Fatigue Damage Evaluation Using Nonlinear Lamb Waves with Quasi Phase-Velocity Matching at Low Frequency

Area of Science:

• Materials Science
• Non-Destructive Testing
• Acoustic Materials Science

Background:

• Previous studies on material degradation relied on nonlinear Lamb waves with exact phase-velocity matching.
• The S0-s0 mode pair, exhibiting quasi phase-velocity matching, was less explored for incipient damage evaluation.

Purpose of the Study:

• To investigate the feasibility of using the S0-s0 nonlinear Lamb wave mode pair for fatigue damage assessment.
• To analyze the cumulative second harmonic generation for evaluating microstructural evolution in aluminum alloys.

Main Methods:

• Continuous low cycle fatigue tests were conducted on aluminum alloy specimens.
• Cumulative second harmonic analysis was performed using the S0-s0 Lamb wave mode pair.
• The influence of excitation frequency on damage detection sensitivity was analyzed.

Main Results:

• A characteristic mountain-shaped curve was observed between the normalized acoustic nonlinearity parameter and fatigue life for the S0-s0 mode pair, peaking at approximately 0.65 fatigue life.
• The S0-s0 mode pair effectively detected fatigue damage, with lower excitation frequencies showing higher sensitivity.
• While the S1-s2 mode pair exhibited higher sensitivity, the S0-s0 mode pair demonstrated significant potential for damage evaluation.

Conclusions:

• The S0-s0 nonlinear Lamb wave mode pair is a viable method for effective fatigue damage detection in aluminum alloys.
• Optimizing excitation frequency, particularly using lower frequencies, enhances the sensitivity of the S0-s0 mode pair to microstructural evolution.
• This research expands the application of nonlinear acoustics for non-destructive evaluation of material degradation.