Impact Detection and Location in Operational Environment: An Acoustic Emission Approach

Abstract

Acoustic emission is a non-destructive inspection technique that has been used in a wide variety of applications. However, it has also shown the potential to be used as a structural health monitoring system when the sensors are permanently attached to the structure. For this purpose, PZT wafers (PWAS) have proved to be more suitable as they are less bulky and costly than the standard commercial transducers. Furthermore, some studies have recently shown the benefits of PWAS over encapsulated acoustic sensors, which mainly rely on the capability to measure in-plane (symmetric) and outof- plane (antisymmetric) guided wave motions. The possibility to capture all the elastic wave information opens the potential to identify, locate and characterize on-line the events which are taking place on the structure, e.g. impacts, delaminations, fatigue crack, etc. The normalization of the acquired signals under varying operational and environmental conditions is a common challenge shared among all the monitoring techniques and is strongly dependent upon the application. Some authors have shown the influence of temperature and simulated vibration in impact damage localization, however experimental demonstration of impact location in relevant operating conditions was lacking. In this study, the detection and location of a low energy impact event in thick aluminium plates using sparse sensor clusters have been implemented and demonstrated under a cruise vibration profile of a jet aircraft. As the time of flight (ToF) is unaffected by the external vibrations, a location algorithm based on ToF has been implemented, and its probability of detection and prediction error evaluated. It has been concluded that an acoustic emission system using PWAS could be a feasible solution for the passive monitoring of an in-flight aerostructure.