A Technique to Achieve Uniform Stress Distribution in Compressive Creep Testing of Advanced Ceramics at High Temperatures

Liu, K. C.; Stevens, C.O.; Brinkman, C.R.; Holshauser, N. E.

doi:10.1115/1.2817012

Cited by 8 publications

(1 citation statement)

References 9 publications

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“…5,20,[26][27][28][29][30][31][32] Figure 1 illustrates this behavior, where the logarithm of the minimum creep rate for several different silicon nitrides is plotted as a function of the logarithm of the applied stress. At the same stress, the tensile creep rate is anywhere from 10 to 100 times greater than the compressive creep rate.…”

Section: (2) Experimental Observationsmentioning

confidence: 99%

A New Model for Tensile Creep of Silicon Nitride

Luecke

Wiederhorn

1999

Journal of the American Ceramic Society

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The tensile creep rate of most commercial grades of Si 3 N 4 increases strongly with stress. Although the usual powerlaw functions can represent the creep data, the data often show curvature and systematic variations of slope with temperature and stress. In this article, we present a new approach to understanding the creep of ceramics, such as Si 3 N 4 , where a deformable second phase bonds a deformation-resistant major phase. A review of experimental data suggests that the rate of formation and growth of cavities in the second phase controls creep in these materials. The critical step for deformation is the redistribution of the second phase away from the cavitation site to the surrounding volume. The effective viscosity of the second phase and the density of active cavities determine the creep rate. Assuming that the hydrostatic stresses in pockets of the second phase are normally distributed leads to a model that accurately describes the tensile creep rate of grades of Si 3 N 4 . In this model, the creep rate increases exponentially with the applied stress, is independent of Si 3 N 4 grain size, is inversely proportional to the effective viscosity of the deformable phase, and is proportional to the cube of the volume fraction of the deformable phase.

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