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-matr ix composite was sensed in real time during fatigue by measuring the e lectrical resistance of the composite in the through-thickness directi on. 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 decrea sed upon subsequent unloading in every cycle, thereby allowing strain sensing. The minimum resistance at the end of a cycle irreversibly inc reased during the first 0.1% of the fatigue life. The resistance becam e noisy starting at 62% of the fatigue Life, at which delamination occ urred rapidly and the fraction of laminate area delaminated reached 4. 3%.