平板导体中裂纹缺陷探伤涡流场的求解

SOLUTION OF EDDY CURRENT PROBLEM DUE TO THIN CRACKS IN A PLATE CONDUCTOR

裂纹缺陷是涡流检测中最常遇到的缺陷类型。根据裂纹的特点 ,可以把它近似为一个没有厚度的面缺陷 ,其作用由分布在裂纹面上的等效电流偶极子层代替。使用积分方程法计算其涡流场问题 ,只需要很小的计算量。以前的工作都以无限厚导体为求解对象 ,文中研究了有限厚平板导体 ,结果表明它更加接近涡流检测的真实情况。线圈阻抗的计算值与实验结果进行了比较 ,吻合很好。

A thin opening crack in a plate conductor is much frequently encountered in eddy current nondestructive testing. Considering that the crack thickness is usually very small, it can be taken as a‘surface defect’ with zero thickness. The eddy current field perturbation due to the crack is described as the effect produced by an equivalent current dipole layer located on its surface and the dipole density is found by solving a boundary integral equation.By following a moment method scheme the probe impedance changes due to the crack are evaluated. Because the 3D problem has been reduced to a 2D one, the required computer memory and CPU time are greatly reduced. The numerical predictions are compared with experiments and good agreement is found.