Self-monitoring of strain and damage by carbon fiber polymer-matrix composite

Self-monitoring of damage and dynamic strain in a continuous crossply (0°/90°) carbon fiber polymer-matrix composite by electrical resistance (R) measurement was achieved. With a static/cyclic tensile stress along the 0° direction, R in this direction and R perpendicular to the fiber layers were measured. Upon tension to failure, R in the 0° direction first decreased (due to increase of degree of 0° fiber alignment) and then increased (due to 0° fiber breakage), while R perpendicular to the fiber layers increased monotonically (due to increase of degree of 0° fiber alignment and delamination). Upon cyclic tension, R (0°) decreased reversibly, while R perpendicular to the fiber layers increased reversibly, though R in both directions changed irreversibly by a small amount after the first cycle. For a 90° unidirectional composite, R (0°) increased reversibly upon tension and decreased reversibly upon compression in the 0° direction, due to piezoresistivity.