Creep and cyclic durability of CVI SiC/SiC composites

Isothermal creep and sustained-peak low-cycle fatigue (SPLCF) tests were conducted on as-fabricated and precracked chemically vapor infiltrated (CVI) SiC-fiber-reinforced SiC-matrix (SiC/SiC) composites with Hi-NicalonTM-S fibers from 1200 to 1450 degrees C in air at stresses up to 150 MPa and for exposure times up to 400 hr. The creep behaviors were analyzed by using a modified Norton-Bailey equation. The residual in -plane tensile properties of those specimens that survived 300- to 400 -hr runout were measured. Results indicate that the asfabricated composites show better durability under creep than under SPLCF and retain a significant percentage of their in -plane tensile properties after runout. In contrast, durability and residual in -plane tensile properties of the precracked composites under similar creep and SPLCF testing conditions decreased with an increase in temperature as well as an increase in stress. Failure mechanism(s) and factors influencing durability of the composite are discussed.