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脉冲涡流是一种可以对飞机多层铆接结构中缺陷进行有效检测的无损检测技术。本文通过研究低频涡流与脉冲涡流检测技术,设计和实现了圆柱形差分检测传感器,对铆钉周围出现的缺陷进行了检测。通过轴向扫描时获得的峰值曲线对缺陷的轴向宽度进行了定量检测。通过缺陷的瞬态感应电压信号,利用峰值、过零时间等特征量对缺陷造成的不连续性和损耗程度进行了检测分析。试验结果证明文中设计的圆柱形差分传感器可以对多层铆接结构中的缺陷进行有效检测,低频脉冲技术在飞机铆接结构缺陷的检测中具有很好的使用前景。 相似文献
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脉冲涡流技术是一种可以对飞机多层结构中缺陷实施有效检测的方法。交变磁场测量技术是一种精确测量表面裂纹的非接触式无损检测方法。提出了脉冲涡流磁场测量(PECFM)技术,并对其进行了理论分析。在设计了相应传感器的基础上,对多层铝板结构中的缺陷进行了检测实验,实验结果与理论分析相一致。实验证明PECFM技术可以有效地实现多层结构中缺陷的识别与定量检测。可以预见,PECFM技术将会在无损检测领域中发挥很大的作用。 相似文献
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传统脉冲涡流检测技术对缺陷的检测灵敏度不高,需采用差分的方法来增强缺陷信息.本文提出了一种改进型的脉冲涡流无损检测方法,其无需差分就可以对缺陷进行定量,具有较大的理论价值和应用价值,采用改进的脉冲涡流技术对腐蚀缺陷的深度和体积进行了检测,并采用一种新的"频谱分离点"的腐蚀缺陷识别方法,提高了腐蚀缺陷分类识别的正确率. 相似文献
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对腐蚀缺陷的边缘进行准确识别是无损检测领域的一个难点,直接影响着腐蚀成像的效果.采用阵列脉冲涡流对腐蚀缺陷进行了检测,针对传统无损检测中只从时域提取特征造成识别正确率较低的问题,根据脉冲涡流具有丰富频率成分的特点,从时域和频域分别提取特征量,提出了一种基于主成分分析的阵列脉冲涡流腐蚀缺陷边缘识别方法,提高了缺陷边缘识别的正确率. 相似文献
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Time-Frequency Analysis of Pulsed Eddy Current Signals 总被引:9,自引:0,他引:9
M. S. Safizadeh B. A. Lepine D. S. Forsyth A. Fahr 《Journal of Nondestructive Evaluation》2001,20(2):73-86
Detection and measurement of the material loss due to corrosion in aircraft fuselage lap splices are of great importance to life management of ageing aircraft. Pulsed eddy current (PEC) techniques have shown the potential to fully characterise these structures. However, variations in the probe lift-off, the interlayer gaps and material thinning produce similar PEC signals, making signal interpretation very difficult. This paper describes time-frequency analysis algorithms applied to pulsed-eddy current signals from lap-joint specimens containing simulated flaws. The effect of probe lift-off, interlayer gap, and material thinning on PEC signals is examined in three-dimensional space (amplitude-time-frequency). This study shows that the time-frequency analysis of PEC signals provides specific visual patterns that can be related to the interlayer gap, lift-off, and material loss. 相似文献
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航母作为人类有史以来最大的军事装备,是一项复杂的巨系统工程,使用的材料种类繁多,工作环境复杂。针对航母使用的苛刻环境条件,介绍了航母用材的通用选材原则,并且对船体结构材料、管路及附件材料的特殊选材要求分别进行了阐述。介绍了航母用材的腐蚀特点:一是腐蚀环境多样,防护要求高,防腐设计难度大;二是系统组成复杂,设备数量多,腐蚀故障影响大;三是舱室结构复杂,施工空间小,防腐修理难度大。针对腐蚀特点提出了航母用材的腐蚀控制需求,从腐蚀控制技术体系、腐蚀控制手段、材料防腐蚀性能3个方面阐述了航母用材的不足和差距,并针对性地提出了航母用材腐蚀控制的建议和对策。 相似文献
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为了有效地从腐蚀防护角度为飞机异种金属选材提供指导,针对飞机特定的服役环境,通过有限元仿真和腐蚀实验研究飞机典型搭接结构的腐蚀行为。对铝合金、复合材料及搭接件进行了实验室的周浸实验,然后通过极化曲线测量实验、宏微观形貌的观察、疲劳测试、XRD等表征手段研究7B04铝合金与CCF300/QY9511复合材料搭接件的电偶腐蚀规律,并以极化曲线测得的电化学参数为边界条件,建立了搭接件的腐蚀仿真模型。结果表明,在周浸实验0周期和10周期后,铝合金的自腐蚀电位和自腐蚀电流密度分别为-802 mV和2.357×10-7 A/cm2,-872 mV和1.477×10-6 A/cm2,复合材料则分别为-240 mV和6.217×10-7 A/cm2,-98 mV和2.286×10-7 A/cm2,随着腐蚀周期的延长7B04铝合金材料呈现自腐蚀速率加快、自腐蚀电位负移的变化趋势,而复合材料呈现自腐蚀电位正移、自腐蚀速率缓慢增大的变化趋势;搭接件腐蚀产物逐渐增多,腐蚀程度越来越严重;疲劳寿命随着腐蚀周期的延长而降低;随着腐蚀周期延长,腐蚀坑深度逐渐增大;腐蚀的产物包括Al(OH)3,Al2O3,AlCl3;搭接件仿真结果与加速腐蚀实验后的结果具有良好的一致性。该研究给出了飞机典型搭接结构的易腐蚀部位,揭示了电偶腐蚀规律,为飞机结构的腐蚀防护指明了方向。 相似文献
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《IEEE transactions on instrumentation and measurement》2006,55(5):1620-1627
Critical aircraft structural components, such as wings and fuselages, are exposed to harsh environments that vary considerably in temperature and moisture content. In most cases, the corrosion is hidden under paint and primer and cannot be visually detected. The initiation of corrosion is preceded by the presence of corrosion precursor pitting. Near-field millimeter-wave nondestructive testing (NDT) methods have been successfully used for detecting corrosion precursor pitting in exposed as well as painted aluminum substrates. However, near-field millimeter-wave measurements are susceptible to clutter that may mask indications of small defects such as pitting. Standoff distance variation produces an unwanted intensity gradient on an image and may be considered the most undesired clutter-producing effect. This paper presents a differential millimeter-wave probe consisting of a pair of radiating apertures. It is shown that the differential nature of this probe tends to significantly reduce the undesired effect of standoff distance variation, thereby enhancing probe detection sensitivity. Furthermore, when this probe is used for the purpose of millimeter-wave imaging, it produces defect indications with unique features that help in distinguishing the defect from noise. This dual differential probe was used for detecting corrosion precursor pitting. The design of the probe and the results of detecting various pittings are presented in this paper. 相似文献
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基于光纤光栅的铝合金腐蚀监测研究 总被引:1,自引:1,他引:0
铝合金腐蚀是导致航空器性能下降的主要原因之一.铝合金腐蚀初期以点蚀为主,体积几乎不改变,结合铝合金腐蚀的这一特点,设计了基于光纤光栅的薄片型和应力束缚型两种腐蚀监测结构,对铝合金腐蚀进行了实验研究.腐蚀发生前,对光纤光栅施加一定预应力,随着腐蚀的发生应力被逐渐释放,通过测量传感波长的漂移量就可以得到铝合金的腐蚀情况.实验表明,基于光纤光栅的腐蚀监测结构能够真实的反应铝合金的腐蚀情况,并且光纤光栅本身具有体积小、抗电磁干扰、耐腐蚀的特点,非常适合于航空器的铝合金腐蚀监测. 相似文献
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In this study, cadmium sulfide (CdS), polypyrrole (PPy) nanowires, and their heterojunctions have been electrochemically synthesized.
Morphology of the nanowires has been investigated by scanning electron microscopy. Energy dispersed X-ray, X-ray diffraction,
UV–Vis, and FTIR analyses have been used to confirm structure of both CdS and PPy nanowires. For the first time with this
study, CdS/PPy nanowire heterojunctions have been integrated into photoelectrochemical (PEC) cells. It has been also demonstrated
that PEC performance of the nanowires was strongly function of production conditions, such as deposition time and voltage.
The maximum power conversion efficiency of the CdS nanowires obtained in this study was 1.36%. Moreover, efficiencies of the
CdS/PPy nanowires have been reached to 5.00%, which makes them very favorable for PEC applications. 相似文献
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A. JAYA U. H. TIONG G. CLARK 《Fatigue & Fracture of Engineering Materials & Structures》2012,35(1):64-73
Aircraft joints feature prominently in aircraft structural degradation; fatigue cracking and corrosion damage are major issues, which can reduce joint strength and degrade service life. Protecting the structure against corrosion usually involves use of highly developed protective coatings – paints and sealants – and, increasingly, the application of corrosion inhibiting compounds (CICs) which retard corrosion principally by penetrating into crevices and cracks, and displacing water. A combination of coatings and CIC use can provide effective corrosion protection, but both interact – in different ways – with joint structural performance and overall system durability. This paper discusses the interaction between these two corrosion protection measures and fatigue performance of joints. The first issue relates to the extent to which application of CICs (or other lubricants) can cause a reduction in the fatigue life of mechanically fastened joints. The CICs are lubricants which will reduce the friction at the faying surface of the joint, and change the load transfer characteristics of the joint. This paper discusses results from a test program assessing the fatigue life and failure mode of simple riveted lap joints; the results show a distinct reduction in fatigue life for joints containing CICs, and the paper discusses the changes thought to be responsible for the reduction. The second issue discussed is the degradation of protective coatings in service. Joints are key locations for coating cracking and failure, because areas such as sheet ends and fastener heads, where displacements are concentrated, may produce concentrated strain in coatings. So far, however, the potential influence of aircraft loading on coating degradation prognostics has received little attention. This paper discusses the role of joint displacement in service as a factor contributing to degradation in aircraft coatings at joints, and argues that this local strain effect, and indeed structural loading history, needs to be considered in predicting and assessing rates of coating degradation. It describes analyses of displacements in aircraft joints, to identify the levels of strain and to identify the roles and relative contributions of the various deflections in the joints. The results indicate the potential for very large strains in coatings. 相似文献
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A. T. Kermanidis A. D. Zervaki G. N. Haidemenopoulos Sp. G. Pantelakis 《Journal of Materials Science》2010,45(16):4390-4400
Laser welding is increasingly used for the fabrication of lightweight and cost-effective integral stiffened panels in modern
civil aircraft. As these structures age in service, the issue of the effect of corrosion on their damage tolerance requires
attention. In this work, laboratory data on the influence of salt fog corrosion on the fatigue behavior of cladded 6156 T4
aluminum alloy laser welded specimens are presented. The experimental investigation was performed on 6156 T4 laser butt welded
sheets. Prior to fatigue testing the welded joints were exposed to laboratory salt fog corrosion exposure for 720 h. The results
showed that the clad layer offers sufficient corrosion protection both on base metal and the weld. Fatigue testing was followed
by standard metallographic analysis in order to identify fatigue crack initiation sites. Crack initiation is located in all
welded samples near the weld reinforcement which induces a significant stress concentration. Localized corrosion attack of
the clad layer, in the form of pitting corrosion, creates an additional stress concentration which accelerates crack initiation
leading to shorter fatigue life relative to the uncorroded samples. The potency of small corrosion pits to act as stress concentration
sites has been assessed analytically. The above results indicate that despite the general corrosion protection offered by
the clad layer, the localized attack described above leads to inferior fatigue performance, a fact that should be taken under
consideration in the design and maintenance of these structures. 相似文献