ULTRASONIC TECHNIQUES FOR INSPECTING FLAT AND CYLINDRICAL COMPOSITE SPECIMENS.

Ultrasonic techniques are discussed for inspection and evaluation of flat and cylindrical composite specimens. Immersion ultrasonic techniques are described using a 5-MHz broad-band focused transducer in the pulse-echo mode. Two types of recording methods are employed, conventional pen-lift C-scanning and analog scanning, augmented with photographs of oscilloscope traces of the pulse are selected locations. The complete scanning system is described, including a fixture for scanning tubular specimens. The techniques discussed are applied to monitoring flaw growth in graphite/epoxy coupons of left bracket (0/ plus or minus 45/90)//s right bracket //2 and left bracket 0//2/ plus or minus 45 right bracket //2//s layups with four types of initial flaws subjected to fully reversed spectrum fatigue loading. It is found that, in general, flaw growth is greater in specimens of left bracket 0/ plus or minus 45/90)//s right bracket //2 layup than in those of left bracket 0//2/ plus or minus 45 right bracket //2//s layup.