Fiber breakage in polymer-matrix composite during static and fatigue loading, observed by electrical resistance measurement

By measuring the electrical resistance of a continuous unidirectional carbon fiber epoxy-matrix composite along the fiber direction during loading in this direction, fiber breakage was progressively monitored in real time. Fiber breakage occurred in spurts involving 1000 or more fibers. It started at about half of the failure strain during static tensile loading and at about half of the fatigue life during tension-tension fatigue testing. Immediately before static failure, at least 35% of the fibers were broken. Immediately before fatigue failure, at least 18% of the fibers were broken. The fiber breakage was accompanied by decrease in modulus.