An Evaluation of the Use of a Quantitative Image Analyzer to Determine Microhardness Values Page: 3 of 11
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P. E. Teaney and J. E. Scllv
made to determine if repeated measurements
were necessary to obtain accurate results.
The results of a typical plot are shown in
Figure 1. The first value printed out was
plotted against the average of the ten values
for each indentation. It appears to make little
difference which value is used- The first value
is printed out approximately I second after
the number is requested and each following
value in 3 second intervals, requiring ap-
proximately 30 seconds' total time for the
average. A considerable savings in time could
be realized by only taking one value; however,
some scatter occurred occasionally and a plot
that does not match nearly as well could be
obtained by plotting the extreme of the ten
numbers of each indentation. This indicates
that although ten values are unnecessary more
than one should be taken to preclude the pos-
sibility of this occurring by chance.
The results obtained on all three speci-
mens were similar, therefore the results on
only one of the specimens are shown for
Values obtained on a traverse of Knoop
indentations on the example specimen are
shown in Figure 2. This figure compares
values obtained on the Classimat by measure-
ment of the longer diagonal to those obtained
on the Miniload. The Ciassimat values are 15
to 25% higher than those of the Miniload.
The higher values were expected and the
reason for this is shown in Figure 3. The
longer Knoop diagonal makes such a gradual
transition in gray level from the surface of the
specimen into the indentation that selection
of the chords to the extreme edges of the in-
dentation also resulted in selection of chords
outside of the indentation. When this occurs
and a reasonable attempt is made to adjust
the mask area to eliminate the interference,
the only other alternative is to reduce the
chord selection until only chords inside the
indentation are measured. This sometimes
leaves some chords inside the indentation un-
selected. For this reason the length measure-
ment of the diagonal tended to be low.
An attempt was made to obtain more
accurate measurement of the diagonal by ad-
justment of the microscope light. The f stop
of the microscope was increased considerably in
an attempt to obtain more contrast and im-
prove resolution. The diagonals were then
remeasured with the Classimat. The results ob-
tained are shown in Figure 4. The values ob-
tained with the light stopped down showed a
considerable improvement over the original
values obtained. This method, however, still
gave results that tended to be about 5% higher
than the Miniload values.
Values were then obtained on these same
Knoop indentations by area on the Classimat.
By considering the total area the effects of
poor discrimination of picture points in the
extremities of the longer diagonal should be
minimized. Also, area can be measured with
the indentation in any orientation. With the
indentation being in the horizontal direction
the longer diagonal lies along rather than across
the chords of the screen- Discrimination of
picture points in the extremities of the indenta-
tion is much easier in this direction. Figure 5
shows the values obtained with the indentation
in both the horizontal and vertical position.
The results indicate that regardless of the
orientation of the indentation a good correla-
tion with the Miniload values can be obtained.
Additional values were obtained on these same
indentations with the microscope light stopped
down as before. A plot of these values showed
no significant difference from those obtained
by normal lighting.
Classimat values were also obtained on a
traverse of diamond pyramid indentations.
These indentations were parallel with the Knoop
indentations previously analyzed. The values
were obtained by average diagonal length and
area measurements. The results are shown in
Figure 6, along with values obtained on the
The Classimat diagonal measurement values
are again consistently high. However, the
problem encountered with the Knoop diagonal
was not encountered with the diamond pyramid
[MS Proceedir 1971 -- 293
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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/m1/3/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.