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

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