Page 78 - Gear Technology Solutions

Figure 8: Tooth fracture initiated by interference

The root fillet step problem which was discussed in connection with Figure 7 is
investigated closer with Figure 9. Figure 9 shows a profile which is very similar to
the real profile in Figure 7. If the 30° tangent to the root fillet is drawn into the pro-
file, then the tangent point is at or close to the point with the highest notch effect.
The 30° tangent has been proven in numerous finite element calculations and in
analysis of real-world fractures to be the point with the highest risk of a tooth frac-
ture.

Figure 9: Tooth fracture initiated by steps below the root transition

This means that imperfections in the root fillet transition as shown in Figures 7 and
9 can cause tooth fracture if the gearset is used in a power transmission. A frac-

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