Three-dimensional crack depth profile assessment using near-field surface acoustic wave signal response

A method for determining the three-dimensional depth profile of a surface-breaking crack-like feature is presented based on near-field surface acoustic wave signal responses. Three-dimensional finite element models were used to study the forward problem, where the characteristic near-field scattering of a surface acoustic wave incident on a simulated crack was investigated. Experimental validation of the modeling predictions was accomplished using a wedge transducer for surface wave generation and a scanning laser vibrometry system for surface wave detection. The characteristic near-field amplitude response in reflection and in transmission was measured and modeled for flat-bottom, angled, and curved-bottom localized notch features, where a simple linear inversion method was developed, which provided an effective means for characterizing and mapping the three-dimensional depth profile of surface-breaking crack-like features with depths in the micron to millimeter range.