Extraction of bulk wave characteristics from a pulsed ultrasonic polar scan

• Pulsed ultrasonic polar scans for different materials have been recorded.
• Obtained image put on view the bulk wave characteristics of insonification spot.
• Post-processing yields the local directional bulk wave profiles.
• Lensing effect of immersion liquid is demonstrated.

The pulsed ultrasonic polar scan (P-UPS) technique provides a map with characteristic contours reflecting the critical bulk wave angles, which directly relate to the in-plane elastic properties of the insonified material spot. Besides these contours, additional information is captured in a P-UPS experiment which has particular importance for the inspection of anisotropic materials. By extensive post-processing on a single P-UPS experiment, we successfully extracted the local directional (i) critical bulk wave angles, (ii) phase velocity profiles, (iii) slowness curves, (iv) walk-off angles and (v) energy velocity profiles, for the three different polarization states of bulk waves. The procedure is demonstrated and discussed for an isotropic aluminum sample as well as an autoclave manufactured orthotropic [0]8[0]8 carbon/epoxy laminate. In addition, a numerical and experimental investigation of the role of the immersion liquid as a lens for the P-UPS result is performed. This lensing effect permits to zoom in/out on the P-UPS fingerprint, hence broadening the class of materials which can be inspected by the P-UPS technique.