Gears in practice are mostly operated under variable
loads. Even in a continuous process the load can
fluctuate due to acceleration, malfunction,
emergency stops or operating errors. Under these
variable loads a tooth breakage, which mostly
results in a total gear failure, must be avoided with
high reliability. Additionally, demands on modern
gears, regarding costs and weight, are increasing.
With classic sizing of gears, where loads above the
fatigue limit are not allowed, the above goals cannot
be achieved. Using a calculation method, where
loads above the fatigue limit are taken adequately
into account, the operational stability without tooth
breakage can be ensured with predictable safety.
To evaluate tooth root fatigue tests with variable load
amplitude, the applied spectrum of load levels and
the tooth strength in terms of the S-N-curve is
required. The expected spectrum of load levels
during the life cycle can be evaluated by
measurement, simulation or estimation. The S-Ncurve
can either be experimentally derived or standardized
curves as IS0 6336 [lo] can be used.
For safe and operational stable sizing of variably
loaded gears an experimentally verified and easily
applicable calculation method is required. Therefore
tooth breakage fatigue tests on spur, case
carburized gears are carried out in hydraulic
pulsators. Influence of load sequence and load
distribution on the life cycle is examined.Additionally, a possible damaging influence of load levels below fatigue limit is evaluated.