Zero group velocity mode nonlinear ultrasonics for fatigue crack detection

Area of Science:

• Materials Science
• Non-Destructive Testing
• Acoustics

Background:

• Nonlinear ultrasonics is sensitive to incipient damage but susceptible to noise.
• Existing methods struggle with distinguishing crack-induced nonlinearity from other sources.

Purpose of the Study:

• To develop an enhanced nonlinear ultrasonics methodology for fatigue crack detection.
• To leverage zero group velocity (ZGV) modes to amplify nonlinear features at fatigue cracks.

Main Methods:

• Theoretical analysis of ZGV Lamb modes.
• Actuation at half-ZGV frequency to generate second harmonic at ZGV resonance.
• Finite element simulations to validate the enhanced signal features.

Main Results:

• ZGV resonance at fatigue cracks significantly enhances second harmonic signal features.
• Demonstrated superior performance compared to standard actuation methods.
• Characterized nonlinear ZGV generation from temporal, spectral, and spatial viewpoints.

Conclusions:

• The proposed ZGV-based nonlinear ultrasonics method offers enhanced sensitivity and reliability for fatigue crack detection.
• This approach effectively localizes wave energy, amplifying crack-specific nonlinear responses.
• Further research is suggested for practical implementation and broader applications.