Localization of notches with Lamb waves

Area of Science:

• Non-destructive testing
• Materials science
• Acoustics

Background:

• Lamb waves are crucial for inspecting plate-like structures.
• Analyzing their interaction with defects like notches is challenging due to multimode and dispersive nature.
• Noncontact laser ultrasonics offers high fidelity for transient wave measurement.

Purpose of the Study:

• To develop a method for analyzing Lamb wave interaction with notches.
• To establish automated techniques for notch localization using wave scattering.
• To quantitatively understand Lamb wave scattering and mode conversion at notches.

Main Methods:

• Utilizing laser ultrasonics to generate and detect Lamb waves in a notched plate.
• Employing reassigned spectrograms for time-frequency representation (TFR) and dispersion curve analysis.
• Calculating slowness-frequency representations (SFR) to identify reflected and transmitted wave modes.

Main Results:

• Successfully resolved individual Lamb wave modes and their dispersion curves.
• Identified reflected and transmitted wave contributions from the notch using SFRs.
• Developed two complementary, automated techniques for notch localization based on scattering analysis.

Conclusions:

• Time-frequency analysis of laser-generated Lamb waves provides a robust method for notch characterization.
• Understanding Lamb wave scattering and mode conversion is key to accurate defect localization.
• The developed automated techniques offer efficient non-destructive evaluation of notched structures.