Experimental validation of a mumerical model predicting the propagation of acoustic emissions in a wing spar for SHM purposes

An established principle for detecting cracks in structures is to monitor acoustic emissions generated by microcracking. Sensors positioned remotely from the crack site can pick up disturbances due to the propagation of high frequency waves from which the existence and the location of the crack can, in principle, be determined. In the case of thick load bearing structures such as wing spars the problem is complicated by the many wave types that may be responsible for transmitting the disturbance and their differing wave speeds, decay rates and scattering properties. This paper presents experimental activities on an I-beam chosen to resemble a wing spar. A Semi-Analytical Finite Element (SAFE) model is created and used to predict the forced response in both the frequency and time domains. The predictions compare favourably with experimental results obtained up to 40 kHz for an I-beam with approximately anechoic terminations. The efficacy of the model in decomposing the response into constituent waves and therefore assess their relative contributions and times of arrival is demonstrated