Fatigue damage characterization in plain-weave carbon-carbon fabric reinforced plastic composites

The multi-mode fatigue failure process in a plain-weave woven carbon-carbon fabric reinforced polyester matrix composite has been investigated. Enhanced dye penetrant X-ray radiography, scanning electron fractography, optical microscopy, and edge replication techniques have been employed to examine the fatigue damage mechanisms. The 8 ply laminates were obtained from polyester resin-prepreg plain-weave carbon-carbon fabric layers, stacked in three different stacking sequences producing a unidirectional (0)₈, and two angle-plied (0,0,45,-45)_s, and (45,-45,0.0)_s fiber orientations. It is shown that the fatigue failure in the angle-plied (0.0,45,-45)_s and (45,-45,0,0)_s laminates, occurs through a multi-mode damage process, which involves matrix cracking, fiber-matrix debonding, fiber fracture, and delamination. Delamination of the stacked plies was noted to be the dominant damage process, which led to the eventual fatigue fracture in the angle-plied laminates. In the unidirectional (0)₈ laminates, the fatigue failure occurred in a more simple, yet a rather more catastrophic manner. In these laminates, instead of delamination. the fatigue failure occurred predominantly by a fiber fracture process.