Air-coupled ultrasonic testing of diffusion bonds.

Area of Science:

• Materials Science
• Non-Destructive Testing
• Ultrasonic Evaluation

Background:

• Ultrasonic evaluation of diffusion bonds typically uses immersion techniques.
• Interfacial stiffness, derived from echo amplitude, correlates with bond strength.
• Non-contact methods are needed for applications where immersion or contact is impractical or hazardous.

Purpose of the Study:

• To develop a non-contact ultrasonic method for evaluating diffusion bonds in steel plates.
• To overcome the limitations of air-coupled ultrasonics due to impedance mismatch.
• To separate bond status information from geometrical parameters.

Main Methods:

• Theoretical analysis of resonance frequencies in a diffusion-bonded plate-plate structure.
• Utilizing two neighboring resonance frequencies (odd and even) for analysis.
• Developing a formula to extract interfacial stiffness and plate thickness from resonance frequencies.

Main Results:

• Odd resonance frequencies are sensitive to both plate thickness and interfacial bond parameters.
• Even resonance frequencies are sensitive only to plate thickness.
• A single-point measurement allows extraction of both thickness and stiffness, separating bond information from geometry.

Conclusions:

• The proposed theoretical method enables non-contact ultrasonic evaluation of diffusion bond strength.
• Resonance frequency analysis provides a reliable alternative to immersion-based methods.
• Thickness variations between plates do not compromise the accuracy of bond strength predictions.