THEORETICAL DENSITY OF REFRACTORY AND CERAMIC MATERIALS
V. V. Kolomeitsev, E. F. Kolomeitseva, and O. V. Kolomeitseva
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 32 – 39, January, 2001.
The concept of the Mie potential and a new understanding of the nature of the forces acting between structural
components of a substance (atoms, ions, molecules) are used to develop a model allowing for the effect of the
thermal action of particles (the thermal field) on the chemical bonds in the substance. The new concepts on the
chemical bond are used to derive a formula for the theoretical strength of materials in a wide temperature
range. The calculated values of the theoretical strength of Al
(glass), and SiC at 293 K agree well
with the actual strength of whiskers. The established temperature dependence of the theoretical strength of
is adequate to the temperature dependence of the actual strength of whiskers. The theoretical strength is
a physical parameter of a material and can serve as a comparative characteristic for choosing a material for
specific service conditions.
Today’s science of the strength of materials operates with
the categories of strength, strain, and fracture and determines
the interrelations between them.
The majority of researchers agree that the category of
strength involves at least two concepts, i.e., the theoretical
strength connected with the notion of an ideal material and
the actual strength of actual materials determined under vari-
ous loading conditions (mechanical, thermal, electromag-
netic, gravitational, and other loads). The category of frac-
ture has not been defined exactly in the modern strength the
ory, which has given rise to numerous fracture criteria re
viewed in [1 – 6].
Several approaches were developed with the advance
ment of the theory of the structure of substances, which cha
racterize the theoretical density of an ideal material as the
strength of an elastic continuum, an ideal incompressible liq
uid, or a solid body with a defectless structure.
The category of strain has been defined exactly in the
science of actual strength. Depending on the nature of the
strain of an actual material before failure the material is as
sumed to fracture by one of the limiting mechanisms, i.e.,
brittle or plastic. In accordance with the two limiting kinds of
fracture two models of an ideal material have been deve
loped, i.e., an elastobrittle defectless solid body and an ideal
incompressible liquid or ideal plastic continuum (other mo
dels exist too [1, 4]).
Brittle materials (glass, refractories, ceramics, high-
strength steels) deform elastically until their failure when
loaded under normal conditions.
Plastic materials (most
metals, clays, polymers) virtually do not deform until their
failure under a load. However, under certain conditions brit-
tle materials can deform plastically or, vice versa, plastic ma-
terials can deform by the mechanism of brittle fracture.
The deformation under actual conditions depends on the
value of the load, its kind, the rate of its increase, and the
time of action of the load. For example, rapid deformation of
a water stream causes its quasi-brittle fracture, whereas its
slow deformation occurs by the plastic mechanism. Many
brittle materials are compressed under a superhigh pressure
“flow,” i.e., deform in a plastic manner. It is known that tem
perature has an ambiguous effect on the fracture mechanism
of materials [1 – 5].
Plastic deformation of actual materials is caused by the
nucleation, multiplication, motion, and interaction of dislo
cations (structural defects) and, consequently, cannot serve
as a characteristic of an ideal material [1 – 6].
The classification of materials into plastic and brittle
ones is conventional, because there are no absolutely elastic
actual materials due to the dissipation of part of the loading
energy in the deformation process. Absolutely plastic actual
materials do not exist either. However, model representations
of plastic and brittle materials are useful for the study and
prediction of their fracture behavior.
It is commonly assumed [7 – 10] that the strength of a
material is caused by the electromagnetic forces, because the
chemical bonding that appears when the atoms move close to
each other is a result of the interaction of their external and
partially unfilled internal electron orbitals.
The conventional terminology operates with ionic
(heteropolar), covalent (homeopolar), metallic, van der Waals,
and hydrogen types of bonding. In refractory and ceramic
Refractories and Industrial Ceramics Vol. 42, Nos.1–2, 2001
1083-4877/01/0102-0030$25.00 © 2001 Plenum Publishing Corporation
At 293 K and normal atmospheric pressure.