THEORETICAL EVALUATION OF THE ACTUAL STRENGTH
OF SINGLE-PHASE POLYCRYSTALLINE REFRACTORY
AND CERAMIC MATERIALS
V. V. Kolomeitsev, E. F. Kolomeitseva, and O. V. Kolomeitseva
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 5, pp.2–5,May,2002.
Using a modified thermal-shock model, a method for theoretical evaluation of the actual strength of single-
phase polycrystalline refractory and ceramic materials has been developed. A formula for strength analysis
over a wide temperature range has been derived. The calculated actual strength is a parameter for actual mate-
rials and thus can be used for predicting the behavior of materials under loading conditions within the frame-
work of linear elastic fracture mechanics. In the region of Debye temperature, the theoretical strength versus
temperature curve for single-phase materials exhibits a “dip” which, however, fails to be resolved experimen-
tally because of the insufficient accuracy and poor reproducibility of measurements.
In terms of structure and strength,
refractory and ce-
ramic materials can be divided into the following groups:
1. Whisker single crystals.
2. Bulk single crystals.
3. High-density (close to theoretical density) fine-grained
4. Porous fine-grained polycrystalline materials.
5. Porous coarse-grained polycrystalline materials.
6. High-porosity polycrystalline materials.
It stands to reason that any classification is conventional,
since the actual materials may exhibit characteristics com
mon to the classificatory groups. As an example, one may re
fer to composite materials containing single-crystal whiskers
or polycrystalline fibers.
Still, the above classification can be used as a framework
for model simulation and theoretical strength analysis of sin
gle-phase refractory and ceramic materials.
From a practical point of view, of greater interest are ma
terials of groups3–5.
High-porosity polycrystalline materials (structural and
fibrous heat insulators) exhibiting, as a rule, a high strength
have been omitted from consideration in the present study.
The material strength is measured using test specimens
of different shape and size and different mechanical loading
techniques: uniaxial or multiaxial tension and compression,
bending, testing under variable load-rate conditions, etc. In
the case of refractory materials, the most widely used tech
nique is uniaxial compression .
To predict structural failure of refractory and ceramic
materials, one will want to know a reliable correlation be
tween laboratory test data and the load-carrying capacity of
structural components under specified service conditions.
In practice, occasions are quite rare when an approxi
mate correlation between the strength of test specimens and
the performance characteristics of engineering components
made of refractory materials or structural ceramics are known.
Evaluation of the load-carrying capacity of structural
components from laboratory test data poses a problem be
cause the strength (irrespective of the testing technique used)
is not a physical parameter of the given material. Laboratory
test data can serve merely as an indicator of process stability
and quality of a given material manufactured by a given
The strength of materials fabricated under identical con
ditions is determined by a variety of technological factors
and testing techniques used; most commonly, the spread in
experimental data is quite significant. Therefore, it is far
Refractories and Industrial Ceramics Vol. 43, Nos.5–6, 2002
1083-4877/02/0506-0163$27.00 © 2002 Plenum Publishing Corporation
Henceforth, reference is made to the uniaxial tensile strength
measured under normal loading conditions (at 273 K and normal