Assessment of impact damage in carbon-carbon plates with correlation to residual compression strength after impact

Carbon-carbon composites were subjected to low-velocity impacts by a 0.5-in diameter air-driven aluminum sphere. Nominal impact energies ranged from 1/4 to 2 ft-lb. The samples were examined ultrasonically with conventional C-scan and with an advanced technique to image the damage through the thickness of the material. The samples were then tested to failure in compression, and a comparison was made between the compression strength and the imaged damage. Strength-degrading, low-energy impact damage in thin-gauge, uncoated carbon-carbon was easily detected ultrasonically, and the damage areas from the C-scans generally corresponded with those determined microscopically. Also, the ultrasonic technique for determining the volumetric damage profile was successfully utilized for this class of materials