A Modified Principal Component Analysis Method for Honeycomb Sandwich Panel Debonding Recognition Based on Distributed Optical Fiber Sensing Signals

The safety and integrity requirements of aerospace composite structures necessitate real-time health monitoring throughout their service life.To this end,distributed optical fiber sensors utilizing back Rayleigh scattering have been extensively deployed in structural health monitoring due to their advantages,such as lightweight and ease of embedding.However,identifying the precise location of damage from the optical fiber signals remains a critical challenge.In this paper,a novel approach which namely Modified Sliding Window Principal Component Analysis(MSWPCA)was proposed to facilitate automatic damage identification and localization via distributed optical fiber sensors.The proposed method is able to extract signal characteristics interfered by measurement noise to improve the accuracy of damage detection.Specifically,we applied the MSWPCA method to monitor and analyze the debonding propagation process in honeycomb sandwich panel structures.Our findings demonstrate that the training model exhibits high precision in detecting the location and size of honeycomb debonding,thereby facilitating reliable and efficient online assessment of the structural health state.

Assessment of the ballistic response of honeycomb sandwich structures subjected to offset and normal impact

In the present study,experimental and numerical investigations were carried out to examine the behavior of sandwich panels with honeycomb cores.The high velocity impact tests were carried out using a compressed air gun.A sharp conical nosed projectile was impacted normally and with some offset distance(20 mm and 40 mm).The deformation,failure mode and energy dissipation characteristics were obtained for both kinds of loading.Moreover,the explicit solver was run in Abaqus to create the finite element model.The numerically obtained test results were compared with the experimental to check the accuracy of the modelling.The numerical result was further employed to obtain strain energy dissipation in each element by externally running user-defined code in Abaqus.Furthermore,the influence of inscribe circle diameter and cell wall and face sheet thickness on the energy dissipation,deformation and failure mode was examined.The result found that ballistic resistance and deformation were higher against offset impact compared to the normal impact loading.Sandwich panel impacted at 40 mm offset distance required 3 m/s and 1.9 m/s more velocity than 0 and 20 mm offset distance.Also,increasing the face sheet and wall thickness had a positive impact on the ballistic resistance in terms of a higher ballistic limit and energy absorption.However,inscribe circle diameter had a negative influence on the ballistic resistance.Also,the geometrical parameters of the sandwich structure had a significant influence on the energy dissipation in the different deformation directions.The energy dissipation in plastic work was highest for circumferential direction,regardless of impact condition followed by tangential,radial and axial directions.

Three-point bending of honeycomb sandwich beams with facesheet perforations

A novel square honeycomb-cored sandwich beam with perforated bottom facesheet is investigated under threepoint bending,both analytically and numerically.Perforated square holes in the bottom facesheet are characterized by the area ratio of the hole to intact facesheet（perforation ratio）.While for large-scale engineering applications like the decks of cargo vehicles and transportation ships,the perforations are needed to facilitate the fabrication process（e.g.,laser welding）as well as service maintenance,it is demonstrated that these perforations,when properly designed,can also enhance the resistance of the sandwich to bending.For illustration,fair comparisons among competing sandwich designs having different perforation ratios but equal mass is achieved by systematically thickening the core webs.Further,the perforated sandwich beam is designed with a relatively thick facesheet to avoid local indention failure so that it mainly fails in two competing modes：（1）bending failure,i.e.,yielding of beam cross-section and buckling of top facesheet caused by bending moment;（2）shear failure,i.e.,yielding and buckling of core webs due to shear forcing.The sensitivity of the failure loads to the ratio of core height to beam span is also discussed for varying perforation ratios.As the perfo-ration ratio is increased,the load of shear failure increases due to thickening core webs,while that of bending failure decreases due to the weakening bottom facesheet.Design of a sandwich beam with optimal perforation ratio is realized when the two failure loads are equal,leading to significantly enhanced failure load（up to 60%increase）relative to that of a non-perforated sandwich beam with equal mass.

Fabrication and compressive performance of plain carbon steel honeycomb sandwich panels

Plain carbon steel Q215 honeycomb sandwich panels were manufactured by brazing in a vacuum furnace. Their characteristic parameters, including equivalent density, equivalent elastic modulus, and equivalent compressive strength along out-of-plane （z-direction） and in-plane （x-and y-directions）, were derived theoretically and then determined experimentally by an 810 material test system. On the basis of the experimental data, the compressive stress-strain curves were given. The results indicate that the measurements of equivalent Young＇s modulus and initial compressive strength are in good agreement with calculations, and that the maximum compressive strain near to solid can be up to 0.5-0.6 along out-of-plane, 0.6-0.7 along in-plane. The strength-to-density ratio of plain carbon steel honeycomb panels is near to those of Al alloy hexagonal-honeycomb and 304L stainless steel square-honeycomb, but the compressive peak strength is greater than that of Al alloy hexagonal-honeycomb.

Structural-acoustic coupling characteristics of honeycomb sandwich plate based on parameter sensitivity analysis

The structural-acoustic coupling model for isotropic thin elastic plate was extended to honeycomb sandwich plate(HSP) by applying Green function method.Then an equivalent circuit model of the weakly-strongly coupled system was proposed.Based on that,the estimation formulae of the coupled eigenfrequency were derived.The accuracy of the theoretical predictions was checked against experimental data,with good agreement achieved.Finally,the effects of HSP design parameters on the system coupling degree,the acoustic cavity eigenfrequency,and sound pressure response were analyzed.The results show that mechanical and acoustical characteristics of HSP can be improved by increasing the thickness of face sheet and reducing the mass density of material.

Predicting test data of aluminum honeycomb sandwich board based on volterra adaptive filters

Random vibration test was done on aluminum honeycomb sandwich board. The result suggested that chaotic behavior is found in the test data. The Volterra expression can not be gained from the input and output data directly in this paper. The state space reconstruction was used to convert the system observed data into the quasi-input/output pairs, and the second-order Voherra adaptive filter was used to predict the test data. It is shown that combining the state space reconstruction with the Volterra adaptive filter, these chaotic series could be accurately predicted.

A Mini Review on Testing Methods for Mechanical Properties of Natural Fibre Honeycomb Sandwich Structure and Fractography Analysis

This paper is a review of the past research of mechanical testing methods for natural fibre honeycomb sandwich structure as well as failure modes analysis at a microscopic level by using Scanning Electron Microscope (SEM). As the world is garnering attention towards renewable resources for environmental purposes, studies of natural fibre have been increasing as well as the application of natural fibre throughout various industries such as aerospace, automobiles, and construction sectors. This paper is started with brief information regarding the honeycomb sandwich structure, introduction to natural fibre, its applications as well as the factors affecting the performances of the structure. Next, the mechanical testing methods are listed out as well as the expected outcomes obtained from the respective testing. The mechanical properties are also identified by conducting lab tests according to the ASTM standard for sandwich and core structures. The microstructure of the deformed samples is then examined under Scanning Electron Microscope (SEM) by using different magnifications to study the failure mechanisms of the samples. The images obtained from the SEM test are analyzed by using fractography which will show the failure modes of the samples. This article is based on past research conducted by professional on the related topic.

Quasi-distribution Appraisal about Finite Element Analysis of Multi-functional Structure Made of Honeycomb Sandwich Materials

A new appraisal method（QDA, quasi-distribution appraisal） which could be used to evaluate the finite element analysis of multi-functional structure made of honeycomb sandwich materials is developed based on sub-section Bezier curve. It is established by simulating the distribution histogram data obtained from the numerical finite element analysis values of a satellite component with sub-section Bezier curve. Being dealt with area normalization method, the simulation curve could be regarded as a kind of probability density function（PDF）, its mathematical expectation and the variance could be used to evaluate the result of finite element analysis. Numerical experiments have indicated that the QDA method demonstrates the intrinsic characteristics of the finite element analysis of multi-functional structure made of honeycomb sandwich materials, as an appraisal method, it is effective and feasible.

The effect of bucking on the mechanical properties of honeycomb sandwich structure

Static compression test on the Honeycomb sandwich structure with surface core defect carry out in this paper. The specimen divided into four groups, one had no defect, one had circle defect, the other two groups had rectangular defect in different direction. In the process of loading the strain gauge which located on the specimen surface in each group record the strain transformation of the specimen surface. Through the Static load test on the fatigue testing machine, fracture load of each specimen was record. According to the data, how the size and shape of the defect influence the compression static strength of Honeycomb sandwich was discussed, and inspecting defects direction how to affect the structural static slrength by means of theoretical analysis and data fitting, meanwhile the shape of the defects in structure how to effect buckling was discussed too.

Stress Concentration around the Embedding of the Honeycomb Sandwich Structure

Honeycomb structures and other sandwich materials are being used as designs which have demanded high-stiffness and lightweight structures. The embedding design can further decrease the total weight of the products. Embedding will inevitably generate defect of the honeycomb and cause stress concentration. This study mainly discusses the tensile stress distribution near the defect in a quantitative way with the finite element and analytical method. The prediction function of the stress distribution is proposed. X and y directional stress distribution properties are found. These results are proved to be validate through a representative defect case. The bending stress distribution is investigated through material mechanics method and the prediction equation of the maximum bending stress is given.

Experimental study of 3D printed carbon fibre sandwich structures for lightweight applications

Honeycomb sandwich structures are widely used in lightweight applications.Usually,these structures are subjected to extreme loading conditions,leading to potential failures due to delamination and debonding between the face sheet and the honeycomb core.Therefore,the present study is focused on the mechanical characterisation of honeycomb sandwich structures fabricated using advanced 3D printing technology.The continuous carbon fibres and ONYX-FR matrix materials have been used as raw materials for 3D printing of the specimens needed for various mechanical characterization testing;ONYX-FR is a commercial trade name for flame retardant short carbon fibre filled nylon filaments,used as a reinforcing material in Morkforged 3D printer.Edgewise and flatwise compression tests have been conducted for different configurations of honeycomb sandwich structures,fabricated by varying the face sheet thickness and core cell size,while keeping the core cell thickness and core height constant.Based on these tests,the proposed structure with face sheet thickness of 3.2 mm and a core cell size of 12.7 mm exhibited the highest energy absorption and prevented delamination and debonding failures.Therefore,3D printing technology can also be considered as an alternative method for sandwich structure fabrication.However,detailed parametric studies still need to be conducted to meet various other structural integrity criteria related to the lightweight applications.

A Mini Review on Natural Fiber Honeycomb (NFH) Sandwiched Structure Composite: Flexural Perfomance Perspective

Natural Fiber Honeycomb (NFH) sandwiched structure composite is a type of composite that uses natural fiber as the reinforcement material and honeycomb structure in the form of a sandwich panel. The demand for commercial use of natural fiber-based composites is increasing in the past few years in many industrial sectors. The increase in popularity of natural fibers is because of their particular properties, price, health benefits, and recyclability. This paper aims to analyze the data and analysis of the past research about NFH sandwiched structure composite in terms of the materials used to make the NFH, the physical and mechanical properties, and their applications. Based on the literature review conducted, there were many types of materials used to make the NFH sandwiched structure composite. Some experimental tests were planned and conducted to analyze the mechanical properties of the NFH and its potential to be used in the desired industries. However, there are not many implementations of NFH composite in the construction industry. This is due to the concern related to the issue of the structural integrity of the NFH composite. From the literature review conducted, most of the research shows a positive analysis of the mechanical properties and the potential of the developed NFH to be used for the targeted industry in the study. Therefore, it can be observed that the material used in this study has a high potential to be used in the construction industry.

挖补修理蜂窝夹芯结构侧压强度的可靠性及灵敏度分析

以挖补修理复合材料蜂窝夹芯结构为研究对象,考虑胶层性能的不确定性,通过ABAQUS-MATLAB-Python联合仿真,建立挖补修理蜂窝夹芯结构侧向压缩渐进损伤分析模型,得到随机变量与其所对应的输出响应。基于蒙特卡罗法进行可靠性分析,采用基于方差和失效概率的全局灵敏度分析方法进行参数灵敏度分析。结果表明:外载荷在不同数值区间下结构失效概率具有较大差异,在接近极限破坏载荷时失效概率显著增加;胶层厚度方向的弹性模量和面内两个相互垂直方向上的剪切模量对挖补修理蜂窝夹芯结构侧压强度方差和失效概率的影响较大。

基于分布式光纤的蜂窝夹层结构脱粘损伤监测

航空航天蜂窝夹层结构服役环境恶劣,需要发展相应的结构健康监测技术以保证结构的安全运行。脱粘损伤因发生在内部胶层而难以监测,该文采用埋入胶层的分布式光纤传感器对蜂窝夹层结构脱粘损伤进行监测。在预埋损伤监测试验中采用高强光纤和边界浅槽的方式提高传感器存活效率,得到脱粘损伤应变特征。采用参数化建模方式对不同损伤位置进行大量有限元模拟,加入白噪声后得到含有脱粘损伤特征的13500组数据。将模拟数据代入卷积神经网络进行训练,训练后的网络对试验损伤数据的识别准确率达到98.84%。该方法能够识别20 mm^(2)脱粘损伤,同时定位平均误差小于4 mm。

泡沫填充负泊松比蜂窝夹层结构的抗爆性能数值模拟

为研究爆炸荷载作用下泡沫填充负泊松比蜂窝夹层结构(Foam-filled Auxetic Honeycomb Sandwich Structure,FAHSS)的动态响应及其对混凝土板的防护性能,利用有限元软件,考虑应变率对材料动态本构特性的影响,建立FAHSS在爆炸荷载下的有限元数值模型。通过已有负泊松比蜂窝夹层结构(Auxetic Honeycomb Sandwich Structure,AHSS)的爆炸试验对数值模型进行验证,基于验证模型分析爆炸荷载作用下FAHSS的损伤破坏规律、能量吸收特性及其对混凝土板的应力分布影响,并与AHSS和FSS(Foam Sandwich Structure)进行对比。在此基础上综合考虑聚氨酯泡沫材料密度、爆炸比例距离及填充材料等因素对FAHSS抗爆性能的影响。研究结果表明:FAHSS中的泡沫填充降低了负泊松比蜂窝夹层结构的破坏程度;随着聚氨酯泡沫材料密度的增加,FAHSS中的泡沫材料吸收能量增加;随着比例距离的增加,FAHSS的破坏程度逐渐降低,破坏形态也由局部破坏转变为整体破坏。

蜂窝板几何参数对芯子剪切模量测量值的影响

为了通过三点弯曲试验获得蜂窝芯子较准确的剪切模量,基于商用铝蜂窝夹层板几何参数与典型剪切模量值,对三点弯曲试验有限元仿真模型进行校验,研究了蜂窝夹层板几何参数对测得芯子剪切模量值的影响规律。利用Sobol法对各影响因素进行灵敏度分析,拟合得到简化代理模型。基于简化代理模型,给出了三点弯曲试验中蜂窝夹层板几何参数适用可行域。研究结果表明,蜂窝夹层板几何参数对芯子剪切模量测量值的影响程度由大到小的顺序为芯子密度、面芯厚度比和面板厚度。在给定的可行域内,通过三点弯曲方法测得的蜂窝芯剪切模量精度良好,可为实际工程提供参考。

储罐内浮盘受力变形的流固耦合数值模拟

为提高浮盘在储罐中的安全性,通过ANSYS Workbench中的ICEM CFD、FLUENT平台,根据三明治夹芯板理论来等效浮盘的蜂窝板结构,同时使用流固耦合的方法研究浮盘在卡盘工况下,液体密度不同、防转装置处于不同位置以及蜂窝的正六边形边长对浮盘受力变形的影响。结果表明:浮盘表面的压力与浮盘的变形量随着液体密度的增大而增加;在一定的范围内,浮盘的总变形量随着防转装置距离浮盘边缘距离的增大呈现先增大再减少的状态;当蜂窝正六边形边长从5 mm增加到40 mm时,浮盘的变形量逐渐增大,在防转装置距离浮盘边缘2.25 m时,浮盘在四周约束的变形量大于在防转装置卡顿下的变形量,大约相差2 cm。可见,通过改变防转装置的位置以及缩小浮盘蜂窝正六边形的边长可以减小浮盘的变形。

蜂窝夹层结构无损检测方法研究综述

蜂窝夹层结构是一种层合复合材料,具有优异的力学性能,被广泛应用于航空航天、建筑以及汽车制造等领域。由于自身结构及服役工况的复杂性,蜂窝夹层结构容易在制造、服役等阶段产生蒙皮-蜂窝芯界面脱粘、蒙皮分层、夹杂、蜂窝芯格变形、芯格塌陷、节点开裂、蜂窝积水等多种形式的缺陷。因此,开展蜂窝夹层结构无损检测方法的研究具有重要意义。本文回顾了国内外文献中出现的针对蜂窝夹层结构的无损检测方法,分析了各种单一检测方法的原理、应用优势及局限性。随后,概述了将多种单一方法复合的检测方法在蜂窝夹层结构缺陷全面检测上的应用,并指出应用智能算法可实现蜂窝夹层结构缺陷的定量和分类识别。最后,对蜂窝夹层结构无损检测的研究和应用趋势进行了简要总结和展望。

三明治式飞行器热防护结构研究进展

三明治式先进热防护结构广泛应用于航空航天装备。然而,由于上述结构多为板面与芯体组合形式,加之通道内流场的综合作用,其换热机理呈现出复杂、多变及强耦合的特点,难以针对真实结构及环境工况开展计算、仿真及实验工作。为此,致力于为飞行器热防护结构设计、仿真、试验、优化工作提供可靠技术支撑,本文选取蜂窝夹芯结构、波纹板夹芯结构和点阵夹芯结构,对于点阵夹芯结构又从四面体、金字塔、X型和Kagome型点阵着手,对国际、国内主要研究团队近年来相关流动与换热研究成果进行综述。阐述了3种热防护结构的结构形式和发展历程,分析了板面与芯体组合作用下的换热形式及隔热机理,归纳总结了现有研究不足之处与发展趋势。可以看出,点阵夹芯相比蜂窝与波纹板夹芯结构,由于其芯体内复杂湍流的存在,换热效率高、温度梯度小,具有更好的隔热潜力。

一种新型四孔异形蜂窝包装夹层结构力学性能研究

目的随着新材料和新结构的发展,包装材料结构要求在包装运输过程中对产品具有更高的保护能力。为了丰富包装材料结构并在保证力学性能条件下设计新型蜂窝结构。方法以传统正六边形蜂窝结构为基础构建新型四孔异形蜂窝结构,通过对可降解树脂材料的试件进行理论分析、仿真分析和实验验证研究其力学特性。结果新型四孔异形蜂窝包装夹层结构横向和纵向的力学性能,相较于传统的正六边形和正八边形蜂窝结构提升了17%,具有更好的外载荷承载能力。结论本研究对包装材料结构给出了新的思路,对包装行业的发展起到支持作用。