Accession Number:



Discrimination between Fatigue Cracking and Mechanical Damage in Aircraft Fastener Holes by Eddy-Current Phase Rotation

Descriptive Note:

Technical Report

Corporate Author:

Defence Science and Technology Group Fishermans Bend Victoria Australia

Report Date:


Pagination or Media Count:



Fatigue cracking in metallic aircraft structure often originates at fastener holes and can be detected using the nondestructive inspection technique of bolt-hole eddy-current BHEC testing. BHEC testing is based on detection of a disturbance in the induced current or magnetic field caused by a surface-breaking crack in the bore of the hole. However, if the surface of the hole contains benign mechanical damage or superficial scoring, false positives can be produced leading to potentially unnecessary maintenance on a hole that is otherwise sound. In principle, analysis of the phase of the eddy-current response can assist in distinguishing fatigue cracking from such mechanical damage. In the present work, a systematic BHEC and fractographic study has been conducted by inspecting several hundred fastener holes in ex-service FA-18 aircraft bulkheads, following fatigue testing. The results demonstrate that measurement ofthe relative phase of the eddy-current response provides additional information which can assist in discrimination between genuine cracks and mechanical damage.

Subject Categories:

  • Military Forces and Organizations
  • Mechanics
  • Aircraft

Distribution Statement: