Critical evaluation of the compression creep test

The compression creep test is analyzed with respect to the friction at the loaded ends of the specimen. An analytical and a finite-element solution performed for large deformations reveals that friction leads to a strain-independent reduction of the creep rate which only depends on the stress exponent of the creep law and the geometry of the specimen. The assumed material behavior is a time-dependent, isochoric, nonlinear viscosity. Compression creep tests on 3-mol%-yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) have been analyzed. The determination of a stress exponent corresponding to the decreasing stress state in the specimen during large deformations results in a higher resolution of the stress-strain-rate relationship derived from a certain number of creep tests. For 3Y-TXP the compression creep tests reveal a decreasing stress exponent with increasing stress