Our overall goal is to understand the relationship between the nano- and micro-scale structure of materials and ultrasonic wave propagation. We use this knowledge to better understand and characterize damage evolution in materials.
Specifically, ultrasound is a powerful nondestructive evaluation (NDE) method used to detect damage in critical components, e.g. energy infrastructure, aircraft, and bridges. Different ultrasonic techniques are sensitive to damage over a wide range of length scales. Linear ultrasound (e.g. wave velocity, attenuation) can be used to evaluate the effective stiffness, porosity, or defects whose length scale is on the order of the wavelength of the propagating wave. On the other hand, nonlinear ultrasound exploits nonlinear wave propagation to characterize very early-stage damage that occurs at nano- and micro-scales (e.g., dislocations, precipitates, microcracks) in structures well before macroscopic cracking and failure. When a propagating wave interacts with these nano- and micro-structural features, a second harmonic is generated as a result of nonlinear interactions. We are using this phenomenon to characterize very early stage damage in materials, such as fatigue, radiation damage, or defects due to additive manufacturing processes. We are also studying how phononic materials, i.e. periodic structures that induce wave filtering properties, can be integrated in NLU measurements to improve their sensitivity.
Current areas of research include: