Numerical analysis of ultrasonic wave propagation and scattering in oligo-crystalline materials

Abstract

Oligo-crystals contain only a few crystalline grains and are often used in the fields of micro-electromechanics, turbine blades and shape memory alloys. To date, there has not been any study on the ultrasonic evaluation of oligo-crystals. In this work, we modeled the microstructure of oligo-crystalline copper foil using the phase field method, and carried out a finite element analysis of the oligo-crystal. Data were generated through multiple simulations and the data were analyzed statistically to assess the effects of ultrasonic testing configuration, the size of the transducer aperture, the types of texture, and the internal flaws on the propagation and scattering characteristics of ultrasonic waves. The results showed that the majority of conventional ultrasonic evaluation techniques failed to work for oligo-crystals. Firstly, ultrasonic velocity and attenuation coefficient in a given oligo-crystal are not constant when measured in different ultrasonic configurations and with different aperture sizes. Secondly, oligo-crystals are characterized by a rather low level of grain noise, possibly due to the low density of grain boundary. Thirdly, for a side drilled hole of a given size and depth in an oligo-crystal, the simulated amplitude and time-of-flight of flaw echoes are highly variable, which makes flaw location and flaw sizing very difficult. More in-depth research on physical modeling and experimental verification of ultrasonic testing are clearly needed for oligo-crystals in the future.