A model-based approach to crack sizing with ultrasonic arrays

Area of Science:

• Nondestructive Testing
• Ultrasonic Imaging
• Materials Science

Background:

• Ultrasonic phased arrays are crucial for flaw detection and characterization.
• Current imaging techniques rely on subjective thresholding for flaw size estimation.
• An objective approach is needed to improve the accuracy of flaw sizing.

Purpose of the Study:

• To develop an objective mathematical model for ultrasonic flaw sizing.
• To determine crack length using the Born approximation and scattering matrix properties.
• To validate the model with experimental data from welded austenitic plates.

Main Methods:

• Exploited the relationship between scattering matrix central lobe width and crack size.
• Derived an analytical expression for crack length via the Born approximation.
• Developed an objective sizing matrix (OSM) comparing experimental and modeled scattering matrices.

Main Results:

• The model accurately estimates crack length, including subwavelength defects.
• Derived an analytical expression for array discretization error.
• Experimental data from a 6 mm crack yielded an initial estimate of 7 mm, improved to 6.4 mm using multifrequency averaging.

Conclusions:

• The proposed objective approach enhances flaw sizing accuracy in ultrasonic nondestructive testing.
• The method is effective for subwavelength defects and less sensitive to array discretization at greater distances.
• Multifrequency averaging further refines crack size estimation, demonstrating practical applicability.