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.