Accession Number:

ADA279871

Title:

Eddy Current for Detecting Second-Layer Cracks Under Installed Fasteners

Descriptive Note:

Final rept. 30 Sep 1991-31 Oct 1993

Corporate Author:

SOUTHWEST RESEARCH INST SAN ANTONIO TX

Report Date:

1994-02-01

Pagination or Media Count:

110.0

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 WLMLLP, 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.

Subject Categories:

  • Transport Aircraft
  • Couplers, Fasteners and Joints
  • Electricity and Magnetism

Distribution Statement:

APPROVED FOR PUBLIC RELEASE