8. New Technology Roots
A technique for ultrasonically inspecting 135 mm artillery projectiles has been demonstrated. Noncontact EMAT's placed on the outside of the projectile excited 2.25 MHz surface waves and 1.8 MHz angle shear waves which were used to detect EDM slots on both the inner and outer surfaces. The defect locations and sizes, 0.051 em (0.020 in.) deep and 0.508 em (0.200 in.) long were chosen on the basis of fracture mechanics analysis. Each was detected with signal-to-noise ratios in excess of 30 dB. These results indicate that it is feasible to construct a system for full inspection of projectiles at normal production line rates. Among the desirable features of such a system are the absence of an ultrasonic couplant, the resulting potential for high speed operation, and the convenience with which multiple transducers can be incorporated to achieve high coverage and to gain additional information for defect characterization.
Fortunko, C. M., "Artillery Projectile Inspection with EMAT's" (1978). Proceedings of the ARPA/AFML Review of Progress in Quantitative NDE, September 1976–June 1977. 58.