THE CHARACTERIZATION OF CRACK-LIKE DEFECTS USING ULTRASONIC IMAGES

The use of ultrasonic arrays to image and size crack-like defects is an important area in non-destructive evaluation. The features in the ultrasonic data from a crack-like defect provide information about the size and orientation angle of the defect. In this paper, the characteristics of a crack-like defect were measured from its scattering coefficient matrix, when the angular coverage of measurement includes the specular regions of its scattering matrix. Alternatively, the imaged features for a large crack-like defect (its length more than two wavelengths) were directly used to characterize the defect through a rectangular box fitting approach. An efficient hybrid model was used to generate the full matrix of array data from samples with a defect and for a specified inspection configuration. This hybrid model combines far-field scattering coefficient matrix for defects with a ray based forward model. This model offers the potential to compile a look-up table through which defects can be classified and then sized. Good agreement was achieved between simulation and experimental results hence validating this model based approach.