Rapid Ultrasonic Inspection of Army Projectiles
The electromagnetic acoustic transducer (EMAT) is a device of particular interest for rapid nondestructive evaluation (NDE) in assembly line applications because of its noncontact mode of operation. Speed is a crucial factor in the performance of an NDE system designed for the inspection of artillery projectiles where production rates may be on the order of several shells per minute. These requirements severely restrict the reliability of conventional ultrasonic techniques that use fluid couplants. A fully automated micro-processor based inpsection system utilizing multiple EMATs to launch shear vertical acoustic waves traveling at 30 degrees with respect to the surface normal is being assembled to inspect 155 mm projectiles for both ID and OD flaws. The system's ability to detect small defects has been demonstrated by locating semi-elliptical EDM notches having surface lengths of 2.5 mm (0.1 in.) and maximum depths of 0.8 mm (0.03 in.).