Eddy Current for Detecting Second-Layer Cracks Under Installed Fasteners
Abstract
Southwest Research Institute developed an eddy current (EC) laboratory breadboard inspection system to detect second-layer cracks around installed fasteners in two-layer airframe structures with the probe positioned on the first layer (outside surface). Probe design considered both cup- and segment-core configurations as exciter coils and various orientations and positions of sensor coils. Highest sensitivity was obtained with a segment-core exciter covering an 85-degree segment with the sensor oriented normal to the specimen surface and placed near the core outer leg. EC data were presented in two-dimensional color images. The goal of detecting a 2.5-mm second-layer flaw through a first-layer thickness of 6.4 mm was achieved in eight of nine specimen configurations which contained simulated cracks. The specimens included structure geometries containing second-layer edges, first-layer edges, adjacent fasteners, different fastener sizes, different flaw orientations around the hole, and fasteners of different materials (titanium and steel). In fatigue crack specimens supplied by WL/MLLP, where adjacent fasteners were spaced more closely and caused interfering signals, flaw detection was more difficult; however, a 2.5-mm flaw was detected through a 4.5-mm first layer by comparing the signal patterns from adjacent holes. Aircraft, Fastener hole, Two-layer structure, Wing, Eddy current, Nondestructive inspection.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1994
- Accession Number
- ADA279871
Entities
People
- Edith A. Creek
- Gary L. Buckhardt
- Jay L. Fisher
- Robert E. Beissner
Organizations
- Southwest Research Institute