Ultrasonic sizing of short surface cracks

Area of Science:

• Materials Science
• Non-Destructive Testing
• Acoustic Metrology

Background:

• Accurate characterization of surface cracks is crucial for structural integrity assessment.
• Existing ultrasonic methods face limitations in sizing small cracks relative to the wavelength.

Purpose of the Study:

• To develop and validate a unified ultrasonic method for sizing surface cracks across the full range of depth-to-wavelength ratios.
• To enhance the accuracy and repeatability of crack depth measurements using Rayleigh wave analysis.

Main Methods:

• Utilized near-field analysis in both time and frequency domains for Rayleigh wave propagation.
• Extended time-of-flight methods for sub-wavelength crack detection via time delay correlation.
• Solved the inverse scattering problem by comparing experimental scattering coefficients with theoretical models.
• Employed laser interferometry to measure out-of-plane displacement and separated Rayleigh waves from other modes.

Main Results:

• Demonstrated accurate and repeatable sizing of narrow slots and fatigue cracks.
• Achieved reliable measurements for crack depth to Rayleigh wavelength ratios as low as 0.15.
• The unified approach covers the entire range of a/lambda ratios in a single measurement.

Conclusions:

• The proposed ultrasonic method offers a robust solution for surface crack sizing.
• Near-field Rayleigh wave analysis provides high accuracy and repeatability for non-destructive evaluation.
• This technique advances the capability for detecting and quantifying small surface defects.