ANALYSIS AND SYSTEMATIZATION OF DEFECTS INVOLVED
IN THE MECHANICAL STRENGTH DEGRADATION
OF b-SPODUMENE-BASED GLASS CERAMICS
E. I. Suzdal’tsev
and A. P. Sosulina
Translated from Novye Ogneupory, No. 12, pp. 38 – 42, December, 2003.
Structural defects in specimens of densely sintered glass ceramics of b-spodumene composition are analyzed
and the relation between the defect size and mechanical strength of the material is considered. The failure of
specimens is initiated by surface microcracks produced by mechanical grinding; the role of microstructure
inhomogeneities in the degradation of strength properties is emphasized.
As is well known, the strength characteristics of various
materials, including glasses, ceramics, and ceramized
glasses, show a statistic distribution [1 – 4]. A typical statisti-
cally distributed behavior has been observed in quarts ceram-
ics with a porosity of 8 – 10% and densely sintered glass ce-
ramics of b-spodumene composition tested for bending
strength (Fig. 1). These results are remarkable for the fact
that they were obtained on a large number of test specimens
(a total of 101 batches for quartz ceramics and 304 batches
for glass ceramics, 10 to 20 specimens in each batch), fabri-
cated with allowance for the corresponding technological
However, the bending strength measured on an individ
ual specimen may be at variance with the rated value, de
pending on the shape, size, and other properties. This not
withstanding, the mechanical strength is a major characteris
tics of the material that serves as a criterion for its practical
use. For this reason, a knowledge of the rela
tionship strength – structural imperfections (de
fects) – structure provides a route towards fore
casting the strength behavior of a material un
der service conditions.
With this in mind, our goal in the present
study was to gain a deeper insight into struc
tural imperfections (defects) capable of initiat
ing the fracture of specimens, their relation to
the material strength, and to examine in some
detail factors that may affect strength character
istics of glass ceramics of b-spodumene com
The defect analysis was carried out by fractography using
MBS-2 and Neophot-30 optical microscopes and a
JSM-35CF electron microscope. A total of about 500 speci-
mens were analyzed that were sampled from the peripheral
areas of components; for additional examinations, compo-
nents were cut into rings lengthwise.
As was established, brittle fracture in specimens oc-
curred through propagation of a main crack which involved
the formation of three zones each characterized by a specific
speed of crack propagation through the material: (i) focus of
fracture, (ii) fracture mirror zone, and (iii) crest-like zone of
final fracture (afterfracture zone). Most often, the direction
of the afterfracture zone indicates a direction for the incipient
failure of the specimen.
All these defects that initiate the fracture of a test speci
men can be divided into two groups: (i) internal defects and
(ii) surface defects.
Refractories and Industrial Ceramics Vol. 45, No. 2, 2004
1083-4877/04/4502-0105 © 2004 Plenum Publishing Corporation
Tekhnologiya Research and Production Enter
prise, Obninsk, Kaluga Region, Russia.
30 40 50 60
90 100 110 120 130 140
Fig. 1. Bar charts for the distribution of strength s
in specimens tested for bending:
a) quartz ceramics with a porosity of 8 – 10% (a total of 101 batches were tested, with
10 – 20 specimens in each batch); b) densely sintered glass ceramics of b-spodumene
composition (a total of 304 batches were tested, with 10 – 20 specimens in each batch).