Identification of fatigue damage evolution in 316L stainless steel using acoustic emission and digital image correlation

¹ London South Bank University, 103 Borough Rd, London SE1 0AA, UK
² NSIRC, TWI Ltd, Granta Park, Great Abington, Cambridge, CB21 6AL, UK
³ De Montfort University, Gateway House, Leicester LE1 9BH, UK
⁴ TWI Ltd, Granta Park, Great Abington, Cambridge, CB21 6AL, UK
⁵ Mistras Group Ltd, Norman Way, Over, Cambridge CB24 5QE, UK

Abstract

One of the main objectives of Acoustic Emission (AE) monitoring is to identify approaching critical stage of damage in the structure before it fails. State-of-the-art AE analysis is done on the features in both the time and frequency domains. Many features such as centroid frequency, duration, rise-time, count and energy are dependent on acquisition settings; threshold and timing parameters. Incorrect acquisition settings may result in inaccurate classification of the AE source. This work proposes a new feature in the time domain signal based on 2^nd order Renyi’s entropy, which proves to be efficient in identifying different stages of damage. Renyi’s entropy is a measure of uncertainty or randomness of the signals and is directly derived from the distribution of signal amplitude. Therefore, it is independent of threshold and timing parameters. The validity of the proposed parameter is investigated by performing AE monitoring during fatigue endurance test of 316L stainless steel. Digital Image Correlation (DIC) and global strain monitoring was carried out to relate material damage with AE activity. The result shows Renyi’s entropy to be an effective measure to identify critical stages of damage in the material.