Measurement Interpretation and Uncertainty Resulting from Nonlinear Ultrasonic Wave Propagation

Abstract

Nominally identical ceramic-element ultrasonic transducers, of the type used in the aerospace and metals industries for nondestructive evaluation (NDE), often have variability in the peak pressure of the generated ultrasonic pulses. The generated pressures are also high enough for nonlinear propagation to be present in the water medium, often used as coupling in these types of inspections. In this study, a measurement system for monitoring ultrasonic pulse pressure level and nonlinear propagation in water is presented. Several different industrial NDE measurement applications are examined to quantify the impact of variable pressure and nonlinear propagation with respect to test interpretation and measurement uncertainty. In particular, pulse frequency content, velocity measurements, reference block calibrations, and beam-width measurements are examined. In addition, an experimental demonstration of why nonlinear pulse distortion is not normally observed in practice is presented.