Nondestructively monitoring fatigue damage in fiber reinforced composites using acoustic microscopy

Both SLAM (scanning laser acoustic microscopy) and C-SAM (C-scan mode scanning acoustic microscopy) imaging have been employed to nondestructively monitor the damage development in ceramic composites with LAS (lithium-alumino-silicate) glass matrix reinforced with silicon carbide (NICALON) fibers. To evaluate high-temperature fatigue damage in these ceramic composites 10 MHz SLAM images were produced. The results of reserve strength test obtained during four-point bending static tests where the load was monotonically increased until failure occurred correlated with the prediction made based on SLAM image. SLAM enables one to 'see' the geometrical distribution of all kinds of damage in specimens and helps one understand the collective effect of various damages on the variations in mechanical performance. In addition, C-SAM was used to produce the 3-D distribution of the damage, allowing the differentiation between compressive and tensile damage in the four-point-bending fatigued specimens.