Electrochemical impedance spectroscopy as a method to nondestructively monitor simulated in-service damage in a carbon fiber reinforced plastic

Electrochemical impedance spectroscopy has been utilized to nondestructively evaluate simulated, in-service, environmental and mechanical damage in a carbon fiber reinforced epoxy system. A continuous, unidirectional (0 deg ) fiber composite (e.g. AS4 /3501-6) was subjected to immersion (water, sodium sulfate) and fatigue conditions, and subsequently submitted to electrochemical impedance testing. Definitive correlations between the value of the double layer capacitance and the amount of flexural fatigue or moisture uptake were observed. The changes in the electrochemical parameter paralleled changes in the shear strength as a function of damage state. 12 ref.--AA