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 s olution performed for large deformations reveals that friction leads t o a strain-independent reduction of the creep rate which only depends on the stress exponent of the creep law and the geometry of the specim en. The assumed material behavior is a time-dependent, isochoric, nonl inear viscosity. Compression creep tests on 3-mol%-yttria-stabilized t etragonal zirconia polycrystals (3Y-TZP) have been analyzed. The deter mination of a stress exponent corresponding to the decreasing stress s tate in the specimen during large deformations results in a higher res olution of the stress-strain-rate relationship derived from a certain number of creep tests. For 3Y-TZP the compression creep tests reveal a decreasing stress exponent with increasing stress.