基于开放式电容成像的CFRP层压板缺陷检测

碳纤维增强复合材料被广泛用于航空航天领域,在其制造及使用过程中不可避免产生各种缺陷及损伤。如何实现CFRP构件无损快速检测、提高损伤容限探测水平、降低检测成本具有重要意义。针对飞机使用的CFRP层合板,基于电容边缘效应,考虑其各向异性介电常数分布特点,利用开放式4×4阵列电极,以传统电容成像激励测量模式及共轭梯度图像重建算法,对CFRP层合板进行可视化检测。通过仿真和实验,验证了该方法对于CFRP层合板不同损伤缺陷检测的有效性和可行性,为实现非侵入、无辐射、低成本的快速无损结构健康监测奠定研究基础。     

输电线电磁无损检测系统研发

针对传统输电线结构损伤检测系统存在检测效率低、技术落后以及安装繁琐等缺点,设计了一套基于电磁无损检测技术的输电线结构损伤检测系统。该系统利用电磁感应原理,采用涡流检测技术实现对输电线的无损检测。通过DDS技术产生激励信号驱动涡流探头,利用正交锁相放大技术提取输电线损伤信号,最终将采集到的数据发送到上位机中进行分析处理,从而实现对输电线结构损伤的无损检测。实际试验结果表明,系统能有效地监测到输电线结构中的涡流信号,并能根据此信号得出输电线损伤的位置,检测结果符合设计预期。     

面向CFRP板材的平面式电容传感器设计优化

碳纤维复合材料(CFRP)近年来被广泛应用于航空航天领域,实现其结构完整性检测对于航空航天安全至关重要。基于CFRP层合板的各向异性电学特性,提出利用平面电容传感器实现其结构性损伤检测,该方法具有成本低、非侵入、无辐射、操作简单等优点。比较分析了4种不同形状的平面式电容传感器,通过COMSOL软件构建CFRP层合板的3种典型损伤模型,从信号强度、灵敏度、信噪比、测量动态范围和相关系数等指标分析比较4种电容传感器。同时,结合实际测量数据,比较了CFRP表面损伤半径分别为5、2和1 mm时4种传感器的检测性能。结果表明,三角形传感器在相关系数指标上相比于其他传感器有至少9.8%的检测精度提升,能够有效检测和识别CFRP层合板的缺陷。     

用于复合材料蒙皮的FBG正交传感网络研究

为了实现对复合材料蒙皮的结构健康监测与损伤识别,本文在对光纤布拉格光栅(FBG)应变传感器理论分析的基础上,结合CFRP材料特性和波分复用技术设计了一种由16个FBG传感器构成的光纤光栅正交传感网络布局,对碳纤维复合材料(CFRP)蒙皮进行相关准分布式传感网络研究。通过对复合材料中心位置进行逐级加载实验,并提取中心波长漂移量做相关性分析,证明了正交对称FBG传感网络对CFRP蒙皮进行结构健康监测的可行性,同时对称布局位置处的FBG传感器信号具有高度相关性质,相关系数可高达0.9996。实验结果为进一步研究准分布式FBG网络的位置布局优化以及传感网络的可靠性冗余设计提供了依据。     

基于Lamb波时间反转的复合材料结构损伤监测

采用Lamb波时间反转法,对复合材料结构进行在线连续健康监测。利用板中Lamb波时间反转法的原理和自聚焦特点,运用时间反转方法,通过传感器网络的布置,激励并接收Lamb波,从而对复合材料结构实现损伤监测。该方法无需结构无损情况的基准信号,能够对有损结构进行快速的损伤定位及损伤大小判断。采用改进的RAPID算法进行损伤成像,得到的损伤图像可将损伤情况可视化。实验研究表明所提方法可行和有效。     

基于PWAS的层合板导波传播特性和损伤响应FEM分析及试验验证

导波无损检测（Non-Destructive Testing, NDT）技术由于适用范围广、检测速度快等优势,已成为结构安全性检测的重要技术手段之一。不过,导波在各向异性介质中的传播表现为频散特性与波传播方向的关联性、多模态特性与各向异性的相互作用以及不同模态与损伤的相互作用。导波在复合材料无损检测应用中的复杂性对检测技术和检测方法提出了更高的要求,所以对碳纤维复合材料层合板中的导波传播特性和损伤响应进行分析具有十分重要的意义。文中采用理论分析、仿真和试验相结合的方法,对不同碳纤维增强聚合物基（Carbon Fiber Reinforced Polymer, CFRP）层合板中的导波传播特性和各模态波与损伤的相互作用进行了分析。首先根据群速度、波长等参数建立有限元模型,并在边界设置阻尼递增吸收区域来弱化边界反射波的干扰;然后分析基于压电晶片有源传感器（Piezoelectric Wafer active Sensors, PWAS）的不同层合板中导波传播差异,之后在结构中引入损伤来分析不同模态波与不同损伤的相互作用;最后通过试验分析和验证有限元仿真的准确性。     

超声导波在圆管结构损伤定位中的应用

针对结构损伤会影响超声导波传播,提出基于超声导波无损检测的结构健康监测方法。以内径为174mm、外径为194mm、材料为20~#碳钢的圆管结构为例,根据频散方程利用数值法求解其纵向模态以及周向Lamb波频散曲线。同时考虑其频散曲线和波的结构,确定激励频率中心频率为80kHz。在此基础上进行有限元仿真,验证圆管中导波的传播机理及特征。针对此频率圆管纵向模态导波以及周向Lamb波的频散特性、波的结构比较接近,且都与板中的Lamb波相似,从而提出了单点激励、多点接收,并采用椭圆定位的方法,实现圆管结构损伤定位。通过仿真和实验验证该方法对切槽、圆孔等损伤的识别效果,并对损伤定位误差的影响因素进行了分析。     

碳纤维构件挤压渐进损伤无损检测及其图像分析

针对反复出现的小能量挤压是否会对复合材料层合板造成结构损伤,进行了碳纤维构件挤压渐进试验。应用红外无损检测方法采集对象图像,观测损伤结果,采用MATLAB图像分析软件对红外热像图进行数字图像分析。研究结果表明,碳纤维层合板试件在单次小能量挤压作用下,未出现明显缺陷;在小能量挤压重复作用下,会产生结构的损伤缺陷。采用红外热成像检测方法,可以快速、有效、可靠地检测结构损伤。     

基于相控阵的结构损伤范围监测与图像表征

本文针对碳纤维复合材料机翼盒段监测损伤信号微弱难以有效辨识及结构损伤大小的量化问题,提出基于相控阵的碳纤维复合材料结构损伤识别成像与损伤量化方法。利用Lamb波信号在特定方向上的干涉,实现对结构的定向扫描,提高信号的信噪比;通过划分扇环计算其面积进而量化损伤区域大小,同时分析时间延迟执行过程并分析其对损伤识别误差的影响。采用相控阵监测原理在某型无人机碳纤维复合材料机翼盒段上进行实验研究,识别结构中的损伤,对监测结果进行成像,不仅显示结构中损伤的位置并计算量化损伤区域大小,实验研究证明,采用相控阵原理能够有效精确地识别碳纤维复合材料机翼盒段中损伤,图像表征清晰且量化损伤范围准确。     

基于缺陷局部共振内调制机理的复合材料平板损伤识别

相比利用谐波和调制信号的非线性超声无损检测方法,损伤局部共振内调制效应可以大幅增强损伤界面间的非线性行为,且其利用激励频率与损伤局部共振频率间进行调制,输入信号得到简化。当激励信号满足特定的频率条件时,材料的缺陷和损伤局部在超声激励的作用下会产生共振,导致响应信号中出现幅值增强的倍频、超谐波、亚谐波以及激励频率与局部共振频率间的内调制现象。针对损伤局部共振效应构造单自由度非线性模型,并运用多尺度法进行分析,分别考虑平方、立方刚度非线性,推导局部共振内调制现象产生的机理。进行碳纤维复合材料板冲击损伤局部共振调制损伤识别实验分析,验证理论模型分析结果以及缺陷局部共振内调制非线性损伤检测方法的可行性。结果表明,利用缺陷局部共振内调制效应可以有效地识别复合材料板的冲击损伤。     

A method for the localization of damage in a CFRP plate using damping

In the past 25 years, the scientific and industrial communities have made great efforts on the fields of damage detection and structural health monitoring (SHM). However, no single approach has proven appropriate for all situations. Composite materials, which are receiving an increasing attention in the aeronautical industry, namely carbon fibre reinforced plastics (CFRP), are very sensitive to impacts of medium and low energy. Typically, barely visible impact damage (BVID) will occur, constituting an unsafe failure of difficult assessment. To assess (detect, locate and quantify) damage in this kind of material is still a challenge, especially if a huge amount of sensors or expensive equipments at hand are not used. In this work, a methodology that makes use of a reduced amount of conventional sensors is explored, with the aim of locating damage for a low cost on components that are subjected to impacts during service. This represents a considerable benefit, namely for the assessment of damage in aeronautical components, compared to most methods used today. This work can also give a major contribution to the research community since uncommon approaches will be used to model damage in composite materials, namely the modal damping factor as the main feature for damage localization.     

Effect of fuzzy C means technique in failure mode discrimination of glass/epoxy laminates using acoustic emission monitoring

Acoustic emission is one of the powerful techniques that can be used for in situ structural health monitoring of composite laminates. One of the main issues of AE is to characterize the different damage mechanisms from the detected AE signals. Unsupervised Pattern recognition has been one of the techniques used for the identification of a specific failure mode in composites from Acoustic emission data. Cross ply composite laminate of size 300 × 300 mm is fabricated using Vacuum bag molding. ASTM D3039 Standard tensile specimens are cut from the laminate and these specimens are subjected to uni axial tensile test under Acoustic Emission monitoring. Fast Fourier transform analysis (FFT) and Short Time Fast Fourier Transform (STFFT) analysis are performed on the Wave forms of the AE hit data obtained during the conduct of tensile test to characterize the failure modes in crossply specimens. Fast Fourier Transform enabled calculating the frequency content of each damage mechanism. In this paper Fuzzy C Mean clustering is performed for the AE parameters obtained from the test and the efficiency of this technique is being investigated using FFT AND STFFT analysis.     

基于C#的飞机疲劳试验实时预警系统设计

为满足飞机疲劳试验对试验数据实时监控的需求,采用C#语言开发了一套飞机疲劳试验实时预警系统。该系统以疲劳试验数据管理系统为基础,计算各测量点、各工况的平均值和标准差,通过多种方法设定预警阈值。该系统界面友好、功能完备,可实现疲劳试验数据的实时监控,能够及时发现异常试验数据,尽早发现结构损伤并采取有效措施,可以大幅降低维修成本、缩短维修周期。     

Effect of Cycling Low Velocity Impact on Mechanical and Wear Properties of CFRP Laminate Composites

The mechanical and wear properties of CFRP laminate were investigated using a method of cycling low velocity impact, to study the trend and mechanism of impact resistance of the CFRP laminate under repeated impact during its service process. The interface responses of CFRP laminate under di erent impact kinetic energy during the cycling impact process were studied were studied experimentally, such as impact contact duration, deformation and energy absorption. The worn surface morphologies were observed through optical microscopy and a 3?D surface profiler and the cross?sectional morphologies were observed through SEM to investigate the mechanism of impact material dam?age. Based on a single?degree?of?freedom damping vibration model, the normal contact sti ness and contact damp?ing of the material in di erent wear stages were calculated. It shows the failure process of CFRP laminate damaged by accumulated absorption energy under the cycling impact of di erent initial kinetic energy. The results indicate that the sti ness and damping coe cients will change at di erent impact velocities or cycle numbers. The damage mechanism of CFRP laminates under cycling low kinetic energy is delamination. After repeated experiments, it was found that there was a threshold value for the accumulated absorption energy before the failure of the CFRP laminate.     

Effects of cutting edge radius and fiber cutting angle on the cutting-induced surface damage in machining of unidirectional CFRP composite laminates

Carbon fiber reinforced polymer composite laminates are anisotropic, inhomogeneous, and mostly prepared in laminate form before undergoing the finishing operations. The edge trimming process is considered as one of the most common finishing operations in the industrial applications. However, the laminate surface is especially prone to damage in the chip formation process, and the most common damage mode is burrs. Burrs may increase cost and production time because of additional machining; they can also damage the surface integrity. Many studies have been done to address this problem, and techniques for reducing burr size in material removal process has been the focus of the research. Nonetheless, the combined effects of the cutting edge radius and the fiber cutting angle on the burr formation have seldom been conducted, which in turn restricts to find out the mechanism of burr formation. The purpose of the present paper is to study the particular mechanism that leads to burr formation in edge trimming of CFRP laminates and investigate the effects of fiber cutting angle and cutting edge radius on burr formation. The results indicate that the burrs are prone to form in the fiber cutting angle range of 0° < χ < 90° when a large cutting edge radius of the tool is used for both milling and drilling of CFRP composites.     

Distributed structural health monitoring with a smart sensor array

This paper presents work on smart sensor arrays for distributed structural health monitoring (SHM) and damage diagnosis. The goal of the work was to implement local vibration-based diagnostic algorithms inside a smart ‘black box’ to demonstrate the feasibility of distributed health monitoring for damage detection and location. Dynamic transmissibility features for SHM and the smart-processing platform are described in detail and various damage configurations in two large test structures, a representative three-storey building and a rotorcraft fuselage, are diagnosed. The results show that the near real-time integrated monitoring system works well in spite of certain limited environmental fluctuations (e.g. temperature, input levels) and boundary condition non-linearities. Wired piezoelectric arrays of accelerometers are implemented in conjunction with the black box.     

Smart optical-fiber structure monitoring based on granular computing

Using an optic fiber self-diagnosing system in health monitoring has become an important direction of smart materials and structure research. The buried optic fiber sensor can be used to test the parameters of the composite material. The granular computing method can reach the requirement of damage detection by analyzing digital signals and character signals of the smart structure at the same time. The paper investigates an optic fiber smart layer and presents a method for realizing optic fiber smart structure monitoring and damage detection by using granular computing. After the analysis, it is presumed that optic fiber smart structure monitoring based on granular computation can identify the damage from complex signals.     

CFRP及叠层结构螺旋铣孔专用刀具切削性能评价

碳纤维增强复合材料(CFRP)及由钛合金Ti-6Al-4V和CFRP组成的金属复合材料叠层结构广泛应用于现代航空工业。大型客机结构件之间主要通过铆接和高锁螺栓连接,根据波音与空客公司发布的数据显示,最新一代B787与A380上装配孔的数量已超百万,装配过程中的制孔效率与质量直接决定了客机整体装配效率及关键结构件的疲劳寿命,从而间接影响了客机的生产成本以及飞行可靠性。随着飞机数字化装配的快速发展,传统的钻孔工艺会产生很多加工缺陷,工序复杂,加工孔质量不能满足要求,因此,有必要优化制孔工艺,设计新型专用刀具。本文通过研究螺旋铣孔运动学特性,分析螺旋铣孔的工艺特点,设计了一种新型螺旋铣孔专用刀具,并以加工过程的轴向切削力、出入口加工质量以及刀具磨损为评价指标,验证该新型专用刀具的切削性能。结果表明,专用刀具在干切削条件下能够实现复材孔无分层、钛合金孔无毛刺加工,大幅提高刀具寿命,解决了传统立铣刀对CFRP及CFRP/钛合金叠层结构进行螺旋铣孔时刀具寿命低、加工质量差等问题。     

Smart optical-fiber structure monitoring based on granular computing

Using an optic fiber self-diagnosing system in health monitoring has become an important direction of smart materials and structure research. The buried optic fiber sensor can be used to test the parameters of the composite material. The granular computing method can reach the requirement of damage detection by analyzing digital signals and character signals of the smart structure at the same time. The paper investigates an optic fiber smart layer and presents a method for realizing optic fiber smart structure monitoring and damage detection by using granular computing. After the analysis, it is presumed that optic fiber smart structure monitoring based on granular computation can identify the damage from complex signals.