Quantitative Acoustic Emission for Damage Detection in Complex Geometries

Acoustic Emission (AE) method is a passive nondestructive evaluation (NDE) method based on the release of elastic waves by active flaws in structures. Since 1950s, the AE method has been applied as a qualitative NDE method to detect discontinuities by real time monitoring. While the AE method is successful in identifying and localizing active flaws, the method has not been fully utilized as a quantitative NDE method due to several challenges: unknown conversion behavior of sensor, complex source mechanism and influence of background noise. In this study, the goal is to address the major challenges of AE in terms of sensor behavior, influence of operational noise, and quantitative AE measurement and contribute our effort to achieve better understandings of acoustic emission. The study has three major components: (i) The multi-physics numerical models of AE sensors are built and validated by experiments. (ii) With the proper design of the laboratory scale test, the fatigue crack growth is simulated, and the corresponding AE signals are collected. Spline geometry of helicopter gearbox system is selected as the test structure to simulate a complex geometry and integrate with the field data obtained from the NAVAIR test facility. (iii) The recorded AE signals are embedded into the streamed signals obtained from the NAVAIR prototype test to evaluate the detectable AE signal in highly noisy operational environment and develop an efficient signal processing method. The purpose is to show the ability to extract fatigue crack signal embedded in noise signal and released from a complex geometry.