In the E-2C Hawkeye's wing center section, stress fractures have been
identified in the main beam web section. The cracks occurred in several web section
attachment holes. Previous work, concerned with fatigue data, used a finite element
code to design a specimen which modeled the actual section of the beam at one
particular fastener hole near wing station 49. Acoustic emission testing was used to
determine if crack initiation could be identified. In this work, acoustic emission
techniques were applied to the monitoring of multiple cracks. The E-2C fatigue
spectrum was used to load the specimens but fatigue testing was not an objective.
Specimens were modified by drilling holes and attaching angles that represented the
structural shapes used to attach the section to the wing skin. The original one-hole
configuration and the new multiple hole specimen configuration were tested. The
cap angles were found to create a great deal of noise containing frequency
components below 400kHz. Special high pass filters were fabricated which
eliminated most of this noise. It was shown that linear location could be used to
discriminate between crack growth signals and the filtered noise signals.http://archive.org/details/realtimedetectio00flatLieutenant, United States NavyApproved for public release; distribution is unlimited
