Effect of different fiber orientations on compressive creep behavior of SiC fiber-reinforced mullite matrix composites

The compressive creep behavior of monolithic mullite and a composite made o f mullite reinforced by 40 vol% SiC fiber were investigated at temperatures from 1100 to 1200 degrees C and under stresses from 5 to 55 MPa in air wit h a loading direction parallel and perpendicular to the fiber direction. Fo r both situations the composite exhibits better creep resistance than monol ithic mullite, although there is a creep anisotropy. The improvement in cre ep resistance when the fibers are parallel to the loading directions is due to the shedding of the applied stress on the SiC fibers, and the improveme nt in creep resistance when the fibers ave perpendicular to the loading dir ection occurs because the fibers inhibit the lateral deformation of the mul lite matrix along the fibers. The improvement mechanisms of the composites were confirmed further by their creep-recovery study, which indicated that the two types of composite specimens exhibit both an apparent creep-recover y behavior on load removal, due to the relaxation of the residual stress st ate between the mullite matrix and the SiC fibers after unloading. (C) 1999 Elsevier Science Limited. All rights reserved.