Generation Mechanism of Nonlinear Rayleigh Surface Waves for Randomly Distributed Surface Micro-Cracks

Area of Science:

• Materials Science
• Solid Mechanics
• Acoustics

Background:

• Surface micro-cracks significantly affect structural integrity.
• Understanding crack characteristics is crucial for material safety and performance.
• Nonlinear ultrasonic methods offer potential for sensitive material characterization.

Purpose of the Study:

• To investigate Rayleigh surface wave propagation in structures with random micro-cracks.
• To explore the ultrasonic nonlinear effects induced by these surface micro-cracks.
• To establish a quantitative relationship between nonlinear acoustic parameters and micro-crack properties.

Main Methods:

• Numerical simulations of Rayleigh surface wave propagation.
• Analysis of ultrasonic nonlinear effects, including harmonic generation.
• Statistical analysis of results from models with varying micro-crack densities and sizes.

Main Results:

• Significant ultrasonic nonlinear effects were observed, characterized by second, third, and quadruple harmonics.
• The acoustic nonlinear parameter showed a linear increase with micro-crack density, proportion of surface cracks, micro-crack zone size, and excitation frequency.
• A clear correlation was established between micro-crack characteristics and the observed nonlinear acoustic response.

Conclusions:

• Nonlinear Rayleigh surface waves are a viable tool for quantitative assessment of surface micro-cracks.
• The study provides a theoretical basis for using nonlinear acoustics in structural health monitoring.
• This research contributes to advanced methods for non-destructive evaluation of materials.