Page 361 - Book Hosokawa Nanoparticle Technology Handbook

6.2 MECHANICAL PROPERTIES FUNDAMENTALS
References 3. Mechanical properties related with texture or
microstructure are locally evaluated.
[1] C.Y.H. Lim, D.K. Leo, J.J.S. Ang and M. Gupta: Wear,
4. Highly concentrated stress field under an inden-
259, 620–625 (2005).
tation brings plastic deformation at room temper-
[2] J.-W. An, D.-H. You and D.-S. Lim: Wear, 255, 677–681
(2005). ature even for brittle materials such as ceramics.
[3] J.L. Oritiz-Merino, R.I. Todd: Acta Matarialia, 53,
The third advantage listed above realizes to evaluate
3345–3357 (2005).
mechanical properties related with the nanostructure of
[4] D.-S. Lim, D.-S. Park, B.-D. Han, T.-S. Kan and
materials, because the indentations can be made just at
H. Jang: Wear, 251, 1452–1458 (2001). the place where the mechanical properties related with
[5] M. Yoshimura, Bull. Jpn. Ceram. Soc., 39, 177–180 texture or microstructure are to be obtained. The second
(2004). one shows another advantage of nanoindentation that
[6] P. Bhimaraj, D.L. Burris, J. Action, W.G. Sawyer, C.G. realizes the evaluation of the mechanical properties of
Toney, R.W. Siegel and L.S. Schadler: Wear, 258, thin films and MEMS devices. Moreover, advantage to
1437–1443 (2005). evaluate mechanical properties with high accuracy is
given due to the first characteristic of nanoindentation
[7] L. Joly-Pottuz, F. Dassenoy, J.M. Martin, D. Vrbanic,
listed above, because experimental errors in conven-
A. Mrzel, D. Mihailovic, W. Vogel and G. Montagnac:
tional indentation technique are usually recognized in
Tribiol. Lett., 18, 385–393 (2005).
the measurement of the size of an extremely small resid-
ual impression. A sharp tip of a conical or pyramidal
6.2.5 Nanoindentation indenter is required to obtain load–unload curves in
nanoindentation, because the effect of the roundness of
What is the most suitable mechanical test for charac- an indenter tip on the curves cannot be ignored for very
terizing materials with nanostructure? Tensile, com- shallow indentations. For this reason, a Berkovich type
pressive and bending tests as well as a test based on indenter is more often chosen in nanoindentation tech-
the fracture mechanics, in which the size of a main nique in comparison with a Vickers indenter.
crack in a specimen is measured, are usually utilized Meyer hardness H and reduced modulus E are
M
r
to evaluate the mechanical properties of conventional driven from indentation loading and unloading curves
materials. Also, tests to obtain hardness, friction- and respectively, as follows [1];
wear-resistance are often adopted. Although these
mechanical tests can be applied for the nanostruc- P
tured materials, correlation between the mechanical H M max 2 (6.2.16)
properties and the nanostructure is hardly obtained gh c
through the tests. Nanoindentation is a unique
mechanical test that can evaluate local mechanical S
properties related with the nanostructure of materi- E 2 gh 2 (6.2.17)
r
als. Details of nanoindentation technique are intro- c
duced in this section.
Indentation technique has been conventionally uti- where P max is the maximum indentation load and, g is
lized to evaluate the hardness of materials, in which a the geometrical factor of an indenter defined by use of
geometrically defined stylus made of a hard material contact depth h and projective contact area A in the
c
c
such as diamond is indented onto the surface of a case of point-sharp indenters (Fig. 6.2.20) as follows;
specimen. Meyer hardness is conventionally evalu-
ated by dividing indentation load by the projected g A c (6.2.18)
area of a residual impression on the surface. In h c 2
nanoindentation defined as depth sensing indentation,
mechanical properties are extracted from indentation The Vickers and Berkovich type indenters utilized
loading–unloading curves obtained from continuous conventionally are geometrically designed to have a
correlation between indentation load and the penetra- g-value of 24.5. In addition, S is the slope of an
tion depth of the stylus from the surface of a speci- unloading curve at the maximum load (Fig. 6.2.21).
men. In comparison with the conventional According to the contact mechanics, the h -value is
indentation, the advantages of nanoindentation tech- given as follows [2] (Fig. 6.2.20); c
nique are listed as follows:
P
1. Measurement of the size of a residual impres- h h max (6.2.19)
c max S
sion on a surface is not required.
2. Preparation of a specimen dimensionally and where is a constant, which is set to be 0.75 for the
geometrically defined well is not required. Vickers and Berkovich indenters [1]. Reduced Modulus

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