An Evaluation of the Use of a Quantitative Image Analyzer to Determine Microhardness Values Page: 2 of 11
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P. E. Tvaney and J. E. Selle
with an automatic scanning stage and a prism
that can be used to automatically rotate the
image 9C*. The camera displays the image
under the microscope on a television monitor
and feeds the signal into a video signal
processing unit which can be used to obtain
from the image on the monitor (1) the mask
area, (2) the area of particles, (3) the number
of chords, and (4) the number of particles.
The desired values are requested from the
video signal processing unit by means of a peg
board- Data are fed into a computer and cal-
culations arc made according to programmed
For rnicrohardness determination tke area
of the particle (obtained by the number of
picture points in the indentation) and the
number of chords (obtained by the number of
TV lines intersected by the vertical diagonal of
the indentation on the screen) were used to
obtain the values.
The Classimat is calibrated so that up to
ten gray levers ranging from white to black
can be discriminated and measured. Since the
microhardness indentation is below and at an
angle to the surface of the specimen, less light
is reflected by the indentation than by the
surface of the specimen. The indentation
therefore shows up darker than the surface of
the specimen, allowing its gray level to be
discriminated and measured.
The Classimat was programmed to obtain
values on the rmicrohardness indentations by
both area and diagonal measurement in order
to determine the advantages and disadvantages
of each method. The method used for obtain-
ing microbardness values by diagonal measure-
ment on the diamond pyramid indentations
is given as an example of the setup required
to use the image analyzer for microhardness
The standard formula for computing
Vickers Hardness is shown in Equation (1):
HV - 1854.5-P (1)
where RV = Vickers Hardness in kg/sq mm
p = applied load in kg
d - the mean value of the diagonals
The standard Vickers formula was modi-
fied slightly and is shown in Equation (2).
Equation (2) is essentially the same as Equa-
tion (1) except it was broken down for step
by step operation of the instrument.
where HYf Vickers Hardness in kg/sq mm
p = applied load in kg
di and d2 =
chord measurements of the
F = conversion factor obtained from
the screen with a stage
The instrument was programmed by
placing pins in a program board. The instru-
ment was requested to (1) measure the number
of chords intersected by the vertical diagonal,
(2) rotate the prism 90*, (3) measure the
number of chords intersected by the remain-
ing diagonal, (4) return the prism and end the
program. The computer was programmed to
make the calculations required by Equation
(2). The result was the Vickers Hardness
number of kg/sq mm and the time interval
from the moment the number was requested
until the number was printed - about
Except for the average Vickers diagonal
measurements, the programs were set up to
print ten values and then average the ten
values for each indentation. A plot was then
292 - IMS hoceedings, 1971
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Teaney, P. E. & Selle, J. E. An Evaluation of the Use of a Quantitative Image Analyzer to Determine Microhardness Values, article, October 1, 1971; Miamisburg, Ohio. (digital.library.unt.edu/ark:/67531/metadc926104/m1/2/: accessed November 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.