A new technique for the ultrasonic detection of internal transverse cracks in carbon-fibre/bismaleimide composite laminates

Through-transmission ultrasonic C-scan imaging with inclined focusing transducers in confocal configuration has been used for the detection of partial and internal cracks in a cross-ply, [0/90/0] carbon/epoxy laminate. A number of partial cracks (intersecting only one edge of a coupon) as well as completely internal cracks were found ultrasonically after the sample was subjected to static loading. The validation of the result by cutting the sample along two lines :in the 0 degrees direction and checking the presence of the internal cracks with an optical microscope shows a good correlation between the ultrasonic image and the optical data. Experimental results show that in the IM7/5250-4 composite, which contains a toughened BMI resin, initiation of transverse cracks under static loading occurs with the formation of partial cracks not necessarily originating at the edge of the sample. (C) 2000 Elsevier Science Ltd. All rights reserved.