Directional information extracted from time reversal scanning to image stress corrosion crack orientation

The time reversed elastic nonlinearity diagnostic (TREND) is a nondestructive inspection technique based on the principle of time reversal and used to scan the surface of a sample to identify and characterize cracks and other defects. TREND utilizes a series of individual time reversal experiments conducted on a grid of points in a region of interest to map out the spatial extent of surficial expressions of cracks and subsurface features that are less than a wavelength below the surface. The focal signatures from each of these experiments can be used to determine not only the location but also the orientation of the crack. We will discuss how this technique can be applied to a stainless steel sample with stress corrosion cracking (SCC) using stationary piezoelectric transducers broadcasting ultrasonic waves and a scanning laser vibrometer setup used to detect the three dimensional vibration of the sample surface. The orientation of the crack is critical to estimate how soon a crack might penetrate through...