Composite Honeycomb Sandwich Panels Research Articles

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.

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.

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%.

Shear performance assessment of repaired honeycomb sandwich composite panels: An experimental and numerical study

AbstractThis article presents an effective test method for evaluating the shear performance of repaired honeycomb sandwich panels consisting of glass fiber/epoxy matrix skin and Nomex honeycomb core. Addressing the insufficient research on the shear performance of honeycomb sandwich panels after repair in existing literature, this study conducted mechanical performance tests on the honeycomb sandwich panels before and after repair using the picture frame test method. Surface strain measurements are obtained using digital image correlation (DIC) techniques, and load–displacement and shear stress–strain curves are generated from the experimental results. The study concludes that the repair method utilized in this investigation is effective in restoring the mechanical properties of the sandwich panels. In addition, finite element models of the honeycomb sandwich panels before and after repair are established, and a comparative analysis is conducted between the experimental and simulation results. The study examines the shear modulus, ultimate load, and failure mode of the repaired and unrepaired specimens. The findings verify the feasibility of the picture frame test method for evaluating the shear performance of honeycomb sandwich panels. This study provides valuable insights into the design of shear performance repair for honeycomb sandwich panels and offers theoretical support for material recycling.

Experimental Investigation on the Fatigue Behavior on Honeycomb Sandwich Composite Panels

This paper aims to study the dynamic behaviors of particular sandwich panels manufactured using three specifications of aluminum honeycomb core with fiberglass or aluminum face-sheet materials. Three groups of panels were designed and manufactured, each including three different sorts of samples, all fabricated with the same thickness. A cantilever fatigue test was conducted on specimens, and the results were collected and presented in curves to detect the factors that affect the panel's endurance. The finding showed that the specimens with aluminum skin had more probability of face-sheet/core delamination. Samples of fiberglass covers showed face-sheets cracks or cores cracks more than delamination failure, while samples of epoxy-filled cores experienced the specimen’s global crack. Generally, specimens with aluminum covers and epoxy-filled cores resisted fatigue load more than other specimens. The larger honeycomb cell-size specimens showed more probability to face-sheet/core delamination failures than samples with smaller cell-size cores.

Influence of Woven Glass-Fibre Prepreg Orientation on the Flexural Properties of a Sustainable Composite Honeycomb Sandwich Panel for Structural Applications.

Owing to the high potential application need in the aerospace and structural industry for honeycomb sandwich composite, the study on the flexural behaviour of sandwich composite structure has attracted attention in recent decades. The excellent bending behaviour of sandwich composite structures is based on their facesheet (FS) and core materials. This research studied the effect of woven glass-fibre prepreg orientation on the honeycomb sandwich panel. A three-point bending flexural test was done as per ASTM C393 standard by applying a 5 kN load on different orientation angles of woven glass-fibre prepreg honeycomb sandwich panel: α = 0°, 45° and 90°. The results show that most of the sandwich panel has almost the same failure mode during the three-point bending test. Additionally, the α = 0° orientation angle shows a higher maximum load prior to the first failure occurrence compared to others due to higher flexibility but lower stiffness. In addition, the woven glass-fibre prepreg orientation angle, α = 0°, has the maximum stress and flexural modulus, which directly depend upon the maximum load value obtained during the flexural test. In addition, the experimental results and analytical prediction for honeycomb sandwich deflection show good agreement. According to the result obtained, it is revealed that woven glass-fibre honeycomb sandwich panels with an α = 0° orientation is a good alternative compared to 45° and 90°, especially when better bending application is the main purpose. The final result of this research can be applied to enhance the properties of glass-fibre-reinforced polymer composite (GFRPC) cross-arm and enhance the existing cross-arm used in high transmission towers.

Effect of an S-shaped reinforced core on the compression properties of composite honeycomb sandwich panel and tube structures

In this study, compression properties of composite honeycomb sandwich panel and tube structures with S-shaped reinforced core was studied. The S-shaped reinforcements was machined from conventional honeycomb core. Quasi-static compression tests showed that the peak force and energy absorption of the proposed sandwich panels were enhanced by up to 85.28% and 31.41% respectively, in comparison to the carbon fiber/aluminum honeycomb sandwich panels. Based on the experimentally validated finite element model, the effects of number of S-shaped reinforcement structures, wall thickness and rotation direction were investigated for mechanical performance of the carbon fiber/aluminum honeycomb sandwich tubes under compression. Numerical results demonstrated that the S-shaped reinforcement structure could change the load transfer path effectively. The mechanical behavior and properties of the honeycomb core with S-shaped reinforcement were significantly influenced by changing the number and distribution of S-shaped reinforcements with different rotating directions. The homodromous structure caused shear damage, while the heterodromous structure showed more stability.

Parameterization of core plug replacement properties for flexural performance optimization of repaired composite honeycomb sandwich panel

As lightweight structures, composite sandwich panels are distinguished by their significant flexural performances, which make them suitable for lightweight design applications, especially in the aerospace industry. These structures are very prone to different damages, which affects the structure’s performance. In this study, the numerical three-point bending test is carried out to evaluate the flexural performance of the damaged and repaired panel by comparing it with the intact panel values. The response surface methodology (RSM) is then adopted to analyze the core plug replacement properties’ effect on the flexural performances of the repaired honeycomb sandwich panel. Adequate models between the core plug replacement design parameters and the repaired panel flexural responses are built and discussed. In addition, aiming to determine the optimized core plug replacement parameters of the proposed repaired panel flexural performances, an optimization technique is implemented.

Cementitious Insulated Drywall Panels Reinforced with Kraft-Paper Honeycomb Structures

Standard building practices commonly use gypsum-based drywall panels on the interior wall and ceiling applications as a partition to protect the components of a wall assembly from moisture and fire to uphold the building code and ensure safety standards. Unfortunately, gypsum-based drywall panels have poor resistance to water and are susceptible to mold growth in humid climates. Furthermore, the accumulation of drywall in landfills can result in toxic leachate impacting the surrounding environment. A proposed solution to the pitfalls of gypsum-based drywall arises in its substitution with a new lightweight composite honeycomb sandwich panel. This study aimed to develop sandwich panels with improvements in flexural strength and thermal insulating properties through the combined use of cementitious binder mix and kraft-paper honeycomb structures. The proposed alternative is created by following standard practices outlined in ASTM C305 to create cement panels and experimenting with admixtures to improve the material performance in order to cater to a drywall panel application. The kraft-paper honeycomb structure is bonded to cured cementitious panels to create a composite “sandwich panel” assembly. The results indicate that the sample flexural strength performed well after 7 days and exhibited superior flexural strength at 28 days, while providing a substantial increase in R-value of 5.84 m2K/W when compared to gypsum-based panels, with an R-value of 5.41 m2K/W. In addition, the reinforced kraft-paper honeycomb with a thick core and addition of flax fibres to the cementitious boards possesses better thermal conductivity, with a reduction of 42%, a lower density, and a lower water vapour transmission in comparison to the thin kraft-paper honeycomb sandwich panel.

A comprehensive analysis of damage behaviors of composite sandwich structures under localized impact

Sandwich structure with honeycomb core and CFRP facesheets is increasingly used in the high-performance fields due to the high specific stiffness and strength. However, it is susceptible to localized low-velocity impacts such as tool drop during maintenance, and thus, understanding the damage behavior is important for a safety design and optimization. The objective of this article is to investigate the influence of the structural parameters and impact energy on the damage behaviors of the composite honeycomb sandwich panels subjected to localized low-velocity impact. An effective computational framework considering complicate damage mechanisms is proposed to predict the failure patterns, load history, and energy absorption. Comparisons with the experimental data show that the error of predictions is within 4% and thus the framework is validated. Then, a comprehensive parametric study is conducted to explore the effects of wall thickness and height of honeycomb, impact energy, and stacking sequences of the laminated facesheets on the impact resistance, damage behaviors, and energy absorption of the sandwich structure. The reported results may be useful in practice.

Fatigue of composite honeycomb sandwich panels under random vibration load

The fatigue test of composite honeycomb sandwich panels has been carried out under random vibration load in this investigation. The test results show that, the failure mode of the honeycomb sandwich structure under random vibration load is the same as that under constant-amplitude load, both of which are core shear failure and the resulting face-core delamination. Based on the test results and the S-N curve of honeycomb sandwich panel under constant-amplitude load, a method has been proposed to predict the fatigue life of composite honeycomb sandwich structures under random vibration load. The core shear stress is taken as the fatigue damage parameter. The validity of the proposed method has been verified by comparing the predicted results with the test results.

Compressive Strength Experiment of Honeycomb Sandwich Composite Panel

The experimental investigation on the compressive properties of honeycomb sandwich composite panels was carried out in this paper. The local compressive specimens and global compressive specimens were manufactured for compressive experiment. The test fixture has been designed and manufactured to examine the compressive behavior of honeycomb sandwich panel. The results indicate that there is no buckling occurred in local compressive specimen skin during the whole compressive experiment. The average failure load of local compressive specimens is 106884 N. The local buckling increases with the loading until the global compressive specimens are unstable. The fracture positions locate along the horizontal line at the middle height of global compressive specimen, which is different from local compressive specimens. The average buckling load and failure load of global compressive specimen are 31850 N and 82282 N respectively.

Fabrication of aluminum honeycomb cored carbon fabric/epoxy composite sandwich structures via vacuum assisted resin infusion technique

AbstractA detailed step‐by‐step fabrication procedural document of thin‐walled aluminum honeycomb sandwich composite structures, panels, and specimens using vacuum assisted resin infusion process was delivered in this paper. By and large, honeycomb sandwich structures are made by keeping the honeycomb core in between two face sheets, which are glued with the help of adhesives. In the present fabrication process, aluminum honeycomb core was glued in between the carbon fabric reinforced epoxy composite face sheets through vacuum assisted resin infusion technique. The present paper is aimed at fabricating two configurations of honeycomb sandwich composite panels namely, without considering any filler material inside the honeycomb cell, with considering the filler material inside the honeycomb cell. Plastic pellets made up of poly carbonate were considered as filler material for stiffening the aluminum honeycomb sandwich composite panels.

Experimental three-point bending test of glass fibre aluminium honeycomb sandwich panel with acoustic emission damage assessment

Due to their complexity, detecting and analysing damage modes in composite honeycomb sandwich panels can be difficult. This article describes the way in which a three-point bending test (3PBT) was performed on a glass fibre aluminium honeycomb sandwich panel (HSP). Acoustic emission (AE) was used to identify damage signals, which were then analysed to determine the positions and characteristics of defects. To locate damage positions, Delta-T mapping was used. The test load was progressively applied in three phases, with the specimen being inspected visually during each phase. A scanning electron microscope (SEM) showed that the most significant damage was local crushing under the test load, which caused matrix cracking, fibre breakage and pull-out. Damage progression and the damage mode were detected using the cumulative energy and frequency spectra of the AE sources for each phase. Matrix cracking frequencies ranged from 30 kHz to 100 kHz, while fibre damage modes ranged from 157 kHz to 322 kHz. The findings highlighted the utility of Delta-T mapping in locating damage positions on sandwich structures under testing. The investigation also emphasised the value of studying frequency spectra and cumulative energy when analysing AE signals.

A multi-area fatigue damage model of composite honeycomb sandwich panels under three-point bending load

The fatigue damage of composite sandwich panels is divided into two parts: the face sheet damage and the core damage. Both the two kinds of damage cause the performance degradation of panels, however only the core damage results in the ultimate failure. In this paper, a fatigue damage model of the face sheet and the core is proposed and three-point bending tests are carried out to obtain the deflection evolution curves. With the proposed model, the fatigue damage can be predicted accurately, which proves the validity of the fatigue damage model proposed in this paper.

Acoustic Emission Source Location in Composite-Honeycomb Sandwich Panel

Acoustic emission is a promising technique for damage detection and location in composite structures. It refers to the process of using a sensor array to detect the elastic waves generated by a damage source within a structure. However, it is challenging to propose suitable and reliable damage location strategies when applying this technique on composite-honeycomb sandwich panels due to their complex nature which affects the acoustic wave propagation. Further, composite-honeycomb sandwich panels are susceptible to damage on either one of their surfaces, yet acoustic emission sensors are likely to be bonded to just one of these surface and the ability of acoustic emission to locate events occurring on the opposite surface from which they are bonded has yet to be explored. This paper seeks to shed light on this phenomenon with an investigation into the ability of acoustic emission to locate sources in a glass fibre aluminium honeycomb sandwich panel, for sources originating from both the front and back surfaces. An array of four sensors was bonded to the front surface of a 820 x 820 mm sandwich panel. Artificial emission sources were generated on both front and back surfaces of sandwich panel. Two location techniques were used to locate the sources; difference in time of arrival, and Delta-T Mapping. For sources generated on the front surface, difference in time of arrival technique located all sources with an average error of 20.2 mm, while Delta-T Mapping located all sources with average error 11.1 mm. For the sources generated on the back surface, opposite to the sensors, difference in time of arrival technique located all sources with average error 42.8 mm, while Delta-T Mapping located them with an average error of 20.78 mm. Overall, Delta-T Mapping technique consistently demonstrates its potential and credibility for source location in complex structures when inspecting the sandwich panel in 2D and 3D, as well.

NDE Terahertz Wave Techniques for Measurement of Defect Detection on Composite Panels of Honeycomb Sandwiches

Terahertz wave (T-ray) technologies have become a popular topic in scientific research over the last two decades, and can be utilized in nondestructive evaluation (NDE) techniques. This study suggests an optimal scanning technique method for honeycomb sandwich composite panels, where skins were utilized with two different skins, namely, carbon fiber-reinforced plastic (CFRP) skin and glass fiber-reinforced plastic (GFRP) skin, as layers of the panel surfaces. Foreign objects were artificially inserted between the skins and honeycomb cells in the honeycomb sandwich composite panels. For this experiment, optimal T-ray scanning methods were performed to examine defects based on the angle between the one-ply thin fiber skin axis and the angle of the electric field (E-field) according to the amount of conductivity of the honeycomb sandwich composite panels. In order to confirm the fundamental characteristics of the terahertz waves, the refractive index values of the GFRP composites were experimentally obtained and analyzed, with the data agreeing with known solutions. Terahertz waves (T-rays) were shown to have limited penetration in honeycomb sandwich composite panels when utilized with a skin of carbon fibers. Therefore, T-rays were found to interact with the electrical conductivity and electric field direction of honeycomb sandwich composite panels with glass fiber skins. The T-ray images were obtained regardless of the electric field direction and the fiber direction. In the honeycomb sandwich composite panels with carbon fiber skins, the T-ray images with higher signal-to-noise (S/N) ratios depended on the scanning angle between the angle of the carbon fiber and the angle of the electric field. Thus, the angle of optimum detection measurement was confirmed to be 90° between the E-field and the fiber direction, particularly when using a carbon fiber skin.

Effects of ballistic impact damage on mechanical behaviour of composite honeycomb sandwich panels

This paper presents the effects of ballistic impact damage on the mechanical behaviour of composite honeycomb sandwich panels. The panels are composed of facesheets made of carbon fibre reinforced laminates and the Nomex honeycomb core. Ballistic tests were conducted in a shooting range using live projectiles of three different calibres. The specimens were subjected to both normal and oblique impacts to simulate the damage to composite sandwich structures that can be inflicted by the use of small weapons or by fragments of anti-aircraft ammunition. The modes and extent of the damage induced have been analysed using optical microscopy, X-ray inspections and computer tomography methods. Structural performance of the intact and ballistically damaged panels has been investigated experimentally using in-plane compression tests, and numerically, based on the finite element modelling and analysis. The reduction in the load-carrying ability caused by the ballistic damage has been assessed for the panels under consideration and compared with that predicted by numerical simulations.