Research of Evaluation of Small Change in Material Construction by Means of Electromagnetic Method

该研究旨在开发一种电磁方法来评估材料结构的无损微小变化。主要研究结果总结如下：研究了不同性质的薄层圆柱形导体上的电磁问题。这种导体正在模拟一种电镀材料。从理论上分析了沿导体纵轴均匀流动的交流电流在表面层和内圆柱体中产生的电磁场，得到了导体表面的交流电势降。此外，考虑到电磁感应对实际测得的交流电位差的影响，将电位差测得的电动势作为互感纳入修正的电位差理论分析中。对工程镀铬圆柱表面的交流电位降进行了测量，得到了交流频率与交流电位降的关系。提出了反问题分析方法。在分析中，镀层厚度、电镀试样的电磁特性和互感均为未知数。将理论计算的交流电势降与实测的交流电势降进行比较，以确定未知因素。通过分析，对涂层厚度、电磁性能和互感进行了评价。评价结果表明，该方法是有效的。

The research has been performed to develop an electromagnetic method for evaluating nondestructively small change in material construction. The main results are summarized as follows :1. The electromagnetic problems on a cylindrical conductor coated with a thin layr, the electromagnetic property of which is different, were treated. Such a conductor is modeling an electroplated material. The electromagnetic fields induced in the surface layr and the inner cylinder by AC current which uniformly flows along the longitudinal axis of the conductor were theoretically analyzed, and the AC potential drops on its surface were obtained. Furthermore, by considering the effect of the electromagnetic induction upon the AC potential drops measured actually, the electromotive force induced on potential measuring proves was included into the modified theoretical analysis of potential drops as the mutual inductance.2. The AC potential drops on the surface of the cylinder coated with chromium electroplated for engineering purpose were measured, and the relation between the AC frequency and the AC potentioal drops was obtained.3. The inverse problem analysis was proposed. In the analysis, coating thickness, the electromagnetic properties of the electroplated specimens and the mutual inductance are treated as unknowns. The theoretical AC potential drops computed are compared with the AC potential drops measured to determine the unknowns.4. By the analysis, the coating thickness, the electromagnetic properties and the mutual inductance were evaluated. The results obtained from the evaluation showed that the present method is valid.