Impact source localisation in aerospace composite structures

Abstract

The most commonly encountered type of damage in aircraft composite structures is caused by lowvelocity impacts due to foreign objects such as hail stones, tool drops and bird strikes. Often these events can cause severe internal material damage that is difficult to detect and may lead to a significant reduction of the structure's strength and fatigue life. For this reason there is an urgent need to develop structural health monitoring systems able to localise low-velocity impacts in both metallic and composite components as they occur. This article proposes a novel monitoring system for impact localisation in aluminium and composite structures, which is able to determine the impact location in real-time without a-priori knowledge of the mechanical properties of the material. This method relies on an optimal configuration of receiving sensors, which allows linearization of well-known nonlinear systems of equations for the estimation of the impact location. The proposed algorithm is based on the time of arrival identification of the elastic waves generated by the impact source using the Akaike Information Criterion. The proposed approach was demonstrated successfully on both isotropic and orthotropic materials by using a network of closely spaced surface-bonded piezoelectric transducers. The results obtained show the validity of the proposed algorithm, since the impact sources were detected with a high level of accuracy. The proposed impact detection system overcomes current limitations of other methods and can be retrofitted easily on existing aerospace structures allowing timely detection of an impact event.

Low‐power global navigation satellite system‐enabled wireless sensor network for acoustic emission localisation in aerospace components

“…The impact localisation algorithm was originally developed by Ciampa and Meo, and it was recently improved by De Simone et al with a linearisation process of the system of nonlinear equations necessary to obtain the coordinates of the AE source and the velocity of propagating waves. With reference to Figure , the proposed impact localisation algorithm requires four PZT receiver transducers surface bonded on the test component.…”

“…Considering one of the sensors as the “reference sensor,” the following formula relates the travel time to reach the reference sensor, t ref , with the time differences, Δt ref, j , between the reference sensor and the other receiver transducers: Substituting Equation into Equation , it leads to the following system of four nonlinear equations: which can be solved for the four unknowns ( x AE , y AE , t ref , c g ) by following the linearisation process reported in De Simone et al Each wireless node was designed to continuously acquire data from the ADC and seek for a signal sample crossing a predefined threshold (see Section 3.2). The time information, t i , was obtained through a time synchronisation of the ADC sampling clock with a clock coherent with the GNSS signal available from the GNSS receiver.…”

“…Aerospace components are susceptible to low‐velocity impact damage that may considerably degrade the structural integrity and, ultimately, lead to catastrophic failure. Impact events typically generate acoustic emissions (AEs) propagating into the component, which can be recorded by sparse arrays of surface bonded piezoelectric (PZT) transducers . The analysis of measured AE waveforms using sophisticated impact localisation algorithms allows retrieving the location of the AE source.…”

“…Components have been chosen consistently to meet low‐power requirements. The coordinates of AE events generated by low‐velocity impacts were determined using a localisation algorithm developed by Ciampa et al This algorithm was here selected among those available in the literature as it does not require any prior knowledge of the mechanical properties of the host material nor the group velocity of propagating waves. A peak amplitude detection system was implemented to process the AE data recorded by the WSN and estimate the TOA.…”

Impact Localization in Composites Using Time Reversal, Embedded PZT Transducers, and Topological Algorithms

“…SHM algorithms for AE localization in composite materials typically rely on the time of arrival (TOA) estimation (Ciampa and Meo, 2010b;Kundu, 2012;Kundu et al, 2012;Emanuele et al, 2017;Seno et al, 2019). However, TOA-based techniques require a relatively large number of receiver transducers measuring the coherent part of the wave field (ballistic wave).…”