An automated approach to crack tip tracking using thermoelastic stress analysis

Speaker:
Middleton, Ceri; University of Liverpool; United Kingdom

Authors:
Middleton, C A.; University of Liverpool; United Kingdom
Gaio, A.; University of Liverpool; United Kingdom
Greene, R.J.; Strain Solutions Ltd; United Kingdom
Patterson, E.A.; University of Liverpool; United Kingdom

ID: ECNDT-0211-2018
Download: PDF
Session: Thermography and Thermosonics 3
Room: H1
Date: 2018-06-14
Time: 13:30 - 13:50

Monitoring of the initiation and propagation of fatigue cracks is important for a wide range of industrial applications, often in environments where access is not simple [1]. Thermoelastic stress analysis (TSA) is a non-destructive measurement technique which maps the surface stresses in a transiently loaded material by measuring the temperature variation of that material using an infrared camera [2]. The distribution of these surface stresses can be used to determine the presence and position of a crack [3], and TSA has been shown to be extremely sensitive to the initiation of cracks before they are visible by other methods [4].

Here, we use TSA to monitor the initiation and propagation of cracks in simple Aluminium alloy 2024-T3 coupon specimens under constant amplitude loading. TSA data has been processed ex situ, using an automated algorithm. This algorithm compares consecutive maps of TSA signal magnitude, and determines the position of the crack tip based on changes in the signal magnitude as the crack initiates and grows. We will present the results of this crack tip tracking during testing of coupon specimens of different geometries. We find that the automated algorithm can detect crack initiation at sub-mm lengths, and that the mapped crack paths match the morphology of crack surfaces imaged after failure.

References
[1] Sakagami, T. 2015 Fatigue Fract. Engng Mater. Struct. 38 755-779.
[2] Greene, R. J., Patterson, E. A. and Rowlands, R. E. 2008 In: Sharpe, W. N. (Ed.) Springer Handbook of Experimental Solid Mechanics ISBN: 978-0-387-26883-5 p743-767.
[3] Diaz, F. A., Patterson, E. A., Tomlinson, R. A. and Yates, J. R. 2004 Fatigue Fract. Engng Mater. Struct. 27 571-583.
[4] Backman, D., Cowal, C. and Patterson, E. A. 2010 Fatigue Fract. Engng Mater. Struct. 33 859-870.