Damage detection of C/C composites using ESPI and SQUID techniques

Three non-destructive evaluation (NDE) techniques, Acoustic Emission (AE), Electronic Speckle Pattern Interferometry (ESPI), and Superconducting Quantum Interference Device (SQUID) current mapping, were examined for use in the damage detection of carbon-carbon composites (C/Cs). These methods were applied to observe the fracture processes of two-dimensionally-laminated (2D) and three-dimensionally reinforced (3D) carbon/carbon (C/C) composites using compact tension and double-edge-notched geometry. The fracture processes of the C/Cs were complicated and were divided into different fracture steps. The AE technique was useful to distinguish between these fracture steps. ESPI was shown to be effective at identification of small-scale delamination of the 2D-C/Cs occurring before the ultimate tensile failure. On the other hand, SQUID current mapping clearly indicated fiber failure, even in cases involving local fiber fracture.