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.