where \(n_{i}\ \)is the number of cycles of load applied within the
stress range and \(N_{i}\ \)represents the failure of the component when
its cycle number is\(\text{\ \ N}_{i}\). When the cumulative damage
(D ) is equal to one, blade failure is assumed to occur.
According to the records of the supplier, the fan had four different
rotating speeds under the actual operating conditions, which were 1600,
1800, 2000 and 2200 r/min respectively. The corresponding number of
start-stop cycles per year was shown in Table 4. Based on the finite
element analysis results, it could be concluded that the stress on the
fan blade under uniform rotation was almost negligible, so the fatigue
caused by start-stop interaction wasz only considered.