Foam-filled Honeycomb Cores Research Articles

Nonlinear vibration behaviours of foam-filled honeycomb sandwich cylindrical shells: Theoretical and experimental investigations

In this study, the nonlinear vibration behaviours of foam-filled honeycomb sandwich cylindrical shells (FHSCSs) are investigated theoretically and experimentally. Initially, a time-domain minimum residual (TDMR) method is first adopted for the analysis of nonlinear free and forced vibrations of the FHSCSs, which is based on a dynamical model developed, with the effective material parameters of the foam-filled honeycomb core being obtained by employing the Gibson method and the Hamilton equivalence technique. Based on the high-order shear deformation shell principle and von Karman's theory, the nonlinear natural frequencies and resonant responses are solved using the Broyden iterative approach and TDMR method. Furthermore, several literature results are utilized for the rough verification of such a method. Meanwhile, the FHSCS specimens are made manually and comprehensive tests with various base excitation energies are undertaken to provide a thorough validation of the current method. It can be found that the largest calculation errors of natural frequencies and resonant responses are 4.9 and 12.3%, respectively. Finally, the influences of the core form and base excitation amplitudes on the nonlinear vibration behaviours of the FHSCSs are examined. It can be noticed that the foam-filled FHSCS structure exhibits a more excellent anti-vibration capability compared to the non-foam-filled structure. The solving method, fabrication technique, and valuable findings in the current study highlight the path for the design and implementation of such advanced shells.

Low-velocity impact resistance of all composite cylindrical shell panels with a foam filled honeycomb core: Theoretical and experimental investigation

The low-velocity impact resistance of all composite cylindrical shell panels (CCSPs) with a foam filled honeycomb core (FFCHC) is studied experimentally and theoretically. Initially, a dynamical model of the FFCHC-CCSPs is proposed, with the equivalent material properties of the core being determined by combining the Hamilton equivalence theory and the Gibson theory. By using the virtual work principle and quasi-static method, together with the von Karman's theory and the high order shear deformation shell theory, the constitutive relationship related to each damage case is derived. Also, by considering the influence of collapse of the FFCHC, the failure criteria and damage modes are modified. The impact displacement, load and impact energy absorption are solved by using the elastoplastic contact principle and energy principle. Several numerical results from the literature are employed for preliminary validation of the model. Furthermore, the FFCHC-CCSP specimens with and without polyurethane foam are fabricated and the detailed measurements associated with different impact energies are performed to provide a solid validation of the present model as well as to evaluate the structural impact resistance. Finally, the influences of the thickness of FFCHC, wall thickness and side length of honeycomb cell and density of foam on the impact resistance of the FFCHC-CCSP structures are discussed, with some useful conclusions being refined for better impact suppression design and manufacture of such advanced shells.

Thermo-Mechanical Behavior of Green Sandwich Structures for Building and Construction Applications

In this work, three different types of sandwich structures were manufactured, each using a Formica sheet (a paper-based sheet) as the skin and perlite/sodium silicate foam as the core, with or without a paper honeycomb. The sandwich structures were fabricated by attaching the Formica sheets on both sides of a paper honeycomb core panel, a perlite/sodium silicate foam core panel, and a perlite/sodium silicate foam-filled honeycomb core panel. The flexural characteristics were studied by a three-point bending test and the thermal conductivity was measured using Lee’s thermal conductivity apparatus. The results demonstrated a significant improvement in flexural properties, including core shear stress, facing stress, bending stress, and energy absorption, when incorporating the paper honeycomb reinforcement. The thermal conductivity and flexural properties of the paper honeycomb reinforced and unreinforced perlite/sodium silicate foam-based sandwich panels were found to be very compatible with existing building materials described in the literature that are used for similar applications. The failure investigation revealed that the sandwiches with paper honeycomb failed prematurely only due to core buckling, while the foam-filled honeycomb core-based sandwiches were able to sustain higher loads while exhibiting material failures such as core shear failure, skin rapture, and delamination. It was found that the foam-filled paper honeycomb sandwich structures can withstand higher bending loads than the foam core-based sandwich structure or the paper-honeycomb-based sandwich structure. These developed sandwiches offer potential as green materials due to the characteristics of their constituent materials and they can provide valuable applications in the thermal insulation of buildings.

An easy-to-implement self-healing smart design for increasing impact strength and crashworthiness resistance of honeycomb sandwich structures

In this paper, the dynamic compression impact response of an aluminum honeycomb core filled with open-cell foams impregnated with self-healing liquid agents was investigated experimentally. Samples were subjected to a variety of impacts in order to determine healing time and self-healing performance. Three different sandwich specimens were developed to evaluate the effectiveness of self-healing. The sandwich specimens are designated as B (empty honeycomb core cells), S (only open-cell soft polyurethane foam-filled honeycomb core cells), and self-healing agent (SHA) (open-cell soft polyurethane foams impregnated with liquid self-healing agents). The test results were presented by considering the crashworthiness and healing efficiency criteria, and the impact characteristics of the samples were compared related to these criteria. After testing, the results demonstrated that the self-healing agent specimens had much fewer buckling deformation and displacement than their counterparts. Significant improvements were achieved in healing efficiencies and crashworthiness evaluation criteria. The peak load and the energy needed to attain peak load are considered healing efficiency criteria. Self-healing agent specimens reached 29.7% and 12.9% more peak loads, and in the energy absorbed up to peak loads 140% and 34.9% higher values than the B and S sandwiches. In the same samples, crushing strain features were acquired as 50% versus 66%, indicating less displacement in self-healing agent specimens than counterparts. The results indicated that an aluminum honeycomb sandwich structure that can heal itself after damage and recover impact characteristics remarkably could be produced practically.

Common Bulkhead Tank Design for Cryogenic Stage of an Indian Launch Vehicle


 
 
 Indian Space Research Organization (ISRO) has been advancing in space technology with its cost-effective techniques. Currently, ISRO, in its cryogenic stages, uses truss type intertank structure, which induces large concentrated loads at the truss interfaces. As a remedial measure, works on closed intertank are being carried out by them, but this configuration will considerably increase the launch vehicle mass compared to truss type. Therefore, after a thorough literature survey, a Common bulkhead (CBH) tank seemed to be the best solution to the aforementioned problem. Detailed research on sandwich-type CBH has been carried out in this paper with the motivation of saving mass and height in launch vehicles. Suitable core and facesheet material were selected. A novel foam-filled honeycomb core is suggested in this work. Several comparisons in various CBH dome designs were carried out to reach for the best possible configuration and composition that can be used. MATLAB®, SolidWorks®, and ANSYS® were used in parallel for all computations dealing with design and analysis. A mass saving of approximately upto 490 kgs and a height reduction of upto 1.755 m was obtained with the final selected configuration with respect to the current GSLV configuration. These savings can add extra payload capacity to ISRO launch vehicles in their future missions.
 
 

Thermo-structural analysis of cryogenic tanks with common bulkhead configuration

In launch vehicles, cryogenic propulsion stages store liquid oxygen (LOX) at 76 K and liquid hydrogen (LH2) at 20 K, generally in two separate insulated tanks connected through tubular truss components. Consequently, load transfer from the LH2 tank to the LOX tank is very much localized, resulting in a nonoptimal design. This article presents an alternative single tankage design using a common bulkhead (CBH) to enhance the payload capability, which enables maintaining LH2 temperature within a specified temperature when exposed to a temperature gradient. A sandwich insulator using aramid honeycomb embedded with polyimide foam keeps the LH2 temperature within 20 ± 1 K is proposed, based on transient heat transfer analysis for 1000 s. The foam-filled honeycomb core is treated as equivalent foam in the analysis as the thermal conductivity of the core and the foam is quite close. The efficacy of the insulator is established by an experiment to measure the back wall temperature when liquid nitrogen is loaded on the top skin of the panel, and the insulator maintains a temperature gradient of 123 K for 1000 s. A good agreement is obtained between the transient finite element analysis results with experimental data. An externally insulated LOX tank configuration with an optimum length of the skirt–cylinder where the temperature reaches 80 K is arrived at based on slosh, buckling, and thermal analyses. No thermal gradient is found across the thickness of the skirt, while the thermal gradient is observed along the length of the skirt as anticipated. An integrated thermo-structural analysis of the cryo-system is carried out considering temperature-dependent material properties. A positive margin for the skirt is obtained. A payload gain of 366 kg is estimated based on the present study for the new design option with a CBH and skirt as compared to the traditional tubular truss arrangements.

Energy Absorption Characteristics of Crash Box of New Honeycomb Core Structure with Foam-Filled

By combining honeycomb core with the traditional crash box, an innovative foam-filled honeycomb core structure crash box is proposed to improve safety performances. Three kinds of honeycomb core crash boxes were obtained by filling the inside of the traditional crash box with the quasi-honeycomb core, the quasi-square honeycomb core and hexagonal honeycomb core. It is deduced that the energy absorption of the quasi-honeycomb core crash box increased by 42.2 %, the peak of the collision force reduced by 8.9 %. The hexagonal honeycomb core crash box and the quasi-square honeycomb core crash box also enhance the energy absorption characteristics, but the peak impact force increased by 5.6 % and 9.6 %. After filling of the Expanded Polypropylene (EPP) foam, the peak collision force of the EPP hexagonal honeycomb core crash box and the EPP quasi-square honeycomb core crash box increased by 10 %, while Fmax of the EPP quasi-honeycomb core crash box reduced by 2.3 % and the energy absorption increased by 54.6 %. Six structures were compared to highlight the energy absorption characteristics of the filling the inside of the traditional crash box with the light in weight honeycomb core and EPP foam. The research results provide a new idea for the design of crash box.

Experimental and numerical study of buckling behavior of foam-filled honeycomb core sandwich panels considering viscoelastic effects

Honeycomb sandwich panels are widely used in marine, aerospace, automotive and shipbuilding industries. High strength to weight and excellent energy absorption are features that make these structures unique. Foam filling the honeycomb core enhances the mechanical properties of sandwich panels considerably. In the present study, the buckling behavior of Nomex honeycomb core/glass-epoxy face sheet sandwich panel for both bare and foam-filled honeycomb core is investigated numerically and experimentally, considering the viscoelastic properties of the sandwich panel. Indeed, the viscoelastic properties of the composite face sheet and foam are determined by relaxation test and are implemented in ABAQUS using VUmat code. The finite element method is also performed using ABAQUS to model the buckling behavior of the sandwich panel incorporating both elastic and viscoelastic material behaviour. The effects of composite face sheet lay-up, core thickness, core cell size, and foam filling are also evaluated. The experimental and numerical results show that the foam increases the critical buckling load and energy absorption.

Development of the fire-retardant sandwich structure using an aramid/glass hybrid composite and a phenolic foam-filled honeycomb

Sandwich structures are increasingly used in high-performance engineering application because of their high specific stiffness, strength, environmental resistance and thermal insulation characteristics. However, poor fire resistance is a critical problem for the use of sandwich structures in engineering applications.In this study, a fire-retardant sandwich structure was developed using a phenolic foam filled honeycomb and carbonized phenolic matrix aramid/glass hybrid composite faces. The sandwich structure was designed to satisfy the limit of critical thermal radiation to humans.To improve the post-fire properties and fire resistance of the glass/phenolic composite, a phenolic coating and an aramid/phenolic composite layer were applied on the surface. The carbonization and impregnation of the phenolic matrix of the composite were repeated twice to eliminate the matrix cracking and delamination by fire exposure. Phenolic foam-filled honeycomb core was used to reduce the thermal conductivity and increase the stiffness and strength of the sandwich. Finally, the thermal insulation and post-fire flexural properties of the sandwich structure were estimated.

A computational multi-scale approach for the stochastic mechanical response of foam-filled honeycomb cores

This paper investigates the uncertainty in the mechanical response of foam-filled honeycomb cores by means of a computational multi-scale approach. A finite element procedure is adopted within a purely kinematical multi-scale constitutive modelling framework to determine the response of a periodic arrangement of aluminium honeycomb core filled with PVC foam. By considering uncertainty in the geometric properties of the microstructure, a significant computational cost is added to the solution of a large set of microscopic equilibrium problems. In order to tackle this high cost, we combine two strategies. Firstly, we make use of symmetry conditions present in a representative volume element of material. Secondly, we build a statistical approximation to the output of the computer model, known as a Gaussian process emulator. Following this double approach, we are able to reduce the cost of performing uncertainty analysis of the mechanical response. In particular, we are able to estimate the 5th, 50th, and 95th percentile of the mechanical response without resorting to more computationally expensive methods such as Monte Carlo simulation. We validate our results by applying a statistical adequacy test to the emulator.

Effective elastic properties of foam-filled honeycomb cores of sandwich panels

Abstract Filling with foams of honeycomb structures has been proposed as some enhancement of honeycomb-cored sandwich material systems. The present study considers aluminum honeycomb cores filled with polyvinyl chloride foams with the aim to predict their material elastic properties. The displacement-based homogeneous technique using 3D finite element analysis is applied to evaluate the effective elastic properties of foam-filled honeycomb cores. The special attention is paid to stress predictions at the skin/core interface and the stress distributions within the honeycomb cell walls. The influence of the foam filler on distribution of local stresses within the cell is examined. The FE modelling is performed with the commercial available software ABAQUS. The structural benefits of the foam-filled honeycomb cores are also discussed.

Analysis of structural performance of sandwich plates with foam-filled aluminum hexagonal honeycomb core

Exploitation experience of honeycomb sandwich structures has shown that one of the most frequently encountered in-service problems is debonding at the interface between face sheets (skins) and core. Filling of honeycomb type cores with foam allows to enhance the damage resistance to the debonding propagation, but on the other hand it changes the structural responses of sandwich structure. The aim of the paper is to estimate of a polymeric foam influence on the free vibration and buckling characteristics of sandwich plates with a hexagonal honeycomb core. The analyses of sandwich plates with hollow and foam-filled honeycomb cores are carried out using the commercially available finite element code ABAQUS. The sandwich plates were modelled on the basis of simplified three-layered continuum models. The displacement-based homogeneous technique using finite element method (FEM) is applied to evaluate the effective elastic properties of core for both hollow and filled with foam honeycomb cores. The comparative results of load carrying capacities and magnitudes of natural frequencies of the sandwich plates are presented. The structural benefits of foam-filled sandwich plates are briefly discussed.

The effect of low-velocity impact on the fatigue life of Sandwich composites

Impact properties and fatigue properties of sandwich composites after impact are addressed. Specifically, the low-velocity impact resistance of carbon fiber faced sandwich composites and how the fatigue life is affected is studied. Two and four layer face sheet carbon fiber sandwich composite samples with foam filled honeycomb core were impacted in a low velocity drop tester at 10, 20, and 30 J with varying masses and velocities of the impactor. After impact the area of damage is determined using ultrasonic techniques. The fatigue life is then determined and compared to the fatigue life of non-impacted samples in a four point bend test. At all impact energies the impactor completely penetrated the front face of the sample. At 20 and 30 J the impactor also penetrated the back face. The 30 J caused a larger penetration area where as the 20 J caused more delamination of the back face. Two different densities of foam were used for the two layer samples. The two layer high density sample failure was changed from in shear for the virgin materials to bending for the impacted samples. This shows that penetrating the top face has an affect on the fatigue properties of the two layer samples. The fatigue life of the four layer and two layer low density samples does not appear to be affected by the impact.

An investigation on the effect of a small mass impact on sandwich composite plates

This paper investigates the high strain rate response of polymer matrix sandwich composites utilizing foam-filled honeycomb cores by means of a small mass impact. The reinforcement fiber chosen for use in this paper is a simple weave carbon fiber. This paper also investigates the effects of utilizing different laminate configurations in conjunction with investigation of the effectiveness of such laminate during impact loading. In an effort to ascertain more information about the impact situation, compression after impact tests are performed to determine the extent of the damage by observing the degradation of strength associated with the impact event.

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.