Sensing delamination in a carbon fiber polymer-matrix composite during fatigue by electrical resistance measurement

Delamination in a crossply [0/90] continuous carbon fiber polymer-matrix composite was sensed in real time during fatigue by measuring the electrical resistance of the composite in the through-thickness direction. Upon O degrees tension-tension fatigue at a maximum stress of 57% of the fracture stress, the resistance irreversibly increased both in spurts and continuously, because of delamination, which started at 33% of the fatigue life. The resistance increased upon loading and decreased upon subsequent unloading in every cycle, thereby allowing strain sensing. The minimum resistance at the end of a cycle irreversibly increased during the first 0.1% of the fatigue life. The resistance became noisy starting at 62% of the fatigue Life, at which delamination occurred rapidly and the fraction of laminate area delaminated reached 4.3%.