1. In-Flight Acoustic Emission Fatigue Crack Monitoring Eric v. K. Hill, Robert J. Demeski, Christopher L. Rovik and Samuel G. Vaughn III APPROACH/TECHNICAL CHALLENGES Monitor fatigue cracking in notched 7075-T6 aluminum channel beam in laboratory Train SOM neural network to accurately classify fatigue crack growth AE signals from laboratory In-flight AE fatigue crack monitoring: Piper Cadet engine cowling and Cessna Crusader T-tail ACCOMPLISHMENTS/RESULTS Piper Cadet engine cowling during ground operations and Cessna Crusader T-tail during roll/Dutch roll maneuversDetected fatigue crack growth: Piper Cadet engine cowling during ground operations and Cessna Crusader T-tail during roll/Dutch roll maneuvers OBJECTIVES Use self-organizing map (SOM) neural network to classify acoustic emission (AE) failure mechanism data into fatigue cracking, plastic deformation (ahead of crack tip) and rubbing/fretting noises Goal: minimize maintenance costs and extend service lives of aging aircraftGoal: Demonstrate in-flight AE fatigue crack monitoring – minimize maintenance costs and extend service lives of aging aircraft Notched 7075-T6 Aluminum Channel Beam Fatigue Specimen with Riveted and Bolted Attachments

2. AE Source Duration [µs] Amplitude [dB] Fatigue Cracking 0-6,00065-100 Plastic Deformation 0-6,00030-65 Rubbing/Fretting6,000-32,00030-70 Fatigue Specimen with AE Transducers in MTS Machine AE Source Location Plot Fatigue Cracking - s 0 Lamb Wave Fatigue Cracking - a 0 Lamb Wave Rubbing/Fretting SOMClassifier Laboratory Fatigue Crack Growth Monitoring AE Signal Parameters

3. Piper PA-28 Cadet Engine Cowling Expected Fatigue Crack Data Between AE Transducers 1 & 2 Fatigue Crack Data Between AE Transducers 1 & 2 Unexpected Fatigue Crack Data Between AE Transducers 3 & 4 Engine Cowling Fatigue Cracking Predominant During Ground Operations Self-Organizing Map (SOM) Neural Network Results Turbulent Propeller Wash/Engine Vibrations

4. Cessna T-303 Crusader T-Tail Cessna Crusader Redundant Notched Fatigue Structure Mounted in Vertical Tail Fatigue Cracking in T-Tail Redundant Notched Structure Predominant during In-Flight Operations Self-Organizing Map (SOM) Neural Network Results Roll and Dutch Roll Maneuvers