Crack depth measurement by ultrasonics

Bulk and surface wave ultrasonic methods are given for measuring the depth of surface-breaking cracks. Research is considered which relates to techniques for measuring crack depth by studying the scattered pulse amplitude, by using time-of-flight methods, or by carrying out ultrasonic spectroscopic analysis. Measurement of the transit time of bulk waves appears most likely to provide simple and reliable depth measurement in the near future, although further work in the other two areas should lead to the development of valuable techniques. Some suggestions are made of promising directions for future research.