Microscopic Investigation of Tensile Fatigue Damage of C/C and the Metal Impregnated C/C

Microscopic experimental investigation is performed to the fatigue fracture surface of C/C and metal impregnated C/C composites such as Cu-C/C and Si-C/C. These materials have an specific fatigue property that their average residual strength after 10^6 times cyclic loading is higher than the UTS of virgin specimens in every and that most of fatigue fracture occurs less than 10^4 cycles. Their SEM images together with recent macroscopic discussions by the present authors lead to the conclusion that fatigue failure is mainly affected by the interfacial crack at fiber-matrix interface and that in low cycle region strength degradation caused by fiber wear is dominative while in high cycle region the increased interfacial cracks at fiber-matrix interface prevent fibers in the 0 degree layer from fracturing, which makes the residual strength increased