Examination of F/A-18 honeycomb composite rudders for disbond due to water using through-transmission ultrasonics

Abstract

The flight control surfaces of F/A-18 aircraft are composed of carbon/epoxy skin and aluminum honeycomb core composite material that has a known susceptibility to water ingress. The rudder has failed in flight due to moisture induced bond degradation between skin and core. Manual through-transmission Ultrasonic Testing (UT), applied to the rudder surface, currently identifies disbond as a reduction in received signal amplitude. However, water within the honeycomb cells provides significant sound transmission, which may mask disbond. In this study, water was first identified within two in-service rudders using thermography. Precise water locations were then mapped by neutron radiography. Time-base analysis of through-transmission A-scans, obtained using squirter technology, permitted discrimination of cell wall signals from signals that had passed through water within the cells. Examination of received cell wall signal intensities, modeled for disbond in the presence of water, demonstrated potential for identification of disbond even when water was present.

http://dx.doi.org/10.5755/j01.u.66.2.529