Development of the Electrochemical Fatigue Sensor for Improved Durability Assessment of Military Aircraft - Phase 1

摘要

The Electrochemical Fatigue Sensor (EFS) concept, initially developed by the University of Pennsylvania, has the potential to provide information on the early stages of fatigue damage in structural materials. Consequently, its applicability to inspection of military aircraft is being assessed in a multi- phased program. Phase 1, reported here, - established the feasibility of EFS for aircraft applications. EFS measurements were shown to change systematically as fatigue damage accumulated in aluminum alloy 7075-T73511, 4130 steel, and titanium alloy Ti- 6Al-4V. The EFS electrolyte was demonstrated to be benign to these aircraft alloys. Fatigue microcracks on bare metal specimens were detected as small as 75 micrometers in surface length. EFS measurements were also shown to be feasible on primer-coated aluminum alloys, although with decreased sensitivity compared to uncoated material. Measurements on aluminum alloy with both primer and top-coat were problematic due to the high electrical impedance of these coatings. The feasibility of making EFS measurements: a) with small sensors (5 ml of electrolyte and 1.5 sq cm footprint), and b) within the electromagnetic background noise typical of aircraft hangars was also demonstrated. A companion technology, Electrochemical Impedance Spectroscopy (EIS), was adapted for detection of fatigue damage in aluminum alloy 7075. Unlike EFS, EIS does not require the structure to be loaded since it perturbs the material electrically, instead of mechanically. However, EIS is in other respects less mature than EFS, and its application to steel and titanium-alloys remains problematic.