Real-time monitoring of fatigue damage and dynamic strain in carbon fiber polymer-matrix composite by electrical resistance measurement

Real-time monitoring of fatigue damage and dynamic strain in a continuous unidirectional carbon fiber polymer-matrix composite by longitudinal electrical resistance measurement was achieved. The resistance R decreased reversibly upon tensile loading in every cycle, thus providing dynamic strain monitoring. The peak R in a cycle irreversibly increased as fatigue damage occurred, due to fiber breakage. Fiber breakage started to occur at 50% of the fatigue life, but significant growth of the fraction of fibers broken did not start till 55% of the fatigue life. From 55% to 89% of the fatigue life, more than 1000 fibers broke at a time, but not in every cycle. From 89% to 99.9% of the fatigue life, fiber breakage occurred continuously in every cycle. Beyond 99.9% of the fatigue life, fiber breakage occurred rapidly, both continuously and in spurts, with the last spurt occurring at 99.99% of the fatigue life. Catastrophic failure occurred when 18% of the fibers were broken.