Abstract
After a crack on a metal surface has been detected, determining its depth becomes an important practical issue for the fracture analysis and repair considerations. Reliable sizing of tightly closed small cracks was beyond the ability of standard NDE techniques. This limitation has recently been removed by the development of a new ultrasonic evaluation method, where the ultrasonic testing is considered as an inverse problem. An important issue associated with the present development is to analyze the quantitative characterization of the cracks from the perspective of crack length. The present paper is on the investigation of the influence of crack length on the ultrasonic determination of depths of small surface cracks, together with their extent of crack closure. Evaluation results of open as well as tightly closed small surface cracks with different crack lengths verify the method to be a powerful tool for evaluating the depths without involving any information regarding the crack length.
