【作者】 陈佩华；

【导师】 周泽魁； 黄平捷；

【作者基本信息】 浙江大学 ， 控制科学与工程， 2014， 博士

【摘要】 涡流检测技术在航空航天、核工业、石油化工、机械制造等领域应用广泛。本文结合国家自然科学基金项目,围绕板状导电结构缺陷识别和定量化检测开展理论和实验研究,提出了基于远场涡流和常规涡流的复合式涡流检测方法,研究复合式检测系统正向场量数值建模、检测信号与被测材料间映射关系建立、反向缺陷类型判定及尺寸参数预估等关键技术,自主设计研发了新型的复合式涡流检测设备,实现了板状导电结构不同深度缺陷的有效检测,完成了实验验证。主要研究工作和创新点如下：1.针对板状导电结构表面、亚表面和深层缺陷检测的实际需求,提出了平板远场和常规涡流双模复合式检测方法。利用电磁数值技术,研究平板导体检测系统中涡流、能量、磁力线、磁通密度等电磁场量的分布机理与变化特性。计算求解对应不同检测参数的各类电磁场量分布变化形式,分析总结复合式检测系统中被测导体板材质属性、板中缺陷位置、形状等参数对系统中关键电磁场量分布及其变化的影响规律。研究表明利用电磁场量叠加与相位滞后特性的双模复合式板材检测方式可提高系统的表层缺陷检测精度和深层缺陷检测能力,场量分析结果验证了对板状导体材料进行复合式涡流检测的可行性,为检测系统研发和缺陷参数定量化分析奠定了理论基础。2.研究了平板远场／常规复合式涡流检测信号特征,建立了探头检测值与被测材料属性、激励频率、提离距离、缺陷形状、位置、尺寸等关键因素间的映射关系。研究结果表明,综合两类不同涡流检测信号有助于提高系统的缺陷检出及缺陷位置判定能力,利用常规涡流探头阻抗信号中电阻和电感分量对缺陷不同方向尺寸变化具有不同敏感性的特点可提高系统对缺陷尺寸参数的反演精度。研究的涡流检测信号变化规律与涡流电磁场量分析结果吻合,检测信号响应特性规律的研究可为系统开发和缺陷反演推算工作提供正向指导。3.针对无损检测中板状导电结构缺陷类型辨别与缺陷尺寸预估的检测需求,根据探头检测值与缺陷参数间的内在关联与映射关系,利用双模检测信号的互补特性,提出了基于支持向量机和广义回归神经网络技术的复合式涡流检测反演方法。采用群智能算法对分类和回归模型中相关参数进行优化,实现了小样本条件下板状导电结构表层与深层缺陷类型的有效判定和缺陷参数的定量评估。4.研究开发了综合平板远场涡流与常规涡流技术的复合式涡流检测系统。系统采用复合激励方式,同步采集和处理探头双模检测信号,有效克服了单一检测方法深层缺陷检测信号响应微弱或缺陷位置识别不精确等的局限性。系统可实现板状导电结构表层、下表层缺陷的同步扫描检测。相比于常规涡流,复合式系统大大拓宽了平板导体的缺陷可测范围,对导体板中深层缺陷的检测能力与报道的国外远场涡流系统相当,具有重要的工程应用价值。更多还原

【Abstract】 Eddy current nondestructive testing is widely used in the fields such as aviation, the nuclear industry, petrochemical engineering, and machine manufacture. Based on defect recognition and quantitative estimation, a theoretical and experimental study on fault detection in slab-like conductors was performed using the eddy current technique. The project was supported by the National Natural Science Funds.The proposed test method combines a plate remote-field eddy current technique and the common eddy current technique. The numerical modeling of the electromagnetic field、the establishment of the mapping between the detection signal of the probe and the materials being tested、the type determination and size assessment of the flaw etc such key technology were studied in the compound testing system. A new compound detecting device was built and experimentally verified. The device realized flaw detection at different depths on the conductor plate. The various aspects of the study covered in the paper and the innovative concepts presented are listed below:1. To meet the practical needs of fault detection on plate conductive structures in the surface, subsurface, and deep-seated regions, a dual-mode compound testing system was proposed that synthesizes the plate remote-field eddy current technique and the common eddy current technique. Take the advantage of electromagnetic numerical techniques to describe the distribution mechanism and characteristics of the electromagnetic field, such as eddy current, energy, magnetic lines of flux, magnetic flux density, in the system. The distribution form of the field was calculated for different detection parameters. The regular pattern of the key electromagnetic field’s distribution form effected by the key parameters of the tested conductor plate, such as the properties of the measured material, the shape, position and size of the defect etc was analysed and summarized. Dual-mode compound testing system improves the precision of defect detection on the surface, as well as the detectability of deep-seated defects, by utilizing the characteristics of field superposition and phase lag. The analyse of the electromagnetic field enabled the validation of the compound testing system used on conductor plate, and established the theoretical foundation for system design and quantitative inversion estimate of the flaw’s parameter in the compound eddy current testing.2. The property of the detection signals from the common and plate remote-field eddy current techniques was analyzed. Establish the mapping between the detection signal of the probe and the key factors in the testing such as the properties of the measured material, the excitation frequency, the lift-off, the shape, position and size of the defect etc. The results of the experiment show that, synthesize different type of eddy current detection signals can improves the ability of the fault detection and the fault’s position judgement. Taking advantage of the common eddy current detection signal’s characteristics that the resistance and the inductance of the probe has different sensitiveness to the change of the fault’s size in different directions, can improves the precision of inversion on fault’s size. This enabled the validation of the numerical analysis of field quantities. The study on the tendency of the detection signals can provide guidance for system design and quantitative inversion estimate of the flaw’s parameter in the compound eddy current testing.3. To meet the practical needs of type determination and size assessment of the flaw on plate conductive structures in the NDT testing, According to the intrinsic connection between the probe detection signal and the parameters of the flaw, using the complementary characteristics of the common eddy current signal and the plate remote-field eddy current signal, a compound inversion method was proposed what based on Support Vector Machine and generalized regression neural network technique. Some parameter of the classification model and the estimation model were optimized by swarm intelligence algorithm. This enabled a valid judgement of flaw type and quantitative assessment of flaw size in the plate conductive structure for small sample.4. The compound detecting device was built which combined plate remote-field eddy current technique and common eddy current technique. The compound excitation mode was adopted, and the dual-mode detection signal was collected and analyzed synchronously. This approach overcomes the limitations of single-detection systems, such as weak responses from deep defects or the inaccurate estimation of the defect position. Thus, we realized flaw detection at different depths on the conductor plate synchronously. Compared with common eddy current detection devices, the combined system greatly broadens the range in which flaws can be detected in a plate conductor. The detectability of flaws in deep-seated regions of the system matches the detectability of reported plate remote-field eddy current detecting systems abroad, and thus the detection system can be expected to have important applications in engineering.更多还原