Composite Honeycomb Sandwich Research Articles

Damage Resistance of Honeycomb Sandwich Composites under Low-Energy Impact

Damage Resistance of Honeycomb Sandwich Composites under Low-Energy Impact

Coupled thermal-electrical–mechanical characteristics of lightning damage in woven composite honeycomb sandwich structures

In this study, lightning strike damage of woven carbon fibre-reinforced polymer laminates (W-CFRPs) and woven composite honeycomb sandwich panels (W-CHSPs) are simulated using the proposed sequential thermal-electrical–mechanical finite element (FE) coupling model incorporating dielectric breakdown of materials. Surface current with an amplitude of 200 kA and corresponding lightning shockwave overpressure were applied on each composite. The FE model coupled with LaRC05 criterion was used to study the failure behaviours of intralaminar damage and interlaminar delamination of the W-CFRPs and W-CHSPs. A series of lightning strike tests were performed to validate the FE model. Detailed lightning damage assessments and mechanisms were characterized by a combination of visual inspection, image processing, ultrasonic scanning and micro computed tomography (Micro-CT) and showed good agreements with the FE-predicted results. It can be concluded that shockwave overpressure significantly impacts lightning-induced damages, thereby supporting the effectiveness of the newly proposed sequential thermal-electrical–mechanical coupling model, which demonstrates improved predictive accuracy.

Damage behavior of composite honeycomb sandwich structure subject to low-velocity impact and compression-after-impact using experimental and numerical methods

Damage behavior of composite honeycomb sandwich structure subject to low-velocity impact and compression-after-impact using experimental and numerical methods

Bending and compressive properties of ultralight carbon fiber honeycomb sandwich beams via stretching process

Due to excellent thermal stability and high specific strength, there are high requirements for all-carbon fiber composite honeycomb sandwich structure (ACFH) in the field of space observation, especially as the support of space telescope and satellite antenna. However, there are few studies on the mechanical properties of ultra-low density ACFH (ρ < 50 kg/m3). Based on the stretching process, the ultra-low density curved-wall ACFH is prepared, and its three-point bending performance and in-plane compression performance are deeply studied by means of theoretical and experimental methods. The interaction and competition mechanism of various failure modes were primarily revealed based on the failure mechanism map. In addition, the mechanical properties of specimens prepared through stretching process were tested and analyzed. The research results shows that the theoretical prediction and experimental testing agree very well in terms of failure modes and ultimate loads. Finally, some suggestions for improving the mechanical properties of ultra-low density ACFH are given, which lays the solid foundation for its application in advanced engineering fields.

Dynamic response of composite honeycomb sandwich panels subjected to strong dynamic loading

In this paper, composite honeycomb cores were firstly fabricated using a novel hot-press molding method. Under the simulated strong dynamic loading via from foam projectile impact, the dynamic response of composite honeycomb sandwich panels, including deflection, velocity and strain, was obtained by using high-speed camera and three-dimensional digital image correlation (3D-DIC) technology. Then, the damage/failure modes of composite honeycomb sandwich panels were analyzed using scanning electron microscopy (SEM) and ultrasonic C-scan. The results showed that under low impulse impact, panels deformed elastically and mainly suffered delamination damage. The dynamic response was divided into four stages: acceleration, inertia, rebound, and vibration. Under high impulse impact, panels were penetrated. Fiber breakage and matrix cracking were the main failure modes. The dynamic response was divided into four stages: acceleration, inertia, crack generation and cracking. Finally, a progressive damage model based on the strain-based damage criterion of composite fabric and Yeh delamination damage criterion was applied in ABAQUS/Explicit. On this basis, the relation between the honeycomb structure parameters and impact resistance was discussed in detail. Increasing the core height and relative density resulted in reducing the maximum deflection of the back face sheet and attenuating the shock wave. Experimental results and numerical models are of great significance for guiding the design of honeycomb sandwich panels and improving the impact resistance.

Investigation of the Mechanical Properties of Composite Honeycomb Sandwich Panels after Fatigue in Hygrothermal Environments.

Since carbon fibre composite sandwich structures have high specific strength and specific modulus, which can meet the requirements for the development of aircraft technology, more and more extensive attention has been paid to their residual mechanical properties after subjecting them to fatigue loading in hygrothermal environments. In this paper, the compression and shear characteristics of carbon fibre-reinforced epoxy composite honeycomb sandwich wall panels after fatigue in hygrothermal environments are investigated through experiments. The experimental results show that under compressive loading, the load required for the buckling of composite honeycomb sandwich wall panels after fatigue loading in hygrothermal environments decreases by 25.9% and the damage load decreases by 10.5% compared to those at room temperature. Under shear loading, the load required for buckling to occur is reduced by 26.2% and the breaking load by 12.2% compared to those at room temperature.

Analysis of composite honeycomb sandwich panels under blast loads

ABSTRACT This paper presents a novel isogeometric model to analyze the static bending, fre, and forced vibration characteristics of a sandwich of two-layer plates made of auxetic honeycomb core and laminated three-phase polymer/GNP/fiber skin subjected to a double blast load. The two layers are restricted from vertical movement by elastic pins but they can still move in the horizontal plane. The unique feature of the refined first-order shear plate theory with a distribution function g(z) is used to replace the shear correction factor, thereby allowing the shear stress at the top and bottom surfaces to be accurately calculated. The results are derived by the exact Navier solutions for rectangular plates and the IGA method with arbitrary boundary conditions for elliptical and rectangular plate structures. A comprehensive investigation was conducted to evaluate the influence of some parameters on the oscillation of sandwich two-layer plates subjected to double blast load.

Damage mechanism and bending properties degradation of aviation composite honeycomb sandwich structures under laser irradiation

Damage mechanism and bending properties degradation of aviation composite honeycomb sandwich structures are studied under different laser conditions in this paper. Firstly, the damage test of composite honeycomb sandwich structures is conducted. Temperature field and ablation process during laser irradiation are analyzed. Damage morphology and mechanism are verified. Secondly, the influence of laser damage on the bending properties of composite honeycomb panels is studied. Progressive damage process and failure mechanism of honeycomb structures during loading are explored by digital image correlation (DIC) and strain trend. The results show that the temperature at the center point of front surface reaches more than 2000 °C within 1 s under the laser irradiation, while the temperature of back surface exhibits hysteresis. The ablation hole is funnel-shaped and has severe delamination. In the heat affected zone (HAZ), resin matrix has been basically sublimated and oxidized, leaving only carbon fiber bundles and some residual carbon. The honeycomb core in this area has been completely carbonized and deformed. During bending process, the honeycomb core breaks firstly, and strain appears peak at both crack ends, leading the crack extend along both sides. The ultimate load of damaged specimen is 2.35kN, which has a 42.26 % drop compared to that of healthy specimen 4.07kN. Bending properties of specimen are significantly degraded by laser damage.

Energy Absorption and Damage Analysis of Fragments in High-Speed Impact on Composite Honeycomb Sandwich Structures

With the continuous innovation of UAV technology, composite honeycomb sandwich structures are used more and more in the fuselage structure of UAVs, and their anti-high-speed fragment impact performance has become a concern. In order to study the influence of fragments on the damage degree of composite honeycomb structures and analyze the damage difference of different initial velocity fragments on different composite honeycomb structures, based on the numerical simulation results of high-speed impact, the energy absorption characteristics of different honeycomb sandwich structures are analyzed, and the honeycomb structure with better energy absorption is selected for 24 impact experiments. The velocity range of fragment impact is 141–368 m/s. The typical damage of the upper core layer and the lower core layer in each structure is analyzed, and the energy absorption theory is used to compare the conditions of each group. The results show that ST-3-3 has the best energy absorption characteristics. Under different velocity impacts, the energy absorption per unit volume of the ST-3-3 structure reaches 521.6~659.6 × 103 J/m3, which is about 30.6% higher than that of the same design structure. The four groups of composite honeycomb sandwich structures designed in the experiment have obvious deformation in the process of impact, except that the deformation of the bottom skin of the ST-6-6-1 structure is not obvious, and the deformation of the other three groups is more obvious with the increase in structural resistance. This research shows that the reasonable arrangement of the structure and material of the composite honeycomb sandwich can better cope with the impact of high-speed fragments and reduce the damage to the structure.

Experimental study on compression properties of composite aluminum honeycomb sandwich structures

AbstractThe mechanical properties of the carbon fiber and glass fiber composite honeycomb sandwich structure were studied through compression experiments. The influence of different aluminum honeycomb edge lengths, upper and lower panel thickness, aluminum honeycomb thickness, and loading speed on the compression failure load of carbon fiber composite laminates sandwich structure is analyzed. The influence of different aluminum honeycomb edge lengths and thicknesses on the compression failure load of glass fiber composite laminates sandwich structure was studied. The results show that the thickness of the panel has a significant effect on the failure load of the carbon fiber composite laminate sandwich structure, and the loading speed has a significant effect on the failure load of the carbon fiber composite laminate sandwich structure. The greater the loading speed, the greater the value of the failure load. The edge length and thickness of the aluminum honeycomb have a certain effect on the damage load of the carbon fiber composite laminates sandwich structure, but the influence on the mechanical properties of the glass fiber composite laminates sandwich structure is much greater.Highlights The compression performance of composite sandwich structures was experimentally studied. The influence of composite panel thickness was studied. The influence of aluminum honeycomb edge length and thickness was studied. The influence of loading speed was studied.

Low energy impact damage characteristics of epoxy coating on the surface of sandwich composites

AbstractWhen composite honeycomb sandwich structures are subjected to low energy impacts, the upper panel or the honeycomb core often suffers large damages, which are invisible, but affects the structural safety. To achieve non‐destructive detection of these damages, an epoxy resin film (ERF) was designed as a functional coating to display the internal failure features on structure surface. The effect of low energy impacts on the damage modes of the ERF was first investigated, and then the correspondence between the ERF damage characteristics and the structural internal failure was established. Simulation and experimental results showed that with the increase of impact energy, cracks on the ERF expanded from the radial radiation with a small extension range to the circumferential pattern with an increased damage area. Meanwhile, localized delamination appeared inside the upper panel, while the degree of flexure and crushing damage to the core continued to increase. Based on the analysis of the crack extension pattern of the ERF and the damage state of the upper panel and honeycomb core, a specific link between the ERF crack characteristics and the internal damages to the sandwich structure was obtained, which might offer a novel non‐destructive testing method for composite impact damages.Highlights Low energy impact damage in honeycomb sandwich structures was a concern. Impact damage response of epoxy resin film on sandwich composites was studied. Crack extension of the film showed a particular change from radial to annular. Specific link between film crack and sandwich structure damage was established. The results would be helpful for damage detection in sandwich composites.

Effects of impact angles and shapes on CAI strength of composite honeycomb structure

The Compression After Impact (CAI) strength can enhance safety and reliability in engineering applications, improve simulation and prediction capabilities. It is also an important indicator for assessing the damage tolerance capacity of composite structures. The CAI strength is directly influenced by low-velocity impact, which holds significant scientific research implications for evaluating structural safety, optimising design and enhancing material properties. Analysing different impact shapes and angles provide a closer representation of real-world engineering scenarios, rendering results more reliable and valuable. The subject is a CFRP panel with Nomex honeycomb sandwich structure, where both the skin and core are composed of composite materials. Low-velocity impact and compression after impact tests were conducted to establish an integrated and refined finite element model for the CFRP panel with Nomex honeycomb structure. The model’s validity was confirmed by comparing with test results. Various impact shapes and angles were investigated using the established model to examine their influence on the CAI strength of the composite honeycomb sandwich structure. The following conclusions were drawn: (1) Sharper impactors result in lower CAI strength and higher compressive failure displacement. (2) The CAI strength, normalised CAI strength, and failure displacement of the structure increase with the impact angles. Among the tested angles, the 30° impact angle induced the least damage, exhibiting the highest CAI strength, normalised CAI strength, and failure displacement. However, as the angle increases, energy losses between the impactor and specimen increase, impact energy decrease. Consequently, the structural indicators decrease compared to the 30° impact angle.

Non-destructive evaluation of a composite honeycomb sandwich panel with in-plane waviness damage using ultrasonic guided waves

ABSTRACT Composite honeycomb sandwich structures (CHSS) are often manufactured using an autoclave co-cure process, which can introduce in-plane waviness (IW) damage due to fibre misalignment. Such fibre waviness, whether in-plane or out-of-plane, significantly weakens the strength of these structures. Therefore, developing reliable non-destructive evaluation (NDE) techniques is essential for detecting IW. This study presents an NDE technique utilising ultrasonic guided waves (GW) to identify IW damage in CHSS panels. A numerical model was created using COMSOL Multiphysics, where IW damage is simulated through curvilinear coordinate physics, followed by a time-dependent study of GW propagation. This model simulates local fibre orientation changes due to IW damage, enhancing our understanding of GW interaction with IW. Experimental investigations are performed using contact-type transducers to corroborate the numerical observations. The presence of in-plane waviness causes a reduction in the group velocity of the A0 mode, a characteristic that can be exploited for detecting in-plane fibre waviness in CHSS. Also, parametric studies were performed to examine the effects of IW severity (aspect ratio) and increased IW area on GW characteristics. Finally, a technique for IW damage localisation is demonstrated using a convex hull algorithm based on changes in correlation coefficient values of the A0 mode.

Compressive failure analysis of composite honeycomb sandwich panels with impact damage and stepped-scarf repairs

Composite honeycomb sandwich panels (CHSPs) have been widely used in the aerospace industry owing to their lightweight and superior mechanical properties. However, these CHSPs are susceptible to impact damage, leading to a significant reduction in compressive strength and potentially jeopardize aircraft safety. It is crucial to investigate repair methods for CHSPs with impact damage. This paper aims to evaluate the repair performance of CHSPs with impact damage through an analysis of their compressive failure behaviors. To accomplish this, both experimental tests and advanced numerical models are employed. The numerical models for the intact, damaged and stepped-scarf repaired CHSPs are established using the progressive failure analysis model, cohesive zone model and sandwich plate theory. A good agreement is observed between the experimental results and numerical predictions of compressive failure behaviors. Moreover, the validated numerical models are successfully utilized for determining optimum repair parameters by parametric analysis of the repaired CHSPs. The establishment of these numerical models offers an accurate and cost-effective evaluation of repair performance for CHSPs with impact damage, highlighting the novelty and main contribution of this paper.

Mechanical characteristics of auxetic composite honeycomb sandwich structure under bending

Auxetic honeycomb sandwich structures (AHS) composed of a single material generally exhibit comparatively lower energy absorption (EA) and platform stress, as compared to traditional non-auxetic sandwich structures (TNS). To address this limitation, the present study examines the use of aluminum foam (AF) as a filling material in the re-entrant honeycomb sandwich structure (RS). Filling the AHS with AF greatly enhances both the EA and platform stress in comparison to filling the TNS with AF, while the auxetic composite honeycomb sandwich structure effectively addresses interface delamination observed in traditional non-auxetic composite sandwich structures. Subsequently, the positive–negative Poisson’s ratio coupling designs are proposed to strengthen the mechanical features of a single honeycomb sandwich structure. The analysis results show that the coupling structure optimizes the mechanical properties by leveraging the high bearing capacity of the hexagonal honeycomb and the great interaction between the re-entrant honeycomb and the filling material. In contrast with traditional non-auxetic sandwich structures, the proposed auxetic composite honeycomb sandwich structures demonstrate superior EA and platform stress performance, suggesting their immense potential for utilization in protective engineering.

Mechanical property analysis and experimental validation of composite honeycomb sandwich radome considering perforation and impact damage

To carry out the experimental verification of the mechanical properties analysis of the radome considering the damage factors, the test matrix design is carried out according to the finite element analysis method of the equivalent elastic theory and the idea of building block test verification. Firstly, the necessity and basic principle of equivalent elasticity theory in the performance analysis of complex curvature products considering damage factors are explained. Then, combined with the theory, a modular test matrix design is carried out, which should be able to test the correctness of the equivalent elastic modulus. Finally, a case study is carried out, and the difference between the test results and the simulation results is analyzed with the damaged radome as the research object. The results show that the development of the equivalent elasticity theory and the design of the test matrix can make the analysis results meet the engineering requirements.

Study on the Energy Absorption Characteristics of Different Composite Honeycomb Sandwich Structures under Impact Energy

A honeycomb structure is a sandwich structure widely used in fuselage, among which the hexagonal honeycomb core is the most widely used. The energy absorption characteristics and impedance ability of the structure are the main reasons that directly affect the energy absorption characteristics of the honeycomb sandwich structure. Therefore, it is necessary to study the out-of-plane mechanical properties of the composite honeycomb sandwich structure. Based on the numerical simulation results, the energy absorption characteristics of several composite honeycomb sandwich structures are verified by drop hammer impact experiments. The research shows that the transient energy absorption characteristics of the composite honeycomb sandwich structure are mainly related to the cell size of the honeycomb structure. The smaller the size of the front cell, the stronger the overall impact resistance; the strength of the composite honeycomb sandwich structure exceeds that of 7075 aluminum alloy-NOMEX and carbon fiber-NOMEX honeycomb sandwich structures. In this paper, the energy absorption characteristics of composite honeycomb sandwich structures under different impact energy are compared and studied. The displacement, force and energy curves of energy absorption characteristics related to time variables are analyzed. The difference in protective performance between the composite honeycomb sandwich structure and existing airframe structure is compared and studied. The optimal structural design parameters of composite honeycomb sandwich under low-speed impact of drop hammer are obtained. The maximum energy absorption per unit volume of the designed honeycomb sandwich structure is 171.7% and 229.8% higher than that of the NOMEX-AL and NOMEX-C structures. The 6.4 mm and 3 mm cell sizes show good characteristics in high-speed buffering and crashworthiness. The composite honeycomb sandwich airframe structure can improve the anti-damage performance of the UAV airframe structure, ensure the same thickness and lightweight conditions as the existing honeycomb sandwich airframe structure, and improve the single-core bearing mode of the existing airframe structure.

Load-bearing capacity of composite honeycomb sandwich high-speed train floor

ABSTRACT The honeycomb sandwich structure of composite materials has broad prospects for application in the lightweight design of vehicle bodies. This study investigated the influence of relative density and height on an aluminium honeycomb’s out-of-plane quasi-static compression performance through experiments and simulations. The accuracy of the carbon fibre/aluminium honeycomb sandwich panel’s three-point bending model is verified based on the Hashin failure criterion and experimental validation. Furthermore, the load-bearing capacity of the carbon fibre/aluminium honeycomb sandwich floor is analysed, and the factors influencing the load-bearing capacity of the floor are further explored. The results show that the relative density significantly impacts the out-of-plane quasi-static compression performance of aluminium honeycomb, while the height has a minor influence. Compared with the original CRH5-type floor structure, the carbon fibre/aluminium honeycomb sandwich floor has a weight reduction of 45.23%, and it meets the strength requirements under uniformly distributed and concentrated load conditions. Changing the honeycomb wall thickness and panel thickness distribution can improve the load-bearing capacity of the floor.

Efficient design of composite honeycomb sandwich panels under blast loading

Hybrid composite honeycomb sandwich structures (HCHSS) were employed due to high specific strength and stiffness and higher impact resistance property required for the aerospace and defence fields. The numerical modelling of the efficient HCHSS was developed for the core, front and back face plate using the C3D8R elements to determine the realistic failure behaviour for the honeycomb sandwich structure. The ConWep blast simulation loading was applied for the HCHSS. Advanced composite materials were used for the blast analysis of the HCHSS (carbon/epoxy, graphite/epoxy, woven basalt fibres/polypropylene and woven Kevlar fibres/polypropylene). The damage initiation and damage propagation based progressive damage modelling was developed and implemented in the VUMAT code for composite materials to determine the actual failure behaviour of the HCHSS. The face sheets used in this model were of a stainless-steel alloy AL-6XN. The sandwich structure was subjected to blast loads of 1, 2 and 3 kg of TNT and their performance was compared w.r.t both front and back-face deflection. The effectiveness of sandwich panels was further examined by altering the thickness of the core. Fibre-metal laminates (FML) were used in place of the steel face sheets in the panel in order to minimise its mass, and a thorough analysis of the panel’s mass in relation to its peak deflection was carried out. Upon analysing the results, it was noted that the panel with the basalt fibre reinforced polymer (BFRP) core gave the best results compared to other composite materials. For a blast load of 3 kg TNT, the peak back face deflection (PBFD) of HCHSS with a BFRP core decreased by 10.64%, 7.61% and 4.75%, respectively, compared to panels with CFRP, GFRP, and KFRP cores. The peak deflection of the panel decreased as the BFRP core thickness increased. The energy absorption capacity of the panel also increased with increasing thickness. Additionally, it was found that panels with BFRP cores and KFRP-steel laminate face sheets provided the optimum balance of strong blast resistant performance and light weight. Compared to the metallic (steel) sandwich panel, the mass of the sandwich panel with KFRP-steel laminate face sheets and BFRP core was reduced by 33%, but at the same time, its PBFD increased by almost 50%.

Foam-filled aramid honeycomb sandwich composites with high acoustic insulation properties prepared using a unique thermal expansion molding process

Contemporary advancements in technology and the rapid development of transportation systems have led to the rise of noise pollution as a major environmental issue globally. Foam sandwich composites, distinguished by their lightweight yet robust attributes such as high-strength functionality, effectively combine the superior noise insulation properties of foam structures with the strength inherent in their surface skins. However, traditional foam core materials exhibit limitations in terms of mechanical durability and suboptimal interfacial bonding with the surface skin. This study addressed these shortcomings by employing a novel approach involving a self-developed thermally expandable epoxy resin and an aramid honeycomb composite. These components were co-cured with a fiber prepreg, culminating in the formation of enhanced sandwich composites. The composites fabricated through this method demonstrate an impressive average sound insulation capacity of 70 dB, alongside a significant enhancement in the mechanical properties of the core material, surpassing the performance of standalone foam structures.