where \(S_{{a,R}_{0}}\) and \(S_{{m,R}_{0}}\) are the nominal stress amplitude and mean nominal stress when a load ratio is \(R_{0}\).\(\ \)
The equivalent life curve was obtained by using the Goodman curve, and based on the working stress of the fan provided by the supplier, the stress of the fan structure was modified [43]. The modified curve was shown in Fig. 6 and Eq. (12). The predicted life of four different rotating speeds was shown in Table 4.