Table 1. Effect of Varying Shape Factor & Magnification on Nodule Count (Nod/mm2
)‒10µm Trap Size (CM2 & TCC2)
Table 2. Effect of Varying Shape Factor & Magnification on Nodularity (% Area)‒10µm Trap Size (CM2 & TCC2)
Table 3. Effect of Varying Shape Factor & Magnification on Nodularity (% No. Nodules)‒10µm Trap Size (CM2 & TCC2)
Repeatability Tests
Before looking at the results of the ILS and examining the magnitude of the differences observed between the partici- pant laboratories, the magnitude of the variation to be ex- pected for a given laboratory on a single sample was evaluat- ed. Image analysis repeatability tests were performed on an actual sample with a nodularity of 70%-80% (Figure 8). The sample was a cast tensile bar with a 2,3cm (7/8 in.) diameter.
Table 4 summarizes the testing procedures used in these tests, while Table 5 details the results (nodule count, nodu- larity by area and by number %). These tests were conducted using the following parameters, magnification = 100x, shape factor = 0,5 roundness, trap size = 10µm.
International Journal of Metalcasting/Volume 8, Issue 2, 2014
for the nodule count and less than 0,5% for the nodularity. This indicates that the IA results for a given set of fields analyzed is repeatable. Comparing the average results obtained for Tests #1 and #2 yields the influence of selecting different sets of fields in a given sample. In this particular case, the comparison between the two different sets of fields resulted in a 5% difference in the nodule count values (190,5 vs 200,7 Nod/mm2
) and less than 1% variation
in the nodularity values. These differences are believed to be the result of the intrinsic variations which exist locally in a microstructure.10-11
57
The results presented in Table 5 indicate that, when analyz- ing the same series of 25 fields ten times (Tests #1 for a given set of 25 fields and Test #2 for another given set of 25 fields), the error associated with the measurements was ± 1,2 and 0,8 Nod/mm2
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