WAVELET-BASED ACOUSTIC EMISSION DETECTION METHOD WITH ADAPTIVE THRESHOLDING Sunil Menon, Jeffrey N. Schoess, Rida Hamza and Darryl Busch Honeywell Technology Center, 3660 Technology Drive, Minneapolis, MN 55418 ABSTRACT Reductions in Navy maintenance budgets and available personnel have dictated the need to transition from time-based to "condition-based" maintenance. Achieving this will require new enabling diagnostic technologies. One such technology, the use of acoustic emission for the early detection of helicopter rotor head dynamic component faults, has been investigated by Honeywell Technology Center for its rotor acoustic monitoring system (RAMS). This ambitious, 38-month, proof-of-concept effort, which was a part of the Naval Surface Warfare Center Air Vehicle Diagnostics System program, culminated in a successful three-week flight test of the RAMS system at Patuxent River Flight Test Center in September 1997. The flight test results demonsirated that stress-wave acoustic emission technology can detect signals equivalent to small fatigue cracks in rotor head components and can do so across the rotating articulated rotor head joints and in the presence of other background acoustic noise generated during flight operation. This paper presents the results of stress wave data analysis of the flight-test dataset using wavelet-based techniques to assess background operational noise vs. machinery failure detection results. Keywords: Acoustic emission monitoring; condition-based maintenance; fatigue crack detection; helicopter usage monitoring system (HUMS); machinery diagnostics; siructural health monitoring; wavelets. 1. INTRODUCTION Providing safe and reliable cargo transport in today's U.S. Navy fleet is a challenging task. The constraints of a severe operating environment (highly corrosive and high structural loads), damage caused by parts refurbishment and replacement, manufacturing flaws, and requirements to extend the operational life of today's fleet are contributing factors. These problems and structural aging effects have required maintenance inspection intervals as short as 10 hr using nondestructive inspection (NDI) monitoring techniques. Fig. 1 is a 3-mm color photograph of a CH-46 rotor head assembly. This very complex assembly has nine major components: rotor hub, connecting link, connecting link pin, pitch shaft, vertical hinge pin, tie bar, pitch housing, blade attach fitting, and blade attachment pin.The rotor head weighs approximately 750 lb, including the three arms and support instrumentation, and is approximately 6 ft in diameter. Its dynamic structural loads include centrifugal load forces that exceed 60,000 lb. In Smart Structures and Materials 2000: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, Richard 0. Claus, William B. Spillman, Jr., Editors, 71 Proceedings of SPIE Vol. 3986 (2000) • 0277-786X/OO/$1 5.00