CHARACTERIZATION OF WAKE-ZONE TRACTIONS IN AN OXIDATION-INHIBITED CARBON-CARBON COMPOSITE

A novel post-fracture tensile (PFT) experiment has been employed to st udy the bulk pull-out behavior of a two-dimensional, eight-harness sat in-weave carbon/carbon composite. In the PFT test, a pre-cracked speci men is loaded in tension in order to characterize the microstructural features responsible for the bridging tractions that so strongly influ ence the R-curves of these continuous-fiber-reinforced composites. The initial crack extension was found to reduce the maximum tensile stres s monotonically. This behavior was attributed to the increasing damage zone size developed with flexure. The arrest stress level, immediatel y following the maximum tensile stress, apparently arises from largely frictional mechanisms, as governed by the development of matrix damag e. With increasing crack extension, the maximum tensile stress tends t o decay toward the arrest stress, in keeping with a model for increasi ng interfacial damage. The development of damage with crack extension appears to be influenced by both specimen geometry and microstructure, which is emphasized by the characteristic interfacial properties of t his composite with very high-strength fibers with respect to that of t he matrix.