Assessment of single-fiber fragmentation using scanning acoustic microscopy

Scanning acoustic microscopy (SAM) was used to obtain the critical fragmentation length of a 7-μm-diameter carbon fiber embedded in an optically transparent epoxy matrix and was subjected to a standard fiber fragmentation test. The SAM-assessed critical fragmentation length of 356 ± 59.5 μm compared favorably with the value 341 ± 52.3 μm obtained independently from commonly used photoelastic techniques. Additionally, the SAM images allowed an assessment of regions of fiber-matrix debond, including the measurement of an average debond of 61.0 ± 11.8 μm along the fiber from the fragment ends, which could not be obtained with photoelastic methods. The application of SAM to the assessment of optically opaque composite materials is explained in this paper.