Critical Evaluation of the Compression Creep Test

Abstract

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 expbnent 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-TZP the compression creep tests reveal a decreasing stress exponent with increasing stress.

Repeatability and reproducibility of compression strength measurements conducted according to ASTM E9

“…Stresses less than the yield stress of the material model, σ = 190.4 MPa, are shown in white. Consistent with other analyses [29,6], a non-deforming cap forms at the test specimen end. As the specimen deforms, a region of slightly higher stress develops that extends just into the region that the longer, G = 25.4 mm extensometer samples.…”

“…That distance complies with the requirements of E9, and should minimize the effect of the non-uniform stress caused by friction at the specimen ends. No study has examined the sensitivity of the strain measurement to the non-uniform stress at the end of the specimen, but the existence of non-uniform stresses caused by friction is well known [29]. Finite element analysis (FEA), using the commercial finite-element modeling software Abaqus/Standard 6.10 [30], was used to analyze the effect of friction and gauge length on the response of the specimen.…”

Superplastic Flow of Fine‐Grained Yttria‐Stabilized Zirconia Polycrystals: Constitutive Equation and Deformation Mechanisms

“…vs log plots, which gives a single value of n. However, it clearly is evident in experiments where n has been evaluated as a function of the stress level. 23,27 Debschütz et al 23 (iii) On the other hand, the data for specimens prepared from lower-purity powders (blue points in Fig. 1, with a total † The grain size used in this article is the true grain size d ‫ס‬ 1.78L, where L is the average intercept length.…”

“…vs log plots, which gives a single value of n. However, it clearly is evident in experiments where n has been evaluated as a function of the stress level. 23,27 Debschütz et al 23 determined n on a high-purity 3Y-TZP with a grain size of 0.5 m from the slope of log . vs curves at constant load, and they reported a decrease in n from 4.5 to 2.2 as increased from 20 to 50 MPa at 1200°C.…”

Design of 7wt.% Y2O3–ZrO2/mullite plasma-sprayed composite coatings for increased creep resistance

“…Barreling in the YSZ specimens indicates a significant amount of friction between the load cell platens and the ends of the stand-alone coating. 30 The effect of this friction on the present experimental data has not been determined. Barreling was not visually observed in composite or mullite specimens under the conditions investigated.…”