heat from polishing and to act as a carrier for the abrasive materials. The ultrasonic

cleaner was used to remove any abrasive particles and contaminants on the polished

surface of a specimen. The optical analysis was conducted with a NIKON EPIPOT

microscope.

 The laminated composite specimen C2 and the textile composite specimen T1 were

chosen for optical inspection. The specimen details are described in Table 4-2. The

microscopic images for the specimens were compared before and after cryogenic cycling.




















 0.05 mm

Figure 4-8. Cross sectional view of the graphite/epoxy composite specimen C2 before
 cryogenic cycling: (a) 10X magnification; (2) 40X magnification.

 For the graphite/epoxy specimen C2 before cryogenic cycling, no microcrack

propagation observed (see Figure 4-8). Some voids formed in the middle of the 90-degree

layers and between the 0-degree layer and the 90-degree layers. The voids probably

formed during composite fabrication in autoclave. When the graphite/epoxy prepreg was

cured at high temperature, some air bubbles could have been trapped between layers. It is