The Use of Ultrasonic Arrays to Characterize Crack-Like Defects

The use of ultrasonic arrays to image and size crack-like defects is an important area in non-destructive evaluation. In this paper, two approaches are considered for extracting the key parameters of crack length and orientation angle. The parameters for small cracks are inferred from the scattering matrix. For larger cracks, the parameters are extracted directly from a high resolution image. The performance of both techniques is first assessed using a hybrid model to generate the full matrix of array data for a specified inspection configuration. The model combines a ray-based propagation model with scattering matrices to describe wave interaction with a defect. Good agreement is achieved between simulated and experimental results, hence validating this model-based approach. This model is then used to assess the impact of time-domain noise on the characterisation of crack-like defects. For the low-noise case, the scattering matrix approach shows good performance if the crack length is greater than 0.2 wavelengths and the image-based approach is good for crack lengths greater than 0.5 wavelengths. The scattering-matrix-based approach is found to be more sensitive to the addition of noise than the image-based approach. Finally, both techniques are demonstrated experimentally on samples containing more realistic defects.