Mechanical damage and strain in carbon fiber thermoplastic-matrix composite, sensed by electrical resistivity measurement

The volume electrical resistivity of a unidirectional continuous carbon fiber thermoplastic (nylon-6) matrix composite was found to be an indicator of strain and damage during repeated loading in the fiber direction. The through-thickness resistivity irreversibly and gradually decreased upon damage (probably fiber-matrix debonding) during repeated compression or tension. Moreover, it reversibly and abruptly increased upon matrix damage, which occurred reversibly near the peak stress of a stress cycle. In addition, the resistivity increased reversibly upon tension in every stress cycle, and decreased reversibly upon compression in every stress cycle. On the other hand, the longitudinal resistivity irreversibly and gradually increased upon damage. Moreover, it decreased reversibly upon tension in every stress cycle and increased reversibly upon compression in every stress cycle. The through-thickness resistivity was a better indicator of damage and strain than the longitudinal resistivity.