基于空间分布熵的电磁脉冲涡流无损检测方法

Pulse eddy current nondestructive testing method based on the spatial distribution entropy

提出了一种估计非铁磁性金属材料表面及内部微小缺陷几何特征的新方法,在一种平面轴对称双线圈的脉冲电流激励下,测量材料表面三维磁通密度的时空分布情况,沿激励线圈法向对称轴计算三维磁通密度模的空间滑动移除模糊熵。研究结果表明,由材料微小缺陷所造成的电导率局部突变会增加磁场空间分布的无序程度,从而引起熵的增加。在一定范围内,缺陷几何尺寸的增加与熵的增加呈单调递增关系,利用该方法可有效检测金属铝板表面及内部的微小缺陷,并估计出缺陷的几何尺寸。

This paper proposes a novel eddy current testing （ECT） t method that allows the estimation of the surface and in- ternal tiny defect geometrical characteristics of non-ferromagnetic metal using spatial distribution entropy. Pulse current is stimulated into a pair of planar and axisymmetric coils and used to measure the spatial distribution of the three dimensional magnetic flux densities on the material surface. Along the normal symmetry axis of the exciting coil, the fuzzy entropy of the module of the three dimensional magnetic flux density is calculated. Both simulation and experiment study results show that the partial conductivity mutation caused by the tiny cracks of the metal might increase the ramdomness in the spatial distribution of the magnetic field and lead to the entropy increasing. The geometric size of the defect and entropy increasing comply with the monotonously increasing function in a certain range. With the aid of this novel method, the tiny cracks, both on the surface of and inside the aluminum plate, can be detected effectively, and the geometric size of the defect is estimated.