Page 350 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 6 EVALUATION METHODS FOR PROPERTIES OF NANOSTRUCTURED BODY
References with 6 mm in diameter and 30 mm in gauge length
is recommended in tensile test. Radius of curvature at
[1] A. Sawaguchi, T. Toda and K. Niihara: J. Am. Ceram. the shoulder of gauge should be over 30mm. The
Soc., 74, 1142–1144 (1991). specimen should be held by using universal joint to
[2] T. Fukui, S. Ohara and K. Mukai: Electrochem. Solid- restrict bending and twisting mode.
State Lett., 1, 120–122 (1998). Since ceramics are generally hard to be machined
[3] T. Fukui, S. Ohara, M. Naito and K. Nogi: J. Eur. compared with metallic materials, speaking, it is diffi-
Ceram. Soc., 23, 2963–2967 (2003). cult to make tensile specimens with complex shape and
high accuracy. Therefore, bending test is usually
[4] T. Fukui, T. Obuchi, Y. Ikuhara, S. Ohara and K.
applied for strength measurement, which is regulated in
Kodera: J. Am. Ceram. Soc., 80, 261–263 (1997).
JIS R1601. Fig. 6.2.2 shows the relationship between
[5] T. Fukui, S. Ohara, M. Naito and K. Nogi: J. Nanopart.
the strength of SiC nanoparticle dispersed Al O and
Res., 3, 171–174 (2001). 2 3
the volume fraction of SiC nanoparticles [1]. It is
shown that the strength improves by adding a small
6.2 Mechanical properties amount of nanoparticles. Furthermore, it is reported
that the strength also improves by annealing [1]. As
shown in Fig. 6.2.3, strength variation decreases in
6.2.1 Strength, fracture toughness and fatigue behavior nanocomposites [1].
6.2.1.1 Strength 6.2.1.2 Fracture toughness
Strength is one of the most important parameters to According to fracture mechanics, strength is a func-
design the structural components. In recent study, tion of fracture toughness K IC and flaw size.
strength evaluation is needed in functional material Therefore, the fracture toughness is an important
and/or MEMS in order to improve their reliability. parameter to understand strength and reliability.
The strength is evaluated by bending or tensile test. In metallic material, plane strain fracture toughness
In many cases, strength measurement of metallic measurement is regulated in JIS G 0564 and ISO
materials is carried out by tensile test because of 12737. Many kinds of fracture toughness tests of
machinability. Fig. 6.2.1 shows the relationship advanced ceramics have also been proposed.
between strength and grain size of metallic materials. Indentation fracture (IF) method and single edge pre-
In the case of grain size over micrometer, strength cracked beam (SEPB) method is standardized as the
increases with decrease in grain size according to fracture toughness test in JIS R1607. In ISO, SEPB
Hall–Petch relationship. Moreover, the metallic method ISO15732:2003, surface crack in flexure
material has excellent ductility and shows work hard- (CSF) method ISO18756:2003 and chevron notched
ening. Further grain refinement results in restriction beam (CNB) method ISO/DIS24379:2003 have been
of work hardening. As a result, strength decreases established. Fig. 6.2.4 shows the relationship between
with decrease in grain size (inverse Hall–Petch rela- the strength and fracture toughness and the SiC
tionship). In ceramics, tensile test is carried out to content [1]. Both strength and fracture toughness
compare with metallic materials. Use of the specimen increase with an increase in SiC content.

Inverse Hall-Petch relationship

σ y

Hall-Petch relationship
-1/2
= σ + kd
σ y 0

~10-20nm Grain size
Figure 6.2.2
Figure 6.2.1 Effect of SiC content on the strength of Al O –SiC
2 3
Grain size dependence of strength of metallic materials. nanocomposites.
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