Simulating a standard type problem of ultrasonic testing - A contribution to the comparison of ultrasonic models

Models play a key role in all engineering disciplines by allowing simulation of experimental results without time and cost of constructing specimens and performing measurements. However, before such models can be used with confidence, it is necessary that they be validated. Ultimately, this must be done by comparison of model-based simulations to benchmark experiments. As a first step within this process, a simple problem is addressed that will allow a preliminary comparison of the various models available. Using a point source superposition method, the signal from spherical and crack-like reflectors observed in a pulse-echo measurement are predicted. Normally incident longitudinal waves, generated by circular focused and unfocused transducers, respectively, of 5 MHz center frequency are assumed in an immersion geometry. Two sets of scattering objects are considered: spherical pores of diameters ranging from 0.125 mm to 4 mm centered at a distance of 25.4 mm into an aluminum block, and circular cracks of the same diameters and depth. As a reference waveform for the incident signal a raised-cosine time function is considered. To predict the electric voltage signal generated in the transducer, Auld's reciprocity formula is used, while the scattering process at the defect is modeled using Kirchhoff's theory. Reference measurements performed at a similar configuration will be also presented.