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Nonlinear acoustic response through minute surface cracks: FEM simulation and experimentation
Koichiro Kawashima1, Ryuji Omote, Toshihiro Ito
1Department of Mechanical Engineering, Nagoya Institute of Technology, Japan. kkawas@megw.mech.nitech.ac.jp
Ultrasonics
|August 6, 2002
Summary
Minute surface cracks generate nonlinear ultrasonic responses when subjected to Rayleigh waves. Compressive stress influences crack closure, affecting wave transmission and leading to a noticeable second harmonic amplitude.
Area of Science:
- Materials Science
- Non-destructive Testing
- Acoustics
Background:
- Surface cracks can alter the propagation of ultrasonic waves.
- Nonlinear ultrasonic phenomena are sensitive to crack characteristics and stress conditions.
Purpose of the Study:
- To numerically analyze the second harmonic generation of Rayleigh waves interacting with surface cracks.
- To experimentally validate the nonlinear ultrasonic response of a surface crack model.
Main Methods:
- Semi-explicit finite element method (FEM) with special crack elements.
- Numerical simulation of Rayleigh wave propagation through a cracked aluminum block.
- Experimental detection of the second harmonic component of leaky Rayleigh waves using a PVDF transducer.
Main Results:
- Numerical analysis showed distorted waveforms and a noticeable second harmonic amplitude for Rayleigh waves passing through cracks.
- Experimental results confirmed that the second harmonic amplitude is a second-order function of the fundamental wave amplitude.
- The second harmonic amplitude was more pronounced under low compressive stress, indicating crack closure effects.
Conclusions:
- Minute surface cracks exhibit significant nonlinear ultrasonic behavior.
- The second harmonic amplitude of Rayleigh waves is a viable indicator for detecting and characterizing surface cracks.
- Applied compressive stress can be used to modulate the nonlinear response for enhanced crack detection.