Ultrasonic wave dispersion curves with application to crack detection from acoustic emissions in aircraft structures: general methodology and a case study of a wing spar

Zarini, G., Waters, T.P. and Elliott, S.J. (2013) Ultrasonic wave dispersion curves with application to crack detection from acoustic emissions in aircraft structures: general methodology and a case study of a wing spar. RASD 2013, Pisa, Italy. 30 Jun - 02 Jul 2013. 15 pp .

Abstract

An established principle for detecting cracks in structures is to monitor high frequency acoustic emissions generated by micro-cracking. In the case of simple uniform plates the ultrasonic waves that propagate from a crack to a sensor are straightforward to infer from Rayleigh-Lamb theory. However, for built-up structures such as an aircraft wing the wave types responsible for propagating disturbances are potentially numerous, complicated and travel at differing velocities.

In this paper a comparison between the dispersion curves obtained with various plate theories is presented and their applicability to plates of thickness commonly used in aircraft is discussed. Of equal importance is the prediction of free wave propagation in beam-like structures such as wing spars, the geometrical complexity of which may necessitate a numerical approach. The Semi-Analytical Finite Element (SAFE) method is applied here to predict the free wave propagation characteristics of an I-beam structure, which is adopted to resemble a wing spar. The resulting wave modes and dispersion curves are presented. The main aim of this paper is to identify which established analytical or numerical approaches are appropriate for modelling wave propagation in aircraft wing structures at few hundred kHz. This will facilitate future studies focussed on the number, placement and dynamic response of sensors.

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