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Analysis and Design of Machine Elements
52
Figure 2.9 Reason for surface
fatigue failure.

Surface fatigue failure includes pitting and spalling. Pitting originates with surface
cracks and each pit has a relatively small surface area. Spalling originates with sub-
surface cracks and the spalls are thin ‘flakes’ of surface material [13]. Both pitting and
spalling occur due to insufficient surface strength. It is believed that Hertz stress, the
number of cycles, surface finish, hardness, lubrication and temperature all influence sur-
face strength of an element [2]. Consequently, it is advisable to take measures to reduce
loads, to increase surface hardness and to improve surface smoothness and lubrication
with the ultimate goal of increasing resistance to surface fatigue failure.

References

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