Structural health monitoring of composite materials is limited by the lack of fundamental understanding of early stage damage at the local material level. This includes damage precursor formation on fiber surfaces, within the matrix, and at the fiber-matrix interface/interphase. In this effort, we present a micro-/nano-scale technique for characterizing damage precursor formation on individual carbon fibers exposed to cyclic tensile loads. Nanoindentation and atomic force microscopy (AFM) were used to study the local properties of the individual microfibers before and after global loading events. An AFM image analysis was used to track evolution of topography on the fiber surfaces. The work is a first step toward understanding damage precursor formation in individual microfibers; the work is expected to enable multiscale composites modeling efforts as well as enable the development of future self-sensing materials.

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