Advanced Acoustic Emission (AE) monitoring techniques for aerospace structures

This thesis contains the development of advanced Acoustic Emission (AE) monitoring techniques for aerospace structures. The techniques developed in this work explore AE’s ability to detect, locate and characterise signals. Experimental studies were conducted on a range of structures made from typical aerospace materials, including carbon fibre composite, GLARE and high grade steel; and the data collected from these studies was processed using the newly developed AE techniques, in order to determine their effectiveness. The work was divided into three main areas of research: 1. AE Source Location A location test was conducted on a GLARE fuselage panel specimen with complex geometric features in order to test the effect that altering the training grid resolution has on the accuracy of the delta-T mapping location technique. Delta-T mapping yielded more accurate results than the conventional Time of Arrival (TOA) method and the development of this technique formed the basis from which AE signals could be confidently located. 2. Damage Identification A fatigue test was conducted on a pre-notched, 300M grade steel, cantilevered beam which was monitored using both AE and Digital Image Correlation (DIC) during loading. The work considered the detection and tracking of fatigue crack growth. A novel form of data acquisition and analysis called an Additive Hits Analysis (AHA) was proposed and developed. The AHA provided a similar result to a conventional wavestreaming approach which was also used, though it did so in a much more streamlined manner. Specific delta-T mapping located signals were used to determine the frequency bands of interest for the cracking process to be tracked. DIC was noted as being a useful tool for validation of AE testing. 3. Characterisation on Large Scale Specimen A buckling test was conducted on a large-scale carbon fibre composite specimen which was monitored using AE and DIC. The work focused on the detection, location and characterisation of signals occurring in the specimen due to the applied loading. An ultrasonic C-scanner was used to quantify the damage which occurred in the specimen and this was found to be a useful tool for validation. A novel form of the modal analysis technique Measured Amplitude Ratio (MAR) called Automated Corrected MAR was developed. The new method was found to be able to successfully distinguish between in and out-of-plane signals arising in the specimen during the test whilst also providing time saving benefits over conventional methods. The combination of delta-T mapping with the Automated Corrected MAR results proved useful to the analysis.