中文摘要：

由于多层金属结构由于服役环境较为恶劣，其结构的亚表面层材质电气性能会出现劣化，直接威胁到大型、复杂装备的安全运转。本文提出一种新型提离交汇点，即脉冲涡流差分信号提离交汇点，并基于该交汇点，提出一种对多层结构亚表面层材质劣化进行检测和评估的新方法。通过理论及实验研究，对本文所提出的新型提离交汇点特性及其对多层结构亚表面层材质劣化评估的灵敏度进行了集中探究。研究发现，与传统磁场信号提离交汇点相比，差分信号提离交汇点对金属部件亚表面层材质劣化灵敏度较大，体现了脉冲涡流差分信号提离交汇点在金属部件亚表面层材质劣化定量评估中的优势。

英文摘要：

Because of the rigorous working environment, Subsurface Material Degradation （SMD） occurs in the stratified metallic structures which are extensively employed in industries such as aerospace and energy fields. This directly influences the angle operation of crucial components in the large-scale complex appara- tus. This paper investigates a new Lift-off Intersection Point （LOI） via theoretical study of Pulsed Eddy Current Testing （PECT）. Following the analysis of the forward problem of the new LOI, a method for e- valuation of SMD in stratified metallic structures is proposed. Through experiments the proposed method displays some advantages. By using it the sensitivity of PECT based on the new LOI to subsurface material degradation is higher than that of the traditional-LOI based PECT, which benefits the quantitative evalua- tion of subsurface material degradation occurred within the practical stratified metallic structures.