Sensing damage in carbon fiber and its polymer-matrix and carbon-matrix composites by electrical resistance measurement

Fatigue damage was sensed in real time in continuous carbon fiber and its polymer-matrix and carbon-matrix composites by electrical resistance measurement in the fiber direction. In a polymer-matrix composite, fiber breakage overshadows fiber damage in causing the resistivity of the composite to increase irreversibly. In a carbon-matrix composite, fiber breakage and matrix cracking caused the resistivity to increase irreversibly, such that these two mechanisms cannot be distinguished. Fatigue damage was detected from 50% of the fatigue life onward for the polymer-matrix composite, and from 0% of the fatigue life onward for the carbon-matrix composite.