In-situ monitoring of damage in CFRP laminates by means of AC and DC measurements

Periodical maintenance NDT-based inspections are generally used for almost all complex technological structures today. The idea of using specific sensors integrated in the structure for structural real time monitoring (or health monitoring) is now in progress. Carbon-fibre-reinforced polymers (CFRP) are increasingly used as structural parts, especially in the aircraft industry. This work deals with the possibility of detecting in-situ damage in CFRP by the use of DC or AC electrical property measurements. Monotonic tests under post-buckling bending conditions are being performed on cross ply [0/90]s and [90/0]s carbon/epoxy laminates. The monitoring of electrical resistance and capacitance changes, linked to the modifications of the conduction paths in the composite, and occurrence of voids during loading, allowed the detection of damage growth. It seems that DC electrical conduction allows to detect fibre failure, but AC measurements are more suitable for monitoring matrix cracks (delamination, fibre/matrix debonding or transverse cracks).