Abstract: The remote-field eddy-current (RFEC) technique has been shown to be highly sensitive to cracks and corrosion that are embedded deep in multi-layer aircraft structures. This paper shows the effectiveness of the approach in detecting cracks in double-layered specimens with fasteners, as well as corrosion specimens. The crack specimens, made by Lockheed George Company in 1980, had two layers held together with ten fasteners. The total thickness is 0.356' for Group A and 0.446' of Group B, respectively. Fatigue cracks were made on different layers and at different depths. The corrosion specimens are of 0.063' thick with 0.006' or 0.002' corrosion wall thinning. Another one or two much thicker plates of aluminum are placed on top of one corrosion specimen during a test. All tests were conducted using a newly developed RFEC system that includes a probe specified for inspecting thick plates. The effect of different parameters, such as excitation frequency, excitation to pick-up coil separation distance, and probe to fastener distance, were studied to determine the optimal test parameters. The system will be demonstrated along with the presentation. !1
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机译：摘要：事实证明，远场涡流（RFEC）技术对深深嵌入多层飞机结构中的裂缝和腐蚀非常敏感。本文展示了该方法在检测带有紧固件的双层试样以及腐蚀试样中的裂纹方面的有效性。洛克希德·乔治公司（Lockheed George Company）于1980年制造的裂纹试样有两层，由十个紧固件固定在一起。 A组的总厚度为0.356'，B组的总厚度为0.446'。在不同的层和不同的深度产生了疲劳裂纹。腐蚀试样的厚度为0.063'，腐蚀壁厚度为0.006'或0.002'。在测试过程中，将另一块或两块厚得多的铝板放在一个腐蚀试样的顶部。所有测试均使用新开发的RFEC系统进行，该系统包括专门用于检查厚板的探头。研究了不同参数的影响，例如励磁频率，励磁到拾波线圈的分离距离以及探头到紧固件的距离，以确定最佳的测试参数。该系统将与演示一起进行演示。 ！1
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