【作者】 王晶；

【导师】 潘红良； Noritaka Yusa；

【作者基本信息】 华东理工大学 ， 机械设计及理论， 2013， 博士

【摘要】 在工业科技以及经济高速发展的当今社会,大量导电结构设备被用于各种工业领域,如航空航天,核能发电等。随服役时间的增加,环境影响使某些缺陷形成于这些导电结构设备中,如腐蚀性裂纹。为了确保这些设备的安全性和使用高效性,有必要定期对其实施无损检测。涡流检测是一种非接触的无损检测方法,具有操作简单、快速等优点。本文在分析了国内外涡流检测缺陷技术研究现状的基础上,针对涡流检测应用中有关裂纹的反演模型优化和金属板深层缺陷检测方法的问题,进行了研究。以SUS316不锈钢板上的应力腐蚀裂纹为试样,讨论了应力腐蚀裂纹的反演模型优化。提出了两种新的模型：基于各向异性导电性应力腐蚀裂纹模型和基于分布导电性的应力腐蚀裂纹模型。连同基于均匀导电性应力腐蚀裂纹模型,有限元分析得出三种模型的模拟信号,将这些模拟信号与实验信号比较。实验信号由十字型差动探头在50kHz和100kHz时收集。研究表明：尽管应力腐蚀裂纹的等效宽度和等效电导率随频率改变,等效电阻基本不随频率变化。应力腐蚀裂纹具有一定导电性,甚至可达4%的不锈钢板电导率。基于分布导电性的裂纹模型能最有效表达应力腐蚀裂纹的特性。分布导电性裂纹模型的裂纹本体电导率应小于等效电导率,而裂纹边缘电导率应大于等效电导率。裂纹尺寸大则导电性边缘深度也大。以三组分别位于SUS304、SUS316L和Incone1600金属板的热疲劳裂纹为试样,讨论了热疲劳裂纹的反演模型优化。提出了基于均匀导电性的热疲劳裂纹模型和基于带扰动性电磁性能边缘的热疲劳裂纹模型。分别将两种裂纹模型得出的模拟信号和实验信号比较。实验信号由十字型差动探头在三种检测频率下收集。研究发现：热疲劳裂纹的等效电导率很小,具有强烈的非导电性。对于位于SUS304金属板上的热疲劳裂纹,利用带扰动性电磁性能边缘的裂纹模型得出的模拟信号,比基于均匀导电性的裂纹模型得到的模拟信号,更接近于实验信号。尺寸大的热疲劳裂纹其最佳磁性层宽度也大。研究了金属板深层缺陷的远场涡流检测方法。提出了新的评估方法,即以金属板表层缺陷为参考对象,对远场涡流检测金属板深层缺陷的应用进行讨论。从实验和仿真两方面,具体分析了线圈放置方向、检测频率、线圈间距以及金属屏蔽物几个因素对远场涡流检测金属板深层缺陷的能力的影响。同时评价了背景噪音对信号的影响。结果表明：相比立式线圈,采用卧式线圈更有利于远场涡流检测金属板深层缺陷的检出率的提高。使用低频率以及采用大线圈间距可以提高远场涡流检测金属板深层缺陷的能力。最后从电磁场作用原理出发,揭示了线圈放置方向、检测频率、线圈间距影响远场涡流检测金属板深层缺陷能力的原因。更多还原

【Abstract】 Conductive materials are widely used in kinds of industry, like aerospace, nuclear power fields and so on. It is important to guarantee the safe running of conductive structures. Therefore carrying out periodical non-destructive testing is necessary for these conductive components. Eddy current testing distinguishes itself by fast scanning, no need for couplant and so on. This study focuses on numerical modeling of nature cracks (stress corrosion crack, thermal fatigue crack) based on eddy current signal and detection of back-side flaw of plate by remote field eddy current testing.Firstly, numerical modeling of stress corrosion crack (SCC) is discussed. SCCs artificially introduced into a SUS316plate are prepared for the research. We gather the eddy current signals by a plus point probe with50kHz and100kHz. The profiles of SCCs are revealed by destructive tests. Two kinds of model of SCC are proposed, model with anisotropic conductivity and model with distributed conductivity. The simulated eddy current signals by these two models and those by model with uniform conductivity are analyzed based on experimental eddy current signals. The results show that the equivalent resistance of a crack is almost unchanged even though the equivalent conductivity and equivalent width depend on the exciting frequency. SCC is conductive, even in some cases equivalent conductivity of SCC could be4%base materials’conductivity. Model with distributed conductivity is the best one showing the electromagnetic characteristics of SCC among these three models. Large cracks tend to have deeper high conductive edges.Secondly, numerical modeling of thermal fatigue crack (TFC) is studied from view point of eddy current simulation. Three group TFCs are respectively artificially introduced into SUS304, SUS316and Incone1600plates. Eddy current testing is carried out to gather signals by a plus point probe and destructive test is performed to confirm the true profiles of the cracks. Two kinds of model of TFC are proposed, model with uniform conductivity and model with electromagnetic variation in the vicinity of crack. We compare the simulative signals by these two models with experimental signals. The results reveals that TFC is much less conductive than SCC if they are assumed to have uniform conductivity inside. Taking consideration of magnetization induced by the thermal fatigue process enables eddy current signals to be analyzed more quantitatively. Large cracks tend to have wider magnetic layers. Thirdly, Detection of back-side flaw of plate is discussed by remote field eddy current testing. Effects of several factors, including orientation of coils, exciting frequency, coil interval, shields on ability of detection of back-side flaw of plate are analyzed by simulations and experiments. The results show that utilization of coils whose axes are parallel to surface of the plate, enhance the ability of detection on the back-side flaw of plate, comparing with use of coils whose axes are perpendicular to surface of the plate. Ability of detection on the back-side flaw of plate could be compared to ability of detection on near-side flaw of plate as long as the relative low frequency and relative far coil interval are used at the same time even no shield is involved. Numerical investigations are conducted to reveal the fundament from view point of magnetic flux density.更多还原