Processing of ultrasonic array signals for characterizing defects. Part II: Experimental work

This is Part II of the two-part paper aimed at integrating the numerical synthesis and experimental investigation of the ultrasonic wave propagation model for quantitative nondestructive evaluation. The first part of the paper focused on synthesizing and predicting measured signals using the boundary element method and the deconvolution technique based on the comparison between the signals obtained from defective and undamaged (reference) specimens. In the second part, we present an inversion technique which allows us to obtain the position and size of the defect. The inversion scheme is processing the frequency domain information rather than time-domain time-of-flights or vibration eigenmodes. This technique is tested experimentally for the case of a side-drilled hole with a non-trivial location in terms of standard pulse-echo techniques. It is shown that the scheme is particularly effective when the information of the defect is masked by other predominant signal components.