DETERMINATION OF THIN FILM'S MECHANICAL PROPERTIES

27
of a blunt punch indenting an elastic solid (Loubet et al, 1984, Doerner and Nix,
1986 ). They obtained:
Figure 3.4 Characteristic region of load-depth diagram
S
dP A
= = 2Er
(3.2) and where
dh π
s
2
1 1−ν
1−ν
0
= + (3.3)
E E
r
E o
2
Er is called reduced modulus or combined modulus, S=dP/dhs is the
experimentally measured stiffness of the upper portion of the unloading data, which
is the slope of the curve fitted straight line of the initial part of unloading, A is the
projected contact area of the indenter at maximum loading condition, E and ν are
Young’s modulus and Poisson’s ratio for the specimen, and E o and νo are the same
parameter for the indenter.
The substitution of reduced modulus in Equation (3.2) for indentation test data is
valid (A.C. Fischer-Cripps, 2001). Because of the utilization of the slope or
unloading stiffness, it makes no difference whether or not the deflection of the
indenter is accommodated explicitly or transferred to that occurring within the