Samples were then cut from the composite cores and inspected in an X-ray computed tomography machine prior to testing. Mechanical tests on the honeycomb structures yielded compression strengths of up to 35 MPa and specific energy absorption values in excess of 47 kJ/kg. When normalized by the density of the core, the resulting values of specific strength were significantly higher than those measured on traditional core materials. The unidirectional cores failed as a result of longitudinal splitting through the thickness of the core, whereas the multidirectional honeycombs failed in a combined splitting/fiber fracture mode, absorbing significantly more energy than their unidirectional counterparts. Increasing the weight fraction of fibers served to increase the strength and energy-absorbing capacity of the core. Finally, it was also shown that introducing a chamfer acted to reduce the initial peak force and precipitate a more stable mode of failure.

Effective Control of Composite Honeycomb Structures on the Tip Leakage Flow in Turbine Cascade

AbstractTwo innovative composite tip structures that combine a honeycomb with a prismoid or spherical bottom have been proposed to actively control the tip leakage flow in a turbine cascade. The me...

Experimental and simulation investigation of temperature effects on modal characteristics of composite honeycomb structure

Modal analysis is the basis of the structural dynamics design and optimization. When operating in a thermal environment, the structure may be affected by the temperature in diverse aspects. In this paper, a sandwich structure composed of carbon fiber woven skins and a Nomex honeycomb core is taken as the research object. Temperature effects on its modal characteristics are investigated by experiments and simulations. During the test, natural frequencies and modal damping ratios of the specimen change with temperature dramatically, while each mode exhibits a particular trend. Although the temperature-dependent material property of the skin is identified as the essential factor of the variations in the modal parameters, the modulus components of the skin material have different sensitivities to the temperature change. As a result, correlations between the natural frequencies and modulus components are related to the corresponding mode shapes. And these correlations are studied by the finite element analysis.

Damage-induced acoustic emission source identification in an advanced sandwich composite structure

This paper proposes an acoustic emission (AE) based real-time health monitoring framework to efficiently identify the probable damage initiation/propagation locations in advanced sandwich composite structures. Towards this, numerical simulations and laboratory experiments on damage-induced AE-wave propagation in an aramid honeycomb composite structure have been carried out using a randomly selected sensory network. The simulation results are successfully validated with laboratory experiments. Eventually, the damage-source/AE-source regions are efficiently identified by applying an evolutionary algorithm – Particle-Swarm-Optimization based monitoring framework, which uses the registered AE-signals from the sensory network. A thorough assessment of different AE-source locations was carried out to evaluate the performance and the robustness of the proposed online monitoring strategy. The results clearly represent the efficiency of the framework for localizing the AE-source locations in such advanced and complex structures. Moreover, the proposed framework is reliable, independent of sensor positions, and not dependent upon the operator’s expertise.

Blast resistance and parametric study of sandwich structure consisting of honeycomb core filled with circular metallic tubes

Abstract Hierarchical sandwich structures have been popularly investigated due to its promotion in structural stress and stiffness. A composite Honeycomb structure Filled with Circular Tubes (short as HFCT) was proposed in the previous study. In this paper, the blast resistance performances of sandwich plate filled with HFCT core (short as SP-HFCT) are investigated numerically by considering plastic dissipation energy, deflection of back face-sheet and deformation modes. The comparisons of performance between the general honeycomb sandwich plate (short as GHP) and the SP-HFCT illustrate that the composited filling mode can effectively improve blast resistant capacity by reducing the maximum deflection of the back plate and improving the ratio of plastic energy dissipated by cellular core to the total plastic energy dissipated by sandwich plate. Parametric analyses are performed to evaluate the influence of matching effect between container and filler, filling mode and blast loading on the resistance performance of SP-HFCT. The results show that a stronger honeycomb container filled with weaker circular tubes is a more favorable configuration of HFCT core. Meanwhile, by filling circular tubes into a buckling area, a considerable mass efficiency improvement with respect to deflection resistance can be obtained. With the increasing of stand-off distance, the effectiveness of SP-HFCT against blast loads will be boosted.

Investigation of impact force on aluminium honeycomb structures by finite element analysis

In this study, the behaviour of aluminium honeycomb structures under low-speed impact has been investigated by experimental and finite element analysis method. The production of aluminium honeycomb composite structures was carried out using different adhesives of different widths and heights. The low-velocity impact experiments of the honeycomb structures produced were performed according to ASTM D7766 standard. As a result of the experiment, the force values which caused damage to the structure were measured according to the time, and the maximum force values were taken. Findings have shown that the decrease in cell width, the increase in cell height, and depletion of multiwall carbon nanotubes increase the maximum impact force values in honeycomb composite structures. It is seen that the results obtained by the finite element method and the experimental results are approximately 85% in agreement. There was no statistically significant difference between the results as a result of conducted t-test.

Nanocrystalline Aluminum Truss Cores for Lightweight Sandwich Structures

Substitution of conventional honeycomb composite sandwich structures with lighter alternatives has the potential to reduce the mass of future vehicles. Here we demonstrate nanocrystalline aluminum-manganese truss cores that achieve 2–4 times higher strength than aluminum alloy 5056 honeycombs of the same density. The scalable fabrication approach starts with additive manufacturing of polymer templates, followed by electrodeposition of nanocrystalline Al-Mn alloy, removal of the polymer, and facesheet integration. This facilitates curved and net-shaped sandwich structures, as well as co-curing of the facesheets, which eliminates the need for extra adhesive. The nanocrystalline Al-Mn alloy thin-film material exhibits high strength and ductility and can be converted into a three-dimensional hollow truss structure with this approach. Ultra-lightweight sandwich structures are of interest for a range of applications in aerospace, such as fairings, wings, and flaps, as well as for the automotive and sports industries.

Disbond detection in a composite honeycomb structure of an aircraft vertical stabilizer by fiber Bragg gratings detecting guided ultrasound waves

Efficient and accurate nondestructive inspection systems that save time can benefit scheduled maintenance of aircraft structures. Portable nondestructive inspection techniques capable of scanning larger area structures could find great utility and save considerable time and labor. Contemporary fixed location nondestructive inspection systems, such as the gold standard water-coupled ultrasound imaging by the “squirter” require structural disassembly of the part to be inspected and transportation to/from dedicated location. For large aircraft structures, such as vertical or horizontal stabilizers, this adds weeks to the off-site nondestructive inspection process. An on-site ultrasound detecting method for larger areas, comprising a flexible transducer panel of embedded fiber optic Bragg gratings that is lightweight and portable, and reusable over different structures, is described here. It is shown that this fiber Bragg grating embedded ultrasound transducer panel and readout hardware–software system can map tiny surface displacements of guided wave ultrasound, onsite, over an area of approximately 2 square feet in just over 10 min. The test sample is a sandwich structure with composite skins on both sides of an aluminum metal honeycomb section of an aircraft vertical stabilizer with an artificial engineered disbond. The ultrasound propagation data acquired at 612 positions over the large area, enables in situ nondestructive inspection of defects/ damage by comparing post-damage data with baseline data, and is independent of the material information.

Fatigue fracture of fiber reinforced polymer honeycomb composite sandwich structures for gas turbine engines

Fiber reinforced polymer honeycomb composite sandwich structures are commonly used in different industries. In particular, they are used in the manufacture of gas turbine engines. However, fiber reinforced polymer honeycomb composite sandwich structures often have a manufacturing flaw. In theory, such flaws due to their rapid propagation reduce the durability of fiber reinforced polymer honeycomb composite sandwich structures. In this paper, bending fatigue tests of fiber reinforced polymer honeycomb composite sandwich structures with manufacturing flaws were conducted. Comparative analysis of fatigue fracture of fiber reinforced polymer honeycomb composite sandwich specimens was conducted before and after their bending fatigue tests. The analysis was based on the internal damage X-ray observation of fiber reinforced polymer honeycomb composite sandwich specimens.

Detecting Water in Composite Sandwich Panels by Using Infrared Thermography

Honeycomb composite structures widely used in aviation are sturdy and light-weight but they may accumulate water from the atmosphere during aircraft operation. The presence of water in honeycomb cells leads to a higher airplane mass and excessive corrosion of aluminum cores, while the frozen water endangers panel integrity. This work describes the use of infrared thermography for detecting water trapped in aviation honeycomb cells.

Experimental research and use of finite elements method on mechanical behaviors of honeycomb structures assembled with epoxy-based adhesives reinforced with nanoparticles

This study utilized experimental and finite element methods to investigate the mechanical behavior of aluminum honeycomb structures under compression. Aluminum honeycomb composite structures were subjected to pressing experiments according to the standard ASTM C365. Resistive forces in response to compression and maximum compressive force values were measured. Structural damage was observed. In the honeycomb structure, the cell width decreased as the compressive force increased. Results obtained with finite element models generated using ANSYS Workbench 15 were validated. Experimental results paralleled the finite element modeling results. The ANSYS results were approximately 85 % reliable.

Optimal Design of Multi-Layer Absorbent Honeycomb Cellular Composite Material Structure

Next generation aircraft rely heavily on lightweight honeycomb composite structures for improved electromagnetic wave scattering and stealth capabilities. This paper investigated the optimal design and analysis methods of multi-layer absorbent honeycomb composite structures. The effective electromagnetic parameters of anisotropic object were calculated accompany with the formulation of reflectivity for incident wave. A genetic algorithm is employed to optimize the RCS of the absorptive honeycomb composite in desired angle range. The thickness and the volume fraction of absorptive materials are adopted to optimize the effective electromagnetic parameters under different polarized modes. Single and multi layer absorptive honeycomb composite were been studied. The results show that the thickness of the first absorptive layer plays a key role on the reflectivity of honeycomb structure. Therefore, it is advised to arrange the absorptive layers such that the EM absorption properties increases from outside to inside.

Ultrasonic guided wave propagation and disbond identification in a honeycomb composite sandwich structure using bonded piezoelectric wafer transducers

A coordinated theoretical, numerical, and experimental study is carried out in an effort to understand ultrasonic guided wave propagation and interaction with disbond, as well as, to identify disbond in a honeycomb composite sandwich structure using surface-bonded piezoelectric wafer transducers. In contrast to most of the work done previously, a fast and efficient two-dimensional semi-analytical model based on global matrix method is used to study dispersion characteristics as well as transient response of the healthy honeycomb composite sandwich structure subjected to relatively high-frequency piezoelectric wafer transducer excitations. Numerical simulations are then conducted using commercially available finite element package, ABAQUS, in order to explore guided wave propagation mechanisms due to the presence of disbond. Numerical simulations are further broadened to investigate the effect of disbond size on the amplitudes and group velocities of propagating guided wave modes. A good agreement is observed between the theoretical, numerical and experimental results in all cases studied. It is noticed that the presence of disbond, in particular, amplifies the first anti-symmetric (A0) mode and increases its group velocity. Finally, based on these modal behaviors, the location of an unknown disbond, within the piezoelectric wafer transducer array is experimentally determined by applying a probability-based damage detection algorithm.

Guided wave propagation in a honeycomb composite sandwich structure in presence of a high density core

A coordinated theoretical, numerical and experimental study is carried out in an effort to interpret the characteristics of propagating guided Lamb wave modes in presence of a high-density (HD) core region in a honeycomb composite sandwich structure (HCSS). Initially, a two-dimensional (2D) semi-analytical model based on the global matrix method is used to study the response and dispersion characteristics of the HCSS with a soft core. Due to the complex structural characteristics, the study of guided wave (GW) propagation in HCSS with HD-core region inherently poses many challenges. Therefore, a numerical simulation of GW propagation in the HCSS with and without the HD-core region is carried out, using surface-bonded piezoelectric wafer transducer (PWT) network. From the numerical results, it is observed that the presence of HD-core significantly decreases both the group velocity and the amplitude of the received GW signal. Laboratory experiments are then conducted in order to verify the theoretical and numerical results. A good agreement between the theoretical, numerical and experimental results is observed in all the cases studied. An extensive parametric study is also carried out for a range of HD-core sizes and densities in order to study the effect due to the change in size and density of the HD zone on the characteristics of propagating GW modes. It is found that the amplitudes and group velocities of the GW modes decrease with the increase in HD-core width and density.