Durability of graphite-fiber-reinforced PMR-15 composites aged at elevatedtemperatures

Earlier work that reported relationships between compression properties and elevated-temperature aging duration and weight losses also pointed out the apparent influence of surface layer formation and growth on the retention of compression properties during extended aging times. Since that time, fur ther studies have focused on evaluating the growth of the surface layer. Th e composition and features of this layer were found to change as the aging temperature changed. Microcracks and small voids initiated and advanced inw ard at all temperatures. Visible oxidation at the surface occurred only at temperatures above 260 degrees C. Relationships between layer thickness, ag ing time, and temperature were evaluated and empirically formulated. Then, the compression properties were graphically related to the surface layer th ickness with excellent correlation.