Non-destructive Evaluation (NDE) is the process of using non-invasive procedures to inspect or characterize an object without altering its form, fit, or function. Ultrasonic testing is one of the most popular NDE techniques due to its wide range of applicable materials and non-hazardous operations to personnel or equipment. One of its disadvantages, traditionally, is the requirement for manual, in contact, inspection and extensive technical knowledge to interpret the results. This dissertation addresses these problems through experimental validation of a two-part inspection technique: passive transfer function defect detection followed by synthetic aperture imaging defect quantification. First, results from full-scale experiments on rails up to 80 mph are used to validate the high-speed, non-contact, passive defect detection prototype. Next, results from a real-time ultrasonic imaging prototype for rail flaw sizing are used to demonstrate fast, straightforward, quantification of defect geometry.

Passive ultrasonic inspection and ultrasonic imaging are complementary technologies: the first is for high-speed detection of suspect regions but does not label the type or size of defects; whereas, the second is for defect verification of suspect regions and visually displays the precise defect size and orientation. The ability to quickly inspection regions of interest and subsequently accurately quantify the extent of damage is integral for a reliable and cost-effective resource management program.