A technique for measurement of ultrasonic waves propagating in time-varying media

Abstract

Laser Doppler Vibrometry (LDV) is often used in nondestructive testing to make high-fidelity, non-contact structural dynamic measurements. However, synchronized measurement on slow, structural dynamics (SD) and fast, ultrasonic (US) time scales can yield additional useful information about the overall condition of elastic structures. This work presents a technique, Dynamic Asymmetric Transmission Measurement (DATM), that enables time-aligned measurements of large-scale structural dynamics via LDV and small-scale ultrasonic signals to provide information at a particular global dynamic state of an elastic structure. This approach is applicable to structural health monitoring and generalizable to the measurement of guided ultrasonic waves propagating in structural components subjected to time-varying stress states. We demonstrate the utility of DATM by detecting and characterizing time-varying stress conditions caused by local nonlinearity due to surface-breaking cracks resulting in time-varying asymmetric transmission of US signals in beam and plate structures. The test methodology to synchronize LDV and US data is presented together with example measurements. [Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.]