Honeycomb Composite Structures Research Articles

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.

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.

Additively Manufactured Carbon-Reinforced ABS Honeycomb Composite Structures and Property Prediction by Machine Learning.

The expansive utility of polymeric 3D-printing technologies and demand for high- performance lightweight structures has prompted the emergence of various carbon-reinforced polymer composite filaments. However, detailed characterization of the processing-microstructure-property relationships of these materials is still required to realize their full potential. In this study, acrylonitrile butadiene styrene (ABS) and two carbon-reinforced ABS variants, with either carbon nanotubes (CNT) or 5 wt.% chopped carbon fiber (CF), were designed in a bio-inspired honeycomb geometry. These structures were manufactured by fused filament fabrication (FFF) and investigated across a range of layer thicknesses and hexagonal (hex) sizes. Microscopy of material cross-sections was conducted to evaluate the relationship between print parameters and porosity. Analyses determined a trend of reduced porosity with lower print-layer heights and hex sizes compared to larger print-layer heights and hex sizes. Mechanical properties were evaluated through compression testing, with ABS specimens achieving higher compressive yield strength, while CNT-ABS achieved higher ultimate compressive strength due to the reduction in porosity and subsequent strengthening. A trend of decreasing strength with increasing hex size across all materials was supported by the negative correlation between porosity and increasing print-layer height and hex size. We elucidated the potential of honeycomb ABS, CNT-ABS, and ABS-5wt.% CF polymer composites for novel 3D-printed structures. These studies were supported by the development of a predictive classification and regression supervised machine learning model with 0.92 accuracy and a 0.96 coefficient of determination to help inform and guide design for targeted performance.

Three-Dimensional Finite Element Modeling of Ultrasonic Vibration-Assisted Milling of the Nomex Honeycomb Structure

Machining of Nomex honeycomb composite (NHC) structures is of critical importance in manufacturing parts to the specifications required in the aerospace industry. However, the special characteristics of the Nomex honeycomb structure, including its composite nature and complex geometry, require a specific machining approach to avoid cutting defects and ensure optimal surface quality. To overcome this problem, this research suggests the adoption of RUM technology, which involves the application of ultrasonic vibrations following the axis of revolution of the UCK cutting tool. To achieve this objective, a three-dimensional finite element numerical model of Nomex honeycomb structure machining is developed with the Abaqus/Explicit software, 2017 version. Based on this model, this research examines the impact of vibration amplitude on the machinability of this kind of structure, including cutting force components, stress and strain distribution, and surface quality as well as the size of the chips. In conclusion, the results highlight that the use of ultrasonic vibrations results in an important reduction in the components of the cutting force by up to 42%, improves the quality of the surface, and decreases the size of the chips.

Mechanical and piezoresistive performance of additively manufactured carbon fiber/PA12 hybrid honeycombs

This study investigates a novel self-sensing honeycomb composite structure composed of two distinct cellular layers with differing unit cell architectures, specifically hexagonal and re-entrant designs. Short carbon fiber (CF)/polyamide 12 (PA12) composite filaments with 0, 5 or 15 wt.% CF content were utilized to additively manufacture the honeycomb structures via Fused Filament Fabrication (FFF), and their mechanical and piezoresistive self-sensing characteristics were experimentally investigated under quasi-static in-plane and out-of-plane compression at both room temperature and elevated temperatures. The results reveal that the hybrid hexagonal/re-entrant (HR) honeycombs mechanically outperform their non-hybrid double-layer and single-layer counterparts under in-plane loading, reporting an increase in collapse strength and energy absorption by factors of 1.64 and 2.25, respectively. These improvements are attributed to the mechanical interactions occurring at the interface between the auxetic and non-auxetic layers within the hybrid structure, effectively enhancing its structural attributes. Furthermore, the double-layer honeycombs display excellent strain-sensing capabilities within the elastic regime, with gauge factors reaching values as high as 146. Mechanical tests conducted at elevated temperatures reveal that the CF/PA12 honeycombs retain a significant portion of their elastic modulus, strength and energy absorption even at 125 °C, while maintaining high gauge factors of up to 72.4. These honeycombs also exhibit pronounced thermoresistive behavior, evidenced by a decrease in electrical resistance of up to 41.3 % with increasing temperatures from 25 to 125 °C. Considering their exceptional combination of thermo-mechanical, thermoresistive and piezoresistive characteristics, these hybrid double-layered CF/PA12 honeycombs hold promise for potential applications in multifunctional lightweight structures, offering integrated temperature and strain-sensing capabilities.

Reduced graphene oxide/nonwoven fabric filled honeycomb composite structure for broadband microwave absorption

The prevalence of electromagnetic pollution in daily life has led to a rapid escalation in the demand for high-performance electromagnetic absorption and protection materials. Herein, a composite material consisting of reduced graphene oxide (RGO)/nonwoven absorbent was prepared and filled into honeycomb structures. The single-layer nonwoven/honeycomb composite, with a thickness of 5 mm, demonstrates an effective absorption bandwidth (reflection loss ≤ −10 dB) reaching 12.1 GHz (5.9 GHz–18 GHz) and a minimum reflection loss of −37 dB. This is attributed to the synergistic absorption effects of conduction loss, interfacial scattering, dielectric relaxation, and multiple scattering losses. Furthermore, the bilayer composite structure demonstrates the capability to achieve full band absorption of 2 GHz–18 GHz with a thickness of only 10 mm, giving carbon materials a thin and lightweight absorption effect. In addition, the composite materials exhibit excellent mechanical properties. This study presents a new idea for the design and manufacture of broadband, lightweight, and high-performance microwave absorbers, which holds significant potential in the field of electromagnetic pollution prevention and absorption.

Numerical Simulation of Rotary Ultrasonic Machining of the Nomex Honeycomb Composite Structure

Nomex honeycomb composite (NHC) cores have seen significant growth in recent years, particularly in the aeronautics, aerospace, naval and automotive industries. This development presents significant challenges in terms of improving machining quality, requiring the use of specialized cutting tools and favorable cutting techniques. In this context, experimental studies have been carried out to highlight the characteristics of the milling of NHCs by rotary ultrasonic machining (RUM). However, the rapid motion of the cutting tool and the inaccessibility of the tool/part interface prevent the visualization of the chip formation process. For this purpose, a three-dimensional numerical model for milling the NHC structure using RUM technology was developed by Abaqus Explicit software. On the basis of this model, the components of the cutting force, the quality of the machined surface and the chip accumulation in front of the cutting tool were analyzed. The numerical results agree with the experimental tests, demonstrating that the use of RUM technology effectively reduces the cutting force components. An in-depth analysis of the influence of feed component Fy on the quality of the generated surface was carried out, revealing that the surface quality improved with low values of feed component Fy. Furthermore, the impact of ultrasonic vibrations on the accumulation of chips in front of the cutting tool is particularly optimized, in particular for large amplitudes.

Unsupervised deep learning framework for temperature-compensated damage assessment using ultrasonic guided waves on edge device

Fueled by the rapid development of machine learning (ML) and greater access to cloud computing and graphics processing units, various deep learning based models have been proposed for improving performance of ultrasonic guided wave structural health monitoring (GW-SHM) systems, especially to counter complexity and heterogeneity in data due to varying environmental factors (e.g., temperature) and types of damages. Such models typically comprise of millions of trainable parameters, and therefore add to cost of deployment due to requirements of cloud connectivity and processing, thus limiting the scale of deployment of GW-SHM. In this work, we propose an alternative solution that leverages TinyML framework for development of light-weight ML models that could be directly deployed on embedded edge devices. The utility of our solution is illustrated by presenting an unsupervised learning framework for damage detection in honeycomb composite sandwich structure with disbond and delamination type of damages, validated using data generated by finite element simulations and experiments performed at various temperatures in the range 0–90 °C. We demonstrate a fully-integrated solution using a Xilinx Artix-7 FPGA for data acquisition and control, and edge-inference of damage. Despite the limited number of features, the lightweight model shows reasonably high accuracy, thereby enabling detection of small size defects with improved sensitivity on an edge device for online GW-SHM.

DIAGNOSTICS OF THE ADHESIVE JOINT CONDITION IN MULTILAYER HONEYCOMB STRUCTURES MADE OF POLYMER COMPOSITE MATERIALS BY CONTACT LASER-ULTRASONIC EVALUATION

Multilayer polymer composite honeycomb structures were investigated by Contact Laser-Ultrasonic Evaluation (CLUE). The size of adhesive fillets connecting honeycomb core with Carbon Fiber Reinforced Composite (CFRC) skin is determined. The correlation of strength indicators with the presence and size of adhesive fillets was confirmed. The possibility of non-destructive evaluation of local strength of CFRC structure with CLUE is dicussed.

Investigation of rotary ultrasonic vibration assisted machining of Nomex honeycomb composite structures

Investigation of rotary ultrasonic vibration assisted machining of Nomex honeycomb composite structures

Preparation and sound insulation of honeycomb composite structures filled with glass fiber

AbstractHoneycomb composite with excellent mechanical–physical properties had attracted extensive attention. To achieve outstanding sound insulation while maximizing the high‐performance of honeycomb composite, this article reported a honeycomb composite structure filled with glass fiber (HFG) based on a paper‐making process and the corresponding sandwich structure. Pulping parameters, mechanical property, air permeability and sound insulation of HFG were analyzed. The results showed that the hanging index and settling height of glass fiber slurry were inversely proportional to the beating degree, which was beneficial for reducing the coefficient of variation (CV) of HFG with value of 4%–6%. The maximum improvement in tensile strength and bursting strength of HFG were 70% and 53%, respectively. In addition, sound transmission loss (STL) of HFG was proportional to cell size, density, filling amount and thickness of the honeycomb. Compared to HFG, sandwich structure consisting of HFG and glass fiber/hot melt fiber panels effectively improved STL, especially at low‐mid frequencies. It was also found that designing holes on the surface of sandwich structure could further improve STL in certain frequency bands. The structure offered a lightweight and high‐performance response for construction, transportation and infrastructure.Highlights This article designs a new type of honeycomb filled glass fiber via paper‐making process, aiming to improve the comprehensive performance of honeycomb. By the design of embedded structure, the maximum improvement in tensile strength and bursting strength of honeycomb were 70% and 53%, respectively. By designing perforated, embedded and laminated structures, sound insulation has been improved, while reducing material quality.

The analysis of crashworthiness and dissipation mechanism of novel floating composite honeycomb structure against ship-OWT collision

High-energy ship collisions can cause catastrophic damage to offshore wind turbines (OWTs). This paper proposes a novel floating composite honeycomb anti-collision structure to reduce damage caused by ship-OWT high-energy collisions. The typical collision scenarios are conducted to investigate the damage analysis of anti-collision structures and the dynamic response of OWT with and without anti-collision structures via ABAQUS/Explicit. Regarding the configuration of the composite honeycomb anti-collision structure, the elastic-plastic theory of sandwich beams is proposed and an elastic-plastic analysis on the sandwich wall honeycomb core structure is performed to investigate its dissipation mechanism and obtain homogeneous material parameters of the cells. The homogenization parameters are incorporated into the ship-OWT anti-collision analysis to evaluate their applicability. The collision simulation results demonstrate that the proposed anti-collision structure is capable of effectively absorbing 80% of the initial kinetic energy and significantly reducing the dynamic response of the structure. In elastic-plastic analysis, the proposed elastic-plastic theory of sandwich beams effectively addresses the elastic-plastic behavior of honeycomb with sandwich walls, yielding results consistent with the stress-strain curve obtained from finite element analysis (FEA). In the coupled analysis, the obtained parameters of the homogenized honeycomb validate its effectiveness and enhance computational efficiency. Valuable results are given for the engineering design.

The effect of temperature on guided wave signal characteristics in presence of disbond and delamination for health monitoring of a honeycomb composite sandwich structure with built-in PZT network

Guided wave (GW) based structural health monitoring (SHM) techniques being developed by researchers frequently use amplitude and group velocity variations between healthy and damage-affected GW modes to detect and localise damage. Nonetheless, external variables such as temperature and moisture influence these features, which were not considered in previous studies, particularly in the presence of damage in honeycomb composite sandwich structures (HCSSs). Therefore, a coordinated numerical and experimental study was carried out in an effort to examine the characteristics of GW propagation in an HCSS for two damages: a disbond between the face sheet and the core, and delamination between the face sheet layers for a temperature range of 0 ∘C–90 ∘C. Computationally efficient two-dimensional numerical models were developed using COMSOL Multiphysics that takes into account a variety of temperature-related phenomena, such as thermal stresses and changes in the material properties of honeycomb sandwich and piezoelectric wafer transducers (PZTs). The amplitude and group velocity of the fundamental anti-symmetric (A0) mode are found to increase in the presence of a disbond and decrease in the presence of face sheet delamination. However, it is observed that there is a linear decrease in the amplitude of A0 mode for both the healthy and damaged cases with an increase in temperature. Since the A0 mode is widely employed for interrogation due to its defect sensitivity, an amplitude and group velocity adjustment equation with temperature change is proposed. Finally, considering the amplitude difference of normalised A0 mode, the two damages are localised within a network of PZTs by using a probability-based signal difference coefficient method, which is found to be efficient and reliable for SHM of HCSS under variable temperature conditions.

Effect of nanoclay‐cellulose adhesive bonding and hybrid glass and flax fiber face sheets on flax fiber honeycomb panels

AbstractThis study investigated the feasibility of using natural fiber material to create honeycomb cores, as traditional cores made of aluminum, Nomex, and petroleum‐based materials are not environmentally friendly. The natural fiber honeycomb cores were formed using a 3D printed molding process and were bonded to flax and glass fiber facings to improve the durability of the structures. The addition of cellulose and nanoclay to the adhesive enhanced the flexural strength of the structures by 7.43% and 10.48%, respectively, while also absorbing 8.67% and 8.91% more impact energy than structures bonded with epoxy alone. However, the compressive strength decreased by 10.79% and 13.6% with the addition of cellulose and nanoclay to the adhesive, respectively. Tensile properties were also studied, and the tensile strength of hybrid facings was found to be 69.45% higher than those using solely flax facings. Additionally, hybrid facings effectively reduced moisture uptake, making them hydrophobic and reducing water uptake by 46.89% compared to solely flax facings. Overall, natural fiber honeycomb composite structures showed comparable performance to Nomex and aluminum honeycomb composites, offering favorable properties while being constructed using environmentally friendly materials. The efficient manufacturing process using additive manufacturing makes these structures readily customizable and scalable, leading to their implementation in numerous applications such as aerospace, automotive, and marine industries.

Design and fabrication of an all-composite ultra-broadband absorbing structure with superior load-bearing capacity

With the rapid development of electronic information technology, there has been an increasing demand for lightweight multifunctional microwave absorption structures in aerospace and marine applications. In this work, a novel curved-walls composite honeycomb structure (CWCHS) composed of quartz fiber reinforced composite (QFRC), chopped carbon fiber/glass fiber composite felt (CCF/GFC) and carbon fiber reinforced composite (CFRC) was designed. Multi-scale optimization was carried out to achieve both ultra-broadband absorption and superior mechanical performance. Analytical model of absorption characteristic and mechanical properties were also constructed. The −10 dB absorption bandwidth (90% absorptivity) of the proposed CWCHS achieves 38 GHz (2-40 GHz, containing S, C, X, Ku, K and Ka bands) with an average reflectivity of −16.5 dB (98% absorptivity). Moreover, the absorption performance of the CWCHS shows excellent angle stability within 40° incidence angle. The CWCHS exhibits a remarkable load-bearing capacity, with strength of 31.3 MPa at a density of 0.21 g/cm3. Overall, the proposed CWCHS provides a promising approach for the development of lightweight multifunctional absorption structure and has potential applications in the new generation of inlet grilles and integrated skins.

Study of Equivalent Mechanical Properties and Energy Absorption of Composite Honeycomb Structures

In this study, an analytical model based on classical laminate theory (CLT) is proposed to predict the equivalent mechanical characteristics of three-dimensional (3D) printed fiber-reinforced polylactic acid (PLA) honeycomb structures. Higher rigidity and strength in comparison with the structures made of pure isotropic materials are presented by employing fiber-reinforced PLA. Tensile tests and finite elements studies are conducted to verify the developed analytical relationships. A good agreement is found between the experimental, numerical, and analytical results. Consequently, the mechanical characteristics of the aforementioned structures can be properly predicted using the presented analytical relationships. Moreover, the study examines the impact of using commingled yarn instead of single yarn as a fiberglass strut and finds higher ultimate tensile strength. Compression tests are also conducted to examine the energy absorption capacity of polyurethane foam-filled and hollow honeycomb structures. Finally, a parametric study is conducted to evaluate the effects of geometry on the elastic modulus and Poisson’s ratio of the honeycomb structures.

Study on the penetration resistance of a honeycomb composite structure coated with polyurethane elastomer

In this study, the ballistic performance of the composite structure was investigated and studied by experiment and finite element analysis in order to study the anti-penetration performance of a polyurethane elastomer-coated honeycomb sandwich construction. Six kinds of target plate structures with different configurations were prepared by changing the hard segment content and coating position of polyurethane elastomer. The first-stage light gas gun device is used to conduct impact experiments at various speeds, and the finite element simulation computation is performed using LS-DYNA. Based on the experimental and finite element results, the ballistic limit velocity and specific energy absorption of different target configurations were analyzed, and the failure forms, damage areas, and failure mechanisms were discussed. The findings demonstrate that the polyurethane elastomer coating enhances the honeycomb sandwich structure’s ballistic limit performance by 40.6% to 51% and that the honeycomb core of the target plate with the coating on the front panel has a larger area of collapse. This fully exploits the benefits of the honeycomb structure in the energy absorption process and makes up for the weaknesses of the honeycomb sandwich structure’s subpar energy absorption effect under local impact loads. Therefore, the front panel coating has better ballistic limit performance. The coated polyurethane with medium hardness demonstrated the best ballistic limit performance for the various polyurethane hardness. The ballistic limit speeds of the front panel and back panel coatings increased by 51% and 48.8% respectively, in comparison to the uncoated target plate. After comparing the structure of polyurea coating, it is found that the ballistic limit performance of polyurethane coating with medium hardness is higher than that of polyurea coating structure, and the negative growth of the ballistic limit performance of the whole structure caused by the coating of rigid polyurea on the back panel is effectively avoided.

Multidisciplinary Design and Optimization of Variable Camber Wing with Non-Equal Chord

Since the taper ratio of most wings is not equal to 1, the beam-disk trailing edge deflection mechanism originally designed for the rectangular wing is not fully applicable to the non-equal chord wing. Moreover, it is not only expected that the wing shape can achieve excellent aerodynamic performance under different flight conditions, but one also needs to consider whether the flexible skin can achieve this deformation. This paper used the honeycomb composite structure with zero Poisson’s ratio as the flexible skin of the trailing edge for the variable camber wing, and designed the beam-disk trailing edge deflection mechanism for the non-equal chord wing. The aerodynamic configuration was optimized considering the deformation capability of the skin, and the multidisciplinary design and optimization method of the variable camber wing with non-equal chord was studied. The results show that the aerodynamic performances of the optimized non-equal chord wings were better than before under all given flight conditions. The flexible skin could withstand the strain caused by the maximum deflection of the trailing edge of the wing, and the weight of the wing structure was reduced by 47.1% compared with the initial design when the structural stiffness and strength were satisfied.

Fabrication and mechanical behavior of an all‐composite interlocked triangular honeycomb sandwich structure: Experimental investigation and numerical analysis

AbstractThe interlocked composite honeycomb structures have high specific strength and specific stiffness, convenient processing, and low cost with great application potential in aerospace, marine, construction, and civil fields. In this study, an effective method is proposed for manufacturing an all‐composite interlocked triangular honeycomb (CITH), and the quasi‐static mechanical properties of the honeycomb and the corresponding sandwich structure (CITHSS) are examined. Through experimental tests, the basic mechanical properties of CITH and CITHSS are analyzed. Further, the effective strength and stiffness coefficient of the slotted carbon sheets constituting CITH are measured through tensile experiments. The in‐plane stiffness model of CITH is derived based on the continuous equivalent method. The failure strength models of CITHSS are also established. At the same time, the failure modes under three‐point bending and edge compression loads are predicted. The experimental results reveal that compared with the interlocked Kagome and square honeycomb, the specific strength of CITH is increased by 27.8% and 24.4%, respectively. Further, the specific stiffness is increased by 148.4% and 8.3%, respectively. Compared with aluminum honeycomb sandwich, the compressive and bending specific strengths of CITHSS are increased by more than 46.5% and 15.2%, respectively. The debonding failure and edge effect are found to be the main weakness of CITHSS. Overall, CTIH and CITHSS exhibit excellent mechanical properties and create feasible options for processing complex multifunctional composite honeycombs by interlocking technology.

Carbon Fiber Composite Honeycomb Structures and the Application for Satellite Antenna Reflector with High Precision

Carbon Fiber Composite Honeycomb Structures and the Application for Satellite Antenna Reflector with High Precision