Laser generation of Lamb waves for defect detection: experimental methods and finite element modeling

Area of Science:

• Materials Science
• Non-Destructive Testing
• Acoustics

Background:

• Lamb wave propagation is crucial for inspecting thin structures like aluminum sheets.
• Laser-based ultrasound offers a non-contact method for generating these waves.
• Defect detection and characterization are vital for structural integrity assessment.

Purpose of the Study:

• To model and experimentally investigate the propagation of laser-generated Lamb waves in an aluminum sheet.
• To analyze the interaction of these waves with defects.
• To compare finite element analysis (FEA) results with experimental data.

Main Methods:

• Finite element analysis (FEA) was employed to model Lamb wave propagation.
• Pulsed laser beams were used for wave generation.
• Electromagnetic acoustic transducers (EMATs) were utilized for wave detection.
• Time-frequency analysis, specifically the Wigner transform, was applied.

Main Results:

• The frequency content of received Lamb waves is enhanced when the generation point is directly over a defect.
• This enhancement was observed in both modeled (FEA) and experimental results.
• Individual Lamb wave modes were successfully identified using time-frequency analysis.

Conclusions:

• The study confirms that the positioning of laser-generated Lamb wave excitation significantly impacts defect detection sensitivity.
• FEA provides a reliable method for modeling Lamb wave-defect interactions.
• EMAT detection coupled with advanced signal processing enables effective defect characterization.