In-situ modal decomposition of acoustic emission events arising from low-velocity impacts

Abstract. In the field of structural health monitoring (SHM), it is common to employ the use of sensors to provide information about the state of a platform, particularly when concerned with whether damage has occurred as a result of impact. Acoustic emission (AE) sensing using piezoelectric elements is well suited to the detection of guided plate waves arising from impact events on thin-walled aerospace structures. This paper presents a systematic evaluation of impact induced AE with increasing velocity and explores changes in the resulting signals model content. A spring-loaded mechanism is used to accelerate ball bearings up to 7 m/s and the corresponding AE event is recorded using a LAMDA (Linear Array for Modal Decomposition and Analysis) sensor. This LAMDA sensor is an in-situ sensing capability that allows for frequency-wavenumber decomposition of the acquired acoustic signal into its constituent modes, which can then be mapped against theoretical dispersion curves for the material under investigation. To date, most research in the low velocity regime is concerned with the fundamental antisymmetric (A0) and symmetric (S0) wave modes from multiple sensing locations. Using LAMDA, it is possible to build a more complete picture of an impact signal, not currently achievable with conventional sensing methods.