Investigation and modeling of anisotropic compression creep for a unidirectional all-oxide CMC

Abstract

Compression creep of WHIPOXTM, an all-oxide ceramic matrix composite, with a unidirectional fiber alignment was investigated. Experimental results showed a high creep anisotropy with lowest strain rates in case of loads applied parallel to fibers. Stress and temperature dependencies were figured out to gain essential relations for creep: Stress-sensitivity of strain rates varied with the fiber orientation having its maximum at specimens with fibers parallel to applied load. Activation energy for creep was independent of the direction of the applied load. In order to calculate material’s non-linear, time-dependent deformation behavior at high temperature, a description according to Hill on the mesoscopic scale was tested. Since creep behavior was not captured sufficiently by this model, numerical simulations on the microscopic scale were conducted. Assigning different creep parameters to fibers and matrix, more information about fiber-matrix-interactions could be obtained. Deformation mechanisms in terms of fiber rotation and the role of matrix compressibility were in focus. It appeared that matrix compaction influences deformation behavior and should not be neglected in creep description.