机器人辅助激光超声检测系统及参量匹配方法

为解决飞行器复合材料构件的非接触、高精度无损检测问题,提出基于关节型机器人的激光超声检测系统及光声学参量匹配方法。采用有限元方法建立层状复合材料模型,计算分析材料层状各向异性导致激光超声的非对称分布、声束倾斜和畸变特征,结合实验分析得出利用激光超声表征分层的光声学参量匹配方法。在系统设计上,利用1 064 nm波长的Nd:YAG脉冲激光器激励超声波,利用基于光折变效应的双波混合干涉测量系统探测超声信号,激励和探测激光由光纤传导并投射至被检测工件表面,采用精密六轴关节型机器人作为C型扫描装置,建立系统的实验室原型,实现碳/环氧复合材料试样的C型扫描检测,得到试样中模拟缺陷的分布、形状和尺寸特征,验证了检测系统及参量匹配方法的有效性。研究结果表明,研制的机器人辅助激光超声检测系统可以实现碳/环氧复合材料内部直径1 mm以上分层的检测与成像,在飞行器复合材料构件的无损检测方面具有应用前景。     

基于空耦超声共振法的复合材料测厚技术研究

为解决当前传统超声检测技术对复合材料的检测耦合剂污染和检测效率低等问题,提出空气耦合超声共振法来检测复合材料薄板的厚度,从而确定缺陷的大小。利用 COMSOL 有限元仿真软件对复合材料进行建模,设置不同厚度及不同大小缺陷的物理模型来对比实验,后处理求解并进行快速傅里叶变换,提取谐振频率计算出复合材料的厚度。结果表明,超声共振法可对复合材料进行定性、定量检测;当复合材料的厚度越薄时,超声信号产生的谐振频率越大,则复合材料中所含缺陷范围越广,分层现象越严重;其检测精度可达 0.1 mm 左右,相对误差范围分布在 5% 以下。实验证明了该测厚技术的可靠性,为超薄复合材料板缺陷厚度的测量提供一定的参考和借鉴。     

相位编码脉冲压缩方法在空气耦合超声检测信号处理中的应用

由于声波在空气介质中的衰减及气固界面巨大声阻抗差导致空气耦合超声透射信号信噪比差,大大影响检测结果的可靠性及缺陷定量精度。针对上述问题,基于雷达系统相位编码脉冲压缩技术的基本原理讨论匹配滤波器的设计及其在空气耦合超声检测中的实现,分析不同巴克码信号、带宽及载波周期数对脉冲压缩效果的影响,并以玻璃纤维复合材料(Glass fiber reinforced polymer,GFRP)试样为对象,对比用单频正弦及相位编码脉冲压缩方法获得的透射超声信号信噪比及C扫描缺陷定量精度。试验结果表明选择换能器中心频率作为13位巴克码信号带宽时,脉冲压缩信号主瓣脉宽最小、幅值最大;相位编码脉冲压缩后超声信号信噪比较单频信号提高了12.4 dB,缺陷边缘更清晰且定量精度较单频信号提高了12%。说明在空气耦合超声检测中采用相位编码脉冲压缩技术能显著提高接收信号信噪比及缺陷定量精度。     

分层缺陷对复合材料结构疲劳寿命影响研究

介绍一种新研制的含缺陷复合材料压缩试验装置 ,并采用压缩疲劳试验方法研究中央分层和边缘分层缺陷对飞机复合材料结构疲劳寿命的影响。研究结果表明 ,试件疲劳破坏的起始位置与预制缺陷位置一致。含分层缺陷复合材料结构的疲劳寿命不仅与缺陷尺寸 ,而且与缺陷位置有关。该研究结果为制定生产和使用过程中缺陷或损伤的控制标准提供重要依据     

复合材料结构中R区的超声波反射行为及其检测应用

复合材料已成为现代飞机制造的非常重要的选材,复合材料结构R区缺陷会影响其受力和传载。R区开敞性差、声波反射复杂等影响超声检测及其缺陷识别与定量评估。为此,基于超声波在R-区的反射行为,利用宽带窄脉冲超声反射回波时域特征和成像特征进行复合材料结构R区缺陷检测与量化评估及层深定位。计算结果表明,入射角小于3°时,可以获得较好的声波透射效果。试验结果表明,入射声波在R区蒙皮表面、底面、层间、分层形成的反射信号具有明显不同的时域特征和B-扫描图像特征,对于12个铺层的R-区蒙皮,不同深度分层波幅变化不超过2.5 d B;分层深度定位准确性达1个铺层内;采用水膜方法可以获得稳定的超声耦合效果;利用所使用的换能器及检测系统的超声B-扫描成像,可以直观地再现入射声波在复合材料R区的反射行为,有效地揭示R区分层缺陷深度分布、取向长度;检测分辨率和表面检测盲区可以达到单个复合材料铺层的厚度,约0.125 mm。解剖结果验证了实际超声检测结果的正确性。为复合材料结构R区提供了一种非常有效的检测技术和缺陷定性定量方法,已经得到了非常重要的实际检测应用。     

SiCp颗粒增强铝基复合材料非共线非线性响应试验观察

采用粉末冶金方法制备的碳化硅颗粒增强铝基复合材料(SiCp/Al)受加工过程工艺影响较易出现SiCp颗粒分布不均等缺陷。传统的金相法及声速扫描法检测该缺陷存在破坏试样及定位困难且灵敏度不高等问题;基于谐波的穿透式共线非线性无损检测方法检测灵敏度高,但易受到其他非线性试验来源的干扰。为解决这一问题,利用基于波束混叠的非共线非线性超声检测方法,观察SiCp/Al的非共线非线性响应,探讨使用该方法检测粉末铝基复合材料非均匀性缺陷的可行性;建立非共线非线性超声检测试验系统,发现LY12铝合金及SiCp/Al试样内部的波型转换与波束混叠现象;利用非共线技术的空间可达、波型转换及频率方向可控等性质,成功剔除了非线性的试验来源,从试验上证明该方法能够观测试样内部的非线性,具备检测SiCp/Al试样均匀性的潜力。试验方法与结果为进一步研究非共线混叠波与粉末铝基复合材料均匀性的相关关系及扫查方法奠定基础。     

飞机复合材料损伤无损检测方法及其选择

随着复合材料在飞机上的广泛应用,其损伤检测和修复问题变得越来越突出。论文介绍了飞机复合材料的损伤特征和可用于飞机复合材料损伤无损检测的目视、敲击、阻抗、谐振、超声、射线照像、红外热图和声发射等检测法,并结合实际介绍了不同类型复合材料结构和缺陷检测方法的选择。     

飞机多层结构中裂纹的定量检测及分类识别

对飞机机身多层结构中的缺陷进行定量检测是无损检测领域的一个难点,脉冲涡流是目前有效的能对这种类型缺陷进行定量检测的技术。采用时频分析的方法实现了对飞机结构中出现的裂纹的定量检测。针对脉冲涡流在裂纹分类中存在的识别正确率较低的问题,提出一种新的称为频谱分离点的缺陷识别方法,提高了缺陷分类识别的正确率,理论分析与试验结果相一致,验证了所采用方法的正确性。     

碳纤维复合材料孔隙率的超声评价方法研究

孔隙是碳纤维复合材料内部最常见的缺陷之一,空隙的大小及分布对构件的力学性能有重大影响。以热压成型的碳纤维单向增强复合材料为检测对象,利用超声衰减法和非线性超声检测方法对三种孔隙率不同的试样进行对比试验,提取超声检测的特征参量,实现了对碳纤维复合材料孔隙率大小的表征。     

超声成像自动检测系统开发

采用常规超声检测工件时,检测效率低,无法得到直观的检测结果。为了提高超声检测的检测速度、检测适用范围及灵活性,采用电子扫描、动态闸门、信号去噪及成像算法,结合三轴机械扫描架,研制了超声成像自动检测软硬件系统。采用双晶探头对4 mm厚的碳纤维复合材料试样内分层孔缺陷进行了检测扫查试验,对检测系统的性能进行了初步验证。通过对-6 dB法成像矩阵数据进行双线性插值法的方式,对碳纤维复合材料分层孔缺陷进行定量分析,孔缺陷面积定量误差降低了6%～7%,直径定量误差降低了3%～4%,有效提高了缺陷定量精度。试验结果表明所研制的系统能够实现对试件内缺陷信号特征提取及成像,满足检测的要求。     

碳纤维复合材料孔加工研究现状

根据碳纤维复合材料的特性和制造加工中存在的问题,综述了碳纤维复合材料孔加工时加工工艺、钻头几何参数及其材料、机床振动、材料制备缺陷等因素对钻削加工损伤(尤其是分层损伤)的影响和抑制方法、钻削建模与仿真以及叠层孔加工等方面的研究最新进展,重点关注了钻削诱导的分层损伤形成机理以及一些特殊工艺,如振动辅助钻削、螺旋铣削孔加工、磁性胶体垫板孔加工技术和高速钻削技术等对碳纤维复合材料孔加工质量改善效果。     

Thrust force and delamination of core-saw drill during drilling of carbon fiber reinforced plastics (CFRP)

Due to the inherent anisotropy and inhomogeneous nature of polymer-based composite materials, their cutting mechanism differs in many respects from conventional metallic materials. Amongst all machining operations, drilling using a twist drill is the most commonly applied method for generating holes for riveting and fastening structural assemblies. Most of the previous research correlates the drill geometry and feed rate to thrust force and delamination on the performance of a twist drill. The Taguchi method has been used to solve many engineering problems. In this investigation, drilling-induced thrust force and delamination by core-saw drill during drilling CFRP laminates were selected as quality character factors to optimize the drilling parameters to obtain the smaller-the-better characteristics. For thrust force and delamination quality character factors, the optimum conditions in drilling were also A₁B₁C₃, (i.e., diameter ratio = 0.55, feed rate = 8 mm/min and spindle speed = 1,200 rpm).     

Application of grey fuzzy logic for the optimization of drilling parameters for CFRP composites with multiple performance characteristics

Carbon Fibre Reinforced Plastic (CFRP) composite materials have potential applications in various domains. In machining, drilling is essentially required to join different structures. But CFRP drilling poses many problems that decrease the quality of holes. In this paper, Taguchi’s L₂₇ orthogonal array is used to perform drilling of CFRP composite plates. To improve the quality of the holes drilled, the optimal combination of drilling parameters is chosen using grey relational analysis. Grey fuzzy optimization of drilling parameters is based on five different output performance characteristics, namely, thrust force, torque, entry delamination, exit delamination and eccentricity of the holes. Analysis of variance (ANOVA) is used to find the percentage contribution of the drilling parameters and found that feed rate is the most influential factor in drilling of CFRP composites.     

Comparison between response surface methodology and radial basis function network for core-center drill in drilling composite materials

Drilling using twist drill is the most frequently used secondary machining for fiber-reinforced composite laminates and delamination is the most important concern during drilling. The drill design and drilling parameters associated with thrust distribution on the drilling-induced delamination are presented. The core-center drill has been found to be more advantageous than the core drill in reference and practice experiences. Response surface methodology (RSM) is a very practical, economical, and useful tool for the modeling and analysis of experimental results using polynomials as local approximations to the true input/output relationship. Due to the radial basis function network’s (RBFN) fast learning speed, simple structure, local tuning, and global generalization power, researchers in the field of manufacturing engineering have been using RBFN in nonlinear manufacturing studies. The present paper compares these two techniques using various drilling parameters (diameter ratio, feed rate, and spindle speed) to predict the thrust force for a core-center drill in drilling composite materials. The obtained results indicated that RBFN is a practical and an effective way for the evaluation of drilling-induced thrust force.     

Scanning of the internal structure part with laser ultrasonic in aviation industry

The detection of internal defects is a major production and safety issue for the newest generations of aircraft. New materials and manufacturing processes in the aircraft industry demand efficient quality assurance in manufacturing and inspection in maintenance. Advanced metallic material processes (titanium) are used or developed for the production of heavily loaded flying components (in fan blade construction). The inspection of these parts mainly made out of titanium (or CFRP) requires the determination of the percentage of bonded grain sizes around 10-30?μm. This is primarily due to the advantages of a high signal-to-noise ratio and good detection sensitivity. In this article, a diagnosing method of the blade interior by means of the laser ultrasonic is presented. Identification of small fatigue cracks presents a challenging problem during nondestructive testing of fatigue-damaged structures. Laser ultrasonic is a technique that uses two laser beams; one with a short pulse for the generation of ultrasound and another with a long pulse or continuous coupled to an optical interferometer for detection. The results of research of the internal blade structure are presented.     

Drilling-induced damage in uni-directional glass fiber reinforced plastic (UD-GFRP) composite laminates

Uni-directional glass fiber reinforced plastic (UD-FRP) composite materials are a feasible alternative to structural members that bear loads in only one direction. FRP composite materials have excellent properties in the direction of the fibers. Drilling- induced damage acts as an inhibitor to their application, as the holes act as stress concentration sites for failure under loading. The present study is an attempt to study the influence of drilling-induced damage on the residual tensile strength of uni-directional composite laminates and to propose a mathematical model correlating the residual strength with the drilling parameters. A finite element model (FEM) is also developed to study the drilling-induced damage in composite laminates.     

Experimental characterization and finite element modeling of critical thrust force in cfrp drilling

Composite laminates are used in many applications in ae-rospace/defense industries due to their high strength-to-weight ratio and corrosion resistance properties. In general, composite materials are hard-to-machine materials which exhibit low drilling efficiency and drilling-induced delamination damage at exit. Hence, it is important to understand the drilling processes for composite materials. This article presents a comprehensive study involving experimental characterization of drilling process to understand the cutting mechanism and relative effect of cutting parameters on delamination during drilling of carbon fiber reinforced plastic (CFRP). Thrust force and torque data are acquired for analyzing the cutting mechanism, initiation and propagation of delamination, and identification of critical thrust force below which no damage occurs. An FE model for prediction of critical thrust force has been developed and validated with experimental results. A [0/90] composite laminate is modeled simulating the last two plies in exit condition and a thin interface layer is inserted in between the plies to capture delamination extent. The tool geometry is modeled as “rigid body” with geometric features of twist drill used in experiments. The tool is indented on the workpiece to simulated tool feeding action into the workpiece. The FE model predicts the critical thrust force within 5% of the experimentally determined mean value.     

ROTARY ULTRASONIC MACHINING OF CARBON FIBER-REINFORCED POLYMER: FEASIBILITY STUDY

Carbon fiber-reinforced polymer (CFRP) has been widely used in aircraft components, automotive parts, and sporting goods. Hole machining is the most frequently employed operation of secondary machining for fiber-reinforced composites. However, challenges (delamination, splintering, burr, short tool life, low machining precision, and low surface quality) still remain for their widespread applications. Rotary ultrasonic machining (RUM) is a non-conventional machining process that has been used to drill holes in composite materials. However, it has not been used to drill this type of CFRP. In this article, RUM is introduced into drilling holes in this type of CFRP for the first time. The feasibility to machine carbon fiber-reinforced epoxy using RUM is investigated experimentally. Chips, edge chipping, surface roughness, tool wear, and thrust force were measured. Effects of RUM process variables (rotation speed, vibration amplitude, and feedrate) on thrust force and surface roughness were studied. Results showed that RUM could be used to drill holes in CFRP with high productivity and low tool wear. A better surface was produced by higher rotation speed and lower feed rate.     

Evaluation of a novel approach to a delamination factor after drilling composite laminates using a core–saw drill

Drilling is the most commonly applied method for hole making of fiber-reinforced materials owing to the need for structure joining. Delamination is the most common defect during drilling because of the heterogeneity of both the fibers and the matrix. The delamination, in general, is an irregular shape and size, containing long and fine breaks and cracks at the exit of the drilled hole, especially in the drilling of carbon-fiber-reinforced plastic (CFRP). On the other hand, a core–saw drill is designed to reduce the threat of chip removal in drilling composite materials. Since the thrust force of core–saw drill is distributed toward the periphery, the core–saw drill allows a larger critical thrust force than the twist drill at the onset of delamination when drilling composite materials. The aim of this paper is to present a novel approach of the equivalent delamination factor (F _ed) to characterize drilling-induced delamination using a core–saw drill and compare it with the adjusted delamination factor (F _da) and the conventional delamination factor (F _a). The experimental results indicated that the F _ed obtained is considered suitable for characterizing delamination at the exit of a hole after drilling CFRP.