新型分形平面涡流传感器裂纹检测机理研究

For the problem of poor performance of traditional flexible planar eddy current sensors in special direction and short length crack detection, the fractal geometry and information entropy theories will be used to optimize the performance of flexible planar eddy current sensors. The main contents of the research include the following aspects: (1) A series of novel kinglike fractal curves will be proposed by self-similarity iteration from a circle initiator, and the fractal dimension and other geometry, such as perimeter, area and so on, of new geometry will be studied. (2) The FEMs of eddy current sensors designed by Koch curve and new fractal geometry will be developed, and the change rule of eddy current distribution induced by eddy current sensors for different factors will be studied by the method of information entropy. (3) The two series of fractal curve will be designed by three types eddy current sensors, which include absolute measurement, differential excitation and differential measurement, and the change rule of sensor’s performance of different factors will be studied by the experiment method. (4) The relationship between the eddy current distribution information entropy and performance of eddy current sensors influenced by different factors will be investigated. The eddy current conditioning method based on fractal geometry and the eddy current distribution evaluation method based on information entropy will provide theoretical reserve and optimization guidance in flexible eddy current sensor design in the areas of nondestructive testing and structure healthy monitoring.

本课题针对传统柔性平面涡流传感器对特殊方向短裂纹检测性能不足的缺点，拟采用分形几何与信息熵理论，优化柔性平面涡流传感器的性能。主要研究内容包括：(1)提出一系列以圆为初始子通过自相似迭代生成的环状分形几何图形，并研究该系列图形的分形维数和其它几何特征，如周长、面积等；(2)建立科赫曲线和新几何图形构成的平面涡流传感器的有限元仿真模型，并以信息熵作为涡流分布定量评价指标，探究平面涡流传感器在试件中感应出涡流分布随各影响因素的变化规律；(3)设计绝对测量、差动激励和差动测量方式的由两个系列分形几何图形构成的平面涡流传感器，并通过实验研究传感器性能随检测条件和线圈几何特征的变化规律；(4)研究传感器感应出涡流分布信息熵与其对裂纹检测性能之间的相关性。基于分形几何和信息熵的涡流分布调理方法和定量评价方法，为无损检测和结构健康监测领域的平面柔性涡流传感器设计提供理论储备和优化指导。

机械装备由于功能的需要，其零部件结构越加复杂，由于高温、高腐蚀、高应力等极端服役条件，导致该类零部件失效的概率增加，严重威胁装备服役的安全性，故对其进行无损检测与评价意义重大。为解决传统平面柔性涡流传感器对特殊方向裂纹探测时漏检率高的问题，本项目提出一种新型分形曲线，用于平面柔性涡流传感器电磁感应新结构的设计中，以提高平面柔性涡流传感器对各个方向短裂纹探测的一致性。针对这一新方法，在确立项目所提新型分形涡流传感技术的基础上，进行了系列研究工作：1) 建立了新型分形曲线生成的迭代函数系统并研究了其几何特征；2) 研究了基于新型分形曲线和科赫分形曲线作为线圈结构的绝对式、差激励、差测量等多种平面柔性涡流传感器的裂纹检测性能与机理；3) 建立了基于信息熵、交叉熵、相对熵、JS散度涡流场能量在不同视角下分配的均匀程度的定量评价指标，并研究了不同激励线圈的涡流场随激励频率和提离距离变化时的演化规律；4) 确立了涡流裂纹相互作用效率的涡流场定量评价方法。项目的研究成果有望为平面柔性涡流传感器的性能评价与电磁感应结构的设计提供新方法与新思路。