Assessment of single-fiber fragmentation using scanning acoustic microscopy

Scanning acoustic microscopy (SAM) was used to obtain the critical fragment ation length of a 7-mu m-diameter carbon fiber embedded in an optically tra nsparent epoxy matrix and was subjected to a standard fiber fragmentation t est. The SAM-assessed critical fragmentation length of 356 +/- 59.5 mu m co mpared favorably with the value 341 +/- 52.3 mu m obtained independently fr om commonly used photoelastic techniques. Additionally, the SAM images allo wed an assessment of regions of fiber-matrix debond, including the measurem ent of an average debond of 61.0 +/- 11.8 mu m along the fiber from the fra gment ends, which could not be obtained with photoelastic methods. The appl ication of SAM to the assessment of optically opaque composite materials is explained in this paper.