Visualization of time evolving wavefront advance in polycrystalline materials

The nondestructive quantification of polycrystalline grain feature information in aerospace materials is an important area of recent research, where spatially-resolved measurements related to mean grain size, grain size distribution, and crystallographic orientation are needed for engineering analysis and material state awareness evaluations. In the present effort, the interaction of ultrasonic surface acoustic waves (SAW) with a dual-microstructure nickel polycrystalline material is studied, where an innovative wavefront imaging method is utilized to visualize and study the time-evolving advance of the primary, forward propagating wavefront through microstructure grain features on the material surface. The method involves a first-arrival, time-gated analysis of scanning laser vibrometry signal content, where the apparent motion of the wavefront through individual and clustered grains is observed and attributed to local changes in the orientation-dependent crystallographic slowness.